Investigating Atlantic Salmon Dive Behavior in the Norwegian and Barents Seas

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By Grant Voirol, SRC Intern

Atlantic salmon, Salmo salar, are both an economically and ecologically important organism. An anadromous fish, Atlantic salmon spend most of their lives at sea before swimming into freshwater rivers to spawn. While at sea, Atlantic salmon periodically migrate to depths deeper than 10 meters. One proposed model of their diving behavior is that the salmon dive to deeper colder waters to feed before returning to shallower warmer water to digest. In this way, they can maximize their energy conservation (Reddin et al 2004). However, in colder waters of the most northern Atlantic, temperatures of shallower water are not significantly warmer than the depths that salmon can reach. So what factors govern Atlantic salmon diving behavior in these colder waters?

Picture 1

Atlantic salmon are both popular sport fish throughout the Atlantic as well as important predators and prey. Photo: Hans-Petter Fjeld (CC-BY-SA).

A recent study sought to find out. To do so, researchers studied post-spawning Atlantic salmon in the Norwegian and Barents Seas over season and daily timescales. Three populations from the three rivers Orkla, Alta, and Neiden, were caught and tagged using pop-up satellite archival tags (PSATs) and data storage tags (DSTs). PSATs measure temperature and depth and are attached externally to the salmon. They release themselves from the fish if a predetermined period of days goes by, the fish dives to a depth that will harm the tag (1200 meters), or the tag registers a constant depth, usually meaning the fish has died. Once they release themselves, the tags send a signal to satellites where the data collected as well as its position can be downloaded. DSTs are inserted internally in the salmon and measure temperature and depth at a much higher resolution. However, since the tags are inserted into the salmon, these salmon must be recaptured in order to retrieve the data. Recapture was dependent on fishers who would receive a reward for returning the tags to the researchers.

The findings show that the three groups of salmon displayed similar patterns of dive behavior during the sampled period. On the seasonal time scale, salmon went to deeper depths during winter and spring following the depth of the mixed layer (Figure 1). On daily timescales, the salmon occupied greater depths during daylight hours and returned to nearer to the surface during nighttime hours (Hedger et al. 2017).

Figure 1

Median dive depth per month. Solid line shows depth of the mixed layer. Increases in dive depth occur during the months of November to May. (Hedger et al. 2017)

A better understanding of the distribution and behavior of different populations of Atlantic salmon is important in order to know if different management practices need to be employed in different areas. Furthermore, this information gives us a better picture of the role that Atlantic salmon play in the Northeast Atlantic as both a predator and prey species.

Works Cited

Hedger RD, Rikardsen AH, Strøm JF, Righton DA, Thorstad EB, Næsje TF (2017) Diving behaviour of Atlantic salmon at sea: effects of light regimes and temperature stratification. Mar Ecol Prog Ser 574:127-140.

Reddin DG, Friedland KD, Downton P, Dempson JB, Mullins CC (2004) Thermal habitat experienced by Atlantic salmon (Salmo salar L.) kelts in coastal Newfoundland waters. Fish Oceanogr 13: 24−35.

A comparative analysis of the behavioral response to fishing boats in two albatross species

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By Andriana Fragola, SRC Intern

This paper examines the behavior of the Wandering Albatross (WA) and Black-Browed Albatross (BBA), and how they are affected by the toothfish longline fleet in Kerguelen and Crozet (Collet et al. 2017). To do this, lightweight GPS loggers were attached to adult albatrosses of both species to track their movements. To track the fishing boats, VMS data was provided to the researchers which allowed them to log their movements (Collet et al. 2017).

Calculations were done to establish the maximal distance that birds were seen flying towards the fishing boats. To isolate the different behaviors of the albatross the researchers established “encounter” as well as “attendance” behaviors to assess the responses of the birds to these fishing vessels (Collet et al. 2017). Encounters were defined as more by chance when the birds were in flight, while attendance behavior was defined as sitting in the water within a close range of the vessels (Collet et al. 2017).

Figure 1

[Source: Collet et al. 2017]

Results demonstrated that the Black-Browed Albatross (BBA) did not come into contact with fishing vessels as often as the Wandering Albatross (WA) (Collet et al. 2017). BBA also seemed to forage in areas that were a greater distance from the fishing vessels than WA (Collet et al. 2017). When the vessels were absent, BBA were not seen foraging in the regions where the vessels typically operate, while WA were (Collet et al. 2017).

Although WA are the larger and more dominant species, they were not observed pursuing the fishing vessels as much as the researchers had expected (Collet et al. 2017). BBA had an 80% chance of being attracted to fishing vessels, while WA had a lesser 60% chance of being attracted to the boats (Collet et al. 2017).

There were apparent differences between these two species and their utilization of fishing fleets as a means for foraging (Collet et al. 2017). This paper suggests that the energetic needs of each species can be an indicator of the risks associated with foraging from anthropogenic sources (Collet et al. 2017).

Figure 2

[Source: Collet et al. 2017]

It is vital to understand how species are becoming reliant on anthropogenic sources for food because this can affect their nutritional health. The quality of the fish that albatross are getting from these fishing vessels may not have the nutritional value of the fish they typically hunt. Further, if generations of these animals become dependent on these unnatural food sources, this can lead to issues – if the availability of that source becomes compromised, and birds are reliant to the extent that they do not have the skill to forage on their own.

Work Cited

Collet, J., Patrick, S. C., & Weimerskirch, H. (2017). A comparative analysis of the behavioral response to fishing boats in two albatross species. Behavioral Ecology, 28(5), 1337-1347.

Local taboos could help conserve marine fisheries in Tanzania

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By Jess Daly, SRC Intern

In developing nations it is often difficult to effectively enforce marine conservation laws because of a lack of staff and funding. With so little government intervention, it may be unclear to what extent the rules are being followed. A 2017 study by Shalli et al. examined how alternative methods of management might be affecting fisheries in Tanzania.

Specifically, the focus of this project was how traditional knowledge and local taboos alter the behavior of local fisherman. Traditional knowledge is wisdom that is passed down through generations, and taboos are a subcategory that includes the belief that certain actions are either too immoral or too sacred to be done in good conscience. The study examined six different Tanzanian fishing communities (4 rural and 2 urban), and used a wide variety of survey methods to gather information, including observation of fishing practices, a questionnaire given to fishers, and interviews with village leaders.

Figure 1

A fisherman goes out with his boat in the waters off of Dar-es-Salaam, Tanzania. [Grant, Milton. “Fishing in Tanzania.” United Nations Photo. 01 May 1991. https://www.flickr.com/photos /un_photo/34848229512]

Those who were given the questionnaire were also asked to provide their ages, genders, education levels, and lengths of residency. Across all of the villages, the majority of fishers were men who were between the ages of 30-40 and had a primary school education or less. However, when asked about local taboos, it was the uneducated elders who were able to provide the most information.

It was discovered that a wide variety of taboos exist within the Tanzanian fishing communities. The first is that certain fish species should not be eaten; reasons given for non-consumption included religious beliefs and fear of toxicity. Specific species and explanations of the taboos varied in the different villages, but all of them discussed dietary restrictions in one way or another. While the trend was present, however, the study found that nearly 50% of respondents did not comply with this taboo. A second class of taboos includes several actions involving the creation and deployment of fishing gear (such as women not touching new nets). These rules were more closely followed, with 44% of respondents claiming that they stringently complied with them, partially because of fear of social backlash. Almost 77% of fishers admitted noncompliance with taboos related to restrictions before or during fishing. More than 97% did not adhere to local taboos that prohibit fishing on certain sacred reefs, and nearly 47% claimed that they fished on certain prohibited days (such as religious holidays).

Figure 2

A graph depicting the levels of compliance to six different “categories” of taboos by different groups of fisherman as either strong, weak, or none. [Shalli et al. https://www.dropbox.com /sh/iyrngyxjy05qhm5/ AACAfkJqi4aOBqumSsEb0cZNa? dl=0&preview=shalli+et+al+2017.pdf]

Many of the local taboos, if they were widely followed, would aid in marine conversation by limiting things like fishing days, target species, fishing in sensitive reef areas, and catch size. While it appears that the majority of taboos are ignored in practice due to growing village populations and an increased demand for fish, it is believed that if local fishermen were educated in how these taboos actually affect population sizes, they would be more likely to observe them. In addition, local conservation laws should be aligned with existing taboos to highlight just how much they could aid in successful fisheries management.

Work Cited

Shalli, Mwanahija Salehe, et all. 2017. The role of local taboos in management of marine fisheries resources in Tanzania. Marine Policy 85: 71-78.

Food abundance, prey morphology and diet specialization influence individual sea otter tool use

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By Molly Rickles, SRC Intern

In this study, Fuji looked into how ecological factors impact sea otter’s tool use. Sea otters are known to be near shore foragers that carry food on the surface, and have been observed to use tools to eat their prey. In many other species, tool use has been found to be a response to a lack of food, since the tools allow the animal to eat less preferential species easier. This means that individuals that are found at sites with limited food will have a more specialized diet. Researchers wanted to see if this would be the same with sea otters.

In this study, sea otters were tagged from 2000-2014 in five study areas across California. The individuals were tagged using a plastic cattle tag on their hind flippers as well as with an implanted VHF radio transmitter. The animals were observed as foraging for food when they were found to be repeatedly diving underwater and returning to the surface. The results of these foraging dives provided the data, which included the dive outcome, prey identification, time spent handling prey and if tools were used. Once data was collected, groups were classified based on the most prevalent prey item, which included: Abalone, crab, mussel, clam, urchin and snail. In addition, AIC statistics were made for each model, and then compared to select the best-supported model based on the data.

Figure 1

This figure shows the various sites where sea otters were tagged and researched. Even though many of the sites are close together, each site had different prey species present which presented different scenarios for the sea otters. (Source: Fujii, J. A., Ralls, K., & Tinker, M. T. (2017). Food abundance, prey morphology, and diet specialization influence individual sea otter tool use. Behavioral Ecology. doi:10.1093/beheco/arx011)

It was found that crab was the most common prey item. In addition, in sites where food was limited, sea otters were found to have more diversity in prey. Results showed that adult females were the most common tool-users, and that snails were the most common prey eaten with tools. Sea otters who most often ate snails were found to be more likely to use tools to eat other types of prey, since they were accustomed to using tools to eat snails. This also went the other way, since species that ate prey that did not require tools were less likely to use tools with more difficult to eat species.

Figure 2

This graph shows the predicted probabilities of tool use among the different food groups consumed by sea otters. Sea otters that eat snails have the greatest chance of using tools to consume snails as well as other prey. (Source: Fujii, J. A., Ralls, K., & Tinker, M. T. (2017). Food abundance, prey morphology, and diet specialization influence individual sea otter tool use. Behavioral Ecology. doi:10.1093/beheco/arx011)

These results show that dietary differences among the individual sea otters played a role in tool use, especially when food resources declined. Researchers observed that older sea otters used tools more frequently, showing that tool use requires time and energy spent learning to be successful. In addition, pups raised by females who used tools were commonly seen using the same tools and eating the same prey, suggesting that mothers teach it, which could be an area for future research. This study proved both the necessity hypothesis and the opportunity hypothesis, showing that tool use increases when prey is limited and that tool use improves prey capture, making it a beneficial skill.

Work Cited

Fujii, J. A., Ralls, K., & Tinker, M. T. (2017). Food abundance, prey morphology, and diet specialization influence individual sea otter tool use. Behavioral Ecology. doi:10.1093/beheco/arx011

Horizontal and vertical movements of white marlin tagged off the Yucatan Peninsula

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By Luisa Gil Diaz, SRC Intern

In “Horizontal and vertical movements of white marlin, Kajikia Albida, tagged off the Yucatan Peninsula”, Vaudo et al research the ecology and habitat use of white marlin to improve management measures, particularly within fisheries. White Marlin are a highly migratory and prized sport fish that has recently come under threat. Annually, 10,000 are caught in the United States. However, the highest source of white marlin mortality is when they are bycatch in loglines intended for swordfish and tuna. These billfish are being unintentionally killed off at unacceptable numbers, and while management policies have been implemented, they have focused on quotas and the practice of releasing individuals (Graves and Hordosky, 2015) and have not been very effectual. In fact, “The stock [of white marlin] is currently considered to be overfished with biomass believed to be half of that necessary to achieve maximum sustainable yield” (ICCAT, 2014). Vaudo et al’s study seeks to learn about the way white marlin use their habitat by tagging and tracking them, in order to determine where and how fishing should be allowed.

Image 1

The white marlin is a prized sports fish of conservational concern.

