TOOTH WEIGHTS OF JUVENILE MALE NORTHERN FUR SEALS, CALLORHINUS URSINUS

Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus , collected on St. Paul Island, Alaska, from 1948 to 1984 were compared. The relationship between these variables was investigated for individual and combined age classes. A density-dependent increase in mean tooth weight occurred during a decline in fur seal abundance. Consistent, though poorly understood, differences in tooth weight were found among males associated with different rookeries (breeding grounds). Storing the teeth for long periods may affect the weights, but such effects, if any, are too small to account for the changes observed.     

DENSITY DEPENDENCE IN NORTHERN FUR SEALS (CALLORHINUS URSINUS)

This paper summarizes, updates, and interprets information on density-dependent dynamics of populations of the northern fur seal ( Callorhinus ursinus ). Density-dependent changes observed in these populations have involved various aspects of growth (body length, body weight, tooth weight, and size of other skeletal parts, especially the skull), survival, age at maturation, incidence of disease, and time spent foraging. For the population of northern fur seals on St. Paul Island of the Pribilof Islands, which was observed during a major increase and during two significant declines, density-dependent changes that occurred during the growth of the population were reversed during the declines. The Robben Island population in the western Pacific declined after 1965, and the decline was accompanied by changes similar to those observed during the declines on the Pribilof Islands. Although data are not available for all age and sex classes, it appears that most or all components of the populations exhibit similar changes. The overall implication of these changes is that current populations on Robben Island and the Pribilof Islands are reduced to levels below what could be supported by the resources available in their environments. Density dependence for this species is consistent with that of other large mammals, specifically in that vital rates for fur seals ate related to density in a nonlinear fashion.     

ANALYSIS OF SWIM VELOCITIES DURING DEEP AND SHALLOW DIVES OF TWO NORTHERN FUR SEALS, CALLORHINUS URSINUS

Swim velocities at 15-sec intervals and maximum depth per dive were recorded by microprocessor units on two "mixed diver" adult female northern fur seals during summer foraging trips. These records allowed comparison of swim velocities of deep (>75 m) and shallow (<75 m) dives.
Deep dives averaged 120 m depth and 3 min duration; shallow dives averaged 30 m and 1.2 min. Mean swim velocities on deep dives were 1.8 and 1.5 m/sec for the two animals; mean swim velocities on shallow dives were 1.5 and 1.2 m/sec. The number of minutes per hour spent diving during the deep and shallow dive patterns were 11 and 27 min, respectively.
Swim velocity, and hence, relative metabolic rate, did not account for the differences in dive durations between deep and shallow dives. The long surface durations associated with deep dives, and estimates of metabolic rates for the observed swim velocities, suggest that deep dives involve significant anaerobic metabolism.     

AUDIOMETRIC ASSESSMENT OF NORTHERN FUR SEALS, CALLORHINUS URSINUS

Aerial and underwater audiograms for two young female northern fur seals ( Callorhinus ursinus ) and one young female California sea lion (Zalophus californianus) were obtained with the same procedure and apparatus. Callorhinus hears over a larger frequency range and is more sensitive to airborne sounds than Zalophus or any other pinniped thus far tested in the frequency range of 500 Hz to 32 kHz. Sensitivity of Callorhinus to waterborne pure tones, ranging from 2 to 28 kHz, is equal or superior to all other pinnipeds tested in this same frequency range. Like Zalophus , the upper frequency limit for underwater hearing (as defined by Masterton et al. 1969) in Callorhinus is about one-half octave lower than the three phocid species thus far tested. Callorhinus' upper frequency limit in air is about 36 kHz and under water it is about 40 kHz. Comparison of air and water audiograms shows Callorhinus is no exception to previous behavioral findings demonstrating that the „pinniped ear” is more suitable for hearing in water than in air. Similar to Zalophus and Phoca vitulina, Callorhinus shows an anomalous hearing loss at 4 kHz in air. The basis for this insensitivity to airborne sounds at 4kHz and not at lower or higher frequencies is presumably caused by specialized middle ear mechanisms matching impedance for waterborne sounds. Critical ratio curves for Callorhinus are similarly shaped to ones obtained for humans but are shifted upwards in frequency. Compared to all other marine mammals thus far evaluated, the critical ratios for Callorhinus are the smallest yet reported.     

