Large increases of harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata) on Sable Island, Nova Scotia, since 1995

Beach surveys for harp (Phoca groenlandica) and hooded (Cystophora cristata) seals documented a dramatic increase in their numbers on Sable Island in the mid-1990s. From late 1994 to 1998, 1,191 harp and 870 hooded seals, mostly young animals, were recorded on the island whereas, in the 1980s, no more than 5 animals of both species were observed each year. Of the 2,061 harp and hooded seals examined, 41.7% were found alive, 26.7% were killed by sharks, and 31.6% were found dead but intact. This increase in numbers of harp and hooded seals on Sable Island, which is south of their historic northern range, is consistent with the recent increase of extralimital occurrences of these species along the east coast of North America. However, the large number of seals recorded in this study provides more information on their demography than has previously been possible.     

Hematology and serum chemistry of harp (Phoca groenlandica) and hooded seals (Cystophora cristata) during the breeding season, in the Gulf of St. Lawrence, Canada

Standard hematologic and serum chemistry parameters were determined from 28 harp seals (Phoca groenlandica) and 20 hooded seals (Cystophora cristata) sampled from 6 March 2001 to 13 March 2001 during the breeding season. Whole blood was collected immediately postmortem from harp seal mother-pup pairs and from six hooded seal pups, and from live-captured adult hooded seals and three hooded seal pups; blood was analyzed within 24 hr at a local human hospital. A certified veterinary laboratory validated subsamples of whole blood and analyzed all serum chemistry parameters. Significant interlaboratory differences in mean values of packed cell volume (PCV) and mean cell volume (MCV) were found. Significant differences were found between samples from the five seal groups (adult male hooded seals, lactating female hooded seals, unweaned hooded seal pups; lactating female harp seals, and unweaned harp seal pups) for hematology and most serum chemistry parameters. In general, age-class influenced mean values of PCV, hemoglobin (HB), red blood cell (RBC) counts, MCV, mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), and nucleated red blood cell (NRBC) counts per 100 leucocytes, but most age-related variations were species specific. Harp seal pups had significantly lower mean values of HB, PCV, MCH, and MCHC than did other seal groups, and significantly lower mean RBC counts than did hooded seal pups. Mean NRBC counts per 100 leukocytes were more than three times higher in harp seal pups than in hooded seal pups, but this difference was not statistically significant. Mean MCV were significantly lower in harp and hooded seal pups compared to those of adult harp and hooded seals. Differences in hemograms between pup species were likely because of the precocious development of hooded seal pups, which are weaned within 4 days, compared to 12 days for harp seal pups. Among adult seal groups, male hooded seals had significantly higher mean values of PCV and HB than did female harp and hooded seals, and significantly higher mean RBC counts than did adult female hooded seals. Among adult females, mean values of MCH and MCHC were statistically higher in hooded seals than in harp seals. Adult female harp and hooded seals did not differ significantly in other RBC parameters and mean leukocyte counts. Mean values of glucose, blood urea nitrogen, total bilirubin, alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein, and albumin showed species-specific variations between adults and pups. Except for ALP, few significant differences in mean enzyme activities of aspartate aminotransferase (AST), ALT, creatine kinase and gamma-glutamyltransferase were found between seal groups. Mean concentrations of electrolytes (calcium, phosphorus, sodium, potassium, chloride, magnesium, and total carbon dioxide) varied with age class, but variations in potassium and magnesium were species specific. Harp seal pups had significantly higher mean phosphorus and potassium levels compared to other seal groups.     