Image 2

A longline consists of a long line with many hooks, it does not discriminate between species and can lead to much bycatch.

To conduct the study, 21 white marlins were captured off the eastern Yucatan peninsula between May of 2014 and June 2016. The marlins were brought on board, and a pump was inserted into their mouths to ventilate their gills with salt water (just like we do!). On board, lower jaw fork length measurements were taken, and pop up satellite transmitting tags were inserted onto the dorsal musculature of the white marlin using an umbrella tag. The pop up tags transmitted information about depth, temperature, and light levels once detached from the Marlin after 365 days. Using the information from the tags, temperature-depth profiles were created, indicating the different temperatures present at different depths throughout the marlin’s habitats. Due to technological limitations, involving the satellite tags, there were some gaps in the data, but enough was collected for data analysis.

Image 3

The Marlin were seen around the Gulf of México, the Caribbean and the northwest Atlantic Ocean (Source: Vaudo et al. 2017).

Using the temperature-depth profiles, analysis on daily temperature profiles the Marlin spent time at were categorized into sets of discrete thermal habitats. The habitats were labeled Habitat A-Habitat G. Maximum daily depth, number of dives, dive length, and dive depth were analyzed at these habitats. Habitat A was the warmest, and the habitat at which the most time (29.5%) was spent daily. It was found that the use of certain waters decreases as cold increases. In fact, 98% of time was spent at waters warmer than 18 degrees Celsius. Temperature also had an effect on the vertical distribution of the swordfish. In warmer waters, dives were deeper and longer. At night, when the water column gets colder, the Marlins stayed within the upper 10 M. These patterns were seen across water columns of different thermal structures across the western Caribbean, the Gulf of Mexico, and the northwest Atlantic. It has been suggested that the reason for this is that the marlins’ are avoiding crossing sharp temperature discontinuities, and that’s why they stay along sub tropical water with a weak thermocline.

This study suggests that the implementation of minimum hook depths for longlines could prevent some Marlin bycatch. It would be an economically feasible strategy that could save. Shorter hooks in the warmer regions were Marlin’s spend more time in deeper water is an easy modification and would be effective in certain areas.

Works Cited

Vaudo, J. J., Byrne, M. E., Wetherbee, B. M., Harvey, G. M., Mendillo, A., & Shivji, M. S. (2017). Horizontal and vertical movements of white marlin, Kajikia albida, tagged off the Yucatán Peninsula. ICES Journal of Marine Science.

ICCAT. 2014. Report for the Biennial Period 2012–13, Part II (2013). International Commission for the Conservation of Atlantic Tunas. Madrid, Spain. 2. 349 pp.

Hoolihan, J. P., Luo, J., Snodgrass, D., Orbesen, E. S., Barse, A. M., and Prince, E. D. 2015. Vertical and horizontal habitat use by white marlin Kajikia albida (Poey, 1860) in the western North Atlantic Ocean. ICES Journal of Marine Science, 72: 2364–2373.

Gut microbiota of a long-distance migratory bird demonstrates resistance against invading environmental microbes

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By Elana Rusnak, SRC intern and MS student

Just as with humans, animals have many kinds of bacteria in their gut that helps them with acquiring the nutrients from the food they eat, as well as boosting their immune system (Khosravi & Maxmanian, 2013). Many species that migrate from breeding to non-breeding grounds during the year may have an increased risk of transmitting harmful bacteria that they pick up from sites they stop at along the way. If migrant guts have a “colonization resistance” to harmful microbes, they will be less likely to carry them along their migratory routes. However, it is also possible that gut communities may become unstable when continually exposed to new strains of bacteria. Migratory species are faced with changes in geography, diet, and physiology, which are all factors that contribute to changes in gut bacteria composition.

Figure 1

Red-necked Stint (Calidris ruficollis) By Patrick_K59 – https://commons.wikimedia. org/w/index.php?curid=45909879

In a study by Risley et al. earlier this year, they looked at the invasion resistance of the gut of the Red-necked stint (Calidris ruficolis) to microbes they ate at various sites along their migratory route (Siberia to Australia). They chose this study species for a few reasons: they migrate to their non-breeding grounds and stay there for at least a year and a half afterward, so it’s easy to track birds that have recently migrated and those that have been there for a long time. These shorebirds also eat by sifting through coastal sediments with their bills, so their food source is readily available to study at known locations. The researchers believed that recently migrated birds would have a different gut community than resident birds, and that their gut community would become more like that of the resident birds over time.

Red-necked stint distribution, with non-breeding areas in blue. By Nrg800 – Own work, https://commons. wikimedia.org/w/index.php? curid=11336387

They caught and sampled 71 total stints in Australia in two groups: recently migrated birds, and resident birds. They isolated and analyzed gut community DNA from each individual, and also sampled sediments from along the migratory route, and compared the bacteria in these sediments to what was found in the guts.

Contrary to what they predicted, less than 0.1% of the gut community in migrating birds came from the local foraging sediments. They found almost no difference in the gut microbes of the recently migrated birds and the resident birds, suggesting that this particular species does not incorporate sediment microbes into their gut as they migrate. However, they did find a high abundance of a single strain of bacteria in the recently migrated birds that decreased over the course of the non-breeding season. This strain may be related to an immune response to compensate for being exposed to so many different kinds of bacteria on their migratory route.

These results show that the Red-necked stint is highly resistant to microbial invasions that are taken in with their food as they migrate. The researchers suggest that this resistance decreases their susceptibility to infection as they visit new locations on their route. Future research could elucidate if this resistance is only found in migratory species, and to further understand the relationship between microbe invasion and infection risk.

Works Cited

Khosravi, A., & Mazmanian, S. K. (2013). Disruption of the gut microbiome as a risk factor for microbial infections. Current opinion in microbiology, 16(2), 221-227.

Risely, A., Waite, D., Ujvari, B., Klaassen, M., & Hoye, B. (2017). Gut microbiota of a long‐distance migrant demonstrates resistance against environmental microbe incursions. Molecular ecology.

Snook in Extreme Environments

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By Delaney Reynolds, SRC Intern

Earth’s climate is warming, and rising temperatures are impacting animal species and their habitats in alarming ways. Since 1970, temperatures have increased approximately 0.17°C (0.3°F) per decade (Dahlman, 2017). Such changes threaten animals’ ability to adapt to increased heat and induced stress. In the article, “Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study,” researchers observed how migration patterns impacted species’ vulnerability to extreme climate events (ECEs), episodes of uncommon climactic periods in which ecosystem structure is transformed beyond what is characteristically normal (Smith, 2011).

Figure 1: Juvenile Snook

A Juvenile Common Snook caught in the Everglades National Park. Image Source: https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=132218&from=mn

The State of Florida enjoys mild lows of 65-41°F during its winter season. Extreme cold fronts, however, occur approximately once every 10 years and can result in colder, more fatal environmental systems. During extreme cold fronts, South Florida’s Everglades National Park often experiences dramatic declines in sportfish populations and, thus, is the experimental ground used to study Snook and climate vulnerability. In 2010, for example, the Park faced one of its most severe cold fronts in a century and saw imperative tropical fisheries decrease 80%.

One of the Park’s residents, the Common Snook, has been useful in studying climate vulnerability because, “the abundance of adult Snook, the most sought after gamefish in the area, decreased by over 90% following the passage of this event” (Boucek, 2017). Once water temperature drops below 60°F, the Snook begin to struggle and become particularly vulnerable.

Looking at Everglades estuaries, Common Snook are observed in various cold-temperature regions. Snook often reside in rivers and for this reason three distinctive areas of the Everglades’ Shark River estuary were studied: the upstream, bay, and downstream zones. The downstream zone consists of the most Snook predators, but also the most Snook prey, and so Snook population and productivity is relatively higher compared to the upstream and bay zones. Passive acoustic telemetry computed Snook distribution patterns predicted for 2012 to 2016 during ECE periods. The researchers found that downstream zones were found to be the warmest, causing little effect on Snook populations, and upstream zones the coldest, killing most tropical fish. When a cold spell is detected in high vulnerability communities, most fish species migrate to areas of higher resistance, ensuring a higher survival rate. When it came to dispersing among less vulnerable habitats, Snook did not portray migration tendencies when detecting ECEs. Another study during the 2010 ECE found that most Everglades Snook showed the same behavior and did not move long distances, but rather made short journeys to areas that would function as a refuge from less severe, but more frequent ECEs (Stevens, 2016).

Figure 2: Snook Habitat Resistance, Animal Distribution, Detection and Response

This figure demonstrates animal distribution in high and low resistance environments, the shaded shapes, as well as their response to ECEs. As shown on the right, when a cold spell is detected in low vulnerability communities, fish will migrate to areas of higher resistance (shown in bright green) and return to their original habitat once it has passed, ensuring a higher rate of survival among the population. Image Source: Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study.

Snook face higher risk of population degradation when they are unable to immigrate to congenial territories, yet their populations did not face large casualties due to the ECEs because they tend to typically dwell in the warmer downstream zone. By staying in warm water areas, the Common Snook helps us better understand how species respond to a change in their habitats’ climate. As ECEs become more common and severe it will be vital to continue to monitor fisheries so as to learn how our warming climate impacts species and their habitats.

Works Cited

Boucek, R. E., Heithaus, M. R., Santos, R., Stevens, P., & Rehage, J. S. (2017, April 7). Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study. Retrieved from file:///C:/Users/derey/Downloads/boucek%20et%20al%202017b.pdf

Dahlman, L. (2017, September 11). Climate Change: Global Temperature. Retrieved October 22, 2017, from https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

Smith, M. D. (2011, April 15). An ecological perspective on extreme climatic events: a synthetic definition and framework to guide future research. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01798.x/abstract

Energetically Pricey Lifestyles and Low Productivity Environments: How the Galapagos Sea Lion Makes Ends Meet

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By Patricia Albano, SRC Intern

Metabolic rate and prey acquisition behavior can be revealing factors in studies examining physiological adaptations to unpredictable environments. Specifically, otariids (sea lions and fur seals) display an energetically expensive lifestyle due to their high costs of thermoregulation which can provide challenges in equatorial regions such as the Galapagos where resources are limited and unpredictable. In this study (conducted by Stella Villegas-Amtmann et. al, 2016), the effect of the Galapagos islands’ low productivity on the Galapagos sea lion (GSL) (Image 1) is explored. To determine how sea lions maintain their energetically expensive lifestyle in limiting environments, researchers measured the field metabolic rate (FMR) and the foraging behavior of lactating female sea lions rearing pups and yearlings. Because lactation is the most energetically costly time in a female mammal’s life history (Hammond and Diamond, 1997; Williams et. al, 2007), the researchers hypothesized that GSL would exhibit a lower FMR in relation to other species as a response to decreased resource availability (Trillmich and Kooyman, 2001), but lactating GSLs rearing yearling pups would display greater FMRs and foraging efforts than those rearing younger pups (~1 year old). This hypothesis was drawn based on literature that suggests that there is a positive relationship between female energy expenditure and pup mass/age before the weaning period at ~3 years of age (Jeglinski et al., 2012; Trillmich, 1986a).

Image 1

Suckling Galapagos sea lion (Zalophus wollebaeki) pup and lactating mother. Source: Wikimedia Commons.

This research was carried out at San Cristobal Island during October and November of 2009. 10 lactating female GSLs and their pups/yearlings were caught using hoop nets. Of the 10 pups, 6 were suckling young pups (~ 1 month old) and the other 4 were suckling yearlings. To analyze prey acquisition behavior, the animals were fitted with GPS tags, time-depth recorders, and radio transmitters. For each sea lion, the researchers calculated % shallow dives (100m depth), mean depths for shallow and deep dives, dive duration, bottom time, maximum distance traveled from the rookery, and time spent diving. Results show that GSLs with yearlings dove further, deeper, and longer than GSLs with younger pups (Table 1). The field metabolic rate measurement of the seals exhibited the same relationship: females with yearlings had a higher FMR than those with young pups. These results confirm the researchers’ hypothesis that GSLs with yearling pups would have a more energetically costly lifestyle than females with younger pups.

Table 1

Galapagos sea lion females’ foraging location, maximum dive parameters, and mean foraging trip parameters. This table includes the age categories of the females’ pups so the relationship between pup age and energy expending activities can be seen. Source: Villegas-Amtmann, S., et al., Adapted to change: Low energy requirements in a low and unpredictable productivity environment, the case of the Galapagos sea lion. Deep-Sea Res. II (2016).

