Thermal limits in young northern fur seals,Callorhinus ursinus

The thermoregulatory abilities of northern fur seals (Callorhinus ursinus) during their first two years in the frigid waters of the North Pacific Ocean may limit their geographic distribution and alter the costs for exploiting different species of prey. We determined the thermoneutral zone of six young northern fur seals by measuring their metabolism in ambient air and controlled water temperatures (0°C–12°C) from ages 8 to 24 mo. We found that the ambient air temperatures within our study (overall 1.5°C–23.9°C) did not affect resting metabolic rates. Calculated lower critical temperatures in water varied between 3.9°C and 8.0°C, while an upper critical temperature in water was only discernible during a single set of trials. These thermal responses provide insight into the possible physiological constraints on foraging ecology in young northern fur seals, as well as the potential energetic consequences of ocean climate change and altered prey distributions.     

Hematology of free-ranging, lactating northern fur seals, Callorhinus ursinus

Thirteen standard hematology values were determined for a healthy and growing population of free-ranging, lactating northern fur seals (Callorhinus ursinus) from Lovushki Island in the Kuril Islands of far-east Russia. Results are presented from 24 females sampled between June and August during the 3-yr period of 2006-08. Hematologic values have been made available for future comparisons with the declining population of northern fur seals on the Pribilof Islands, Alaska, and are compared with published values for other otariid species.     

Telemetry tags increase the costs of swimming in northern fur seals,Callorhinus ursinus

Animal‐borne instruments have become a standard tool for collecting important data from marine mammals. However, few studies have examined whether placement of these data loggers affects the behavior and energetics of individual animals, potentially leading to biasing data. We measured the effect of two types of relatively small data loggers (<1% of animals’ mass and front profile) on the swimming speeds and energy expenditure of four female northern fur seals (Callorhinus ursinus) while swimming at depth. Swim speeds and rates of oxygen consumption were measured as the trained fur seals repeatedly swam an underwater circuit, with or without the tags. We found the placement of either tested tag significantly affected both the behavior and energetics of the fur seals in our study. Diving metabolic rate increased an average of 8.1%–12.3% (depending on tag type) and swim speed decreased an average of 3.0%–6.0% when wearing the tags. The combined changes in velocities and metabolic rates resulted in a 12.0%–19.0% increase in the total energy required by the fur seals to swim a set distance. The demonstrated effects of tags on behavior and energy expenditure may bias data sets from wild animals and potentially incur longer‐term impacts on the studied animals.     

Physical growth of northern fur seals (Callorhinus ursinus): seasonal fluctuations and migratory influences

Growth curves are described for males, pregnant females, and non-pregnant females using morphometric measurements collected from over 18000 northern fur seals ( Callorhinus ursinus ) shot at sea between California and the Bering Sea from 1958 to 1974. Seals of all ages experience seasonal increases and decreases in body mass and length. Seasonal fluctuations of body length may be an artefact of mass displacement caused by seasonal changes in mass. Rapid growth and gain in mass occur during a brief one to three month period as the population migrates northward through the coastal waters of northern British Columbia and Alaska on their way to the Pribilof Islands. Body mass of females and immature males is gradually lost while fasting on land and wintering along the coasts of Washington, Oregon, and California. Pregnant females are both heavier and longer than non-pregnant females of the same age. Body mass in pregnant females levels off with age in contrast with the increasing mass of non-pregnant females. Growth of northern fur seals does not appear to stop at an upper asymptote, but continues throughout their life spans.     

Broad thermal capacity facilitates the primarily pelagic existence of northern fur seals (Callorhinus ursinus)

Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75–3.5 yr old) in ambient air and controlled water temperatures of 2°C, 10°C, and 18°C. Rates of oxygen consumption in ambient air (1°C–18°C) were not related to environmental temperature except below 2.5°C (winter only). However, metabolism was significantly higher during the fall seasonal trials (September–October) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperatures tested (2°C–18°C) except during the summer when metabolic rates were higher in the 2°C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.     

Development of the aerobic dive limit and muscular efficiency in northern fur seals (Callorhinus ursinus)

Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limited foraging ability of pups. Because a marine mammal’s proficiency at exploiting underwater prey resources is based on the ability to store large amounts of oxygen (O₂) and to utilize these reserves efficiently, this study was designed to determine if NFS pups had lower blood, muscle, and total body O₂ stores than adults. Pups (<1-month old) had a calculated aerobic dive limit only ~40% of adult females due to lower blood and, to a much greater extent, muscle O₂ stores. Development of the Pectoralis (Pec) and Longissimus dorsi (LD) skeletal muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the slow MHC I and fast-twitch IIA proteins typical of oxidative fiber types were dominant, but adult muscles contained more (Pec ~50%; LD ~250% higher) fast-twitch MHC IID/X protein characteristic of glycolytic muscle fibers, than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically scaled citrate synthase, β-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activities (all P values ≤0.001). In combination, these findings indicate that pups are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower NFS first year survival.     

