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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

Novel use of epidemiological models to control the spread of unwanted behaviors in marine mammals

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By Cameron Perry, SRC intern

Animal behavior is often learned or passed down through social interactions with other individuals. However, sometimes these socially transmitted behaviors increase exploitation of human resources, which may threaten human safety and economic livelihood (Schakner et al., 2016). Schakner et al. (2016) examined a case study where California sea lions (Zalophus californianus) discovered salmonids that had migrated up the Columbia River to the fish ladders located at the Bonneville Dam. Sea lions began foraging at the dam and increased the mortality of the Columbia River’s salmon and steelhead runs, 13 of which are listed under the Endangered Species Act (Schakner et al., 2016). The mouth of the Columbia River is home to tens of thousands migratory male California sea lions, however, the number of individuals foraging at the Bonneville dam began to sharply increase in 2002. This rapid increase in foraging was attributed to social learning and, in order to protect the endangered salmonids at the Dam, a culling program was established in 2008.

Study area for the case study which shows the Bonneville Dam and the East Mooring Basin where the males aggregate [Schakner et al., 2016]

Study area for the case study which shows the Bonneville Dam and the East Mooring Basin where the males aggregate [Schakner et al., 2016]

Social transmission of behaviors often mimic spread of diseases in a population. Schakner et al. (2016) aimed to use models from disease ecology to estimate the social transmissibility of dam-foraging behavior, explain how social transmission can be modeled similarly to diseases and to finally examine how effective and whether culling was necessary.

A California sea lion (Zalophus californianus) goes for a swim [Wikipedia Commons]

A California sea lion (Zalophus californianus) goes for a swim [Wikipedia Commons]

The benefits of early intervention are well known in infectious disease ecology and the social transmission of dam-foraging behavior in Californian sea lions supported this claim. The results showed that an earlier start to culling would have led to less overall foragers (Schakner et al., 2016). Similarly, if culling started prior to 2005, then fewer individuals would have to be removed than the current numbers. These results together mean that an immediate implementation of a culling program during the 2002 period of sharp increase in foraging behavior could have reduced the negative extent of social transmission and recruitment to the Bonneville Dam (Schakner et al., 2016). This also highlights the need for early culling efforts from a conservation and management aspect to minimize the total number of animals removed.

The authors hope that the Bonneville Dam case study could serve as an example what should be done in similar situations. They provided a novel synthesis of disease ecology models in social transmission and spread of behaviors in wildlife. Animal behaviors can rapidly spread through a population like an infectious disease. Social transmission of behaviors, like infectious diseases, can be managed through early intervention to reduce their spread and reach through a population.

Works cited
Schakner, Zachary A, Michael G Buhnerkempe, Mathew J Tennis, Robert J Stansell, Bjorn K van der Leeuw, James O Lloyd-Smith, and Daniel T Blumstein. 2016. “Epidemiological models to control the spread of information in marine mammals.” Proc. R. Soc. B.

Competitive Interactions Between South American Sea Lions and Fishermen in Southern Brazil

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By James Keegan, RJD Intern

Often, humans and top predatory carnivores compete for the same resources, even in the marine environment. This conflict occurs where fishing operations of humans and feeding areas of the predators overlap. In South America, fishermen complain of adverse competition from South American sea lions, which interact with all types of fishing gear. South American sea lions can interact with fishing effort either directly or indirectly. They can damage the fish captured by nets or the nets themselves, or they can decrease the relative abundance of local fish, decreasing the fishermen’s yield. Conversely, this competition can adversely affect the sea lions, decreasing their populations or changing their diet composition. Machado et al. 2015 sought to understand the competitive influence between humans and South American sea lions by providing the first detailed characterization of direct interactions between coastal gillnet fishing and the sea lions in Brazil.

Off the coast of southern Brazil, medium-scale gillnet fishing is the predominant fishing activity. Gillnets are vertical panels of netting hanging in the water column which allow fish to pass their heads through the netting, but not their bodies. The net then snags onto the fish’s gills as they try and back out, capturing the fish. Gillnet fishing activity in this region was monitored during three periods: 1992 to 1998, 2003 to 2005, and 2011 to 2012. During the surveys, scientists collected vessel characteristics, fishing area and net location gear type, target species, fishing effort (length of the nets and soak time), number of fishing operations (recovery of the net from the water), fish species captured, and the number of South American sea lions present near a net during a fishing operation.

Study area showing two fishing harbors (Imbé and Passo de Torres) in Southern Brazil. The gray circles represent fishing operations based out of Imbé and the gray triangles represent fishing operations based out of Passo de Torres. (Machado et al. 2015)

Study area showing two fishing harbors (Imbé and Passo de Torres) in Southern Brazil. The gray circles represent fishing operations based out of Imbé and the gray triangles represent fishing operations based out of Passo de Torres. (Machado et al. 2015)

Machado et al. 2015 found that South American sea lions interacted with gillnets in 24% of the fishing operations monitored. They also found that interactions increased with increased soak time, and that interactions were significantly affected by the seasons, with more interactions occurring in the winter. Moreover, in 85.3% of the interactions recorded, South American sea lions ate fish caught in the nets. In order to trick or drive the sea lions away, fisherman would resort to tactics like throwing fireworks in the water or putting out decoy nets. Fortunately, no sea lion mortalities occurred during the study due to incidental capture or injury caused by fishermen.

Relative frequency of occurrence of interactions between South American sea lions and coastal gillnet fishing in the two study areas of Imbé and Passo de Torres in southern Brazil during the three study periods (1992-2012). (Machado et al. 2015)

Relative frequency of occurrence of interactions between South American sea lions and coastal gillnet fishing in the two study areas of Imbé and Passo de Torres in southern Brazil during the three study periods (1992-2012). (Machado et al. 2015)

The highest frequency of interactions occurred in autumn and winter. This may be due to the low fish availability during that time, requiring a greater effort from the sea lions to obtain food, which creates a driving force for targeting fishing vessels. However, these interactions seem not to have a great economic impact on fisheries because they do not occur at a high frequency throughout the year, and the amount of fish the South American sea lions consume represents about .8 to 3.5% of the total landed value of the catch (Machado et al. 2015). Nevertheless, South American fishermen have a negative view of the sea lions, saying that they cause a significant economic loss. Moreover, this negative perception will only worsen in the future as fish stocks continue to decrease and competition for this resource increases. In order to alter this perception, a fisheries management system needs to be developed that reduces fishing effort and recovers fish stock. Additionally, by educating fishermen on the real economic impact sea lions have on their production, conflicts between fishermen and sea lions would decrease.

 

References:

Machado, R., Henrique, P., Benites Moreno, I., Danilewicz, Tavares, M., Alberto Crespo, E., Siciliano, S., Rosa De Oliveira, L. (2015). Operational interactions between South American sea lions and gillnet fishing in southern Brazil. Aquatic Conservation: Marine and Freshwater Ecosystems. doi: 10.1002/aqc.2554