摘要:

AbstractThe Pacific walrus population has been depleted and subsequently allowed to recover three times in the past 150 yr. As we see it, the population has been made to fluctuate like anr‐selected species, rather than being maintained at a high, stable level, as befits a K‐selected species. The latest depletion began in the 1930s but was not recognized until 25 yr later, by which time the population had been reduced by at least half. Without benefit of communication, the U.S.S.R. and the State of Alaska put similar protective measures into place by 1960, and in the next two decades the walrus population recovered again, at least doubling in size. By 1980, it already was showing density‐dependent signs of having approached or reached the carrying capacity of its environment. As productivity and calf survival declined sharply in the late 1970s and early 1980s the catches more than doubled. We believe that the combined effects of natural curtailment and human intervention may be bringing the population down again rather rapidly. With the present, crude monitoring methods, delayed management responses, and poor international communications, however, the downward trend may not be acknowledged for at least another decade, by which time the unilateral Soviet and American corrective measures are likely to be too much, too late. Walrus management needs to be based less on response to immediate crisis and more on long term prediction than it has been in the past. Because the U.S.A. and U.S.S.R. are trying to manage the same walrus population, without sufficient communication or consensus and sometimes to opposite ends, an international joint management program needs to be implem

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00210.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe U.S. Fish and Wildlife Service conducted a survey of the walruses in the pack ice of the Chukchi Sea between 16 September and 2 October 1985, as part of a joint effort with the Soviet Union to estimate the size of the Pacific walrus population. American observers conducted censuses from two aircraft along randomly selected north–south lines over the pack ice. The observers counted walruses within a constant viewing angle that corresponded to a total strip width of 1.38 km at an altitude of 152 m.In nine days of flying, 15,312 walruses were observed, of which 10,140 were on 5,764 km2of census strips. Few walruses were observed east of 161°W longitude or west of 170°W longitude, hence the census effort was stratified. Walrus concentrations between 161° and 170° shifted slightly westward during the 2‐wk duration of the censuses. The differences among days in observed walrus density were due to changes in the numbers of walruses on the ice within 37 km of the ice edge. The number of observable walruses in pack ice of the eastern Chukchi Sea was estimated to be 62,177 (SD = 19,480), based on censuses conducted on 29 and 30 September and 1 October. At that time there were also at least 15,238 in Bristol Bay, Bering Sea. The Soviets counted 39,572 on the shores of the western Chukchi and Bering seas and estimated 115,531 in pack ice of the western Chukchi Sea. Summing U.S. and Soviet estimates, the total population of Pacific walruses in 1985 was 232,518. This number was comparable with earlier estimates from censuses conducted jointly by the U.S. and the Soviets. However, information on fraction hauled out, segregation, and movements is needed for more precise es

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00211.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractAntarctic phocid seals and particularly the crabeater (Lobodon carcinophagus) have been observed to display a diurnal cycle in their propensity to haul out on pack ice where they are visible for census. The fact that they are not visible for much of the 24‐h period means that density estimates made over broad geographic areas at various times of the day statistically confound this cycle with geographic variability. Limitation of census observations to times of peak haulout results in extreme logistical difficulties and/or considerable reduction in sample size upon which to base population estimates. Reduced sample size results in high variability in population estimates and broad confidence bands. To develop a model with which to correct density estimates for variability due to diurnal cycle, a series of stationary censuses at fixed locations in the Antarctic continental ice pack was made over significant fractions of several days. A unimodal polynomial model for the observed density variation in any one location was statistically significant; a similar model combining multiple locations with densities standardized to peak daily values was also significant. The latter model was used to make corrections for time of day to density estimates in three test data sets taken over broad geographic areas of the Antarctic. Statistical simulation (bootstrap) methods were used to determine if variances of corrected density estimates were lower than those based on uncorrected observations taken only during the peak haulout times of the day. Results were that 95% interval estimates for corrected densities were narrowed to between 40% and 61% of the uncorrected estimates. While there are additional possible sources of variation in haulout tendency, pending further data collection and analyses, the model developed represents a considerably more precise methodology than either averaging over haulout variability or limiting observations to peak daily period

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00212.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBlood samples from southern elephant seals (Mirounga leonina) from Heard and Macquarie Islands were surveyed electrophoretically for protein variation. Thirty proteins encoded by a minimum of 35 loci were screened, four of which were found to be polymorphic. Statistically significant differences in allele frequencies were found between the two populations at three loci. Heterozygosity estimates for the Heard and Macquarie island populations were 0.034 ± 0.020 (mean ± standard error) and O.029 ± 0.017 respectively, with a Nei distance of 0.007. The findings suggest that the two populations may have diverged genetically and very limited gene flow exists between the islands, a finding consistent with limited information from mark‐recapture stu

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00213.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractObservations on five groups of crabeater seals were conducted between 29 October and 17 November 1985 in the Antarctic pack ice near 66°S 50°E, off Enderby Land. The pups studied were born in the last half of October. Two of them increased in weight at a rate of approximately 4.2kg per day. Pups were weaned in the first half of November at 80–110 kg. The lactation period was 2–3 wk and thus is one of the briefest among pinnipeds. Pups decreased in weight after weaning. The only pup visited after it left the natal floe must have been feeding, as it had lost only 2 kg in a 10–day period during which it moved 13 km. Molt of lanugo appeared to be influenced more by a pup's weight than by whether or not it was

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00214.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00215.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00216.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Book review in this articleApproaches to Marine Mammal Energetics. A. C. Huntley, D. P. Costa, G. A. J. Worthy and M. A. Castellini, eds.Design and Analysis Methods for Fish Survival Experiments Based on Release‐Recapture. Kenneth P. Burnham, David R. Anderson, Gary C. White, Cavell Brownie and Kenneth H. Polloc

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1989.tb00220.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY