A generalized bioenergetic model was used to estimate the food requirements of Steller sea lions Eumetopias jubatus in Alaska, USA. Inputs included age-and sex-specific energy requirements by date, population size and composition, and diet composition and energy content. Error in model predictions was calculated using uncertainty in parameter values and Monte Carlo simulation methods. Our model suggests that energy requirements of individuals were generally lowest in the summer breeding season (June to August) and highest in the winter (December to February) and spring (March to May) mainly due to changes in activity budgets. Predicted relative daily food requirements were highest for young animals (12 ± 3% SD and 13 ± 3% of body mass for 1 yr old males and females respectively) and decreased with age (5 ± 1% and 6 ± 1% of body mass for 14 yr old males and 22 yr old females respectively). The mean daily food requirement of pregnant females predicted by the model was only marginally greater than the predicted mean daily food requirement of non-pregnant females of the same age. However, the model suggested that the mean daily food requirement of females nursing pups was about 70% greater than females of the same age without pups. Of the 3 sets of model parameters (diet, population, and bioenergetic), uncertainty in diet and bioenergetic parameters resulted in the largest variation in model predictions. The model provides a quantitative estimate of the Steller sea lion population's food requirements and also suggests directions for future research. KEY WORDS: Bioenergetic model · Eumetopias jubatus · Food consumption · Steller sea lion · Sensitivity analysisResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 229: 291-312, 2002 third method for estimating food consumption is bioenergetic modeling.Biological systems are governed by the laws of thermodynamics and theoretically reach steady states where energy influx is equal to energy efflux (Wiegert 1968, Galluci 1973. In reality, a true steady state is never reached in nature, but in the long term any biological system must be in energy balance such that Consumption = Feces + Urine + Respiration + Productionwhere 'Consumption' is energy ingested, 'Feces' and 'Urine' are energy egested, 'Respiration' is energy used for work (degraded to heat), and 'Production' is energy deposited as tissue growth, fat storage, eggs, sperm, embryos, exuviae etc. (Klekowski & Duncan 1975). The energy consumption of marine mammals has frequently been estimated using bioenergetic models (Hinga 1979, Naumov & Chekunova 1980, AshwellErickson & Elsner 1981, Doidge & Croxall 1985, Hiby & Harwood 1985, Lavigne et al. 1985, Worthy 1987a, Härkönen & HeideJørgensen 1991, Markussen & Øritsland 1991, Ryg & Øritsland 1991, Markussen et al. 1992, Olesiuk 1993, Ugland et al. 1993, Mohn & Bowen 1996). These models range in detail from simple equations (with few parameters) representing an average individual's annual energy consumption, to detai...

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Three Steller sea lions Eumetopias jubatus were trained to participate in free-swimming, open-ocean experiments designed to determine if activity can be used to estimate the energetic cost of finding prey at depth. Sea lions were trained to dive to fixed depths of 10 to 50 m, and to re-surface inside a floating dome to measure energy expenditure via gas exchange. A 3-axis accelerometer was attached to the sea lions during foraging. Acceleration data were used to determine the overall dynamic body acceleration (ODBA), a proxy for activity. Results showed that ODBA correlated well with the diving metabolic rate (dive + surface interval) and that the variability in the relationship (r 2 = 0.47, linear regression including Sea lion as a random factor) was similar to that reported for other studies that used heart rate to estimate metabolic rate for sea lions swimming underwater in a 2 m deep water channel. A multivariate analysis suggested that both ODBA and dive duration were important for predicting diving metabolic cost, but ODBA alone predicted foraging cost to within 7% between animals. Consequently, collecting 3-dimensional acceleration data is a simple technique to estimate field metabolic rate of wild Steller sea lions and other diving mammals and birds.