STUDY OF VITAMIN A SUPPLEMENTATION IN CAPTIVE NORTHERN FUR SEALS (CALLORHINUS URSINUS) AND ITS EFFECT ON SERUM VITAMIN E

Two experiments were conducted to determine the effect of vitamin A supplementation on serum vitamin E in adult female northern fur seals ( Callorhinus ursinus ). In the first experiment five animals received, in addition to their routine dietary multivitamin supplement, a high-level vitamin A supplement (53 μmol retinyl palmitate/d) for 30 d. Five seals consuming their routine dietary supplement served as controls. Serum vitamin E decreased significantly in animals receiving high-level vitamin A supplements. At the end of 30 d serum vitamin E averaged 18.6 μg/mL in the control animals and 13.4 μg/mL in the animals receiving the high-Ieve1 vitamin A supplement. In experiment 2 ten animals received the high level vitamin A supplement for 60 d. After 30 d, serum vitamin E levels were reduced, but by 60 d had returned to baseline levels. However, the ratio of serum vitamin E to phospholipid, another index of vitamin E status, remained decreased. Although the exact mechanism of interaction is unknown, this study shows that when providing vitamin supplements for captive pinnipeds, vitamin interactions must be considered. The vitamin A supplementation currently used by some institutions seems unnecessary and may have detrimental effects on vitamin E status.     

MAXIMUM NET PRODUCTIVITY LEVEL ESTIMATION FOR THE NORTHERN FUR SEAL (CALLORHINUS URSINUS) POPULATION OF ST. PAUL ISLAND, ALASKA

The goal of this study was to assess the maximum net productivity level for the northern fur seal ( Callorhinus ursinus ) population of St. Paul Island, Alaska. Definitive determination of this level is not possible due to uncertainty in life table parameters and density-dependent changes in those parameters. To account for such uncertainty, repetitive numerical simulations were used to generate frequency distributions of estimates for the maximum net productivity level and related population parameters. This approach systematically varied simulation input parameters, ran a separate simulation with each input parameter combination, and validated the simulations on the basis of comparison with historical observations. Results from validated simulations were compiled in frequency distributions to provide a measure of confidence for MNPL estimates. The distributions confirm that this population is probably well below its maximum net productivity level. Because they reflect the uncertainty in our understanding of northern fur seal population dynamics, these distributions are a more realistic basis for management than single point estimates.     

REPRODUCTIVE SYNCHRONY AND THE ESTIMATION OF MEAN DATE OF BIRTH FROM DAILY COUNTS OF NORTHERN FUR SEAL PUPS

Two methods for estimating the mean date of birth from daily counts of northern fur seal pups ( Callorhinus ursinus ) are presented and applied to data collected on the Pribilof Islands in 1951, 1962, 1963 and 1983. The mean date of birth over the four years was July 9. Reproduction is highly synchronized and consistent from one year to the next. Pupping occurs over a five week period with over 50% of the pups being born during the first two weeks of July.     

THE INFLUENCE OF CLIMATIC SEASONALITY ON THE LIFE CYCLE OF THE PRIBILOF NORTHERN FUR SEAL

Weather conditions recorded from 1956 to 1986 on St. Paul Island, Alaska, were probed to establish their influence upon the northern fur seal's life cycle ( Callorhinus ursinus ). Air temperatures, wind speeds, and relative humidity levels were seasonally decomposed and compared with the timing of pupping and migration. Most pups are born in early July when air temperatures and relative humidity approach their highest annual levels and wind speeds are at their lowest. Weather conditions favor growth and survival of pups from July to September but are unfavorable in June. A rapid deterioration in weather through October and November corresponds with the fall migration of pups and lactating females. The data suggest the pivotal event in the fur seal's life cycle is the timing of birth and survival of nursing pups. As such, the ultimate determinant of the precisely timed fur seal life cycle appears to be climatic seasonality during the breeding season.     

COMPARATIVE POPULATION DYNAMICS OF FUR SEALS

The population sizes, trends, exploitation, and life history parameters for the ten fur seal species and subspecies are summarized. The largest population is that of Arctocephalus pusillus pusillus with approximately two million seals, and the smallest is A. townsendi with approximately 7,000 individuals. Most populations are legally protected, although controlled harvesting may occur. None of the fur seal populations is currently known to be decreasing. Data are presented for parameters related to the survival of pups, juveniles, adults, and territorial males, and to reproduction, including the age of attainment of territorial status, aggregation sizes, age of first parturition, pregnancy rates, sex ratios of young animals, and information on the birth seasons of the different species. Since pinnipeds are often of concern in fisheries management, their daily consumption rates are of importance, and consequently data on body masses are summarized and the paucity of data on consumption rates as a function of body mass noted. A simplified age-structured model is developed, and the results of this model are compared with results from more detailed models based on two published life tables for Callorhinus ursinus. This comparison shows that the use of the simplified age-structured model is justified to explore changes in population growth rate. However, the simplified model does show exaggerated age structure effects compared to the more detailed models. This model is used to compare the population dynamics of those species for which sufficient data are available. Areas in which limited, or no, data are available for the different fur seal species are highlighted.     

