Steller sea lions Eumetopias jubatus and nutritional stress: evidence from captive studies

Abstract

1. Numbers of Steller sea lions Eumetopias jubatus in the North Pacific have declined.According to the nutritional stress hypothesis, this decline is due to reduced food availability. Data from studies conducted on pinnipeds in the laboratory are used here to test if the nutritional stress hypothesis can explain the decline of Steller sea lions. 2.Overall, there is strong evidence for biologically meaningful differences in the nutritional quality of major prey species. Steller sea lions can partly compensate for low-quality prey by increasing their food consumption. 3. There appear to be no detrimental effects of low-lipid prey on sea lion growth or body composition when sea lions can consume sufficient quantities of prey. However, the ability to increase consumption is physiologically limited, particularly in young animals. Overall, it is more difficult to maintain energy intake on a diet of low-quality prey than on a normal diet. 4. Under conditions of inadequate food intake (either due to decreased prey availability or quality, or increased energy requirements) the overall impacts of nutritional stress are complex, and are dependent upon season, prey quality, age and the duration and intensity of the nutritional stress event. 5. Studies on pinnipeds in the laboratory have been instrumental in identifying the conditions under which changes in sea lion prey can result in nutritional stress and the nature of the physiological impacts of nutritional stress events.

Bioenergetics model for estimating food requirements of female Pacific walruses Odobenus rosmarus divergens

“…The ingestion rate should be approximately 5-7% of body mass d −1 to be in agreement with consumption estimates based on stomach contents (Fay 1982) and observations of foraging (Born et al 2003) for walruses. We assumed the maximum possible rate of ingestion was 15-20% of body mass d −1 based on observed upper limits to food consumption by Steller sea lions (Rosen 2009). Our estimates of foraging time and biomass consumption were calculated from data based on observations of free-ranging Atlantic walruses Odobenus rosmarus rosmarus (Born et al 2003).…”

Steller sea lions (Eumetopias jubatus) have greater blood volumes, higher diving metabolic rates and a longer aerobic dive limit when nutritionally stressed

“…Nutritional stress can significantly affect body composition and metabolic rate (for a review, see Rosen, 2009) -and probably affects the aerobic dive limit as a result. Although developmental changes in both O 2 stores and metabolic rate have been demonstrated in pinnipeds, few studies have examined potential variation within individual adult animals.…”

“…Marine mammals have adaptations that result in higher O 2 stores through increased massspecific blood volume, hematocrit (packed cell volume), hemoglobin concentration and myoglobin concentration ([Mb]). Studies with captive animals have shown that Steller sea lions experience changes in body composition due to a loss of lipid stores and lean body mass when on restricted or low-quality diets (for a review, see Rosen, 2009). Such nutrition-induced changes in body composition could potentially alter TBO through changes in muscle mass (due to loss of lean body mass) or blood volume (BV; possibly due to changes in body water content).…”

Exploring local fishery management through cooperative acoustic surveys in the Aleutian Islands

“…While considerable effort has been expended to understand the seasonal nutritional requirements for individual W-SSLs [22][23][24], less is known about the size of local, seasonal prey populations required to support the recovery of W-SSL populations. For instance, the abundance of pollock, Pacific cod, Atka mackerel, and other prey necessary for central Aleutian Islands W-SSLs during the winter and early spring [25,26] is not simply limited to the fish they consume, but also includes the much larger number of fish necessary in the environment to guarantee successful foraging [27][28][29]. Womble et al [27] and Sigler et al [29] concluded that the relationship between Steller sea lion abundance at seasonal haulouts and local prey biomass (e.g.…”