Challenges in seabird by-catch mitigation

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By Hanover Matz, RJD Intern

In this paper, the authors comment on the current conservation status of seabirds and attempts to limit seabird deaths due to by-catch. Two species of seabirds, the albatrosses and the petrels, are particularly vulnerable to the detrimental effects of fisheries such as longlining. These birds normally lay only one egg per clutch and breed infrequently. They have long maturation and generation times compared to other birds, making it more difficult for their populations to recover from high mortality. They are also capable of flying long distances in search of food, crossing many different marine environments. This makes it difficult to implement conservation methods that can protect these birds in every part of the world they inhabit. Some of these species are already considered endangered or critically endangered. In order to fully protect them, an international effort is necessary.

A wandering albatross (Diomeda exulans) off Tasmania, Australia. Photo courtesy of JJ Harrison via Wikimedia Common

A wandering albatross (Diomeda exulans) off Tasmania, Australia. Photo courtesy of JJ Harrison via Wikimedia Commons

Seabirds and human fisheries come into conflict in many of the most productive regions of the ocean, specifically around New Zealand and Australia, the Humboldt Current off Chile, Peru, and Ecuador, the North Pacific, and South Africa. Seabirds are known to be killed as accidental by-catch in longline fisheries, and growing evidence has shown incidental catch of seabirds by trawlers. One difficulty in assessing whether trawling or longlining presents a greater threat to seabirds is the low proportion of entangled seabirds actually recovered from trawling gear. If the birds that collide with the gear cannot be retrieved, it is hard to assess the impact the fishery has. Refining the collection of data on how many seabirds are killed by longlining and trawling will improve conservation efforts.

In South Africa, the use of bird-scaring lines (BSLs) in fisheries has been shown to reduce the mortality of seabirds up to 95%. The trawl fishery previously had proportionally high incidental catches of albatrosses, making this a significant success in terms of protecting threatened species. However, to fully determine how well seabird mortality has been reduced, better data needs to be collected on both the level of by-catch and fishing effort. To reduce the by-catch of seabirds and improve conservation worldwide, the authors stress four important strategies. First, mitigation methods need to be improved with better data and techniques, considering each fishery individually and adapting the methods as necessary. Second, the quality of data collected needs to be increased by improving the programs used to collect it. Third, the fishing industry needs to be engaged by implementing and enforcing by-catch reduction, as well as cooperating to suit the needs of both the fishery and conservation. Finally, cooperation between governments, administrators, and decision makers is necessary to promote better fishing practices and conservation measures. In some fisheries, seabird by-catch mitigation is minimal or nonexistent. While trawling and longlining have been addressed, the effects of purse-seine and gill net fisheries are poorly understood. The threat posed by small scale and artisanal fishing fleets has also not been widely considered. If threatened seabird species are to be protected, it will require both national and international efforts. By improving the science behind the conservation, and cooperating with both governments and fisheries, scientists and conservations will be better able to address this conservation issue in the coming future.

References

1. Favero, M., & Seco Pon, J. P. 2014. Challenges in seabird by‐catch mitigation. Animal Conservation, 17(6), 532-533.

 

 

A Century of Fish Biomass Decline in the Ocean

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By Lindsay Jennings, RJD Intern

There have been many interpretations and heated debates in the scientific community surrounding the trend of global fish populations. Although some advocate increasing trends, others are quick to counter with their evidence of declining trends. And while previous local and regional studies have reported heavy declines of large oceanic predators (e.g. finish and sharks), subsequent studies have reported an increase and abundance of forage fish (e.g. anchovies and sardines). This increase in biomass is thought to be a result of decreasing predator abundance coupled with the consequences of human exploitation. Because ‘fishing down the food web’ is not a universally accepted phenomenon, and to get to the bottom of the debate, Villy Christensen et al. (2014) aimed to specifically evaluate how the biomass of high tropic level species has changed relative to the biomass of lower trophic level species.

Pic 1 - blacktip reef sharks

Blacktip reef sharks scattering a school of forage fish. Photo courtesy of Wikimedia Commons

The researchers built a database with 200 data-rich ecosystem models – currently the most widely used ecosystem modeling approach in the marine environment. These models delivered ‘snapshots’ of how much life was in the ocean at a given point in time and space, between the years 1880 and 2007. From those models, Christensen et al. distributed previously-published and well-documented fish biomass based on habitat preference, ecology, and feeding conditions. With those global distributions, over 68,000 estimates of biomass were obtained for predatory or ‘table’ fish (trophic levels 3.5 and above) and forage fish (trophic levels 2.0 – 3.0). Finally, the spatial models and thousands of predictions of fish biomass were used as the basis for multiple regression analyses to predict actual trends in fish populations.

Global distribution of the ecosystem models used in this study. Color density is indicative of the number of models at each location. Photo courtesy Christensen et al. (2014)

Global distribution of the ecosystem models used in this study. Color density is indicative of the number of models at each location. Photo courtesy Christensen et al. (2014)

Drawing a global picture of how the abundance of fish has changed in the world’s oceans over the last 100 years, results predicted that the biomass of predatory fish in the world’s oceans has declined by two-thirds over the last 100 years. Most alarming though is that 55% of that decline has occurred in the last 40 years. This decline in predatory fish was found to be closely linked to an increase in global fishing effort, indicating that we may have been fishing past the maximum sustainable yield (MSY) for quite some time. Consequently, forage fish biomass has increased over the last 100 years, thought to be result of predation release.

Global spatial distribution of predatory fish for (a) 1950 and (b) 2010. Photo courtesy Christensen et al. (2014)

Global spatial distribution of predatory fish for (a) 1950 and (b) 2010. Photo courtesy Christensen et al. (2014)

While the researchers are confident there will be fish in our oceans in the future, they are quick to point out that those fish assemblages will be very different from the ones we have currently – with small prey fish beginning to dominate marine ecosystems. With advancing technology and increased fishing effort, this study has important implications for the management of our ocean’s marine resources. There must be a wide recognition of the growing importance of forage fish in the marine ecosystem, followed by appropriate measures to make sure these fish stocks, too, do not start to decline.

 

 

Citation: Christensen, V., Coll, M., Piroddi, C., Steenbeek, J., Buszowski, J., & Pauly, D. (2014). A century of fish biomass decline in the ocean. Marine Ecology Progress Series, 512, 155-166.

Marine Pollution: A Look into the Great Pacific Garbage Patch

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By Hannah Armstrong, RJD Intern

Plastics, among other pollutants, are one of the most commonly found in oceans and on beaches globally.  This is mainly for two reasons: first, plastic is very durable and often low in cost, so it is universally used for consumer and industrial products, and second, plastics do not biodegrade completely, remaining in the world’s oceans and on beaches for extended periods if not cleaned up.  All of this accumulating debris can be detrimental for marine life.  Seals, turtles and seabirds often get entangled and drown in abandoned fishing nets and other miscellaneous debris, and toxins both from the breakdown of plastics and those that the plastics themselves absorb, can collect in marine organisms and be damaging to their health and to the aquatic food web as a whole.

In the North Pacific Ocean, there is a gyre that has caused such a drastic collection of debris that it has earned the name The Great Pacific Garbage Patch.  A gyre, as defined by the National Oceanic and Atmospheric Administration (NOAA), is a major spiral of ocean-circling currents; global winds result in ocean currents circling clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere, with an area of high pressure in the center.  In the North Pacific Subtropical Gyre, these ocean circulation patterns are what caused, and is still causing, the substantial amount of debris accumulation, ultimately forming the Great Pacific Garbage Patch.  The Great Pacific Garbage Patch is comprised of the Eastern Garbage Patch, which is located near Japan, and the Western Garbage Patch, which is located in the waters between California and Hawaii.

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A representation of the ocean currents and zones in the North Pacific Region. The two green shaded circles depict the Western and Eastern Garbage Patches, where a substantial amount of marine debris has accumulated (Howell et al. 2012).

Charles Moore, the oceanographer who was among the first to draw media attention to the Great Pacific Garbage Patch, noted that in the last two decades alone, the deposition rate of plastic accelerated past the rate of production.  Moreover, his research on plastics in the ocean showed that between 1960 and 2000, the world production of plastic resins increased 25-fold, while recovery of the material remained below 5%; and between 1970 and 2003, plastics became the fastest growing segment of the US municipal waste stream, increasing nine-fold.  According to Moore, marine litter is now 60–80% plastic, reaching 90–95% in some areas (Moore 2008).  This build-up is already beginning to render its consequences on the marine environment and its inhabitants.

The most obvious concern with a debris build-up caused by the previously described convergence zones is the negative effects it poses on the marine life.  Specifically, this pollution affects at least 267 species worldwide, including sea turtles (86%), seabirds (44%), and marine mammal species (43%) (Laist 1997).  In 2009, Young et. al directed their attention toward an area southeast of the Kroshio Extension near Japan.  They observed a population of Laysan Albatross (Phoebastria immutabilis), taking note that the foraging area of adult albatross originating from Kure Atoll overlapped with the range of the Western Garbage Patch.  This, they realized, is what lead to the transfer of marine plastics from adult albatross to their young.  In fact, the albatross chicks from Kure Atoll, in comparison to the Oahu albatross sample used, were fed nearly ten times the amount of plastic despite having a relatively similar amount of available natural food.  While Young et al. were unable to determine the level of mortality as a result of this plastic ingestion, they did observe mechanical blockage of the digestive tract, reduced food consumption, satiation of hunger, and potential exposure to toxic compounds (Young et al. 2008).

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A photograph of a dead Laysan albatross chick with a diversity of plastics in its stomach. Ingestion of marine debris is a detrimental issue or marine organisms and seabirds (Young et al. 2008).