MOVEMENTS OF SOUTHERN ELEPHANT SEALS AND SUBANTARCTIC FUR SEALS IN RELATION TO MARION ISLAND

Based primarily on an intensive marking/resighting program conducted at Marion Island (46°54'S, 37°45'E) in the Southern Ocean, the inter-island movements of southern elephant seals, Mirounga leonina , and fur seals Arctocephalus spp., were investigated to elucidate their little known pelagic phase. Southern elephant seals, in particular immature animals, readily move between the proximate Marion and Prince Edward islands. Some range as far afield as Iles Crozet, approximately 1,000 km distant where they haul out for the summer molt or during an autumn resting phase. The exchange of individuals between Marion Island and Iles Crozet during the return of immatures for the molt after a winter at sea, suggests overlapping of the foraging ranges of the two populations. Despite their wanderings, the majority of M. leonina from Marion Island probably feed in the proximity of the island, and relocate onto the island for breeding, molting and resting. Of the fur seals, only a few A. tropicalis were seen away from their natal island, in some cases covering distances in excess of 2,000 km. displaying a remarkable dispersal capacity.     

INDICES OF BODY CONDITION AND BODY COMPOSITION IN FEMALE ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA)

An attempt was made to develop simple, inexpensive, rapid means of determining body composition in Antarctic fur seals ( Arctocephalus gazella ). Measurements of total body water ( TBW ) and total body lipid ( TBL ), obtained by hydrogen isotope dilution, were compared to the results of bioelectrical impedance analysis ( BIA ) and morphometric indices of body condition in 52 adult females. TBW was weakly correlated with BIA measurements of resistance ( v = -0.30, P < 0.03). Conductor volume (length2/resistance) was more highly correlated with TBW ( r = 0.75, P < 0.0001) and the inclusion of mass into the predictive equation improved the correlation further ( r = 0.95, P < 0.0001). A body condition index (mass/length) previously used in pinniped studies was positively correlated to TBL ( r = 0.77, P < 0.0001) validating its use as a relative index of condition. However, body mass alone was highly correlated to TBW ( r = 0.94, P < 0.0001) and appears to provide a simple, rapid means of estimating body composition in adult females. This technique may also be applicable to juvenile male Antarctic fur seals.     

ENTANGLEMENT IN MAN-MADE DEBRIS OF ANTARCTIC FUR SEALS AT BIRD ISLAND, SOUTH GEORGIA

Neck collars of man-made marine debris were seen on 208 Antarctic fur seals (and removed from 170) during the 142 days of the 1988–1989 pup-rearing season at Bird Island, South Georgia. This represents at least 0.1% of the total Bird Island population and a minimum of 0.4% of animals in the best covered areas; a maximum value might approach 1%. Polypropylene straps (packaging bands) formed 59% of collars, nylon string (16%), fishing net (13%) and six other materials comprised the rest. Males accounted for 71% of entanglements, 88% of which were of young (1–4 yr old) animals; females accounted for 64% of animals older than this. Obvious physical injury was being caused to 30% of animals and only on 19% of animals was the collar loose enough potentially to come off. The magnitude of the problem at South Georgia is similar to that with northern fur seals at the Pribilof Islands, where a significant population decline has occurred concurrently. Antarctic fur seals are still increasing in numbers but stricter controls on the jettisoning of debris into the Southern Ocean ate needed if the entanglement problem is not to increase beyond the level of a potential threat.     

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.     

DEVELOPMENT OF HEMOGLOBIN, HEMATOCRIT, AND ERYTHROCYTE VALUES IN GALÁPAGOS FUR SEALS

We studied the ontogeny of hemoglobin concentration, hematocrit and erythrocyte counts in the Galapagos fur seal ( Arctocephalus galapagoensis , Heller 1904). Two hundred and fifty-three animals were sampled between the ages of 22 d and > 8 yr, of which 46 were adult females. Body mass increased steadily with age from 6.1 ± 1.2 kg in 1-mo-old pups ( n = 27) to 28.5 ± 3.3 kg in adult females. Even adult females increased in mass with age. Hemoglobin (Hb), hematocrit (Hct), and red blood cell (RBC) values all increased in a logarithmic fashion with age up to 2 yr. Blood values for pups were Hct: 35.5 ± 4.1%; Hb: 12.9 ± 1.3 g/dl; RBC: 4.1 ± 0.3·10⁶/μl. Half-year-old fur seals (Hct: 42.1 ± 3.2%; Hb: 15.7 ± 1.3 g/dl; RBC: 4.9 ± 0.5·10⁶/μl; n = 50) were the oldest age group to show significantly lower blood values than adult females ( P < 0.001 for all three parameters). Yearling blood values (Hct: 47.2 ± 3.6%; Hb: 17.3 ± 1.6 g/dl; RBC: 5.6 ± 0.4·10⁶/μl; n = 56) did not differ significantly from those of adult females ( P < 0.32; P < 0.26; P < 0.23, respectively). Blood values of adult females were lower than those of 2-yr-olds (Hct: 49.6 ± 2.4%; Hb: 18.5 ± 1.2 g/dl; RBC: 5.7 ± 0.3·10⁶/μl; n = 31). These differences were significant only for RBCs ( P < 0.003). Up to the age of 1 yr, age was the best predictor for blood values, thereafter mass tended to be a better predictor. Female juveniles between the ages of 150 and 600 d had higher blood values than same-age males. The relationship of blood value development to diving activity is briefly described and the results are compared to values of other marine mammals. Ontogeny is discussed in relation to the development of these blood values in terrestrial mammals.     