Melatonin potentiates the vasoconstrictive effect of noradrenaline in renal artery from newborn hooded seals (Cystophora cristata) and harp seals (Phoca groenlandica)

Isometric tension was recorded by force displacement transducers in ring segments of the inferior branch of the renal artery from newborn hooded seals (Cystophora cristata, n=6), harp seals (Phoca groenlandica, n=3) and domestic pigs (Sus scrofa f. domestica, n=5). Arterial segments were mounted in heated organ baths and exposed to graded concentrations of noradrenaline (NA) and adrenaline (A), alone or together with melatonin. The melatonin concentration in the bath was similar to the plasma concentration normally found in each experimental animal. Melatonin alone did not affect the tension in any of the species, but melatonin potentiated the contraction induced by NA in hooded and harp seal arteries to a maximum of about 25% above the resting, pre-stretch level. The selective melatonin receptor antagonist luzindole reduced this potentiation by 80%. Species-specific concentrations of melatonin did not potentiate the NA-effect in the domestic pig or the A-induced contraction in any of the species. The results indicate that melatonin specifically increases the NA-sensitivity of smooth muscles in renal arteries from newborn seals. It is presumed that similar effects may operate in foetal and maternal seals and may influence their circulation during maternal diving.     

Experimental evidence of seawater drinking in juvenile hooded (Cystophora cristata) and harp seals (Phoca groenlandica)

This study was undertaken to measure whether young harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata) drink seawater and, if so, to investigate how the excess salt load is handled. Blood and urine samples were collected from hooded seal pups (n=3) and harp seal pups (n=3) after 2 weeks of freshwater exposure, at intervals during 3 weeks of seawater exposure and, finally, after 2 weeks of re-exposure to fresh water. Total water turnover, as measured by injection of tritiated water, was 2200 ml · day⁻¹ and 3300 ml · day⁻¹ in hooded seals and harp seals, respectively. The extent of mariposia was taken as the difference between total water turnover and influx of water through food (free and metabolic water) and respiratory water exchange. Seawater drinking amounted to 14% and 27% of total water turnover (r_H2O) for the hooded seals and harp seals, respectively. Further evidence of mariposia was obtained from an increase in the excretion rate of the urine osmolytes Na⁺, Cl⁻ and Mg²⁺, during the period of seawater exposure. It is concluded that water influx due to seawater drinking can not be excluded as a source of error when estimating food consumption of free-ranging harp seals and hooded seals, by use of labeled water techniques. Accepted: 11 May 2000     

Melatonin is rhythmic in newborn seals exposed to continuous light

We have investigated the effect of continuous light and darkness on plasma levels of melatonin in relation to the extremely large and active pineal gland typically found in newborn seals. Plasma levels of melatonin in captive newborn harp (Phoca groenlandica) and hooded seals (Cystophora cristata) were generally extremely high, with peak concentrations ranging from 0.8 ng/ml to 62.3 ng/ml. Moreover, plasma melatonin showed a similar, pronounced rhythmicity, both outdoors under natural light conditions (hooded seal only) and indoors under either 30 h of continuous light (490 lux) or 30 h of darkness (0 lux). In all animals, the melatonin rhythm was closely associated with the outdoor light-dark cycle. We suggest that the melatonin rhythmicity in newborn seals is mainly under circadian control and that it originates by maternal influence in the foetus. Daytime plasma concentrations of melatonin were also measured in foetal hooded seals and their mothers. The foetal melatonin level was similar to daytime levels in newborns and was about five times higher than in their mothers, which indicates a significant flow of foetal melatonin to the mother. We speculate that the large pineal gland and high melatonin levels in the newborn seals are temporary consequences of a foetal strategy to affect the maternal blood supply during diving.     

The effects of climate change on harp seals (Pagophilus groenlandicus)

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data.     

Gross anatomy of the gastrointestinal system of harp seals (Phoca groenlandica)

The gross anatomy of the gastrointestinal system of 12 harp seals ( Phoca groenlandica ) was investigated. Harp seals have a typical carnivore monogastric stomach. The tissue wet weight of the stomach of harp seals represented 27.01 (S.D. 3.99)% ( n = 12) of the total gastrointestinal tract (GI-tract). All animals were killed while resting on the ice, and had empty stomachs, but when expanded with water to a 30cm pressure the stomach contained 0.60 to 1.60 litres, representing 1.00 (S.D. 0.26)% ( n = 12) of the body mass. The small intestine ranged in length from 20.44 to 25.32m, being 14.36 (S.D. 1.58) times the body length, and the tissue wet weight constituted 67.61 (S.D. 4.55)% of the total GI-tract ( n = 12). Both caecum and colon were short, maximally 5 and 78 cm, respectively, being 0.022 (S.D. 0.005) and 0.38 (S.D. 0.06) times the body length ( n = 12). The caecum tissue wet weight was only 0.18 (S.D. 0.04)% of the total GI-tract weight, while the colon tissue wet weight contributed to 5.33 (S.D. 1.19)% ( n = 12). It is concluded that harp seals have relatively long intestines compared to minke whales eating a comparable diet in the North Atlantic Ocean.     

Gut length, food transit time and diving habit in phocid seals

The southern elephant seal (Mirounga leonina) has the ability to dive for 2 h and reach depths of 1200 m. This creature is also exceptional in having a small intestine that is 25 times body length. Krockenberger and Bryden advanced the hypothesis that the long small intestine has developed to compensate for the extended periods with reduced or even abolished intestinal blood perfusion during diving. To test this hypothesis we have measured small-intestinal lengths in crabeater (Lobodon carcinophagus), Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossi), leopard (Hydrurga leptonyx), harp (Phoca groenlandica), ringed (Phoca hispida) and hooded (Cystophora cristata) seals and related them to available data on their maximal dive duration. We found no significant correlation (P > 0.05) between intestinal length relative to body length and diving ability, but we found that small-intestinal internal area was significantly (P < 0.05) related to body length. A crude scanning electron microscopical examination of the small intestines of Weddell, crabeater, hooded and harp seals failed to reveal any gross anatomical differences between small-intestinal surfaces. This suggests that gut dimension in this variety of phocid species with widely differing diving ability is not related to diving habit, but is instead related to body size. The transit time of digesta was determined in two 1-year-old harp seals by use of radiopaque polyethylene rings of 4-mm diameter followed by X-ray examination, as markers for the solid phase passage, and chromium ethylene-diaminetetra acetic acid (Cr-EDTA) as a marker for the liquid phase. The transit time for the Cr-EDTA marker was 6.9 h ± 0.5 SE (range 4.5–8 h, n= 7), while 80% of the polyethylene markers appeared in the colon after 17.6 h ± 1.0 SE (range 14–21.5 h, n= 6) and were sometimes retained in the colon for several hours before defecation. These transit times did not change significantly (P > 0.05) in response to repetitive diving over a period of 8 h. This indicates that the often-used Cr-EDTA is not a good measure for digesta passage time when used alone in seals, and that the hypothesis of Krockenberger and Bryden is most likely wrong. Received: 17 December 1997 / Accepted: 4 May 1998     

ESTIMATING STRUCK AND LOSS RATES FOR HARP SEALS (PAGOPHILUS GROENLANDICUS) IN THE NORTHWEST ATLANTIC

One of the major sources of unreported mortality during the commercial harp seal ( Pagophilus groenlandicus ) hunt in the Northwest Atlantic is the number of animals that are killed but not recovered or reported, commonly referred to as struck and lost. With the significant expansion of the hunt in Canada and in Greenland during the mid-1990s, there is a concern that the number of seals lost may have reached a level that is not sustainable relative to current harvest levels. To address this problem a study examining struck and loss rates was initiated in 1998 and 1999. Loss rates for young seals taken on the ice varied from 0% to 1.9% and from 0% to 10.0% when taken in the water. Seals greater than one year of age had loss rates of 0%–4.9% when taken on the ice and 13.8%-50.0% when taken in the water. These estimates are lower than those recently reported for Northwest Atlantic harp seals.     

The effect of body fat on basal metabolic rate in adult harp seals (Phoca groenlandica)

Three adult harp seals (Phoca groenlandica) were fed different daily amounts of capelin (Mallotus villosus), and their body composition determined by use of the tritiated water method at different levels of fattening. Basal metabolic rate (BMR) was measured after 5 days of fasting by indirect calorimetry, and was on average 1.1 W.kg-1 when 45% of body mass (BM) was fat and 2.3 W.kg-1 when body fat was reduced to 13% of BM. This suggests that body fat contributes little to BMR in these animals. It follows, that predictions of BMR on the basis of BM is questionable in seals, in which body fat may change seasonally between 20 and 60% of BM.     