This study shows a remarkable ability of sea lions to reduce their metabolic needs to adapt to the low productivity ecosystem of the Galapagos islands. However, while this species shows an impressive plasticity in responding to environmental changes, in comparison to other higher latitude ostariids, endangered GSLs live in an environment that requires them to exert a significantly greater amount of effort in order to maintain their and their offspring’s metabolism. If warming trends in equatorial waters continue and productivity in the Galapagos proceeds to decrease (Bopp et al., 2013), GSLs already functioning at their lower physiological limit may not be able to adapt further.

Works Cited

Hammond, K.A., Diamond, J., 1997. Maximal sustained energy budgets in humans and animals. Nature 386 (6624), 457–462.

Trillmich, F., Kooyman, G.L., 2001. Field metabolic rate of lactating female Galapagos fur seals (Arctocephalus galapagoenis): the influence of offspring age and environment. Comp. Biochem. Phys. A 129 (4), 741–749.

Trillmich, F., 1986a. Attendance behavior of Galapagos sea lions. In: Gentry, R.L., Kooyman, G.L. (Eds.), Fur Seals: Maternal Strategies on Land and at Sea. Princeton University Press, Princeton, New Jersey, pp. 196–208.

Villegas-Amtmann, S., et al., Adapted to change: Low energy requirements in a low and unpredictable productivity environment, the case of the Galapagos sea lion. Deep-Sea Res. II (2016), http://dx.doi.org/10.2016/j.dsr2.2016.05.015

Williams, T.M., Rutishauser, M., Long, B., Fink, T., Gafney, J., Mostman-Liwanag, H., Casper, D., 2007. Seasonal variability in otariid energetics: implications for the effects of predators on localized prey resources. Physiol. Biochem. Zool. 80 (4), 433–443.

Sea Lions in our Changing Ocean

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By Amanda Stoltz, SRC Intern

If you’ve ever gazed upon sea lions loafing about in the Californian sun, you might be inclined to think that they are lazy animals. However, as with most marine mammals, sea lions live an active life under the water’s surface. Much of their underwater behavior is unknown to scientists, but a recent study by Neises et al., titled “Examining the metabolic cost of otariid foraging under varying conditions,” explores how sea lions could be affected by warming oceans that cause prey to migrate to deeper waters further offshore.

Sea lions are much better divers than we are, but how long can they spend underwater searching for food before they begin to experience physiological consequences? When marine mammals dive below the surface of the water, the oxygen in their body decreases while the carbon dioxide in their body increases. The authors hypothesized that when a sea lion has to work harder to fish for its prey, the ability of its body to sequester carbon dioxide into bicarbonate diminishes. This hypothesis is difficult to test through observation, so the authors created an enclosure where they could control the amount of prey and test for the energetic cost of diving for prey using a technique called open flow respirometry. The researchers constructed an airtight plexiglass dome with an inflow hole for air and an outflow hole for the sea lion respiratory data to be collected (Fig. 1).

Figure 1

Left: Breathing dome. A nylon hose connected the dome to the TurboFox respirometer for data collection. The white arrow on the top of the respirometry chamber indicates the flow of air into the chamber. The white arrow perpendicular to the top arrow indicates the direction of airflow though the outflow hole leading to the respirometer. Middle: The male sea lion in the drag harness used during cost increased trials. Right: The female sea lion in the drag harnesses used during cost increased trials.

The study was conducted at Moss Landing Marine Laboratories in California using two California sea lions (Zalophus californianus). In order to simulate a high prey encounter rate, the researchers released 36 fish per session, while in a low prey encounter rate the researchers released only six fish. In the experiment, the sea lions controlled the number of dives, dive duration, and surface intervals. Behavior data was collected by multiple real-time cameras installed throughout the enclosure.

The scientists found that while there was no significant difference in oxygen depletion between low and high prey scenarios, the amount of accrued carbon dioxide was significantly higher during low prey scenarios. This proves the researcher’s hypothesis, and reveals that carbon dioxide may be a more sensitive physiological marker than oxygen consumption when examining the metabolic cost of foraging in sea lions.

These findings will help support the conservation of sea lions in our changing seas. In 2015, the stranding rate of sea lions was 10 times the average stranding level, and NOAA listed prey availability as one of the likely causes (NOAA Fisheries, 2015). Closer examination of carbon dioxide as a physiological marker in sea lions will provide scientists with greater insight into the effect of limited prey on these iconic marine mammals.

