摘要:

AbstractThis 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 fa

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPolar bears were held in captivity and fasted for an average of 38 d prior to being fed for three days. Blood samples were collected prior to feeding and then at one and three days post‐feeding in 1984 and at one, four, and seven days post‐feeding in 1985. The ratio of serum urea to serum creatinine varied significantly in 1984, rising from a pre‐feeding mean of 11.0 (SE = 2.6) to 32.0 (SE = 3.2) on the first day post‐feeding and then dropped to 22.8 (SE =3.2) in the last sample. In 1985, the ratio of serum urea to serum creatinine increased from a pre‐feeding mean of 15.8 (SE = 2.3) to 61.2 (SE = 10.6) after three days of feeding and dropped to a mean of 29.2 (SE = 5.1) seven days after feeding ended. Serum urea levels varied over the study period in both years. No significant variation in serum creatinine levels was found in 1984, but in 1985, serum creatinine levels demonstrated significant variation, declining from the pre‐feeding mean of 1.83 mg/dl (SE = 0.29) to 0.96 mg/dl (SE = 0.12) in the last sample.The findings suggest that polar bears can have a low serum urea to serum creatinine ratio, similar to that found in hibernating black bears, or higher ratios after feeding. Polar bears can rapidly return to a fasting serum urea to creatinine ratio after food is withheld. Polar bears may demonstrate urea conservation, similar to that found in black bears, and may be able to move between a fasting and a feeding metabolism based on food availability throughout the year, an adaptation to life on the lab

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe size and composition of groups of harbor seals at two haul‐out sites were studied during the breeding season of 1989, in the Passamaquoddy Bay region of Atlantic Canada. Evidence of segregation both by age and sex was found in the distinct composition of the two groups. One group contained mainly males and no pups, and the other had a sex ratio not significantly different from one and contained pups. The proportion of females increased at the nursery site with the onset of birthing in the region while the proportion of males increased through the breeding season at the other site. No increase in the number of adults, in total, was detected over the study period, suggesting that sexual segregation and not a change in haul‐out frequency was responsible for the disparity in the sex structure of the two groups. The proportion of juveniles was significantly greater at the male dominated site than at the nursery s

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe harbor seal (Phoca vitulina) has its northernmost distribution at the Norwegian arctic archipelago of Svalbard. Little information exists on this particular harbor seal population. The present paper summarizes this information, and gives the result of surveys of harbor seals conducted in Svalbard in 1984, 1985 and 1987. These surveys show that harbor seals in Svalbard are limited to the area around Prins Karls Forland, the westernmost island in the archipelago. The harbor seal population at Prins Karls Forland numbers at least five to six hundred animals.

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractNeck 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

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00249.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00250.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1990.tb00251.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY