MARINE MAMMAL RESEARCH NEWSLETTER   |   February 2015 (Issue 12)

THIS JUST IN


2014
 
The decline of Steller sea lions (Eumetopias jubatus) in the North Pacific: insights from indigenous people, ethnohistoric records and archaeological data.
Maschner, H. D. G., A. W. Trites, K. L. Reedy-Maschner and M. Betts. 2014.
Fish and Fisheries 15:634-660.
abstract
A number of hypotheses have been proposed to explain the most recent decline (1977-2012) of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. We examined hypotheses about fisheries competition, environmental change, predation, anthropogenic effects, and disease using observations of modern Aleut and archaeological, ethnohistoric, and ethnographic data from the western Gulf of Alaska and Aleutian Islands. These data indicate that Steller sea lion numbers have declined and recovered repeatedly over the past 4,500 years and were last at critically low numbers during the 1870s-1930s. Steller sea lions appear to have been more abundant during the cool periods—and lower during the warmer periods. Observations by local peoples, explorers, early government surveyors, and biologists since the late 1800s suggest that low populations of Steller sea lions have been associated with high populations of Gadidae fishes (Pacific cod – Gadus macrocephalus and walleye pollock – Theragra chalcogramma), and are consistent with the ocean climate hypothesis to explain the decline of sea lions. They suggest that removals by people and killer whales (Orcinus orca) did not cause the sea lion declines, but could have compounded the magnitude of the decline as sea lion numbers approached low densities. Archaeological, anthropological and ethnohistorical analyses demonstrate that fluctuations have occurred in the North Pacific over hundreds to thousands of years, and provide context for understanding the changes that occur today and the changes that will continue to occur in the future.
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2014
 
Improving accuracy of DNA diet estimates using food tissue control materials and an evaluation of proxies for digestion bias.
Thomas, A.C., S.N. Jarman, K.H. Haman, A.W. Trites and B.E. Deagle. 2014.
Molecular Ecology 23:3706-3718.
abstract
Ecologists are increasingly interested in quantifying consumer diets based on food DNA in dietary samples and high-throughput sequencing of marker genes. It is tempting to assume that food DNA sequence proportions recovered from diet samples are representative of consumer's diet proportions, despite the fact that captive feeding studies do not support that assumption. Here, we examine the idea of sequencing control materials of known composition along with dietary samples in order to correct for technical biases introduced during amplicon sequencing, and biological biases such as variable gene copy number. Using the Ion Torrent PGM©, we sequenced prey DNA amplified from scats of captive harbour seals (Phoca vitulina) fed a constant diet including three fish species in known proportions. Alongside, we sequenced a prey tissue mix matching the seals’ diet to generate Tissue Correction Factors (TCFs). TCFs improved the diet estimates (based on sequence proportions) for all species and reduced the average estimate error from 28 ± 15% (uncorrected), to 14 ± 9% (TCF corrected). The experimental design also allowed us to infer the magnitude of prey-specific digestion biases and calculate Digestion Correction Factors (DCFs). The DCFs were compared to possible proxies for differential digestion (e.g., fish% protein,% lipid,% moisture) revealing a strong relationship between the DCFs and percent lipid of the fish prey, suggesting prey-specific corrections based on lipid content would produce accurate diet estimates in this study system. These findings demonstrate the value of parallel sequencing of food tissue mixtures in diet studies and offer new directions for future research in quantitative DNA diet analysis.

keywords     next-generation sequencing; diet analysis; pinniped; correction factors
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2014
 
Inflation and deflation pressure-volume loops in anesthetized pinnipeds confirms compliant chest and lungs.
Fahlman, A., S.H. Loring, S.P. Johnson, M. Haulena, A.W. Trites, V.A. Fravel and W.G. Van Bonn. 2014.
Frontiers in Physiology Vol 5(433)
abstract
We examined structural properties of the marine mammal respiratory system, and tested Scholander's hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised in an aquatic facility. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance.
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2014
 
Steller sea lions (Eumetopias jubatus) have greater blood volumes, higher diving metabolic rates and a longer aerobic dive limit when nutritionally stressed.
Gerlinsky, C.D., A.W. Trites and D.A.S. Rosen. 2014.
Journal of Experimental Biology 217:769-778.
abstract
Marine mammal foraging behavior inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.

keywords     Steller sea lion, blood volume, nutritional stress, diving metabolism, oxygen stores, dive behavior
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