Works Cited

Neises, V., Zeligs, J., Harris, B., Cornick, L. 2017. Examining the metabolic cost of otariid foraging under varying conditions. J. Exp. Biol. 486: 352-357.

NOAA Fisheries, 2015. 2015 elevated California sea lions strandings in California. http:// www.westcoast.fisheries.noaa.gov/ mediacenter/faq_2015_ca_sea_lion_strandings. pdf

A Bird’s Eye View of Illegal Fisheries

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By Mitchell Rider, SRC Intern and MS student

Seabirds have been attracted to vessels for centuries, but more recently, they have been observed to aggregate in large quantities near fishing vessels to feed on fish scraps or bait (Croxall et al. 2012; Phillips et al. 2016). Their interactions with fishing vessels have been observed and quantified using Global Positioning System (GPS) combined with vessel monitoring-system (VMS) data, however, this type of analysis can only be carried out with declared vessels whose position can be tracked within exclusive economic zones (EEZs). Therefore, there is little information available on the interaction of seabirds and fishing vessels outside the EEZs. In their study “Use of radar detectors to track attendance of albatrosses at fishing vessels”, Weimerskirch et al. (2017) set out to estimate the efficiency of fitting newly developed GPS loggers to wandering albatrosses (Diomedea exulans) (Fig. 1), foraging from the Crozet Islands, to detect fishing vessels at sea in addition to observing the extent to which the fishing vessel operations were overlapping with D. exulans foraging range.

Figure 1

Photo of Diomedea exulans [https://commons.wikimedia.org/wiki /Diomedea_exulans#/media/File:Diomedea_ exulans_in_flight_-_SE_Tasmania.jpg]

Birds from Possession Island, Crozet Islands, were hand caught and an XGPS radar logger was taped to their back feathers. These radar loggers could detect interactions between the birds and fishing vessels by measuring radio emissions at a certain frequency that is used in marine radars. From this interaction data, the authors could determine three different types of behaviors of birds associated with the radar detections: fly pasts, follows, and vessel attendance (Fig. 2). Fly pasts occurred if there were a few successive radar detections but no significant change in the route of the bird, however, successive radar detections associated with a linear direction was noted as a follow. Vessel attendance was noted as successive radar detections in a restricted area where the bird alternated between flying and sitting on the water. This data was combined with VMS data of French long-line fishing vessels to note the distance between the GPS tagged birds and the fishing vessels.

Figure 2

Movement pattern of wandering albatrosses (yellow and orange lines) equipped with biologging devices that detect radar emissions and record the position of boats (green dots): (a) attending behavior, (b) fly-past behavior, and (c) follow behavior where the red line is the track of the vessel (Wiemerskirch et al. 2017).

A total of 43 foraging trips were recorded from with the XGPS radar loggers and Wimerskirch et al. (2017) discovered that 79.5% of the loggers recorded interactions with vessel radars. Among the three types of interactions with ships, D. exulans was noted to spend the highest percentage of radar detections in attendance of the ships (64.7%), followed by fly pasts (23.9%), and follows (8.8%). In general, the birds spent a large amount of time behind the vessels, which suggested more of an attraction to the vessel, instead of a spatial overlap. Even though there is this significant interaction between D. exulans as fishing vessels, the answer as to why these birds are attracted to fishing vessels is not clear. However, these findings suggest that this method of radar detection on seabirds could become an effective way to manage marine ecosystems. More specifically, radar detection on seabirds could be used to detect the location of illegal fishing vessels outside of EEZs.

Works Cited

Croxall, J. P., Butchart, S. H., Lascelles, B., Stattersfield, A. J., Sullivan, B., Symes, A., & Taylor P. (2012). Seabird conservation status, threats and priority actions: a global assessment. Bird Conservation International 22:1–34.

Phillips, R., Gales, R., Baker, G., Double, M., Favero, M., Quintana, F., Tasker, M., Weimerskirch, H., Uhart, M., & Wolfaardt, A. (2016). The conservation status and priorities for albatrosses and large petrels. Biological Conservation 201:169–183.

Weimerskirch, H., Filippi, D. P., Collet, J., Waugh, S. M., & Patrick, S. C. (2017). Use of radar detectors to track attendance of albatrosses at fishing vessels. Conservation Biology.