We examined the digestion and passage times of bones and other hard parts from pollock, herring, salmon, and sandlance recovered from two juvenile captive Steller's sea lions (Eumetopias jubatus) subjected to varying activity levels. Key bones that could be identified to species were distributed over an average of 3.2 scats (range 1–6) following a single meal, with pollock remains occurring in significantly more scats than other species. Relying on otoliths alone to determine the presence of prey resulted in significantly fewer prey being identified than if other structures were also used (such as vertebrae, jaw bones, and teeth), particularly for salmon. Using either technique, there were significant differences in the likelihood that bones would be recovered from the series of scats produced following a meal, with pollock recovery exceeding herring (by three‐fold) and sandlance (by eight‐fold). Differences between species were reduced when recovery was calculated on a per scat basis rather than over multiple scats. Active animals passed greater numbers of bones, but the overall effect on prey recovery estimates was not significant. Defecation times of prey structures from a meal were variable and ranged from an initial 2–56 h to a final 28–148 h. The time interval to pass 95% of recovered structutes varied by a factor of two among prey species, and was highest for pollock due to retention beyond 65 h.

The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and the Aleutian Islands may be the result of them eating too much pollock (a gadid fish) instead of a more balanced and diverse diet containing fattier fishes, such as herring or sandlance. We sought to test this junk-food hypothesis by feeding six captive Steller sea lions (ages 0.9-4.5 years) only pollock or herring. All sea lions gained mass while eating herring. However, eating only pollock for short periods (11-23 d) caused the study animals to lose an average of 6.5% of their initial body mass (0.6 kg/d) over an average feeding trial of 16 d (initial mass averaged 125 kg). The animals were allowed to eat as much pollock as they wanted but did not increase their food intake to compensate for the low energy they were receiving. The sea lions showed progressive metabolic depression while losing body mass on a pollock-only diet. The loss of body mass while eating pollock was due to the lower gross energy content of pollock versus herring, the higher cost of digesting pollock, and the increased energy loss from digesting the larger quantity of fish needed to compensate for the lower energy content of pollock. Thus, our sea lions would have had to eat 35-80% more pollock than herring to maintain similar net energy intakes. Results from our captive-feeding studies are consistent with the junk-food hypothesis and have serious implications for Steller sea lions that have been eating primarily pollock in the Gulf of Alaska and the Aleutian Islands. Résumé : Le déclin des Otaries de Steller (Eumetopias jubatus) dans le golfe d'Alaska et les îles Aléoutiennes est peut-être attribuable à la consommation excessive de goberge (un gadidé) au lieu d'un régime équilibré et diversifié contenant des poissons plus gras tels le hareng et le lançon. Nous avons tenté d'éprouver cette hypothèse du régime de mauvaise qualité (junk-food hypothesis) en nourrissant six Otaries de Steller en captivité (âgées de 0,9 à 4,5 ans) uniquement de goberge ou uniquement de hareng. Toutes les otaries ont subi des augmentations de masse à la consommation de hareng. Cependant, la consommation de goberge pour de courtes périodes (11-23 jours) a entraîné des pertes moyennes de 6,5 % de la masse initiale (0,6 kg par jour) au cours d'une période alimentaire d'essai de 16 jours (masse initiale moyenne de 125 kg). Les animaux pouvaient manger autant de goberge qu'ils voulaient, mais ils n'ont pas augmenté leur consommation totale pour compenser la perte d'énergie encourue. Les otaries ont subi une dépression métabolique progressive par perte de masse lorsqu'ils ont adopté le régime constitué uniquement de goberge. La perte de masse au régime de goberge est attribuable au contenu énergétique brut réduit des goberges comparativement à celui des harengs, au coût énergétique supérieur de digestion de la goberge, et à la perte énergétique plus grande encourue lors de la digestion dune quantité de poisson plus grande nécessaire pour compenser le contenu énergétique plus faible de la g...

