(1/58) Heart rate and behavior of fur seals: implications for measurement of field energetics.
Archival data loggers were used to collect information about depth, swimming speed, and heart rate in 23 free-ranging antarctic fur seals. Deployments averaged 9.6 +/- 5.6 days (SD) and totaled 191 days of recording. Heart rate averaged 108.7 +/- 17.7 beats/min (SD) but varied from 83 to 145 beats/min among animals. Morphometrics explained most variations in heart rate among animals. These interacted with diving activity and swimming speed to produce a complex relationship between heart rate and activity patterns. Heart rate was also correlated with behavior over time lags of several hours. There was significant (P < 0.05) variation among animals in the degree of diving bradycardia. On average, heart rate declined from 100-130 beats/min before the dive to 70-100 beats/min during submersion. On the basis of the relationship between heart rate and rate of oxygen consumption, the overall metabolic rate was 5.46 +/- 1.61 W/kg (SD). Energy expenditure appears to be allocated to different activities within the metabolic scope of individual animals. This highlights the possibility that some activities can be mutually exclusive of one another. (+info)
(2/58) Lunar cycles in diel prey migrations exert a stronger effect on the diving of juveniles than adult Galapagos fur seals.
In our study of the development of diving in Galapagos fur seals, we analysed changes in diving activity and body mass trends over the lunar cycle. Based on previously observed lunar cycles in colony attendance patterns, we hypothesized a greater impact of prey migrations of deep scattering layer organisms on younger fur seals. Using electronic dive recorders, we determined that seals dived less and deeper on moonlit nights than at new moon, and incurred body mass losses. These changes in foraging over the lunar cycle correlate with the suppression of the vertical migration of prey by lunar light. All effects were more pronounced in juveniles than adult females, with greater relative mass loss during full moon, which must (i) negatively affect long-term juvenile growth rates, (ii) lengthen periods of maternal dependence, and (iii) contribute to the lowest reproductive rate reported for seals. This underlines the importance of studying ontogeny in order to understand life histories, and for determining the susceptibility of animal populations to fluctuations in food availability. (+info)
(3/58) Gross and microscopic visceral anatomy of the male Cape fur seal, Arctocephalus pusillus pusillus (Pinnipedia: Otariidae), with reference to organ size and growth.
The gross and microscopic anatomy of the Cape fur seal heart, lung, liver, spleen, stomach, intestine and kidneys (n = 31 seals) is described. Absolute and relative size of organs from 30 male seals are presented, with histological examination conducted on 7 animals. The relationship between log body weight, log organ weight and age was investigated using linear regression. Twenty five animals were of known age, while 6 were aged from counts of incremental lines observed in the dentine of tooth sections. For the range of ages represented in this study, body weight changes were accurately described by the exponential growth equation, weight = w(o)r(t), with body weight increasing by 23 % per annum until at least 9-10 y of age. Organ weight increased at a rate of between 25 % and 33 % per annum until at least 9-10 y of age, with the exception of the intestines, where exponential increase appeared to have ceased by about 7 y. The relationship between body weight and organ weight was investigated using logarithmic transformations of the allometric equation, y = ax(b), where the exponent b is 1 if organ weight is proportional to body weight. Most organs increased in proportion to the body. However, the heart, liver and spleen had exponents b > 1, suggesting that these organs increased at a faster rate than the body. The basic anatomical features of the viscera were similar to those of other pinnipeds, with some exceptions, including the arrangement of the multilobed lung and liver. Apart from the large liver and kidneys, relative size of the organs did not differ greatly from similar sized terrestrial carnivores. The histological features of the organs were generally consistent with those previously described for this species and other otariids. The heart, as in other pinnipeds, was unlike that of cetacea in not having unusually thick endocardium or prominent Purkinje cells. Notable histological features of the lungs included prominent fibrous septa, prominent smooth muscle bundles, cartilage extending to the level of the alveolar sacs and ample lymphoid tissue. The spleen had a thick capsule, well developed trabeculae and plentiful plasma cells. Abundant parietal cells were present in the fundic glands and lymphoid follicles were present in the gastric lamina propria, particularly in the pyloric region. Small intestinal villi were very long but this could have resulted from underlying chronic inflammation. Lymphoid follicles were prominent in the colon. The kidney reniculi each had a complete cortex, medulla and calyx, but a sportaperi medullaris musculosa was not identified. (+info)
(4/58) The ontogeny of metabolic rate and thermoregulatory capabilities of northern fur seal, Callorhinus ursinus, pups in air and water.
Young pinnipeds, born on land, must eventually enter the water to feed independently. The aim of this study was to examine developmental factors that might influence this transition. The ontogeny of metabolic rate and thermoregulation in northern fur seal, Callorhinus ursinus, pups was investigated at two developmental stages in air and water using open-circuit respirometry. Mean in-air resting metabolic rate (RMR) increased significantly from 113+/-5 ml O(2 )min(-)(1) (N=18) pre-molt to 160+/-4 ml O(2 )min(-)(1) (N=16; means +/- s.e.m.) post-molt. In-water, whole-body metabolic rates did not differ pre- and post-molt and were 2.6 and 1.6 times in-air RMRs respectively. Mass-specific metabolic rates of pre-molt pups in water were 2.8 times in-air rates. Mean mass-specific metabolic rates of post-molt pups at 20 degrees C in water and air did not differ (16.1+/-1.7 ml O(2 )min(-)(1 )kg(-)(1); N=10). In-air mass-specific metabolic rates of post-molt pups were significantly lower than in-water rates at 5 degrees C (18.2+/-1.1 ml O(2 )min(-)(1 )kg(-)(1); N=10) and 10 degrees C (19.4+/-1.7 ml O(2 )min(-)(1 )kg(-)(1); N=10; means +/- s.e.m.). Northern fur seal pups have metabolic rates comparable with those of terrestrial mammalian young of similar body size. Thermal conductance was independent of air temperature, but increased with water temperature. In-water thermal conductance of pre-molt pups was approximately twice that of post-molt pups. In-water pre-molt pups matched the energy expenditure of larger post-molt pups while still failing to maintain body temperature. Pre-molt pups experience greater relative costs when entering the water regardless of temperature than do larger post-molt pups. This study demonstrates that the development of thermoregulatory capabilities plays a significant role in determining when northern fur seal pups enter the water. (+info)
(5/58) Skin temperatures during free-ranging swimming and diving in antarctic fur seals.
This study tests the hypothesis that an endothermic homeotherm should minimise heat flux in cold polar waters by minimising skin temperature. Temperature variability was measured at the surface of the skin of three Antarctic fur seals (Arctocephalus gazella) at intervals of 2 s over a total of 9.7 days while they were swimming and diving freely in polar waters at temperatures of 1.5-4 degrees C. The temperature difference ( capdelta T) between skin on the dorsal thorax and the water varied from more than 20 degrees C to close to equality over periods of less than 1 h. Shorter-term variations in capdelta T of up to 5 degrees C occurred in association with diving, although these types of variations also occurred without diving. In general, capdelta T began to decline during the descent phase of a dive and began to increase again during the ascent or at the end of the dive. One of the three individuals examined showed little variation in capdelta T, which remained low (approximately 3 degrees C) throughout the experiment. In the other two fur seals, capdelta T tended to decline during periods of sustained diving and usually increased during periods spent at the surface. Mean calculated heat flux varied from 95 to 236 W m(-)(2) depending on the individual. Metabolic rates based on these calculated heat fluxes were towards the lower end of those measured in previous studies using different methodologies. The study has shown that Antarctic fur seal skin temperature is highly dynamic and suggests that the thoracic surface is an organ used for active thermoregulation. (+info)
(6/58) Variation in the mitochondrial control region in the Juan Fernandez fur seal (Arctocephalus philippii).
The Juan Fernandez fur seal (Arctocephalus philippii was allegedly extremely abundant, numbering as many as 4 million prior to sealing which continued from the late 17th to the late 19th century. By the end of the sealing era the species was thought to be extinct until they were rediscovered at Alejandro Selkirk Island in 1965. Historic records would suggest that the species underwent a substantial population bottleneck as a result of commercial sealing, and from population genetic theory we predicted that the genetic variability in the species would be low. We compared the mtDNA control region sequence from 28 Juan Fernandez fur seals from two islands in the Juan Fernandez Archipelago (Chile). Contrary to expectation, we found that variation in the Juan Fernandez fur seals is not greatly reduced in comparison to other pinniped taxa, especially given the apparent severity of the bottleneck they underwent. We also determined minor, but significantly different haplotype frequencies among the populations on the two islands (Alejandro Selkirk and Robinson Crusoe Islands), but no difference in their levels of variability. Such differences may have arisen stochastically via a recent founder event from Alejandro Selkirk to Robinson Crusoe Island or subsequent genetic drift. (+info)
(7/58) How does a fur seal mother recognize the voice of her pup? An experimental study of Arctocephalus tropicalis.
In the subantarctic fur seal Arctocephalus tropicalis, mothers leave their pups during the rearing period to make long and frequent feeding trips to sea. When a female returns from the ocean, she has to find her pup among several hundred others. Taking into account both spectral and temporal domains, we investigated the individual vocal signature occurring in the 'female attraction call' used by pups to attract their mother. We calculated the intra- and inter-individual variability for each measured acoustic cue to isolate those likely to contain information about individual identity. We then tested these cues in playback experiments. Our results show that a female pays particular attention to the lower part of the signal spectrum, the fundamental frequency accompanied by its first two harmonics being sufficient to elicit reliable recognition. The spectral energy distribution is also important for the recognition process. Of the temporal features, frequency modulation appears to be a key component for individual recognition, whereas amplitude modulation is not implicated in the identification of the pup's voice by its mother. We discuss these results with respect to the constraints imposed on fur seals by a colonial way of life. (+info)
(8/58) Ascaridoid nematodes and associated lesions in stomachs of subadult male northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska: (1987-1999).
Stomachs from subadult male northern fur seals (SAMs) (Callorhinus ursinus) (n = 5,950) from St. Paul Island, Alaska, were examined from 1987 to 1999 for lesions and parasites. On gross examination of these stomachs, parasite nodules were evident in 92% of the stomachs and active and healing ulcers were found in 14% and 10%, respectively. Prevalence of nematodes from 1987 to 1997 was 88% for 5,700 SAMs for which numbers of parasites were estimated but not identified to the genus level. All nematodes recovered from 250 SAMs examined in 1998 (n = 124; 99% infected) and in 1999 (n = 126; 91% infected) were identified and counted. Prevalences in 1998 and 1999 were 5% and 0% for Anisakis spp., 52% and 18% for Contracaecum spp., and 96% and 89% for Pseudoterranova spp., respectively. (+info)