In addition to threats of ingesting pollutants, marine species face threats of entanglement and a phenomenon known as “ghost fishing.” This occurs when fishing gear is lost or abandoned, but continues to fish and wipeout resources (Moore 2008).  As a means of remediating entanglement, often a result of nets and six-pack soda rings among other pollutants, some manufacturers aim to chemically alter the plastic in the event that it ends up in the ocean.  Chemical changes can allow the polymer to absorb UV-B radiation from sunlight, breaking it down into a smaller, less-harmful product.  The resulting polymer, however, is hardly more biodegradable (Moore 2008).

With the ever-increasing abundance of plastics in the marine environment, concerns too, are growing.  With other environmental problems, most notably climate change, it will be critical to begin (and continue) to study and understand how rising atmospheric and sea temperatures will affect ocean circulation, wind and debris movement patterns.  If drastic changes occur within the North Pacific region, and specifically the area encompassed by the Great Pacific Garbage Patch, then the resulting marine pollution accumulation and retention and could be drastic as well.

 

References:

Derraik, Jose G.B. The pollution of the marine environment by plastic debris: a review.  Marine Pollution Bulletin 44 [842-852].  2002.

Howell, Evan A et al. On North Pacific circulation and associated marine debris concentration.  Marine Pollution Bulletin 65-1 [16-22].  2012.

Moore, Charles James.  Synthetic polymers in the marine environment: A rapidly increasing, long-term threat.  Environmental Research 108-2 [131-139].  2008.

Young, Lindsay C et al. Bring Home the Trash: Do Colony-Based Differences in Foraging Distribution lead to Increased Plastic Ingestion in Laysan Albatrosses?  Plos One. 2009.

 

14 things our lab accomplished in 2014

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1) We published “Evolved for extinction: the cost and conservation implications of specialization in hammerhead sharks,” a review of hammerhead biology and conservation that was featured on the cover of BioScience! Read it here: 

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2) We led 65 shark research trips, including two trips to our Tiger Beach research site in the Bahamas!

3) We published “Considering the fate of electronic tags: interactions with stakeholders and user responsibility when encountering tagged aquatic animals,” which was featured on the cover of “Methods in Ecology and Evolution.” Read it here: 

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4)  We brought over 1,200 citizen scientists out on the research vessel with us to learn about sharks, participate in our scientific research, and learn about local conservation issues. They ranged in age from 10 to 73,  came from 46 states and 40 countries, and included representatives from 33 schools, community organizations and corporations.

5) We published “an assessment of the scale, practices, and conservation implications of Florida’s charterboat based recreational shark fishery,” which was featured on the cover of Fisheries. Read it here

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6) We caught, measured, sampled and tagged 331 sharks of 11 species. The most common species we caught was the nurse shark (151 individuals). We also caught 6 Atlantic sharpnose, 25 blacknose, 15 blacktips, 15 bulls, 10 Caribbean reefs, 19 great hammerheads, 26 lemon sharks, 27 sandbar sharks, 1 scalloped hammerhead and 36 tiger sharks.

7) We published “Physiological stress response, reflex impairment, and survival of five sympatric shark species following experimental capture and release,” an important paper showing how the stress of being caught by fishing gear can harm or kill a shark even if it is eventually released. Read it here

8 ) We attached satellite tags to 19 sharks: 8 great hammerheads, 1 scalloped hammerhead, and 10 tiger sharks. You can track all of our satellite tagged sharks here using Google Earth, and you can adopt your own, name it, and join us when we tag it here 

9) We published “Vulnerability of oceanic sharks as pelagic longline bycatch,” an analysis of how different species of sharks react to being caught as bycatch in commercial fisheries. Read it here.

10)  Our students presented their research at major scientific conferences, including Sharks International, the American Elasmobranch Society meeting, and the International Marine Conservation Congress!

11) We published three papers from our morphometric analysis project! Read them here: 1, 2, and 3.

12) Our research was covered in many media outlets, including Al Jazeera America, the South Florida Sun-Sentinel, and CBS News!

13) Our interns wrote dozens of blog posts on a huge variety of topics related to ocean science and conservation.

14) We passed 4,000 fans on our Facebook page, which continues to share ocean science and conservation news! Have you “Liked” our page?

Thanks for your continued support! With your help, 2015 will be even better!

Fishermen Views on Marine Protected Areas

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By Alice Schreiber, RJD Intern

As fish stocks continue to decline, Marine Protected Areas are becoming increasingly popular methods of conserving marine habitats and preserving species. The success of these areas depends upon the existing legal framework, acceptance by the community, and an effective management system [1].

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Being aware of how fishermen socially perceive MPAs is crucial when establishing them and creating management guidelines. MPAs are established areas where fishing pressure is reduced by designating the amount of fishing effort, time available for fishing activity, species that can be caught, gear permitted, or catch limits [2]. At times, Marine Protected Areas may completely restrict fishing or some areas may be designated Marine Reserves which function as no-take zones. The expectation is that the MPA will “maintain or restore marine biodiversity and ecosystem function,” as well as “improve socioeconomic conditions by increasing revenues from fisheries production due to an increase in the size and number of fish migrating out of the MPA [3]”.  Without taking into account the stakeholders’ perception of the reserve, enforcing management of Marine Protected Areas would be nearly impossible.

A new study by Monalisa Silva and Priscila Lopez, sheds some light on how to determine fishermen’s perceptions of MPAs and what criteria influence the opinions the fishermen have about the MPA. When evaluating perception among fishers, four questions are asked: (1) if a fisherman born in a place subjected to the limitations of an MPA has a more conservationist attitude; (2) if young, part-time, non-selective fishers are more flexible and adaptable to changes in the reserves, (3) if full-time fishermen who were born in a community under the influence of an MPA have greater participation in the establishment of management; and (4) if fishermen born in a community under the influence of an MPA have more positive opinions than immigrant fishermen regarding the protected areas [2].

Asking these questions allows researchers and policy makers to understand which individuals within a community are less likely to comply with the regulations, and as such, which individuals would benefit from more education or incentives regarding the protected areas. Compliance will not be at adequate levels if there is not a proper understanding from the public of why MPAs are needed.

Three MPAs in the states of Rio Grande do Norte served as the location for the study, in which one hundred fishermen were interviewed. The fishermen were between the ages of 21 and 77 years old and had an average fishing experience of 29 years. They were split into four groups, depending on their age, birthplace, type of fishing gear, and their level of dependence on fishing. They then took a questionnaire, which assessed their perception of biodiversity conservation, flexibility and adaptability, participation in management, and opinions about MPAs.

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The results of this study were able to confirm that older fishermen using selective gear have a more conservationist perception, full-time fishermen who use selective gear have lower flexibility and adaptability, and older fishermen tend to have more positive opinions regarding the MPA [2]. Flexibility and adaptability are important in regards to MPA compliance. Selective fishing gear allows fishermen to target a specific species or size of fish and when that fish stock collapses or is not longer allowed to be fished, they have very little flexibility in their choices. Encouraging fishermen to work in other areas part-time or to explore different resources beyond fish may help to ease the lack of flexibility.

Taking into account stakeholder perception is extremely important for the proper and effective management of MPAs. Compliance issues result from misconceptions of the conservational goals and from heavy dependence on fishing as their primary or only income. Being considerate of these issues allows for more effective management of MPAs and a more positive perception from fishermen and the affected community.

 

Works Cited

Salm, Rodney V., John R. Clark, and Erkki Siirila. Marine and coastal protected areas: a guide for planners and managers. IUCN, 2000.

Silva, Monalisa RO, and Prisicla FM Lopes. “Each fisherman is different: Taking the environmental perception of small-scale fishermen into account to manage marine protected areas.” Marine Policy 51 (2015): 347-355.

Pomeroy, Robert S., et al. “How is your MPA doing? A methodology for evaluating the management effectiveness of marine protected areas.” Ocean & Coastal Management 48.7 (2005): 485-502.

 

Commercial Shrimp Trawling: the profit does not out weigh the damaging effects on rest of the ecosystem

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By Laurel Zaima, RJD Intern

ABSTRACT

Commercial shrimp fisheries’ main objective is to maximize their target catch in order to make the most profit. Commercial shrimp fisheries satisfy this goal by the utilization of trawl nets. Trawling is a very destructive form of fishing, and unfortunately, does not take into consideration ecological consequences. Trawling, by the use of beam or otter trawls, is used to maximize their catch of shrimp; however, it also maximizes their landings of by-catch. The amount of by-catch far out weighs the amount of shrimp and target species caught in trawls.  The majority of by-catch, which comprise of non-commercial fish, juveniles, and benthic debris, are landed and discarded back into the ocean dead. The dumping of by-catch then contaminates the water and contributes to the death of other species living in the area. As the weighted trawl nets are dragged across the ocean floor, the benthic habitat is destroyed and collected by the net. Trawling destroys complex habitat structures and seagrass beds, and changes the biochemical composition of the sediment. The alterations to the substrate and damages to habitat configuration can induce an ecological shift of the organisms that live in that area. Invertebrates are especially sensitive to the change of the benthic habitat, and therefore, are indirectly affected by trawling. The invertebrate communities are also directly affected by trawling due to disturbance or mortality. Trawling can inhibit the growth of fish to their natural size as well. Trawl nets catch some species of fish so frequently they are unable to grow into adulthood before they are caught, which leads to truncated size distributions of those species. Trawl nets are also responsible for a shift in organisms of a site and trophic cascades, and cause an imbalance in the ecosystem. The studies conducted about trawls provides a plethora of evidence that confirm commercial trawl shrimp fisheries are unsustainable and cause detrimental harm to the ecosystem.