Management plans for North Atlantic right whales Eubalaena glacialis focus on preventing mortality from ship strikes and fishing gear entanglement. However, recovery may also be limited because individuals are under nutritional stress. We quantified the food requirements of North Atlantic right whales by age, sex and reproductive state and compared their predicted needs with field estimates of prey consumption to assess whether any demographic group of right whales might be nutritionally stressed. Energy requirements were estimated using a bioenergetics model that accounted for uncertainty in energy inputs and outputs. Consumption was estimated with prey samples taken near feeding whales in Cape Cod Bay (n = 28 net collections) and the Bay of Fundy (n = 19 optical plankton recordings). We found that calves required the least energy (~1767 MJ d −1 ) and that lactating females required the most (~4120 MJ d −1 ). Juveniles required considerably more energy than adult males and non-reproductive females. Our estimates of energy requirements for juveniles (~1906 MJ d −1 ), adult males (~1793 MJ d −1 ), and nonreproductive females (~2104 MJ d −1 ) compared favorably with estimates of actual consumption in Cape Cod Bay and the Bay of Fundy (i.e. they differed by ≤15%), suggesting that our model was reliable. However, lactating females appear to have obtained considerably less than their predicted energy requirements in both habitats. These findings suggest that lactating females may be experiencing an energy deficit, which may affect reproductive rates and slow population recovery. Nutritional stress may thus be limiting the recovery of North Atlantic right whales.KEY WORDS: Bioenergetic model · Eubalaena glacialis · Nutritional stress · Energetic consumption · Calving rate · Reproductive interval Resale or republication not permitted without written consent of the publisher Editorial responsibility:

SUMMARYThe metabolic costs of foraging and the management of O 2 and CO 2 stores during breath-hold diving was investigated in three female Steller sea lions (Eumetopias jubatus) trained to dive between 10 and 50 m (N=1142 dives). Each trial consisted of two to eight dives separated by surface intervals that were determined by the sea lion (spontaneous trials) or by the researcher (conditioned trials). During conditioned trials, surface intervals were long enough for O 2 to return to pre-dive levels between each dive. The metabolic cost of each dive event (diveϩsurface interval; DMR) was measured using flow-through respirometry. The respiratory exchange ratio (V O 2/V CO 2) was significantly lower during spontaneous trials compared with conditioned trials. DMR was significantly higher during spontaneous trials and decreased exponentially with dive duration. A similar decrease in DMR was not as evident during conditioned trials. DMR could not be accurately estimated from the surface interval (SI) following individual dives that had short SIs (<50 s), but could be estimated on a dive by dive basis for longer SIs (>50 s). DMR decreased by 15%, but did not differ significantly from surface metabolic rates (MR S ) when dive duration increased from 1 to 7 min. Overall, these data suggest that DMR is almost the same as MR S , and that Steller sea lions incur an O 2 debt during spontaneous diving that is not repaid until the end of the dive bout. This has important consequences in differentiating between the actual and 'apparent' metabolic rate during diving, and may explain some of the differences in metabolic rates reported in pinniped species.

Ecosystem-based management (EBM) of marine resources attempts to conserve interacting species. In contrast to single-species fisheries management, EBM aims to identify and resolve conflicting objectives for different species. Such a conflict may be emerging in the northeastern Pacific for southern resident killer whales (Orcinus orca) and their primary prey, Chinook salmon (Oncorhynchus tshawytscha). Both species have at-risk conservation status and transboundary (Canada–US) ranges. We modeled individual killer whale prey requirements from feeding and growth records of captive killer whales and morphometric data from historic live-capture fishery and whaling records worldwide. The models, combined with caloric value of salmon, and demographic and diet data for wild killer whales, allow us to predict salmon quantities needed to maintain and recover this killer whale population, which numbered 87 individuals in 2009. Our analyses provide new information on cost of lactation and new parameter estimates for other killer whale populations globally. Prey requirements of southern resident killer whales are difficult to reconcile with fisheries and conservation objectives for Chinook salmon, because the number of fish required is large relative to annual returns and fishery catches. For instance, a U.S. recovery goal (2.3% annual population growth of killer whales over 28 years) implies a 75% increase in energetic requirements. Reducing salmon fisheries may serve as a temporary mitigation measure to allow time for management actions to improve salmon productivity to take effect. As ecosystem-based fishery management becomes more prevalent, trade-offs between conservation objectives for predators and prey will become increasingly necessary. Our approach offers scenarios to compare relative influence of various sources of uncertainty on the resulting consumption estimates to prioritise future research efforts, and a general approach for assessing the extent of conflict between conservation objectives for threatened or protected wildlife where the interaction between affected species can be quantified.