Winter distribution of harp seals (Phoca groenlandica) off eastern Newfoundland and southern Labrador

The winter distribution of Newfoundland harp seals (Phoca groenlandica) was determined using sighting data collected during January and February from 1991 to 1995 aboard research vessels that covered the northeastern continental shelf between 46–55°N and 47–54°W. Data were standardized for effort and sighting conditions. Visual appraisals of data were made using a Geographical Information System. In contrast to historical perceptions, offshore areas such as the northern part of the Grand Banks (48–49°N and 49–51°W) appear to be extremely important to wintering harp seals. Southeastern shifts in distribution appear to have occurred since the early 1990s, particularly between the 1991–1993 and 1994–1995 periods. This southern shift in range agrees with the recent increase in extralimital occurrences of harp seals along the North American east coast. Concurrent changes in environmental conditions suggest that physical and biological factors may influence the distribution of this population. Accepted: 22 May 2000     

THERMAL FUNCTION OF PHOCID SEAL FUR

In phocid seals, blubber serves as the main thermal insulation instead of fur. The thermal function of fur, at least in adult phocid seals, has therefore been questioned. We measured the relative contribution of fur to the combined thermal resistance (insulation) offered by blubber, skin, and fur in newborn and adult harp ( Pagophilus groenlandicus ) and hooded ( Cystophora cristata ) seals, in air and water, to elucidate the role of fur as insulation in phocid seals. In air the fur contributed 90% of the combined thermal resistance of blubber, skin, and fur in newborn harp seal pups and 29% in adulrs, whereas in hooded seals the fur contributed 73% in newborn pups and 34% in adults. When submerged the thermal resistance of the fur was reduced by 84%-92%, and contributed 65% to the total insulation in newborn harp seal pups and 3% in adults, and 26% in newborn hooded seal pups and 5% in adults. We conclude that in air the fur of phocid seals makes an important contribution to the insulation of pups, and also contributes considerably to the insulation of adult animals. In water, even though the thermal resistance of the fur is dramatically reduced, the fur still contributes substantially to the insulation of pups, but its contribution in adults is negligible.     

Structure of the testis in neonate and adult harp seals,Pagophilus groenlandicus

Summary The structure of the seminiferous tubules in neonate harp seals, Pagophilus groenlandicus, was essentially similar in one-, five and ten-day old animals. The tubules were small in diameter, devoid of lumina and contained predominantly supportive cells. The interstitial cells in the neonates were large, numerous and highly vacuolated. They became smaller and appeared less active in the ten-day old animals compared with the one-day old seals, although they were still considerably more numerous and vacuolated than in testes taken from adult harp seals.The work was supported by grants from the National Science and Engineering Research Council of Canada (J.F.L. and K.R.) and from the Donner (Canadian) Foundation (K.R.)     

Summer feeding ecology of harp seals (Phoca groenlandica) in relation to arctic cod (Boreogadus saida) in the Canadian high arctic

Summary The diet and feeding behaviour of harp seals, Phoca groenlandica, was examined in two high arctic locations. Fish otoliths were used to evaluate dietary composition and aspects of the population dynamics of the major prey species, arctic cod, Boreogadus saida. Harp seals, primarily adults, arrive in the high arctic in mid to late June and depart by early October. Their migration is undertaken specifically for feeding. Harp seals feed intensively on arctic cod, often occurring in dense multispecies aggregations in late summer. The average weight of harp seal stomach contents was high; glutted individuals contained as much as 6% of their body weight in food. Although arctic cod declined in abundance between years, size of cod ingested was similar between areas and years, and overlapped completely with cod taken by other marine mammals. Age/size segregation of arctic cod may account for poor representation of fish <3 years old in the seal diet. Widespread reproductive failure of arctic cod could have a profound influence on the energy balance of adult harp seals since there does not appear to be an alternate food source of equivalent energy value and abundance in arctic waters. Increasing harp seal populations will likely result in increased competition with a host of arctic cod predators, particularly ringed seals.     