 

KEYWORDS

Commercial Fishery

Trawls

By-catch

Catch per Unit Effort

Ecosystem

 

INTRODUCTION

People all around the world love to eat shrimp and it serves as a staple in many cultural dishes. The high global demand for shrimp makes marine shrimp fisheries a very profitable and competitive market. The majority of all marine fisheries prioritize maximum profit by exploiting their target catch per unit effort. This drives competing shrimp fisheries to a variety of methods to outcompete each other. Commercial fisheries increase the amount of fishing effort by increasing their number of fishing vessels or by extending the duration of their fishing trips. There is advancement on fishing techniques and equipment to exploit the behavior and habitat preferences of target species. The greed of marine fisheries often leads to unsustainable fishing practices, a severe depletion of the target species, pollution and destruction of the marine habitat, and a negative effect on the ecosystem. In the case of shrimp fisheries, they maximize their catch per unit effort by using commercial fishing gear called a trawl. Trawling involves pulling a weighted, sock shaped net through a water column or on the sea floor in order to exploit the catch of a target species. Most commercial shrimp fisheries use beam trawls because they are specifically designed to target benthic species, like shrimp, that either bury or rest on the benthic sediment (Jennings and Kaiser, 1998). Beam trawls are comprised of a rigid beam held off the seabed by two beam shoes; the net headline is fixed at an open position and attached to the beam; the footrope is attached to the beam shoes (Jennings and Kaiser, 1998).

Beam trawl design.

Beam trawl design.

Tickler chains are gear used with trawls because they are designed to penetrate the upper layers of the sediment in order to disturb the target species that are buried in the sediment (Jennings and Kaiser, 1998). The disturbance then forces the target species to swim up and into the path of the trawl. The other kind of trawl is called otter trawls. Otter trawls are comprised of two rectangular otter boards or doors, attached to the towing warps, which keep the mouth of the net open (Jennings and Kaiser, 1998). The heavy weight of the boards can penetrate the soft sediment up to 15 centimeters (Krost et al. 1990). Otter trawls also utilize invasive tickler chains that are attached between the otter boards (Harden-Jones and Scholes, 1974), or damaging rockhopper gear, a type of ground fishing gear that is hopped over rocky substrata (Jennings and Kaiser, 1998). Unfortunately, both categories of trawls are designed to prioritize maximum catch of anything in its path and do not consider the destructive effects it has on the ecosystem. Therefore, trawling is considered the world’s number one marine ecosystem damaging agent. Commercially fishing for shrimp with trawls is an unsustainable fishing practice and causes detrimental harm to the ecosystem.

 BY-CATCH

 Trawl inefficiency: amount of by-catch vs. target species

 Trawls are one of the most unsustainable methods of fishing because trawls catch an outrageously high amount of by-catch in comparison to the amount of target shrimp or commercially profitable fish. Trawls run through the water column or on the sea floor and collect everything in its path, and the majority of organisms caught in trawls are useless by-catch. By-catch refers to marine species or organisms that are unintentionally caught while fishing for a target species. By-catch does not necessarily refer to the death of the inadvertently caught organisms; however, the by-catch of commercial fisheries often dies before it can be released back into the ocean. Fulanda (2003) determined that shrimp trawling in Ungwana Bay was a threat to marine resources due to trawls’ inefficiency. During a survey spanning for a total of 296 trawling hours for a seven-day period on three shrimp fishery vessels, shrimp only constituted of 13.7% of the total catch and 14.4% was commercially profitable fish of the total catch (Fulanda, 2003). This equates less than a third (28.1%) profitability of all the organisms caught within the trawl net. The rest of the catch within the trawl net (79.1%) is all by-catch that is often times discarded back into the ocean dead because these organisms are either non-commercial fish, juveniles, or benthic debris. The majority of the by-catch was due to non-commercial fish, such as Branchyura (crabs), leiognathidae (ponyfish), Apogonidae and Squillidae (Fulanda, 2003). The juveniles caught as by-catch were mostly undersized commercial fish (Fulanda, 2003). The high inefficiency of trawl nets is a serious threat to the future of the commercial fisheries. The commercial fisheries’ actions have a negative feedback on themselves, and if they continue to deplete their own resource, the fishery will not survive. Fortunately, there are some simple solutions to reduce the amount of by-catch caught by trawl nets. The high quantities of juveniles caught as by-catch could be easily avoided by decreasing the mesh size of the trawl nets and by avoiding trawling in shallow areas where juveniles primarily reside (Fulanda, 2003).

By-catch mortality rates

 The by-catch organisms of commercial fisheries have varying mortality rates depending on the stress tolerance of the species. Meyer et al. (1999) found that mojarra were highly susceptible to mortality from the trawl nets and the mojarra encompassed 60% of the total catch in August (Meyer et al., 1999). This indicates that over 50% of the trawls’ catch possibly died as by-catch. The differing species mortality from trawling may have an influence on the species diversity and composition of that area with long term trawling (Meyer et al., 1999). The mortality rate of species exposed to trawl nets was also seen to have an inverse relationship with size. Fritz and Johnson (1987) found that a potential explanation for the differences in trawl mortality rate between small and large sized fish could be attributed to larger fish having a greater proportion of muscle tissue and larger energy stores than smaller fish; larger fish with these characteristics are able to avoid net contact during prolonged trawl tows. Therefore, littler, less strong fish are left susceptible to higher rates of stress and mortality from trawl nets. High mortality rates of small fish from trawl by-catch can have a cascading effect on the commercial fisheries. High mortality of small fish depletes an essential food source for juveniles and can reduce the stock of juvenile fish (Meyer et al., 1999). The decline of juveniles can reduce the reproductive potential of a target species and prevent that species from replenishing their stock. This, in turn, can hurt a commercial fishery because their target species’ stock is being exhausted.

By-catch dumping

Harris and Poiner (1990) assessed the quantity and composition of by-catch from commercial prawn trawling in Torres Strait, Australia over a 2-year period. They found that a wide range of marine organisms were caught as by-catch including cephalopods, crabs, rock lobsters, scallops, sharks, rays, snakes, turtles, and mostly teleost fish (Harris and Poiner, 1990). Apart from the small amount lobsters and squid, nearly all the by-catch (approximately 99%) was discarded dead (Harris and Poiner, 1990). Majority of the time, the by-catch, whether dead or alive, is dumped back into the ocean. The large amount of dead by-catch pollutes and contaminates the water, which can result in more organismal death in that area. Fulanda’s (2003) study also found that by-catch dumped back into the waters is an environmental and health hazard because of fouling and contamination of the waters and fish harvested by artisanal fishermen. This study found that a better use of by-catch is to “off-load” it to the artisanal fishing boats that have very low catches due to their low levels of fishing technology (Fulanda, 2003).

By-catch of infaunal species and effects

 A study conducted by Jennings and Kaiser (1998) found that a trawl net’s by-catch of non-target infaunal species have drastically affected the benthic communities. Their study found that the by-catch of the infaunal bivalve, Arctica islandica, and the heart urchin, Echinocardium cordatum, by a beam trawl indicates that the tickler chains penetrated hard sandy substrate to at least a depth of 6 cm where these organisms primarily reside (Jennings and Kaiser, 1998). The invasive nature of trawls not only collects these benthic species as by-catch, but it also destroys the benthic habitat.

 

DESTRUCTION OF BENTHIC HABITAT

 Trawling effects on different bottom types

 Trawls have been designed to maximize their contact with the seabed in order to attempt to catch most amount of shrimp, however, this method demolishes the benthic habitat. The different types of bottom habitats have varying resilience to trawling. In order to understand how different bottom types respond to shrimp trawl fishing, Wells et al. (2008) conducted a study to identify the differences in community structure among sand, shell, and reef habitats in trawled and non-trawled areas in the Gulf of Mexico. They found differences in the habitat characteristics, and therefore, differences in the biotic community structure between trawled and non-trawled areas, which suggest that trawling may impact the benthic ecosystem (Wells et al., 2008). The patterns they observed from trawl fishing specifically indicated that more complex habitats, such as complex shell-rubble habitats, are more sensitive to the effects of fishing activities like trawling (Wells et al., 2008).

A. The coral community and seabed on an untrawled seamount; B. The exposed bedrock of a trawled seamount.

A. The coral community and seabed on an untrawled seamount; B. The exposed bedrock of a trawled seamount.

The destruction of complex habitats consequently reduces the amount of refuge for resident species, and can further result in a loss of species diversity and/or abundance of that trawled area.

Trawling varying effects of mud-bottom substrata

Multiple studies have indicated that the consequences of trawling are most apparent in relatively high relief, complex areas of seabed such as boulders, gravel, and rippled sand bottoms (Auster and Langton, 1999; Wells et al., 2008). However, trawling effects are still evident on mud substrate, and it can affect small-scale physical, chemical and biological habitats (Simpson and Watling 2006). Trawling on a mud-bottom habitat also may reduce the habitat structure by the removal or the death of the sediment dwelling organisms that increase the physical heterogeneity in soft sediments by burrowing and feeding (Simpson and Watling, 2006). Simpson and Watling (2006) further investigated the impacts of shrimp trawling on the mud-bottom habitat. They assessed the effects of trawl induced sediment disturbances on the habitat structure by the burrow density and the sediment porosity. Burrows increase the sediment surface area exposed to the overlying water column, are areas of chemical reactions with oxygen, dissolved metals and other elements in solution, and are sites of enhanced diagenesis and nutrient cycling (Aller, 1982). The reduction in burrow densities due to trawling is expected to impact the localized sediment elemental cycling and organic matter (Aller, 1994; Aller, 1982). Sediment porosity is and indicator of sediment grain size, arrangement, and the capability of the sediment to support animals (Simpson and Watling, 2006). Simpson and Watling (2006) found that trawling indeed had changed the porosity and sediment grain size to an extent, but it did not have a significant change to the porosity of the fishing grounds. In terms of burrow density, they found that the burrowing density was more abundant in trawled areas, which indicates that mud-bottom fishery grounds have a high recovery recolonization (Simpson and Watling, 2006). They concluded that in this area mud-bottom habitat could with stand trawl fishery efforts without a lasting impact on the overall habitat. However, Smith et al. (2000) also examined the effects of commercial trawl fisheries on a mud-bottom habitat in the eastern Mediterranean Sea and his study showed differing results. He found that there was a strong negative impact of trawling on the benthic macrofauna and megafauna, and a significant change in the sedimentary organic carbon, chlorophyll, and phaeopigments in trawled areas (Smith et al., 2000). The differences between the results of these two studies indicate that trawling has variable effects depending on the area being trawled and the bottom type of that area. Therefore, trawl-fishing grounds should be tested for resilience to trawl disturbance prior to committing a site to long term trawling.

Trawl destruction of seagrass beds

Shrimp trawling fisheries that profit off of the catch of live-bait shrimp target different fishing areas of high productivity. A live-bait shrimp trawl fisheries primarily target pink shrimp, Penaeus duorarum. These pink shrimp reside in beds of highly productive turtlegrass, Thalassia testudinum, therefore, live-bait shrimp fisheries run their trawls through these vital ecosystems in a quest for maximum catch per unit effort (Tabb and Kenny, 1969). Trawls have not been known to up root the seagrass beds because turtlegrass has an extensive root system; however, these trawls will damage and break off the turtlegrass leaves and collect them in the trawl net (Woodburn et al., 1957). The demolition of seagrass beds by trawls has the potential to change the composition of the local ecosystem by destroying a key habitat for many local species. Additionally, the trawl nets have a tendency to collect and redistribute the macroalgae and turtlegrass litter throughout different regions of the sea floor (Meyer et al., 1999). This redistribution can significantly reduce the habitat complexity of one area and enhance the complexity of another, which will make the benthic habitat unbalanced (Meyer et al., 1999). Consequently, altering the habitat can have a direct effect on the composition and abundance of the species that reside in that area.

Effects of resuspension of sediment due to trawling

Many benthic environments have a significant nepheloid layer, characterized as a near-bottom region of permanent sediment suspension (Pilskaln et al., 1998). High frequency commercial trawling may have significant effects on the resuspension fluxes of sediment and it may contribute to the maintenance of the nepheloid layer. Pilskaln et al. (1998) wanted to specifically see if the trawling in the Gulf of Mexico, where there is a thick and basin-wide nepheloid layer, increases the resuspension layer and the effects it has on the ecosystem. They observed the nepheloid layer after trawling disturbances of the infaunal organisms that characteristically live in the sediment. Polychaete worms are benthic, infaunal worms that do no swim far above the sediment water interface; however, polychaetes were found caught within the sediment traps deployed in various locations in the Gulf of Mexico (Pilskaln et al., 1998). These results suggest that the trawling fishing gear may be responsible for the artificial resuspension of the bottom sediments, and there by, either resuspending the worms from the sea floor into the nepheloid layer or discharging the worms from the net and bringing them to the surface near the trap site (Pilskaln et al., 1998).  The resuspension of the sediments by trawling directly disturbs the polychaete worms from their natural habitat and it also has biogeochemical consequences. The majority of the nutrients in the continental shelf are from primary production from the sediment, which is derived from organic matter decay and nutrient remineralization (Pilskaln et al., 1998). Trawling effects the sediment nutrient fluxes in several ways. Trawling can bury the fresh, organic matter into subsurface horizons from its normal position at the sediment-water interface, which will shift organic matter decay from aerobic, eukaryotic populations towards anaerobic, prokaryotic metabolism (Mayer et al., 1991). Trawling can also physically enhance the upward flux of remineralized nutrients in the interstitial pore water of the sediment, which will result in the nutrients entering the water column in a large pulse rather than by the usual slower and steady mechanisms (Pilskaln et al., 1998). The abundance of nutrients at one time can have alterations in the rate and type of primary production (Pilskaln et al., 1998). These biogeochemical modifications to the sediment from trawling resuspension can have a cascade effect and also change the species composition of the area. Trawling changes an area chemically, physically, and biologically and these changes have corresponding effects on the organisms that reside in these areas.

 

ALTERATIONS IN THE INVERTEBRATE COMMUNITY

Invertebrate species response to direct trawling

Since trawls have significant effects on the benthic habitat, consequently, trawling alters the abundance and diversity of the benthic community.

Trawling an area can either directly affect the infaunal, invertebrate community by mortality and/or disturbance, or trawling can indirectly affect invertebrates by the destruction of their habitat and/or chemical changes to the sediment. Simpson and Watling (2006) found that there are clear disturbances in the macrofaunal community structure in areas of recently shrimp-trawled areas, where as, there was no detection of disturbance in areas of older (minimum of a year prior) trawling activity. Specifically, trawling-sensitive taxa, like bivalve families Nuculidae and Nuculanidae, were more abundant in untrawled areas because these species could not tolerate the damaging effects of trawls (Simpson and Watling, 2006). Many studies, including Simpson and Watling (2006), have observed trawling affecting invertebrate species differently depending on their life histories. Invertebrate species of large, long-lived animals living near the surface of the sediment are predicted to be more sensitive to trawling disturbance, where as, small, fast growing, regenerating and mobile animals are expected to be more dominant in trawled areas (De Groot, 1984; Rumohr and Krost, 1991; Hall, 1994; Kaiser 1998; Thrush et al., 1998). Unfortunately, this sensitivity corresponds to their mortality rate to trawls as well. The mortality rates of infaunal organisms due to trawling depend on certain life history characteristics, such as body size and depth distribution within the sediment (Duplisea et al., 2002). Fortunately, the macrofaunal communities on mud-bottom trawling grounds have fast recovery rates due to their high reproductive output (Simpson and Watling, 2006). The invertebrates of mud-bottom trawling sites, in comparison to more sensitive species in other habitats, are capable of withstanding the consequences of trawling if there is an adequate amount of time given for recovery between trawls. However, over harvesting or long-term trawling of a centralized location, even a tolerant habitat like a mud-bottom, could result in a semi-permanent degradation of the invertebrate abundance and diversity (Jones, 1992; Auster et al., 1996, Gray, 1997, Jennings and Kaiser, 1998).

Hansson et al. (2000) sought to study the effects of trawling on assemblages of macro fauna in Gullmarsfijorden, Sweden. The study found that there was an overall appearance of a negative trend in abundance of macrofauna within the fjord. Explicitly, the negative effects of trawling declined the abundance of echinoderms, especially the ophiurids (brittle starts) (Hansson et al., 2000). Hansson et al. (2000) found that the ophiurids’ population decreased by an average of 30% at trawled sites in comparison to the untrawled sites. These results are somewhat surprising because ophiuroids have the ability to regenerate lost body parts and it would have been assumed that they would be resistant to trawling (Lindley et al., 1995; Kaiser and Spencer, 1996; Tuck et al., 1998). There is a possibility that the decline in abundance of ophiuroids is due to responses to oxygen stress (Hansson et al., 2000). Ophiuroids may have migrated from protected sediment to a more exposed position on the sediment surface as a response to sub-lethal hypoxia (Rosenberg et al., 1991) induced by the absence of water renewal in the deep parts of the fjord in 1997 (Hansson et al., 2000). Once the Ophiuroids were exposed to the surface of the sediment, they were also exposed to the shrimp trawl nets that either directly destroyed their bodies beyond regeneration or caught them as by-catch.

Invertebrate species response to indirect trawling

Some Invertebrate species are sensitive to alterations in their environment and can be indirectly affected by trawling that destroys their habitat. In looking at the invertebrate community structure after trawling, Wells et al. (2008) study indicated that some invertebrate species such as two brittle stars (O. appressum and O. elegans), a sea star (L. clathrata), and urchin (A. punctulata), a hairy sponge crab (D. antillensis), the shortfinger neck crab (P. sidneyi), and brown rock shrimp (Sicyonia brevirostris) are more abundance in structurally complex, non-trawled areas. Essential complex habitats provides shelter and protection for these invertebrates, and without these structures, these invertebrates are vulnerable and susceptible to predation. Therefore, these species are more sensitive to trawling because it destroys their complex habitats necessary for their survival. The shrimp trawling has variable direct and indirect effects on the invertebrate community depending on the species and the bottom type sediment of a fishing ground; however, the negative impacts of trawling can create a bottom up cascade from the invertebrates to other species of the ecosystem.

 

DISTRUPTIONS IN THE FOOD WEB AND ECOSYSTEM 

Trawls destruction of habitats drive an ecosystem shift

The food web and ecosystem are severely disrupted by the destructive method of trawling and the shrimp commercial fisheries’ high consumption of target species and by-catch. The loss in the structural benthic habitat can result in a shift of residing marine organisms. Wells et al. (2008) found that with the loss of the structural epibenthic community due to trawling resulted in a shift from snappers (Lutjanidae) and emperors (Lethrinidae) towards an ecosystem dominated by lizardfish (Synodontidae) and bream (Nemipteridae). In general, trawled areas become inhabited by species with similar life characteristics, including: small size, short life spans, high mortality, and rapid biomass turnover (DeVries and Chittenden, 1982; Geoghegan and Chittenden, 1982; Murphy and Chittenden, 1991; McEachran and Fechhelm, 1998). Species including the longspine porgy, silver seatrout, large-scale lizardfish, and gulf butterfish are all species that successfully inhabit trawled areas because their life history characteristics will allow them to recover swiftly after the damage (Wells, Cowan, and Patterson, 2008). The destruction to habitats caused by trawls has an influence on the entire ecosystem composition and potentially reduces species diversity.

Trawling triggers truncated size distributions

Some fish species in trawling areas have been seen to have truncated size distributions and reduced median size. In the Gulf of Mexico, the species that showed truncated size distributions over trawled areas were the same species that were the most abundant caught as by-catch in the shrimp trawl fishery (Wells et al., 2008; Chittenden and McEachran, 1976). Similarly, other studies have found that trawling and dredging is the cause of a decrease in biomass and average size of demersal fish and invertebrate fauna (Bianchi et al., 2000; Zwanenburg, 2000, Duplisea et al., 2002). The observations of truncated size distributions of local fish indicates that a species is caught at such a high frequency that they are unable to grow into adulthood before they are caught and captured. This can severely affect the population, abundance, and health of a species.

Manipulation of the ecosystem into a top-down trophic cascade

Trawling also has the ability to manipulate the ecosystem in ways to actually produce more target shrimp by reducing the amount of predators. Salcido-Guevara et al. (2012) discovered that shrimp trawling in La Paz Bay had positive impacts on the shrimp populations because the by-catch from the trawl nets actually reduced the amount of shrimp predators. This study suggested that predator removal had a strong positive impact on the shrimp’s population than does the negative impact of fishing the shrimp (Salcido-Guevara et al., 2012). These results are alarming because the human manipulation of an ecosystem does not always end with the results that are desired or expected. By purposefully decreasing the amount of shrimp predators for their benefit, the fisheries are creating a top-down trophic cascade. A top-down trophic cascade suggests that the apex predators’ populations have the power to alter the rest of the food web; for example, if there is a reduction or depletion of predators, there will be a rise in prey’s population. This trophic cascade continues down the food web and will eventually either deplete or alter the diversity of the primary producers. Trophic cascades can throw the ecosystem food web out of balance, causing expansive negative effects that were not initially considered. Nonetheless, under heavy shrimp fishing pressure, both shrimp and the predator’s biomasses will sharply decline as expected (Salcido-Guevara et al., 2012).

 

DISCUSSION

Shrimp fisheries current trawling methods can have extensive negative impacts on the habitat structure, the benthic invertebrate community, the shrimp population, other local species abundance and diversity, and the overall balance of the ecosystem. The shrimp catch of the commercial trawl fisheries do not out weigh the externality that trawls exert on the ecosystem. With long term and frequent trawling of an area, eventually, benthic habitat will be destroyed, the species diversity and abundance will decrease, and in turn, the target species will also decline. Therefore, there is a negative feedback on the shrimp fishery when utilizing the current design of trawls in high frequency. The implications of these findings confirm that changes need to be made before the destruction of trawling is irreversible. There are some potential solutions to reduce the damaging impacts of trawling. The avoidance trawls is the most effective way to prevent damage; therefore, educating people about the unsustainability of commercial shrimp fisheries and encouraging people to reduce their intake of shrimp can have a large impact on the reduction of damage by trawling. If there is a decline in the demand of shrimp, then the shrimp fisheries will reduce their trawling efforts. Another potential solution is providing alternatives to trawling. Although it’s a less practical solution, self-catching shrimp with a net is encouraged because it is the least invasive to the environment. By employing shrimp catching as a sport or as an ecotourism attraction, people can catch their own dinner and have fun doing it. However, the problem with this is that most people do not live in an area where they can catch their own shrimp so readily.

Commercial shrimp fisheries can also implement their own modifications to their current trawling methods in order to help reduce damage. By limiting the amount of time per trawl tow and the trawl frequency of an area, the bottom habitat and local organisms will be given a chance to recover. Trawling time constraints will prevent a site from being over exploited beyond recovery. Shrimp trawls can also reduce negative impact by modifying the area and the depth at which they tow. Shrimp trawling is seen to have the least destructive effects on certain mud-bottom substrata (Simpson and Watling, 2006). Damage to complex structures and essential habitats can be avoided if commercial shrimp fisheries localized their trawling to a more stress tolerant area, such as mud-bottom habitats.  Fulanda (2003) found that trawling in shallow areas increases their by-catch of juveniles. Therefore, regulations set for a minimum trawl depth will prevent trawls from being towed in too shallow areas where juveniles primarily reside. Modifications to the net design can further improve the reduction of by-catch. Decreasing the mesh of the trawl net can reduce the amount of small fish by-catch and juvenile by-catch (Fulanda, 2003). There are a variety of potential solutions to the damaging effects of trawl nets, but first, the attitude of the commercial shrimp fisheries need to change. Commercial shrimp fisheries need to stop prioritizing their maximum profit for “right now,” and instead, start considering the effects their fishing practices have on the ecosystem and the future of their fishery. With a changed mindset, initiatives for sustainable fishing will be prioritized and shrimp fishing will pose less damaging consequences on the ecosystem.

 

 

REFERENCES

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Aller RC (1994) Bioturbation and remineralization of sedimentary organic matter effects of redox oscillation. Chemical Geology, 114: 331-345

Auster PJ, Langton R (1999) The effects of fishing on fish habitat. American Fisheries Society Symposium 22: 150-187

Auster PJ, Malatesta RJ, Langton RW, Watling L, Valentine PC, Donaldson CL, Langton EW, Shepard AN, Babb IG (1996) The impacts of mobile fishing gear on seafloor habitats in the Gulf of Maine (Northwest Atlantic): Implications for conservation of fish populations. Rev Fish Sci 4: 185-202

Bianchi G, Gislason H, Graham K, Hill L, Jin X, Koranteng K, Manickchand-Heileman S. et al. (2000) Impact of fishing on size composition and diversity of demersal fish communities. ICES Journal of Marine Science 57: 558-571

Chittenden ME, McEachran JK (1976) Composition, ecology, and dynamics of demersal fish communities on the Northwestern Gulf of Mexico continental shelf, with a similar synopsis for the entire Gulf. Texas A&M University Sea Grant Publication 76-208, College Station, TX.

De Groot SJ (1984) The impact of bottom trawling on benthic fauna fo the North Sea. Ocean Manage 9: 177-190.

DeVries DA, Chittenden ME (1982) Spawning, age determination, longevity, and mortality of the silver seatrout, Cynoscion nothus, in the Gulf of Mexico. Fishery Bulletin US 80: 487-500

Duplisea DE, Jennings S, Warr KJ, Dinmore TA (2002) A size-based model of the impacts of bottom trawling on benthic community structure. Canadian Journal of Fisheries and Aquatic Sciences 59: 1785-1795

Fritz KR, Johnson DL (1987) Survival of freshwater drums released from Lake Erie commercial shore seines. N. Am. J. Fish. Manage. 7: 293-298.

Fulanda B (2003) Shrimp Trawling in Ungwana Bay A Threat to Fishery Resources. African Studies Centre: 233- 242

Geoghegan P, Chittenden ME (1982) Reproduction, movements, and population dynamics of the longspine porgy, Stenotomus caprinus. Fishery Bulletin US 80: 523-540

Gray JS (1997) Marine biodiversity: patterns, threats and conservation needs. Biodivers Conserv 6: 153-175

Hall SJ (1994) Physical disturbance and marine benthic communities: life in unconsolidated sediments. Oceanogr Mar Biol Annu Rev 32: 179-239.

Hansson M, Lindegarth M, Valentinsson D, Ulmestrand M (2000) Effects of Shrimp-Trawling on abundance of benthic macrofauna in Gullmarsfjorden, Sweden. Mar Ecol Prog Ser 198: 191-201

Harden-Jones FR, Scholes P (1974) The effect of door-to-door tickler chain on the catch-rate of plaice (Pleuronectes platessa L.) taken by an otter trawl. Journal du Conseil International pour I’exploration de la Mer 35: 210-212.

Harris AN, Poiner IR (1990) By-catch of the prawn fishery of Torres Strait; composition and partitioning of the discards into components that float or sink. Mar Freshwater Res 41: 53-64

Jennings S, Kaiser MJ (1998) The effects of fishing on marine ecosystems. Adv Mar Biol 14: 201-352

Jones JB (1992) Environmental impact of trawling on the seabed: a review. NZ J Mar Freshw Res 26: 59-67

Kaiser MJ, Spencer BE (1996) The effects of beam-trawl disturbance on infaunal communities in different habitats. J Anim Ecol 65: 348-358.

Kaiser MJ (1998) Significance of bottom-fishing disturbance. Conserve Biol 12: 1230-1235.

Krost P, Bernhard M, Werner F, Hukriede W (1990) Otter trawl tracks in Kiel Bay (Western Baltic) mapped by side-scan sonar. Meeresforschung 32: 344-353.

Lindley JA, Gamble JC, Hunt HG (1995) A change in the zooplankton of the central North Sea (55O to 58O N): a possible consequence of changes in the benthos. Mar Ecol Prog Ser 199: 299-303.

Martinet V, Blanchard F (2009) Fishery externalities and biodiversity: Trade-offs between the viability of shrimp trawling and the conservation of Frigatebirds in French Guiana. Ecological Economics 68: 2960-2968

Mayer LM, Schick DF, Findlay R, Rice DL (1991) Effects of commercial dragging on sedimentary organic matter. Marine Environmental Research 31: 249-261

McEachran JD, Fechhelm JK (1998) Fishes of the Gulf of Mexico. University of Texas Press, Austin, TX.

Meyer DL, Fonseca MS, Murphey PL, McMichael RH Jr, Byerly MM, LaCroix MW, Whitfield PE, Thayer GW (1999) Effects of live-bait shrimp trawling on seagrass beds and fish bycatch in Tampa Bay, Florida. Fish Bull 97: 193-199

Murphy MD, Chittenden ME (1991) Reproduction, age and growth, and movements of the gulf butterfish Peprilus burti. Fishery Bulletin US 89: 101-116

Pilskaln CH, Churchill JH, Mayer LM (1998) Resuspension of sediment by bottom trawling in the Gulf of Maine and potential geochemical consequences. Conservation Biology 12: 1223-1229

Rooper CN, Wilkins ME, Rose CS, Coon C (2011) Modeling the impacts of bottom trawling and the subsequent recovery rates of sponges and corals in the Aleutian Islands, Alaska. Continental Shelf Research 31: 1827-1834

Rosenberg R, Hellman B, Johnsson B (1991) Hypoxic tolerance of marine benthic fauna. Mar Ecol Prog Ser 79: 127-131.

Rumohr H, Krost P (1991) Experimental evidence of damage to benthos by bottom trawling with special reference to Arctica islandica. Meeresforsch Rep Mar Res 33: 340-345.

Salcido-Guevara LA, Monte-Luna P, Arreguín-Sánchez F, Cruz-Escalona VH (2012) Potential ecosystem level effects of a shrimp trawling fishery in La Paz Bay, Mexico. Open Journal of Marine Science 2: 85-89

Simpson AW, Watling L (2006) An investigation of the cumulative impacts of shrimp trawling on mud-bottom fishing grounds in the Gulf of Maine: effects on habitat and macrofaunal community structure. ICES Journal of Marine Science 63: 1616-1630

Smith CJ, Papadopoulou KN, Diliberto S (2000) Impact of otter trawling on and eastern Mediterranean commercial trawl fishing ground. ICES Journal of Marine Science, 57: 1340-1351

Tabb DC, Kenny N (1969) A brief history of Florida’s live bait shrimp fishery with description of fishing gear and methods. FAO fish Rep. 57: 1119-1134

Thrush SF, Hewitt JE, Cummings VJ, Dayton PK (1995) The impact of habitat disturbance by scallop dredging on marine benthic communities: what can be predicted from the results of experiments? Mar Ecol Prog Ser 129: 141-150.

Tuck ID, Hall SJ, Robertson MR, Armstrong E, Basford DJ (1998) Effects of physical trawling disturbance in a previously unfished sheltered Scottish sea loch. Mar Ecol Prog Ser 162: 227-242.

Van Dolah RF, Wendt PH, Levisen MV (1991) A study of the effects of shrimp trawling on benthic communities in two South Carolina sounds. Fisheries Research 12: 139-156

Warnken KW, Gill GA, Dellapenna TM, Lehman RD, Harper DE, Allison MA (2003) The effects of shrimp trawling on sediment oxygen consumption and the fluxes of trace metals and nutrients from estuarine sediments. Estuarine, Coastal and Shelf Science 57: 25-42

Wells RJD, Cowan JH Jr, Patterson WF III (2008) Habitat use and the effect of shrimp trawling on fish and invertebrate communities over the northern Gulf of Mexico continental shelf. ICES Journal of Marine Science 65: 1610-1619

Woodburn KD, Eddred B, Clark E, Hutton RF, Ingle RM (1957) The live bait shrimp industry of the west coast of Florida. Florida State Board Conserv. Tech. Ser. 21: 3-33

Zwanenburg KCT (2000) The effects of fishing on demersal fish communities of the Scotian Shelf. ICES Journal of Marine Science 57: 503-509

71 Questions: A Guide for Marine Conservation

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By James Keegan, RJD Intern

The ocean remains an immense resource for humanity, providing food, economic activity, and cultural roots for many. Although these resources are valuable, it is difficult to effectively protect them because our knowledge of marine ecosystems is lacking. To correct this insufficient understanding of the marine environment, Parsons et al. 2014 conducted two workshops in order to establish a list of important questions that would help direct conservation research.  If conservationists can answer these questions, the community’s ability to conserve and mange the world’s marine resources would substantially improve. With the contributions from participants in the fields of science, conservation, industry, and government, Parsons et al. 2014 identified 71 key questions for the preservation of the marine environment. They then grouped these questions into 8 categories, each associated with an aspect of marine conservation: fisheries, climate change, other anthropogenic (human caused) threats, ecosystems, marine citizenship, policy, societal and cultural considerations, and scientific enterprise. Using these questions as guidelines, funders and researchers can develop programs that can greatly benefit marine conservation.

Because oceans are vast, and their environments difficult to access, marine research is expensive and difficult to undertake. Expensive technologies necessary for accessing marine environments, like submersibles, raise costs beyond those typically incurred by terrestrial, or land-based, studies. Moreover, marine conservation research receives funding at a much lower rate than terrestrial conservation. In order to combat these issues, Parsons et al. 2014 sought out to identify a set of questions that, if answered, would contribute immensely to conserving marine ecosystems on a global scale, thus maximizing the returns of the research programs involved. By prioritizing the most important questions facing marine conservation, conservationists can more effectively protect the marine environment with the funding they receive.

A table showing example questions produced by Parsons et al. 2014 for each of the 8 categories.

A table showing example questions produced by Parsons et al. 2014 for each of the 8 categories.

In order to produce their list of key questions, Parsons et al. 2014 conducted a pair of workshops. In their first workshop, held during the second International Marine Conservation Congress (IMCC), 17 participants with varying expertise reviewed an initial list of 631 questions. Parsons et al. 2014 solicited these initial questions from participants at IMCC, professional peer groups, and the Society for Conservation Biology. The 17 participants reduced the number of questions to 316, and Parsons et al. 2014 voted on these remaining questions in their second workshop, ultimately reducing the number to 71. Finally, they grouped these 71 questions into 8 categories: fisheries, climate change, other human produced threats, ecosystems, marine citizenship, policy, societal and cultural considerations, and scientific enterprise.

A flow chart summarizing the steps taken in the workshops. (Parsons et al. 2014)

A flow chart summarizing the steps taken in the workshops. (Parsons et al. 2014)

Each of the 8 categories pose challenges to marine conservationists. Mass extraction of fish and other organisms stress marine ecosystems and can lead to overexploitation. Components of climate change, like warmer waters and ocean acidification, directly affect marine species and indirectly affect ecological interactions. Other human activities negatively impact marine ecosystems, like fertilizer runoff creating oxygen-depleted areas in the ocean, or global shipping routes introducing invasive species into new areas. Because conducting research in the marine environment can be difficult, marine ecosystem processes and population dynamics are poorly understood.  The behavior and lifestyle choices of individual citizen’s significantly impact the health of the marine environment, but the best methods for engaging the public and promoting marine conservation remain illusive. Marine conservation and resource use policy are challenging because marine policy encompasses both the lack of information on marine systems and complex governance issues. Moreover, marine conservation is closely tied with socioeconomic and cultural factors, requiring engagement in such areas with targeted research. Scientific culture itself needs reworking, in that data sharing, collaboration, and funding for fields like taxonomy need to improve. With so many issues facing marine conservation, the questions articulated by Parsons et al. 2014 will help focus the conservation effort.

Past ecological prioritization exercises underemphasized marine issues, so Parsons et al. 2014 highlighted the specific challenges facing marine conservation. Although these questions have not been answered completely, people can, and should, undertake reasonable conservation efforts regarding their subject matter. By serving as a guide for scientific research, these 71 questions, along with evidence-based, participatory, and transparent management, can lead us towards effective marine conservation.

References:

Parsons, E. C. M., Favaro, B., Aguirre, A. A., Bauer, A. L., Blight, L. K., Cigliano, J. A., Coleman, M. A., Côté, I. M., Draheim, M., Fletcher, S., Foley, M. M., Jefferson, R., Jones, M. C., Kelaher, B. P., Lundquist, C. J., McCarthy, J.-B., Nelson, A., Patterson, K., Walsh, L., Wright, A. J. and Sutherland, W. J. (2014), Seventy-One Important Questions for the Conservation of Marine Biodiversity. Conservation Biology, 28: 1206–1214. doi: 10.1111/cobi.12303

Five Ways to Fight Illegal Fishing

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By Lindsay Jennings, RJD Intern

 The issue of illegal fishing has, deservedly, been getting international attention recently but it should be noted that this ‘great ocean heist’ is not a new phenomenon. For far too long fishing boats have been misreporting or underreporting their catches. There simply are not enough fish for these boats to catch so they resort to illegal, unreported and unregulated (IUU) fishing. IUU fishing accounts for $10-$23 billion annually in internationally traded seafood,[1] and to compound the problem, it has been linked to environmental degradation, political instability, slave labor, and the movement of other illicit cargo like drugs and weapons. While there is not one single solution, there can be a complimenting set of actions taken at international, national, and local levels to address this threat, of which the top five are presented below:

  1. Legislation – It is crucial to develop the framework for addressing IUU fishing on a global scale, as this kind of fishing is rarely confined by species or geographic boundaries. Legislation like the Port States Measures Agreement (PSMA) gives countries the opportunity to reduce profitability of IUU fishing by denying port access and services to IUU vessels, better controlling what seafood is coming into their ports.[2] Combined international efforts to pass and implement this global treaty would allow some of the world’s largest and most lucrative ports to not only penalize those who illegally fish but close the market for vessels trying to offload their catch.
  1. Global Vessel Identification – Although the right to fish on the high seas is given to all countries, some are unwilling or unable to enforce their regulations, providing illegal fishermen with ‘flags of convenience.’ When IUU vessels are compromised, crews will often re-flag, or re-register, their vessels to a different port state, evading law enforcement and circumventing international fishing regulations.[3] Similar to a car’s Vehicle Identification Number (VIN) or our Social Security Numbers, Unique Vessel Identifiers (UVI) can be used to ‘tag’ a fishing vessel with a non-transferable, unique number which stays with that vessel until it is permanently taken out of the water. By eliminating the ability for vessels to hide behind a new identity, punishments for illegal fishing activities would dramatically increase.3
Pic 1 - IMO Vessel Number

Unique and permanent vessel identification numbers can help cut down IUU vessels from re-flagging themselves. Credit: Wikimedia Commons

  1. Seafood Traceability – The United States is the second largest importer of seafood,[4] a commodity which earns more in annual trading than coffee, cocoa, bananas, and rubber combined. With the majority of seafood caught out of sight of authorities, it is essential to ensure that what is being caught and sold is done so legally. Traceability programs would require imports to be accompanied with documentation describing vessel, date, location, gear, species, and common name, to ensure traceability from bait to plate.[5] Seafood retailers have the ability to influence consumer behaviors and demand for legal seafood. They can shift the risk to reward ratio of IUU fishing by eliminating market access for illegal seafood, stopping it from ‘paying off.’[6]
  1. Monitoring, Surveillance, and Compliance (MSC) – While legislation and regulations offer a sound framework, they become ineffective if vessels are not complying with those regulations.[7] Enforcement is often lacking or nonexistent on the high seas, therefore MSC systems must be implemented to ensure adequate monitoring and surveillance. The simple use of technology like vessel monitoring systems (VMS) and automatic identification systems (AIS) would guarantee vessels are fishing within legal limits. Beyond VMS and AIS, satellite monitoring and even remote operated drones have proven to be effective,6 allowing authorities to watch fishing effort from 1000’s of miles away and adding a much-needed layer of accountability.
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Portuguese Navy and Gabonese sailors work together to inspect a holding bay for fish aboard an IUU fishing vessel. Credit: U.S. Navy

  1. Development – IUU fishing often stems from developing country’s underlying social, economic, and political issues, meaning they have greater difficulties achieving enforcement and compliance.7 With the primary motivation for IUU fishing being financial gain, coupled with poor economic prospects, incentive will remain to engage in this kind of fishing until alternative jobs pay a higher wage.3,7 Governments and non-governmental organizations should cooperate to develop alternative sources of employment to disincentivize IUU fishing without sacrificing the ability of those fishers to support themselves.
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The Coast Guard Cutter, Rush, escorts a high seas illegal fishing vessel back to port. Credit: U.S. Coast Guard

IUU fishing is one of the most serious threats facing the achievement of sustainable global fisheries and food security. Fortunately, the tools to fight IUU fishing already exist. The responsibility doesn’t lie with one country, but with a strong and coordinated effort of international and national players who can effectively deter fishers from engaging in and benefitting from IUU fishing.

 

[1] Agnew, David J., John Pearce, Ganapathiraju Pramod, Tom Peatman, Reg Watson, John R. Beddington, and Tony J. Pitcher. “Estimating the worldwide extent of illegal fishing.” PLoS One 4, no. 2 (2009): e4570.

[2] Flothmann, Stefan, Kristín von Kistowski, Emily Dolan, Elsa Lee, Frank Meere, and Gunnar Album. “Closing loopholes: getting illegal fishing under control.” Science 328, no. 5983 (2010): 1235-1236.

[3] Gallic, Bertrand Le, and Anthony Cox. “An economic analysis of illegal, unreported and unregulated (IUU) fishing: Key drivers and possible solutions.” Marine Policy 30, no. 6 (2006): 689-695.

[4] NOAA. 2012. Fisheries of the United States 2011. National Marine Fisheries Service and the Office of Science and Technology. Available via: http://www.st.nmfs.noaa.gov/st1/fus/fus11/FUS_2011.pdf.

[5] Borit, Melania, and Petter Olsen. “Evaluation framework for regulatory requirements related to data recording and traceability designed to prevent illegal, unreported and unregulated fishing.” Marine Policy 36, no. 1 (2012): 96-102.

[6] Global Ocean Commission. “Illegal, unreported, and unregulated fishing.” (2013). Available via: http://www.globaloceancommission.org/wp-content/uploads/GOC-paper08-IUU-fishing.pdf

[7] Erceg, Diane. “Deterring IUU fishing through state control over nationals.” Marine Policy 30, no. 2 (2006): 173-179.

Watered Down Medicine: The Influence of Marine Organisms in Medicine

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By Gabi Goodrich, RJD Intern

Ancient people worshipped, prayed, and sacrificed to the ocean for the powers of healing and power it possessed. While the mentality has changed, the influence over people and medicine today has not. With more and more focus on disease and sickness, the search for new and better medicines are an exponentially growing field. Over the past 20 years, around 10,000 known natural substances have been found from isolating marine organisms. Only a mere 28 of these are currently in clinical testing, and some are in pretrial. While only a small number of drugs on the market today are actually derived from marine organisms, the appeal of the new source can be found in the differential compounds of marine dwelling organism versus land-dwelling ones. These few organisms that have been approved by the Food and Drug Administration (FDA) do play an everyday role in the medical field and technology. Horseshoe Crabs have been widely used for their blood, which is used to screen intravenous drugs for bacteria contamination. Still, it is important to remember that marine organisms are not just the macrofauna, but also include sponges, cyanobacteria, corals, and algae. For example, the chemicals located in cyanobacteria have been found as an effective malaria treatment.  Sponges also appear to be a very promising field. Researchers found that many species of sponges, such as Tethya crypta, show signs of anticancer and antiviral agents. Though, many discoveries have already been made using sponges. The drug Halaven, used for metastatic breast cancer, was originally derived from the Halichondria sponge family. Furthermore, the work with nucleosides in the Caribbean sponge Cryptotethya crypta had set the basis for the synthesis of Ara-C, which created Cytarabine, used to treat cancers of white blood cells, in 1969.

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A Caribbean sponge.

It is essential to state that there is a definite paradigm shift in the view of marine organisms as a viable source for new medicines and advances. Scientists are also turning to corals for their naturally occurring source of prostaglandins, which are hormones manufactured in tissues that control activities such as blood clotting and complex inflammatory responses. The trials using prostaglandins are still ongoing. A less common, yet highly used, breakthrough was the use of conotoxins from the venom of marine cone snails. In the natural environment, snails would use this venom to paralyze their prey. In humans, this venoms attack the metabolism at given points. However, a modified mixture of this toxin provides a morphine-alternate and provides a more powerful painkiller than morphine. This discovery came thirty years after the discovery of Ara-C.

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A marine cone snail eating.

The most recent contribution from marine organisms to medicine is the advancement of trabectidin, an alkaloid, from Ecteinascidia turbinata, the mangrove tunicate. In 2008 the Food and Drug Administration approved Yondelis, which is used in antitumor treatment and prevents resistance to chemotherapy. The possibilities for the use of marine organisms and the compounds derived from them are endless. However, many obstacles must be overcome in order to even start testing using these compounds.

With so many advancements, the problem does not lie in the potential of the ocean but rather the resources of location and production. 95% of the ocean has yet to be explored. With such a vast expanse to explore, the technology does not yet support the collection and storage of organisms and molecules. It is important to also remember that pharmaceutical companies work for profit. The time and money it takes to locate and test the organisms far out ways the profit that would be made from the potential new drug, which is why the ocean was overlooked for such a long time. With that being said, the advancement of new technology, the time and effort it takes to test has been reduced significantly from the methods of testing in the past. This in turn, takes less money than in previous years. The DNA sequencing of numerous marine organisms make it easier for scientists to have a better idea of which favorable DNA sequences are in which organisms in a short amount of time. Yet another hurdle is how to handle the problem of exploitation. Professor Steve Yearley, head of the ESRC genomics forum, explains while there are controls for regulating the exploitation of animals, plants and microbes on land, regulating them at sea is going to be infinitely more difficult “We cannot stop pirates off Somalia, so how is someone supposed to protect rare sponges that they find in their coastal waters?” Moreover, because many of these organisms are in limited quantity, the susceptibility to changes like temperature, salinity, acidity threatens to destroy them. With the rapidly changing world it is important to protect the oceans and what they could hold.

 

Works Cited

“Medicines from the Sea.” NOAA. National Oceanic and Atmospheric Administration, n.d. Web. 2 Oct. 2014.<http://www.noaa.gov/features/economic_0309/medicines.html>.

Davis, Alison. “Medicines By Design.” Chapter 3: Drugs From Nature, Then and Now.  National Institutes of Health, July 2006. Web. 2 Oct. 2014 <http://publications.nigms.nih.gov/medbydesign/chapter3.html>.

Gerwick, Bill. “Introduction to Drug Discovery From Marine Organisms.” (n.d.): n. pag. Oregon State University. Web. <http://agsci.oregonstate.edu/aquatic-bt/sites/default/files/Gerwick-New_Medicines_from_the_Sea.pdf>.

Fenical, William. “MARINE BIODIVERSITY AND THE MEDICINE CABINET THE STATUS OF NEW DRUGS FROM MARINE ORGANISMS.” 9.1 (1996): n. pag. The Oceanography Society. Web. <http://www.tos.org/oceanography/archive/9-1_fenical.pdf>.

Levins, Nicole. “Coral Reefs and Medicine | The Nature Conservancy.” Coral Reefs and Medicine | The Nature Conservancy. The Nature Conservency, n.d. Web. 2 Oct. 2014. <http://www.nature.org/ourinitiatives/habitats/oceanscoasts/explore/coral-reefs-and-medicine.xml>.

Maxwell, Sara. “Medicines from the Deep: The Important of Protecting the High Seas from Bottom Trawling.” (2005): n. pag. Natural Resource Defense Council, Mar. 2005. Web. <https://www.nrdc.org/water/oceans/medicines/medicines.pdf>.

Effects of Anthropogenic Noise on Marine Mammals

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By Daniela Escontrela, RJD Intern

A topic of concern in the past few years has been noise pollution in the ocean. Particularly, noise pollution has been thought to affect marine mammal populations since they are so reliant on acoustics for navigation and communication (Erbe 2011). Marine mammals are of special conservation concern because they have been so heavily exploited in the past century via whaling and bycatch (Tyack 2009). The marine mammal protection act was developed 1972 and aimed at protecting and conserving marine mammals and their natural habitats (Tyack et al 2003). However, at the time the marine mammal protection act was passed many of the regulations were based on the pressures of whaling. Now that whaling is better controlled, it is possible that degradation of habitat from multiple sources may pose a bigger threat to marine mammals. One of these impacts that may be causing degradation to marine mammal populations and their environment is noise pollution. (Tyack 2009) The marine soundscape can be complex and for this reason it is hard to study effects of anthropogenic noise on marine mammals. In addition to anthropogenic sounds such as those that come from ships, petroleum exploration and naval sonar, among others, the marine soundscape is also made up of natural ambient sounds such as wind and waves and biological sounds such as calls emitted from marine mammals, fish and crustaceans. (Erbe 2011) This intricate combination of sounds in combination with lack of adequate technology and the difficulty of studying these sometimes elusive animals has made this area of study a hard one.

In 1971 biologist Roger Payne and engineer Douglas Webb were among the first to raise concern over how anthropogenic noise could affect marine mammals. It had been recently discovered that baleen whales used special calls for reproductive purposes. These calls could usually be detected as far away as 280 km away, however, Payne and Webb calculated that with increased ambient noise due to modern commercial ships, these calls were being masked and could only be detected at 90 km distance now. (Tyack 2009) Anthropogenic noise can also mask echolocation clicks which are used by Odontocetes (toothed whales) for finding food and navigation and it can also mask environmental noises that animals listen to such as surf and approaching predators. (Erbe Farmer 2000) If noise masks communication signals, this can disrupt mating systems or parental care and affect reproduction and survival of young in endangered populations. (Tyack 2009) Anthropogenic noises have also been seen to disrupt normal behaviors such as cessation of feeding, resting, socializing and onset of alertness or avoidance. (Erbe Farmer 2000) If foraging is affected by noise this can cause animals to grow more slowly (Tyack 2009). These man made noises can even cause damage to hearing by decreasing auditory sensitivity which can be permanent or temporary. However different animals have different sensitivities and are impacted differently, for example mystecetes (baleen whales) are more sensitive at lower frequencies. (Erbe Farmer 2000)

Early experiments tracked migrating gray whales (mystecetes) as they traveled the corridor of California and found that these whales were sensitive at certain pressure levels when sounds that imitated those from ships or dill rigs were played back to them. Migrating bowhead whales traveling past seismic survey vessels were also studied and found to be sensitive at certain pressure levels. In fact these whales wouldn’t come within 20 km of these areas because the air guns used in these surveys were so intense. It has been shown that many mystecetes show avoidance of certain areas were such loud noises occur. Odontocetes have been harder to study because of their prolonged dives, sometimes exceeding an hour. In the little research that has been done, Odontocetes don’t show the same avoidance of anthropogenic noises that mystecetes show. One study used tagged sperm whales to see how they would respond to the air guns used by seismic survey vessels. The whales were satellite tagged and seismic survey vessels ramped up their air gun array and conducted controlled approaches to tagged whales. None of the seven whales tagged seemed to avoid the vessel. One of the whales remained on the surface and only began a foraging dive after the noise had ceased. The other six whales that were tagged continued their foraging dives. What was found however was that these whales were seen to reduce their swimming effort and they reduced their attempts at catching prey. This suggests not an avoidance pattern like some mystecetes but instead a behavior change, in this case foraging behavior was altered. (Tyack 2009)

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An image of the satellite tag used by Tyack fitted onto the back of a sperm whale

Seismic surveys and pile driving can produce some of the most intense anthropogenic noises in the marine environment. How these activities affect marine species depends on how well the sound propagates underwater, its frequency characteristics and its duration. In a study by Bailey et al 2010 measures of pile driving noise levels were made in NW Scotland. Specifically, they were made during the construction of two offshore wind turbines close to a special area of conservation were a protected population of bottlenose dolphins resided. They found a decrease in sound pressure and an increase in duration with increasing distance from the pile driving site. In fact, noise levels produced during pile-driving were detectable above background underwater noise levels at a distance of 70km. These noise levels were related to noise criteria for marine mammals and they found that bottlenose dolphins and minke whales could exhibit behavioral disturbance up to 50km away and any zones of auditory injury and temporary threshold shifts were likely to have been within a range of 100m. (Bailey et al 2010)

Figure 2 (2)

A graph of peak to peak sound pressure levels from pile-driving activities in relation to distance from the noise source.

Another area of concern when it comes to noise pollution is the naval sonar exercises. In 1998 a letter in the journal nature attributed the cause of the atypical mass stranding of beaked whales to a naval exercise in the area. The same happened again in 2000 in the Bahamas. As of today scientists know of one or two dozen atypical strandings of beaked whales that coincided with the presence of naval ships in the area. One proposition for this is that beaked whales are especially sensitive to these noises although as of date there is no evidence to support this. Another hypothesis is that the naval sonar signals are similar to calls of killer whales which are predators of the beaked whales. It was then proposed that beaked whales may be showing antipredator response since these signals are so similar. This hypothesis was tested with three satellite tagged beaked whales that were exposed to naval sonar signals and calls of marine mammals eating whales. Although the whales didn’t show antipredator response to the extent of stranding, the whales did stop clicking in response to the sound stimulus and in particular reduced their foraging activity. (Tyack 2009)

Another area of concern is how explosives may affect marine mammals. In particular, aside from behavioral changes, how the ear may be affected from this high intensity explosions. Marine mammals evolved from land mammals and such both have similar ears. However, marine mammals have not only had to adapt their ears to the high pressures they encounter during dives but they have also had to develop adaptations to deal with the high noise environment in which they live. The two views are that since marine mammals rely so much on hearing, they can suffer impacts from even minor acoustic trauma. On the other hand, since they have adapted their ears to this high noise environment and since they rely so much on hearing for their lifestyle they are well protected. In a study by Ketten a model was used to asses theoretical pressures that marine mammals may encounter within a 15 km radius of a multi-tonnage mid water explosion. In her study she found that at certain distances and pressures, these blasts could not only cause trauma to the ear but these explosions could indeed be lethal. (Ketten 1995) in other experiments it has been found that noise produced by air gun arrays and explosives could be so intense that it could injure animals in the vicinity. In fact US regulations stipulate that such sound sources be shut down if a marine mammal enters the zone of potential injury. (Tyack 2009)

The studies that have been done so far have shown that marine mammals could indeed be harmed and affected by these anthropogenic noises. However, a lot of these studies have been species specific and it can be hard to extrapolate these results to all marine mammals since they all have different hearing sensitivities. In addition, it is hard to determine whether the responses observed in these studies are due anthropogenic noises or something else. Causation can be hard to study in the wild since there can be so many factors that come into play. Our understanding is limited and there is always the possibility that these animals have evolved to deal with all these noises and more. In fact other studies have shown that some marine mammals can compensate for noise to some point. They can increase the level of their calls, shift their signals out of the noise band or they wait to signal until the noise is reduced. Although we see that animals have been able to adapt it is noteworthy to mention that these adaptations may come with an energy expenditure to the animal. (Tyack 2009)

Future research might focus on using a software that was developed by Erbe and Farmer. They argue that to understand over which range anthropogenic noise impacts marine mammals, we need to understand how the noise propagates away from the noise source and we also need to understand the relationship between received noise levels and impact thresholds. They present a software that does both of these things and in this way we can estimates zones of impact on marine mammals around anthropogenic noises. (Herbe and Farmer 2000) Other research might also focus on controlled exposure experiments (CCEs) as proposed by Tyack et al. This type of research focuses on determining the response of animals to signals that aren’t part of their normal communicative range. Certain considerations need to be taken into account such as selection of subjects and stimuli which should be appropriate to the hypothesis and experiments should be designed to have biological relevance and test biologically significant responses. (Tyack et al 2003)

The science is hard but in due time we might be able to understand how these complex animals are affected by such a wide array of man made noises. However, once this knowledge gap is filled and we finally understand how each species is affected by different anthropogenic noises this begs the question of what will happen next. But more importantly we wonder if we will gather the knowledge in time to save some of these already at risk populations that might be deleteriously affected by anthropogenic sounds.

 

Works Cited:

Bailey, H., Senior, B., Simmons, D., Rusin, J., Picken, G., & Thompson, P. M. (2010). Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals. Marine Pollution Bulletin, 60(6), 888-897.

Erbe, C. (2011). The effects of underwater noise on marine mammals. The Journal of the Acoustical Society of America, 129(4), 2538.

Erbe, C., & Farner, D. M. (2000). A software model to estimate zones of impact on marine mammals around anthropogenic noise. The Journal of the Acoustical Society of America, 108(3), 1327-1331.

Ketten, D. R. (1995). Estimates of blast injury and acoustic trauma zones for marine mammals from underwater explosions. Sensory systems of aquatic mammals, 391-407.

Tyack, P. L. (2009). Human Generated Sound and Marine Mammals. Physics Today, 62(11), 39-44.

Tyack, P., Gordon, J., & Thompson, D. (2003). Controlled Exposure Experiments to Determine the Effects of Noise on Marine Mammals. Marine Technology Society Journal, 37(4), 41-53.