by Dani Escontrela, RJD intern

Fish behavior affects the vulnerability they have to fishing gear and therefore is a key player in determining and moderating the impacts of fishing on wild populations. In a theory known as the foraging arena theory it is explained that behavioral adaptation is driven by two main forces: predation risks caused by natural predators or by fishing. To avoid predation fish will cluster into two groups, one in which they are vulnerable or one in which they are invulnerable to predation. The decision to go into one of these groups will determine the proportion of fish that are vulnerable to fishing gear. There are two mechanisms that can affect the flow of fish from vulnerable to invulnerable pools in response to fishing gear. On the one hand there are evolutionary pressures in which the bolder fish were more often in the vulnerable pool and got taken out of the population by fishing due to their increased risk of being caught. On the other hand, fish could have acquired gear avoidance behaviors through individual or social learning. Either of these explanations leave behind individuals that are harder to catch therefore increasing the number of individuals in the invulnerable pools as fishing pressures increase.

The experiment set out to determine how species-specific behavioral responses to recreational angling gear altered the proportion of vulnerable and invulnerable pools in the wild with increasing fishing pressures. They used two fish species with different foraging ecologies to determine their vulnerability to recreational angling gear. They hypothesized that recreational angling, which is a human predation risk for fishes, causes a change in behavior which in turn causes the proportion of fish in the vulnerable and invulnerable pools to change. They used two fish species that share the same habitat but differ in their feeding ecology. The S. scriba is a carnivorous fish that feeds on mobile prey, making it more vulnerable to fishing, while the D. annularis is omnivorous and feeds on small, sessile prey, making it less vulnerable to fishing. The sampling site was off the coast of the Mediterranean along sea grass beds where these fish resided. The number of fishing vessels were counted at each study site and were an index of predation risk for the fish species. Meanwhile, video was used to record the fish’s behaviors when they were exposed to baited hooks. The latency time was recorded for an individual to ingest the bait on a baited hook; the baited hooks were then cut to void actual capture of the fish.

This experiment found a correlation between risk taking behaviors in relation to angling intensity for S. scriba, however no correlation was found for D. annularis. The experiment showed that some exploited fish species such as the S. scriba become less likely to take risks and therefore more invulnerable with increased fishing pressures. This migration of fish individuals from vulnerable to invulnerable pools may explain decreased catch rates and decreased fish abundance. This study found vulnerability to fishing to be substantially different in S. scriba that inhabited highly exploited sites compared with individuals in lower exploited areas. Three implications can be drawn from these results. First of all, the increased amount of fish species in invulnerable pools due to increased recreational fishing pressures can have implications for population dynamics, food web interactions, the productivity of the fishery and individual fitness. Second, assessing population abundance from hook-and-line-based catch may be unreliable since different fish species and populations have different behaviors therefore affecting how vulnerable they are to being caught. Finally, because behavior and life history traits are often correlated, one should be careful in regards to sampling bias caused by preferential capture of certain behavioral types.

Alós, Josep, Miquel Palmer, Pedro Trías, Carlos Díaz-Gil, and Robert Arlinghaus. “Recreational angling intensity correlates with alteration of vulnerability to fishing in a carnivorous coastal fish species.” Canadian Journal of Fisheries and Aquatic Sciences 72, no. 999 (2014): 1-9.

By Robbie Roemer, RJD student

Paper by Andrew Wright and Line Khyn

Technological advances as well as the need for energy exploration and natural resource utilization have intensified and expanded anthropogenic pressures on the environment. Nowhere are these pressures more prevalent than the marine coastal areas of the globe; fisheries, offshore renewable energy sources, and the ever-increasing demand for petroleum are the highest contributing factors.  This increase in activity subsequently surges the magnitude, extent, and time-interval of adverse effects to the marine biotic ecosystem.

Recently there has been a major shift in the strategy of ecosystem management, including ecosystem based management approaches and marine spatial planning. In order to meet the requirements of these new management approaches, efforts have been implemented to quantify the cumulative impacts of human activity on marine species populations. The authors believe there is sufficient scientific evidence to support limiting the impact to marine organisms, and suggest a six-pronged approach for facilitating the capping of anthropogenic effects to the environment.

Human (or anthropogenic) activity originates in many varieties, including commercial shipping, oil and gas exploration, dredging, hunting, industrial construction, and even fishing. With such a wide variety of activities taking place it is to be expected they introduce numerous threats and stressors to the marine ecosystem including physical disturbances, chemical runoff, and noise pollution. The authors stress the importance of not adding the total impact of all interactions, citing the importance to quantify interactions that could potentially lead to greater overall impacts to the ecosystem. The authors state that ecosystem based management and marine spatial planning may offer solutions to this paradigm, but these potential solutions are data hungry, and move at an incredibly slow pace.  While anthropogenic impacts affect all forms of marine life, the study centered on marine mammals due to particular expertise of the authors.

The Six-Pronged Approach

1. Minimizing Exposure

Exposure of wildlife to human activities at lower measures will undoubtedly have less of an impact than species exposed to higher rates and levels of anthropogenic activity. It is suggested early evaluations as well as Environmental Impact Assessments (EIA) will minimize exposure of a certain species or at the very least, reduce the exposure to sensitive individuals if total avoidance cannot be achieved

2. Management Cycle

Assessing the collective impacts of a project with enough advance of each activities start dates is deemed to be one of the simplest ways for managers to effectively limit the collective impact of the projects. Management cycles can be established so that proposals for human activity within a management area must be submitted by a given deadline so all conjunct activities or projects can be considered simultaneously.  The U.S. National Fisheries Service has already utilized application cycles, establishing application deadlines for all researchers planning to focus on Stellar Sea Lions.

3. Cross-Company Collaboration

In relation to management cycles, the combined effects of multiple anthropogenic projects cannot be evaluated on a linear scale. Instead it is suggested quantitative models be used, accounting for different aspects of the entire proposed list of projects. This will subsequently allow companies to reduce cumulative effects before they submit applications.

4. Zero-Sum Management

Naturally, anthropogenic environmental damage could be curtailed if the current level of impact from human sources was considered the maximum allowable. Zero-sum management effectively represents no additional impact can be added to a population or region, and the impacts from ongoing activities must be offset. This management strategy may be particularly effective for species populations that are severely declining or even data deficient.

5. Uncertainty Built into Thresholds

A caveat to zero-sum management is the need to recognize and accept that the quantified magnitude of any impact is most likely underestimated, regardless of how the magnitude is measured. The recognition of this uncertainty as well as others in management strategies is useful, if not essential, for mitigating anthropogenic effects to marine populations. The need for integrating such uncertainties in management has already been realized and incorporated in the calculation of maximum marine mammal bycatch take for fisheries, which is known as potential biological removal (PBR).

 

6. Facilitating Future Management

The authors suggest that management agencies should require the collection of data to determine the extent to which the marine habitat would be altered. To ascertain anthropogenic stressors, a call for basic biological research be assessed prior to the activity. The authors also propose the publishing of said data to allow public dissemination of the results.

Such management strategies as the ones listed would undoubtedly have significant cumulative effects to reduce anthropogenic effects to marine organisms. Assessing and applying management strategies like these is most important considering the intensification of offshore energy exploration, especially as the potential for energy exploration escalates as the artic opens from climate change.

There are several disadvantages that should be mentioned in implementing such management strategies. Management cycles have been proven to be detrimental to those who propose the anthropogenic activities (industries), which will lessen support for management agencies. Several presumptions also underlie the effectiveness of area based mitigation, such as, different habitats of the overall ecosystem must be viewed as equally important to the species of interest, and species perceive the anthropogenic disturbances as an immediate threat, responding accordingly by utilizing avoidance.

If these shortcomings can be addressed and moderated, the six management approaches listed could have long standing positive effects to mitigate the detrimental anthropogenic effects to the marine ecosystem, used independently or synchronously.

 

Citation:

Wright, Andrew J., and Line A. Kyhn. “Practical management of cumulative anthropogenic impacts with working marine examples.” Conservation Biology(2014).

by Alice Schreiber, RJD intern

Located within the North Atlantic Gyre is a floating ecosystem of brown algae called Sargassum. The seaweed forms clumps the size of fists, or larger raft-like clusters that group together forming a biodiverse habitat, extending up to 100 miles or more, in a place that is otherwise oligotrophic, or lacking in life sustaining nutrients. This mass of algae has come to be known as The Sargasso Sea.

The Sargasso Sea has been designated as “essential fish habitat” and provides a high-productivity location for pelagic fishes and seabirds to feed and spawn. Pelagic Sargassum is a habitat to a reported 100 fish species, four turtle species, and over 145 invertebrates, sponges, fungi, bacteria, diatoms, and protists (Coston-Clements et al. 1991; Trott et al. 2010; Thiel and Gutow 2005a).

Ocean acidification and rising water temperatures caused by an increase of atmospheric carbon dioxide may impact Sargassum and the species that rely on it. Higher levels of CO₂ can stimulate the growth of macroalgae but can reduce the formation rate of calcareous skeletal structures, decreased reproduction, and increase mortality in organisms with shells or calcareous exoskeletons

Huffard et al., published a paper this year hypothesizing that seaweed will survive changing ocean conditions better compared to the faunal organisms in the same community. The data gathered in this study is compared to 88 historical datasets and data taken from 1966 to 1975 from the same location between Bermuda and the Bahamas. Biodiversity, sea surface temperatures and the CO₂ concentration was studied.

The researchers found that sea surface temperatures at one of the stations near Bermuda has increased slightly and gradually since 1969 (Huffard 2014). In the same location pCO₂ has increased since 1984. Mobile macrofauna samples for diversity and evenness were significantly lower in this study compared to ones conducted in 1972 and 1973. A key isotherm in the Sargasso sea has shifted northward and extreme weather events have higher wind speed and wave height. Differences in sampling methods between this study and the historic studies do not allow for statistical comparison, but calcifying bryozoan coverage was low compared to samples taken in the 1970s.

These findings support the hypothesis that different species and animal communities vary in their ability to withstand temperature and pH changes. It is possible that increased acidity due to a lower pH leads to a decrease in bryozoan coverage by negatively impacting their ability to form exoskeletons. Long-term monitoring of Sargassum communities is necessary to determine whether these changes are indicative of a failing ecosystem or just low points of diversity in a naturally varying ecosystem.

Coston-Clements L, Settle LR, Hoss DE, Cross FA (1991) Utilization of the Sargassum habitat by marine invertebrates and vertebrates: a review. NOAA Technical Memorandum NMFS-SEFSC-296

Trott TM, McKenna SA, Pitt JM, Hemphill A, Ming FW, Rouja P, Gjerde KM, Causey B, Earle SA (2010) Efforts to enhance protection of the Sargasso Sea. Proceedings of the 63rd Gulf and Caribbean Fisheries Institute. Nov 1–5, 2010, San Juan, Puerto Rico, pp 282–286

Thiel M, Gutow L (2005a) The ecology of rafting in the marine environment. I. The floating substrata. Oceanographic Marine Biology Annual Revue 42:181–264

Huffard, C. L., von Thun, S., Sherman, A. D., Sealey, K., & Smith Jr, K. L. (2014). Pelagic Sargassum community change over a 40-year period: temporal and spatial variability. Marine biology, 161(12), 2735-2751.