Seawater drinking restores water balance in dehydrated harp seals

The purpose of this study was to answer the question of whether dehydrated harp seals (Phoca groenlandica) are able to obtain a net gain of water from the intake of seawater. Following 24 h of fasting, three subadult female harp seals were dehydrated by intravenous administration of the osmotic diuretic, mannitol. After another 24 h of fasting, the seals were given 1,000 ml seawater via a stomach tube. Urine and blood were collected for measurement of osmolality and osmolytes, while total body water (TBW) was determined by injections of tritiated water. In all seals, the maximum urinary concentrations of Na⁺ and Cl⁻ were higher than in seawater, reaching 540 and 620 mM, respectively, compared to 444 and 535 mM in seawater. In another experiment, the seals were given ad lib access to seawater for 48 h after mannitol-induced hyper-osmotic dehydration. In animals without access to seawater, the mean blood osmolality increased from 331 to 363 mOsm kg⁻¹ during dehydration. In contrast, the blood osmolality, hematocrit and TBW returned to normal when the seals were permitted ad lib access to seawater after dehydration. In conclusion, this study shows that harp seals have the capacity to gain net water from mariposa (voluntarily drinking seawater) and are able to restore water balance after profound dehydration by drinking seawater.     

Trophic level and fatty acids in harp seals compared with common minke whales in the Barents Sea

The objectives of this study were to explore trophic levels and possible diet overlap between harp seals (Pagophilus groenlandicus) and common minke whales (Balaenoptera acutoroostrata) in the Barents Sea using stable isotopes of nitrogen (δ¹⁵N) and carbon (δ¹³C) and fatty acid analyses, and to explore the energy pathways from the plankton to the top predators. Blubber and muscle samples from 93 harp seals and 20 minke whales were collected in the southern Barents Sea in May 2011. The study showed that harp seals were at a higher trophic level than minke whales during spring. This supported previous diet studies suggesting a more fish-dominant diet for seals, as compared with the whales, at this time of the year. The stable isotopes and fatty acids indicated niche separation between the seals and the whales, and between different age groups of the harp seals. Older seals had fatty acid profiles more equal to minke whales as compared with younger seals. Furthermore, while the fatty acid profiles suggested that krill were of particular importance for the young seals, the profiles from older seals and whales suggested that fish dominated their diets.     

Size and distribution of oxygen stores in harp and hooded seals from birth to maturity

Pinnipeds rely primarily on oxygen stores in blood and muscles to support aerobic diving; therefore rapid development of body oxygen stores (TBO₂) is crucial for pups to transition from nursing to independent foraging. Here, we investigate TBO₂ development in 45 harp (Pagophilus groenlandicus) and 46 hooded (Cystophora cristata) seals ranging in age from neonates to adult females. We found that hooded seal adults have the largest TBO₂ stores yet reported (89.5 ml kg⁻¹), while harp seal adults have values more similar to other phocids (71.6 ml kg⁻¹). In adults, large TBO₂ stores resulted from large blood volume (harp169, hood 194 ml kg⁻¹) and high muscle Mb content (harp 86.0, hood 94.8 mg g⁻¹). In contrast, pups of both species had significantly lower mass-specific TBO₂ stores than adults, and stores declined rather than increased during the nursing period. This decline was due to a reduction in mass-specific blood volume and the absence of an increase in the low Mb levels (harp 21.0, hood 31.5 mg g⁻¹). Comparisons with other phocid species suggests that the pattern of blood and muscle development in the pre- and post-natal periods varies with terrestrial period, and that muscle maturation rates may influence the length of the postweaning fast. However, final maturation of TBO₂ stores does not take place until after foraging begins.     