INVESTIGATING TROPHIC RELATIONSHIPS OF PINNIPEDS IN ALASKA AND WASHINGTON USING STABLE ISOTOPE RATIOS OF NITROGEN AND CARBON

We measured stable-nitrogen (δ¹⁵N) and stable-carbon (δ¹³C) isotope ratios in muscle and hair from 7 northern fur seals (Callorhinus ursinus) from the Pribilof Islands, Alaska, and 27 Steller sea lions (Eumetopias jubatus), and 14 harbor seals (Phoca vitulina) from the Gulf of Alaska and coast of Washington State, in order to contrast dietary information derived from isotopic vs. available conventional dietary studies. Stable-nitrogen-isotope analysis of muscle revealed that harbor seals were enriched over sea lions (mean δ¹⁵N = 18.6‰vs. 17.5‰) which were in turn enriched over northern fur seals (mean δ¹⁵N = 16.6‰). Trophic segregation among these species likely results primarily from differential reliance on herring (Clupea harengus), Atka mackerel (Pleurogrammus monopterygius), and large vs. small walleye pollock (Theregra chalcogramma). According to their δ¹⁵N values, adult male Steller sea lions showed a higher trophic position than adult females (mean δ¹⁵N: 18.0‰vs. 17.2‰), whereas adult female northern fur seals were trophically higher than juvenile male fur seals (mean δ¹⁵N: 16.5‰vs. 15.0‰). Each of these observed differences likely resulted from differential reliance on squid or differences in the size range of pollock consumed. Three northern fur seal pups showed higher δ¹⁵N enrichment over adults (mean 17.7‰vs. 15.8‰) due to their reliance on their mother's milk. Stable-carbon isotope measurements of hair revealed a cline toward more negative values with latitude. Segregation in hair δ¹³C between Steller sea lions and harbor seals off the coast of Washington (mean δ¹³C: ?13.6‰vs.?15.0‰) reflected the greater association of harbor seals with freshwater input from the Columbia River. Our study demonstrates the utility of the stable isotope approach to augment conventional dietary analyses of pinnipeds and other marine mammals.     

温度对桃蚜、萝卜蚜体重及种群参数的影响

桃蚜Myrus perslcae、萝卜蚜Lipaphis crystml在能正常产仔的整个恒温范围内,成蚜和新产仔蚜体重随温度的变化都符合二次抛物线,但体重最高值出现较低的温度下．即体重变化主要表现为随温度升高而下降的趋势．在组建蚜虫的生命生殖力表时,以新产仔蚜体重对其在各温度下的生殖事进行校正。并未对计算所得的内禀增长能力rm值及其随温度的变化情况产生明显的影响,不仅没有提供新的信息。相反。这一方法使计算所得rm的值含义模糊。故建议不予采用。     

SUCCESSFUL USE OF A TRANSLOCATION PROGRAM TO INVESTIGATE DIVING BEHAVIOR IN A MALE AUSTRALIAN FUR SEAL, ARCTOCEPHALUS PUSILLUS DORIFERUS

This study reports some of the first foraging behavior data collected for male fur seals. A nonbreeding male Australian fur seal, Arctocephalus pusillus doriferus , captured at a commercial salmon farm in southern Tasmania, Australia, was relocated 450 km from the site of capture. The animal was equipped with a geolocating time-depth recorder that recorded diving behavior and approximate location for the 14.4 d that it took the seal to travel down the east coast of Tasmania and be recaptured at the salmon farm. During its time at sea, the seal spent most of its time over the relatively shallow shelf waters. It spent 30% of its time ashore on a number of different haul-out sites. The deepest dive was 102 m and the maximum duration was 6.8 min. "Foraging" type dives made up 31.2% of the time at sea and had a median duration of 2.5 min and a median depth of 14 m. The seal performed these dives more commonly during the latter part of its time at sea, while it was on the east coast. Unlike other fur seal species studied to date, there was no evidence of a diurnal foraging pattern; it made dives at all times of the day and night.