Clinical blood values of the northern fur seal, Callorhinus ursinus

Clinical blood values are reported for 14 blood components in the northern fur seal (Callorhinus ursinus) and compared with human clinical ranges. Certain values such as cholesterol, globulins and blood urea nitrogen deviate markedly from published human values. The distribution of serum proteins in fur seals, man and northern elephant seals also are given and compared.     

Lymphosarcoma in an infant northern fur seal (Callorhinus ursinus)

An infant northern fur seal (Callhorinus ursinus) died in a rookery on St. Paul Island, Pribilof Islands, Alaska. Grossly, slight enlargement of the mesenteric lymph nodes was seen. Microscopically, a lymphosarcoma composed of sheets of monomorphic lymphoid cells in sections of lymph node and tonsil was seen. Electron microscopy of formalin-fixed tissues revealed several structures that were possible of viral origin in the cytoplasm of the neoplastic cells.     

Inter-island variation in the diet of female northern fur seals (Callorhinus ursinus) in the Bering Sea

The diet of adult female northern fur seals ( Callorhinus ursinus ) is examined through the analysis of faecal material collected during the summer breeding season at three breeding locations in the Bering Sea: St. Paul Island (1988, 1990) and St. George Island (1988, 1990) of the Pribilof Islands Group (USA), and Medny Island (1990) of the Commander Islands Group (Russia). Prey consumption varies annually and accordingly with the physical and biological environment surrounding each island. Juvenile walleye pollock ( Theragra chalcogramma ) is the most common prey of northern fur seals from St. Paul Island; the island is surrounded by a broad neritic environment with widely separated frontal zones and is the greatest distance from the continental shelf-edge. Gonatid squid ( Gonatopsis borealis/Berryteuthis magister and Gonatus madokail Gonatus middendorffi ) were the most common prey of northern fur seals from Medny Island; the island is surrounded by a compressed neritic environment and is adjacent to the continental shelf-edge and the oceanic marine environment. A combination of walleye pollock and gonatid squid is consumed by northern fur seals from St. George Island; the island has a surrounding oceanographic environment intermediate between the other two islands.
Variability in predation on walleye pollock is consistent with fishery information concerning the relative abundance and availability of walleye pollock around St. George and St. Paul Islands. The abundance and availability of these prey resources during the summer breeding season are key factors which influence the health and growth of the northern fur seal populations in the Bering Sea.     

Serum indices of body stores of iron in northern fur seals (Callorhinus ursinus) and their relationship to hemochromatosis

Iron storage disease (hemochromatosis) has been reported in many species of both captive and free‐ranging animals. In this study we examined the relationship between this disease and concentrations of iron analytes in aquarium‐held northern fur seals (Callorhinus ursinus). Sera were analyzed for iron, total iron‐binding capacity (TIBC), ferritin, ceruloplasmin, and haptoglobin concentrations in a retrospective study that included samples taken over a 14‐year period. The animals ranged in age from <1 year to an estimated 23 years. Serum ferritin was measured using an enzyme‐linked immunosorbent assay (ELISA) for canine sera. The results from this assay are the first reported for any pinniped. Serum iron concentrations in presumed healthy animals ranged from 37 to 196 µg/dl, and TIBC ranged from 136 to 484 µg/dl. The transferrin saturation percentage differed significantly between male (41%) and female (63%) adult fur seals, as did the ferritin levels (54 ng/ml for males vs. 500 ng/ml for females). There was a trend toward increased serum ferritin and percent transferrin saturation with age, especially in females. The data also showed a relationship between serum iron and transferrin saturation among eight mother–pup pairs, which suggests that pups may develop increased iron levels due to placental transfer of iron and/or transfer of iron through the milk from iron‐overloaded females. Diet was considered as a factor in the development of hemochromatosis in at least three geriatric female northern fur seals, and their diets were analyzed for iron concentrations. On the basis of these results, the diets were altered by replacing a portion of the high‐iron‐content fish (herring) with a lower‐iron‐content item (squid), and discontinuing iron and vitamin C supplementation (via a multivitamin tablet). Sera were analyzed before, and 1 and 4 years after the dietary changes were implemented. Paired t‐tests showed no significant changes in the iron analytes from pre‐ to post‐diet‐change samples, which indicates that it may be too late to affect iron levels by diet alone in older animals with a chronic history of elevated iron levels. Zoo Biol 23:205–218, 2004. © 2004 Wiley‐Liss, Inc.     

Otolith size and location in digestive tracts of northern fur seals (Callorhinus ursinus): Implications for dietary interpretations

Walleye pollock (Theragra chalcogramma) otoliths (n= 2,706) recovered from stomachs, small intestines, and colons of 43 northern fur seals (Callorhinus ursinus) were evaluated for size and wear by location in the digestive tract. Pollock fork length was regressed on otolith length after correction for erosion, and age was estimated from the calculated body size. Age‐1+ pollock otoliths (≥6.3‐mm length) were concentrated in stomachs while age‐0 otoliths (≤6.2‐mm length) were concentrated in colons. Less than 10% of otoliths were found in the small intestines. Pollock age decreased with progression along seal gastrointestinal tracts. Otolith quality increased along gastrointestinal tracts in numbers ≥20, which was typical of age‐0 otoliths recovered from colons. Otolith distribution by age and quality along gastrointestinal tracts suggests that small (≤12 cm) schooling prey are consumed in large volume and passed as a bolus rapidly through the digestive tract before significant erosion of bony remains occurs; while larger prey are eaten in smaller volume and subjected to otolith erosion due to longer retention in the stomach. Our results illustrate the importance of multiple sampling strategies to comprehensively represent prey size in pinniped diet.     

Photoperiod and delayed implantation in the northern fur seal (Callorhinus ursinus)

An equation for determination of the photoperiod at any given latitude for any given date is presented and used in an analysis of reproductive timing in the northern fur seal in which there is an obligatory delay of implantation. Fur seals breeding on San Miguel Island, California (33 degrees N) displayed a mean date of parturition that was 14 days earlier (P less than 0.001) than that of the parent stock on the Pribilof Islands, Alaska (57 degrees N). Previous studies have shown that changes occur in the corpus luteum, in follicles in the ovary containing the corpus luteum, in concentrations of plasma progesterone and oestradiol-17 beta, and in the uterine lining when there is a mean photoperiod of 12.5 h/day. This photoperiod occurs at both locations at 62 days after the mean dates of parturition, and may act as a cue for the initiation of implantation in these seals.     

Features of sleep in the water by the northern fur seal Callorhinus ursinus

The peculiarities of sleep in water and on land were investigated in four adult Northern fur seals (Callorhinus ursinus) of both sexes. The electrocorticogram of both hemispheres, the neck electromyogram, the electrooculogram and electrocardiogram were recorded with implanted electrodes. The interhemispheric asymmetry of EEG during slow wave sleep was observed in all the animals sleeping in water and on land. The relative amount of interhemispheric slow wave asymmetry was higher during the sleep in water comparing to that on land. The fur seals maintain their special sleep posture on the water surface by moving only one of their front flippers. The asymmetric EEG in fur seals sleeping in the water may be attributed to the asymmetric motor activity of their flippers.     

Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska

Scats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul ( n =2968) and St George Islands ( n =1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO>5%) included Pacific sand lance Ammodytes hexapteus , Pacific herring Clupea pallasi , northern smoothtongue Leuroglossus schmidti , Atka mackerel Pleurogrammus monopterygius , Pacific salmon ( Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south-west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.     

Milk intake and energy expenditure of free-ranging northern fur seal, Callorhinus ursinus, pups

Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expenditure concurrent with milk intake. We concurrently examined milk intake, field metabolic rate (FMR), and body composition of 41 pups over the entire lactation interval in 1995 and 1996 on St. Paul Island, Alaska. One hundred two metabolic measurements were obtained with isotope dilution methods. Mean milk intake did not differ annually but increased with age and mass, ranging from 3,400+/-239 to 6,780+/-449 (+/-SE) mL per suckling bout. Milk energy consumption did not vary with age on a mass-specific basis. No differences were detected in milk volume consumed by male and female pups, either absolutely or on a mass-specific basis. Mass-specific FMR peaked during molting, was lowest postmolt, and did not vary by sex. Pups in 1995 had lower FMR than pups in 1996 and were also fatter. Mean milk energy utilized for maintenance metabolism decreased over time from 77% to 43% in 1995 and remained at 71% in 1996. Pup body mass was negatively correlated with the percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in mass-specific metabolic savings after the molt.     

Fatty acid content of depot fat in the northern fur seal (Callorhinus ursinus)

The fatty acid content of depot fat samples from 15 northern fur seals (Callorhinus ursinus) were determined by gas-liquid chromatography. Callorhinus ursinus has a high proportion of short chain saturated acids: C10, C11, C12, C13, C15. Unsaturated longer chain acids C16:1, and C16:2, and C18:1 also were found. Results obtained are compared to a previously reported milk lipid analysis of the northern fur seal.     

Spermatogenic cycle in seals (Callorhinus ursinus L.)

In the fur-seal germ cells at various stages of development are situated in the spermatic canaliculi as concentric layers in accordance with the stages of the spermatogenic cycle. By means of PAS-reaction 18 stages have been revealed in spermatogenesis of the fur-seal and basing on the first 15 of them, 15 stages of the spermatogenic cycles have been presented. Transformations of the nucleus during the process of spermatids development proceed similar to other animals studied, formation of acrosomes is accompanied with a specific for the given species development of temporal formation--tubulo-bulbar complexes, reduced at terminal stages of spermiogenesis.