Changes in metabolism in response to fasting and food restriction in the Steller sea lion (Eumetopias jubatus)

Many animals lower their resting metabolism (metabolic depression) when fasting or consuming inadequate food. We sought to document this response by subjecting five Steller sea lions to periods of: (1) complete fasting; or (2) restricting them to 50% of their normal herring diet. The sea lions lost an average of 1.5% of their initial body mass per day (2.30 kg/d) during the 9-14-day fast, and their resting metabolic rates decreased 31%, which is typical of a "fasting response". However, metabolic depression did not occur during the 28-day food restriction trials, despite the loss of 0.30% of body mass per day (0.42 kg/d). This difference in response suggests that undernutrition caused by reduced food intake may stimulate a "hunger response", which in turn might lead to increased foraging effort. The progressive changes in metabolism we observed during the fasts were related to, but were not directly caused by, changes in body mass from control levels. Combining these results with data collected from experiments when Steller sea lions were losing mass on low energy squid and pollock diets reveals a strong relationship between relative changes in body mass and relative changes in resting metabolism across experimental conditions. While metabolic depression caused by fasting or consuming large amounts of low energy food reduced the direct costs from resting metabolism, it was insufficient to completely overcome the incurred energy deficit.     

Examining the potential for nutritional stress in young Steller sea lions: physiological effects of prey composition

The effects of high- and low-lipid prey on the body mass, body condition, and metabolic rates of young captive Steller sea lions (Eumetopias jubatus) were examined to better understand how changes in prey composition might impact the physiology and health of wild sea lions and contribute to their population decline. Results of three feeding experiments suggest that prey lipid content did not significantly affect body mass or relative body condition (lipid mass as a percent of total mass) when sea lions could consume sufficient prey to meet their energy needs. However, when energy intake was insufficient to meet daily requirements, sea lions lost more lipid mass (9.16±1.80 kg±SE) consuming low-lipid prey compared with eating high-lipid prey (6.52±1.65 kg). Similarly, the sea lions lost 2.7±0.9 kg of lipid mass while consuming oil-supplemented pollock at maintenance energy levels but gained 5.2±2.7 kg lipid mass while consuming identical energetic levels of herring. Contrary to expectations, there was a 9.7±1.8% increase in metabolism during mass loss on submaintenance diets. Relative body condition decreased only 3.7±3.8% during periods of imposed nutritional stress, despite a 10.4±4.8% decrease in body mass. These findings raise questions regarding the efficacy of measures of relative body condition to detect such changes in nutritional status among wild animals. The results of these three experiments suggest that prey composition can have additional effects on sea lion energy stores beyond the direct effects of insufficient energy intake.     

Changes in glucocorticoids, IGF-I and thyroid hormones as indicators of nutritional stress and subsequent refeeding in Steller sea lions (Eumetopias jubatus)

Physiological responses to changes in energy balance are tightly regulated by the endocrine system through glucocorticoids, IGF-I and thyroid hormones. Changes in these hormones were studied in eight captive female Steller sea lions that experienced changes in food intake, body mass, body composition, and blood metabolites during summer and winter. During a period of energy restriction, one group of sea lions was fed reduced amounts of Pacific herring and another was fed an isocaloric diet of walleye pollock, after which both groups returned to their pre-experimental diets of herring. Cortisol was negatively and IGF-I was positively associated with changes in body mass during periods of energy restriction (mass loss associated with increase in cortisol and decrease in IGF-I) and refeeding (body mass maintenance associated with stable hormone concentrations in summer and compensatory growth linked to decrease in cortisol and increase in IGF-I in winter). Cortisol and IGF-I were also correlated with changes in lipid and lean mass, respectively. Consequently, these two hormones likely make adequate biomarkers for nutritional stress in sea lions, and when combined provide indication of the energetic strategy (lipid vs lean mass catabolism) animals adopt to cope with changes in nutrient intake. Unlike type of diet fed to the sea lions, age of the animals also impacted hormonal responses, with younger animals showing more intense hormonal changes to nutritional stress. Thyroid hormones, however, were not linked to any physiological changes observed in this study.     

Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus)

Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8–9 days, four times over the course of a year to investigate effects of season and prey composition on sea lion physiology. At these levels, the sea lions lost body mass at a significantly higher rate during winter (1.6 ± 0.14 kg day⁻¹), and at a lower rate during summer (1.2 ± 0.32 kg day⁻¹). Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diet types. The majority of the body mass that was lost when eating pollock derived from decreases in lipid mass, while a greater proportion of the mass lost when eating herring derived from decreases in lean tissue, except in the summer when the pattern was reversed. Metabolic depression was not observed during all trials despite the constant loss of body mass. Our study supports the hypothesis that restricted energy intake may be more critical to Steller sea lions in the winter months, and that the type of prey consumed (e.g., herring or pollock) may have seasonally specific effects on body mass and composition.     

The effect of feeding on the metabolic rate in harbour seals (Phoca vitulina)

The heat increment of feeding was estimated in harbour seals (Phoca vitulina). Seals were given different amounts of herring, ranging from 0.8 to 2.65 kg. The caloric content of the herring ranged from 6575 to 12560 kJ·kg^-1 depending on time of year. Metabolic rate increased within 30 min after feeding, and the magnitude and duration of heat increment of feeding depended on the size of the meal and the caloric content of the herring. Measured heat increment of feeding was up to 14.9% of gross energy intake and metabolic rate increased as much as 46% above resting, postabsorptive metabolic rate for 15 h duration in a harbour seal with a body weight of approximately 40 kg.     

No evidence for bioenergetic interaction between digestion and thermoregulation in Steller sea lions Eumetopias jubatus

The increase in metabolism during digestion--the heat increment of feeding--is often regarded as an energetic waste product. However, it has been suggested that this energy could offset thermoregulatory costs in cold environments. We investigated this possibility by measuring the rate of oxygen consumption of four juvenile Steller sea lions (Eumetopias jubatus) before and after they ingested a meal in water temperatures of 2 degrees-8 degrees C. Rates of oxygen consumption of fasted and fed animals increased in parallel with decreasing water temperature, such that the apparent heat increment of feeding did not change with water temperature. These results suggest that Steller sea lions did not use the heat released during digestion to offset thermoregulatory costs.     

Seasonal variability in otariid energetics: implications for the effects of predators on localized prey resources

Otariids, like other wild mammals, contend with a wide variety of energetic demands across seasons. However, due to the cryptic behaviors of this marine group, few studies have been able to examine longitudinal energetic costs or the potential impact of these costs on seasonal or annual prey requirements. Here we evaluated the changes in energy demand and intake of female California sea lions (Zalophus californianus) during reproductive (n=2 sea lions) and nonreproductive (n=3) periods. Monthly measurements included resting metabolic rate, blood hormone levels, body condition (blubber thickness and body mass), and caloric intake for adult sea lions throughout molting, late pregnancy, lactation, and postweaning. We found that maintenance energy demands decreased from 32.0 to 23.1 MJ d(-1) before pupping, remaining stable at 19.4+/-0.6 MJ d(-1) during lactation and postweaning. Energy intake rates to meet these demands showed marked changes with activity level and the reproductive cycle, reaching a peak intake of 3.6 times baseline levels during lactation. Translating this into prey demands, we find that 20,000 reproductively active females on San Nicolas Island rookeries would maximally require 4,950 metric tons of Pacific whiting during a month of the breeding season. This localized impact is reduced significantly with postbreeding dispersal and demonstrates the importance of considering spatial and temporal factors driving the energetic requirements of predators when designing marine protected areas.     

Proportion of prey consumed can be determined from faecal DNA using real-time PCR

Reconstructing the diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analysing the soft-matrix of faecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely nonquantitative, which limits their usefulness for some applications. We further developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the proportion of prey in the diets of Steller sea lions (Eumetopias jubatus), a pinniped species thought to be facing significant diet related challenges in the North Pacific. We first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ～ 12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. We then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions in captivity that were fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7% to 75% contributions per meal (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally <12% for all diets fed. Our findings indicate that real-time PCR of faecal DNA can detect the approximate relative quantity of prey consumed for complex diets and prey species, including cephalopods and fish.     

No Evidence of Metabolic Depression in Western Alaskan Juvenile Steller Sea Lions (Eumetopias jubatus)

Steller sea lion (Eumetopias jubatus) populations have undergone precipitous declines through their western Alaskan range over the last four decades with the leading hypothesis to explain this decline centering around changing prey quality, quantity, or availability for this species (i.e., nutritional stress hypothesis). Under chronic conditions of reduced food intake sea lions would conserve energy by limiting energy expenditures through lowering of metabolic rate known as metabolic depression. To examine the potential for nutritional stress, resting metabolic rate (RMR) and body composition were measured in free-ranging juvenile Steller sea lions (N = 91) at three distinct geographical locations (Southeast Alaska, Prince William Sound, Central Aleutian Islands) using open-flow respirometry and deuterium isotope dilution, respectively. Average sea lion RMR ranged from 6.7 to 36.2 MJ d⁻¹ and was influenced by body mass, total body lipid, and to a lesser extent, ambient air temperature and age. Sea lion pups captured in the Aleutian Islands (region of decline) had significantly greater body mass and total body lipid stores when compared to pups from Prince William Sound (region of decline) and Southeast Alaska (stable region). Along with evidence of robust body condition in Aleutian Island pups, no definitive differences were detected in RMR between sea lions sampled between eastern and western populations that could not be accounted for by higher percent total body lipid content, suggesting that that at the time of this study, Steller sea lions were not experiencing metabolic depression in the locations studied.     

Impact of changing diet regimes on Steller sea lion body condition

A leading theory for the cause of the decline of Steller sea lions is nutritional stress, which led to chronic high juvenile mortality and possibly episodic adult mortality. Nutritional stress may have resulted from either poor quality or low abundance of prey. The objective of this study was to determine whether we could predict shifts in body condition (i.e., body mass or body fat content) over different seasons associated with a change in diet (i.e., toward lower quality prey). Captive Steller sea lions (n= 3) were fed three different diet regimes, where Diet 1 approximated the diet in the Kodiak area in the 1970s prior to the documented decline in that area, Diet 2 approximated the species composition in the Kodiak area after the decline had begun, and Diet 3 approximated the diet in southeast Alaska where the Steller sea lion population has been increasing for over 25 yr. All the animals used in this study were still growing and gained mass regardless of diet. Body fat (%) varied between 13% and 28%, but was not consistently high or low for any diet regime or season. Mean intake (in kg) of Diet 2 was significantly greater for all sea lions during all seasons. All animals did, however, tend to gain less body mass on Diets 2 and 3, as well as during the breeding and postbreeding seasons. They also tended to gain more mass during the winter and on Diet 1, though these differences were not statistically significant. Thus, changing seasonal physiology of Steller sea lions appears to have more impact on body condition than quality of prey, provided sufficient quantity of prey is available. Steller sea lions are opportunistic predators and are evidently able to thrive on a variety of prey. Our results indicate that Steller sea lions are capable of compensating for prey of low quality.     

Molecular scatology as a tool to study diet: analysis of prey DNA in scats from captive Steller sea lions

The DNA of prey present in animal scats may provide a valuable source of information for dietary studies. We conducted a captive feeding trial to test whether prey DNA could be reliably detected in scat samples from Steller sea lions (Eumetopias jubatus). Two sea lions were fed a diet of fish (five species) and squid (one species), and DNA was extracted from the soft component of collected scats. Most of the DNA obtained came from the predator, but prey DNA could be amplified using prey-specific primers. The four prey species fed in consistent daily proportions throughout the trial were detected in more than 90% of the scat DNA extractions. Squid and sockeye salmon, which were fed as a relatively small percentage of the daily diet, were detected as reliably as the more abundant diet items. Prey detection was erratic in scats collected when the daily diet was fed in two meals that differed in prey composition, suggesting that prey DNA is passed in meal specific pulses. Prey items that were removed from the diet following one day of feeding were only detected in scats collected within 48 h of ingestion. Proportions of fish DNA present in eight scat samples (evaluated through the screening of clone libraries) were roughly proportional to the mass of prey items consumed, raising the possibility that DNA quantification methods could provide semi-quantitative diet composition data. This study should be of broad interest to researchers studying diet since it highlights an approach that can accurately identify prey species and is not dependent on prey hard parts surviving digestion.     