DIET OF HARP SEALS (PAGOPHILUS GROENLANDICUS) IN NEARSHORE NORTHEAST NEWFOUNDLAND: INFERENCES FROM STABLE-CARBON (δ13C) AND NITROGEN (δ15N) ISOTOPE ANALYSES

Trophic position, and often the source of feeding of predators in food webs, can be estimated using measurements of stable isotope ratios of nitrogen and carbon in predators and their prey. Muscle samples from 60 harp seals ( Pagophilus groenlandicus ) collected during May 1995 in nearshore waters of New foundland, Canada, were analyzed for δ¹³C and δ¹⁵N values. These values were compared with those for 63 prey samples representing seven species generally collected near the same area. Using diet-tissue isotopic fractionation factors derived from previous studies using captive animals, we infer a greater dependence of harp seals on lower trophic-level prey during April compared with results expected from exclusive diets of Atlantic cod ( Gadus morhua ), Atlantic herring ( Clupea harengus ), Greenland halibut ( Reinhardtius hippoglossoides ), or northern shrimp ( Pandalus borealis ). Our mean δ¹⁵N value for harp seals is lower than previous findings for seals collected on the winter whelping patch and may be a function of interannual or seasonal differences in diet. Subadult seals (aged 1-4 yr) had significantly lower δ¹⁵N values than adults (5 + yr), suggesting that older seals were feeding at a slightly higher trophic level.     

Detection of Cryptosporidium sp. in two new seal species, Phoca vitulina and Cystophora cristata, and a novel Cryptosporidium genotype in a third seal species, Pagophilus groenlandicus, from the Gulf of Maine

Data on the geographic distribution and host specificity of Cryptosporidium spp. are critical for developing an understanding of likely transmission patterns in nature. During a molecular-based survey of fecal samples from 293 terrestrial and aquatic animals in Maine, USA, we detected Cryptosporidium sp. in 11 harbor seals (Phoca vitulina), 1 hooded seal (Cystophora cristata), and 1 harp seal (Pagophilus groenlandicus). None of the terrestrial or freshwater mammal fecal samples or bird samples tested positive for Cryptosporidium sp. However, the sequencing results of the small subunit (ssu) rRNA gene indicate that the seals were infected with an undescribed species of Cryptosporidium , previously isolated only from ringed seals (Phoca hispida) in northern Quebec, Canada. In addition, the Cryptosporidium sp. detected in the harp seal is significantly different from the previously observed Cryptosporidium sp. in other seals. We confirmed the genetic distinctiveness of this Cryptosporidium genotype and the identity of the other Cryptosporidium sp. seal ssu rRNA sequences by using data from the 70-kDa heat shock protein gene. Based on phylogenetic reconstructions of both genes, it seems that either Cryptosporidium canis or C. felis are sister species to the seal associated Cryptosporidium spp. Our findings extend the range of " Cryptosporidium sp. seal" well south of the 55th parallel, add other species to the list of seals affected by Cryptosporidium sp., and highlight the presence of unrecognized population and potentially species level variation in Cryptosporidium.     

Seasonal energetics of northern phocid seals

The metabolic rate of harp (Pagophilus groenlandicus), harbor (Phoca vitulina), and ringed seals (Pusa hispida) was measured at various temperatures in air and water to estimate basal metabolic rates (BMRs) in these species. The basal rate and body composition of three harp seals were also measured throughout the year to examine the extent to which they vary seasonally. Marine mammalian carnivores generally have BMRs that are over three times the rates expected from body mass in mammals generally, both as a response to a cold-water distribution and to carnivorous food habits with the basal rates of terrestrial carnivores averaging about 1.8 times the mean of mammals. Phocid seals, however, have basal rates of metabolism that are 30% lower than other marine carnivores. Captive seals undergo profound changes in body mass and food consumption throughout the year, and after accounting for changes in body mass, the lowest rate of food intake occurs in summer. Contrary to earlier observations, harp seals also have lower basal rates during summer than during winter, but the variation in BMR, relative to mass expectations, was not associated with changes in the size of fat deposits. The summer reduction in energy expenditure and food consumption correlated with a reduction in BMR. That is, changes in BMR account for a significant portion of the seasonal variation in energy expenditure in the harp seal. Changes in body mass of harp seals throughout the year were due not only to changes in the size of body fat deposits, but also to changes in lean body mass. These results suggest that bioenergetics models used to predict prey consumption by seals should include time-variant energy requirements.