Hormone changes indicate that winter is a critical period for food shortages in Steller sea lions

Given that many marine mammals display seasonal energetic priorities, it is important to investigate whether the impact of unexpected food restriction differs during the year. Steller sea lions (Eumetopias jubatus) fed restricted diets for up to 9 days during spring, summer, fall, and winter lost an average of 10% of their initial body mass. We tracked changes in the levels of three hormones (cortisol, total thyroxine-TT4, total triiodothyronine-TT3) and one blood metabolite (blood urea nitrogen-BUN) following a food restriction in relation to season, body mass, body composition, and metabolism. Degree of changes in cortisol, TT3, and BUN after food restriction was significantly affected by season. The greatest changes in cortisol (+231%), BUN (+11.4%), TT4 (-23.3%), and TT3 (-35.6%) occurred in the winter (November/December) when rates of body mass loss were also greatest. Changes in cortisol levels were positively related to total body mass loss, while changes in TT3 levels were negatively related. While greater increases in BUN were related to greater rates of mass loss, the use of BUN levels as an indicator of metabolic state is complicated by the type and level of food intake. The observed changes in hormone levels support morphological data suggesting Steller sea lions may be more strongly impacted by short-term, reduced energy intake during winter than at other times of the year.     

Digestive constraints on an aquatic carnivore: effects of feeding frequency and prey composition on harbor seals

We hypothesized that increased feeding frequency in captive harbor seals would increase nutrient loads and thus reduce retention time and the digestive efficiency of natural prey. We measured daily feed intake and excretion during 6 feeding trials and fed herring (49% lipid), pollock (22% lipid) or an equal mix of each diet over 24 months. Animals were accustomed to feeding at either high or low frequency. Body mass and intake did not vary with season. Although mean retention times were similar between diets and feeding frequencies, solute and particulate digesta markers separated at high feeding frequency. Consistent dry matter digestibility resulted in greater gut fill from pollock than from herring. Digestible energy intakes from pollock were approximately 25% greater than from either herring or the mixed diet. Lipid digestibility of herring declined from 90% to 50% when lipid intake exceeded 60 g kg^–0.75 day^–1. Our hypothesis of a trade-off between intake and digestion was not supported for protein but was supported for lipid. Results of this study imply that a flexible digestive system for harbor seals can compensate for ingesting prey of lower energy density by increasing gut fill and enhancing protein and lipid assimilation, to sustain digestible energy intake.Abbreviations DM dry matter - DEI digestible energy intake - DIT diet-induced thermogenesis - FF feeding frequency - MRT mean retention time Communicated by: G. Heldmaier     

CLASSIFYING PREY HARD PART STRUCTURES RECOVERED FROM FECAL REMAINS OF CAPTIVE STELLER SEA LIONS (EUMETOPIAS JUBATUS)

Feces were collected from six Steller sea lions ( Eumetopias jubatus ) that consumed known amounts of Atka mackerel ( Pleurogrammus monopterygius ), Pacific herring ( Clupea barengus ), pink salmon ( Oncorhynchus gorbuscha ), walleye pollock ( Theragra chalcogramma ), and squid ( Loligo opalacens ). The goal was to determine the numbers and types of taxon-specific hard parts that pass through the digestive tract and to develop correction factors for certain abundantly occurring structures. Over 20,000 fish and squid were consumed during 267 d of fecal collection. During this period, over 119,000 taxon-specific hard parts, representing 56 different structures, were recovered. Skeletal structures and non-skeletal structures accounted for 72% and 28% of all hard parts, respectively. The branchiocranium, axial skeleton, and dermocranium regions of the skeletal system accounted for the greatest number of hard parts recovered. Over 70% of all recovered hard parts were represented by one to six taxa specific structures for each prey type. The average number of hard parts (3.1–31.2) and structure types (2.0–17.7) recovered per individual prey varied across taxa and were used to derive correction factors (to reconstruct original prey numbers). A measure of the variability of hard part recovery among sea lions showed no difference for certain herring, pollock, and squid structures, however, there was a significant difference for salmon and Atka mackerel structures. Identifying all taxon- specific prey hard parts increases the likelihood of identifying and estimating the number of prey consumed.     

Temporal variability in marine feeding of sympatric Arctic charr and sea trout

The marine feeding pattern of anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus was studied during June to August in 1992–1993 and 2000–2004 in a fjord in northern Norway. In general sea trout fed proportionally more on fishes than on crustaceans and insects (81, 1 and 18% by mass, respectively) by comparison with Arctic charr (52, 25 and 22% by mass, respectively). Herring Clupea harengus dominated the total fish diet of both species, but the Arctic charr also fed significantly on gadoids and sandlance Ammodytes spp. While sea trout became virtually all piscivorous at fork lengths ( L _F) ≥250 mm, the Arctic charr was ≥400 mm L _F before shifting totally to a fish diet. Despite annual variation in diet and forage ratios, there was a clear shift in diet from 1992–1993 to 2000–2004. Sandlance and different crustaceans constituted most of the diet during the initial period with a shift towards gadoids and especially herring during the latter period. This shift seemed to be associated with a high abundance of herring larvae during the latter sampling period, indicating a preferential selection on herring when present, particularly by sea trout. Furthermore, an index indicated dietary overlap in years with intensive feeding on herring of both species, and usually differences in the trophic ecology during years feeding mostly on other prey species. In combination, it was hypothesized that the two species reflect the type of marine prey present within a fjord system over time, and therefore provide an index of variation in the production and biological diversity of their potential prey within fjords.     

Body regional distribution and stratification of fatty acids in the blubber of New Zealand sea lions: implications for diet predictions

Fatty acids (FAs) from blubber are often analysed to assess the diet of marine mammals. However, distribution of blubber FAs is not necessarily uniform along the body. It is therefore important to understand the deposition of dietary fat to be able to estimate the diet. We analysed the FA compositions of the thoracic ventral (T region) blubber of 28 New Zealand (NZ) sea lions Phocarctos hookeri by-caught by the southern arrow squid Nototodarus sloani fishery. Each blubber sample was divided into an inner and an outer layer. For 16 of these 28 animals, the pelvic dorsal (P) region was also sampled. The influence of body region and layer was statistically tested on the distribution of blubber FAs. We found minimal differences between the P and T regions (3 out of 29 FAs). The outer blubber layer was more concentrated in short-chain monounsaturated FAs, and less concentrated in saturated FAs, but the degree of stratification was small. Diet predictions from quantitative FA signature analysis (QFASA) applied on different body regions were similar. When applied to different blubber layers, QFASA gave some variation in the contribution of rattails (~25 % in outer blubber vs. ~12 % in inner blubber). Nonetheless, diet predicted from both layers was dominated by similar prey species: octopus, hoki and rattails. Hoki and rattails shared a similar ecological niche. Therefore, feeding ecology of NZ sea lions inferred from the inner or the outer blubber would lead to the same conclusions. In the case of NZ sea lions, the outer layer of blubber, if the only sample accessible, could be a useful tissue for diet inference from FAs.     

Mice with Low Metabolic Rates Are Not Susceptible to Weight Gain When Fed a High‐Fat Diet

Objective: Mice divergently selected for high or low food intake (FI) at constant body mass differ in their resting metabolic rates (RMRs). Low‐intake individuals (ML) have significantly lower RMR (by 30%) compared with those from the high‐intake line (MH). We hypothesized that MLs might, therefore, be more likely to increase their body and fat mass when exposed to a high‐fat diet (HFD). Research Methods and Procedures: We exposed both lines to a diet with 44.9% calories from fat for 3 weeks while measuring FI, fecal production, and body mass and then returned the mice to standard chow. Results: When exposed to the HFD, both lines significantly decreased their FI (MH, 40% to 45%; ML, 31% to 35%). This decrease occurred simultaneously with a significant increase in apparent energy absorption efficiency (AEAE). When returned to chow, FI and AEAE returned to the levels observed prior to HFD exposure. Because of the adjustments in FI, the absorbed energy was maintained in the MLs and, thus, body mass remained constant. The MH individuals overcompensated for the elevated energy content and AEAE on the HFD and, therefore, absorbed lower energy than when feeding on chow. These mice also did not significantly change their body mass when on the HFD and must have made adjustments in their energy expenditures. Both lines and both sexes increased in fat content on the HFD, but these effects were not different between lines or sexes. Discussion: We found no support for the hypothesis that mice with low RMRs were more susceptible to weight gain when fed the HFD.     

The effects of fasting duration on the metabolic response to feeding in Python molurus: an evaluation of the energetic costs associated with gastrointestinal growth and upregulation

The oxygen uptake of Python molurus increases enormously following feeding, and the elevated metabolism coincides with rapid growth of the gastrointestinal organs. There are opposing views regarding the energetic costs of the gastrointestinal hypertrophy, and this study concerns the metabolic response to feeding after fasting periods of different duration. Since mass and function of the gastrointestinal organs remain elevated for several days after feeding, the metabolic increment following a second meal given soon after the first can reveal whether the metabolic costs relate to the upregulation of gastrointestinal organs or merely the metabolic cost of processing a meal. Eight juvenile pythons were kept on a regular feeding regime for 6 mo after hatching. At the beginning of the metabolic measurements, they were fed mice (20% of body mass), and the metabolic response to similarly sized meals was determined following 3, 5, 7, 14, 21, 30, and 60 d of fasting. Our data show that the metabolic response following feeding was large, ranging from 21% to 35% of ingested energy (mean=27%), but the metabolic response seems independent of fasting duration. Hence, the extraordinarily large cost of digestion in P. molurus does not appear to correlate with increased function and growth of gastrointestinal organs but must be associated with other physiological processes.     

Potential use of high levels of vegetal proteins in diets for market-sized gilthead sea bream (Sparus aurata)

The effect of partial or total dietary substitution of fishmeal (FM) by vegetal protein sources on growth and feed efficiency was carried out in on-growing gilthead sea bream (mean initial weight 131 g). The Control diet (FM 100) contained FM as the primary protein source, while in Diets FM 25 and FM 0 the FM protein was replaced at 75% and 100%, respectively, by a vegetable protein mixture consisting of wheat gluten, soybean meal, rapeseed meal and crystalline amino acids. Diets FM 25 and FM 0 also contained krill meal at 47 g/kg in order to improve palatability. At the end of the trial (after 158 d), fish survival was above 90%. Final weight and the specific growth rate were statistically lower in fish fed the Control diet (361 g and 0.64%/d), compared with 390–396 g and 0.69–0.70%/d after feeding vegetal diets. No significant differences were found regarding feed intake and feed conversion ratio. The digestibility of protein and amino acids (determined with chromium oxide as indicator) was similar in all diets. The blood parameters were not significantly affected by treatments. The activity of trypsin and pepsin was significantly reduced after feeding Diet FM 0. In the distal intestine, the villi length in fish fed Diet FM 25 was significantly longer and the intestine of the fish fed the FM 100 diet showed a smaller number of goblet cells. In conclusion, a total FM substitution by a vegetal mix supplemented with synthetic amino acids in on-growing sea bream is feasible.     

Intestinal length of three California pinniped species

Forty-eight intestinal tracts, extracted from both sexes of California sea lions, Harbour seals and Northern elephant seals, were measured. The majority of intestinal tracts were removed from stranded animals that died from various causes. The sea lions and elephant seals, approximately equal in size, were larger than the Harbour seals. All species possess a small intestine which is significantly longer than even the entire gastrointestinal tract of herbivores of comparable size. Elephant seal small intestines, averaging approximately 25 times the seal's body length, were considerably longer than the small intestines of either sea lions (averaged more than 18 times the body length) or Harbour seals (averaged nearly 16 times the body length). However, the large intestines of elephant seals were shorter than either of the other two species. Among the sea lions and Harbour seals the large intestines were approximately equal in length. Sea lions and Harbour seals also showed a close correlation between standard length and total intestinal length. Among elephant seals these two parameters showed greater variability. The functional significance of the extremely long small intestine remains unclear. Certainly, the large body mass and high energy requirements of these animals has contributed to the development of a long intestinal tract. It also appears likely that diet and the high motility rate of digesta influenced the intestinal development. Comparatively, the significantly shorter large intestine of elephant seals probably relates to this species' remarkable capabilities in water conservation and metabolic water retention.