摘要:

AbstractThe number of bowhead whales,Balaena mysticetus, passing within viewing range of the ice‐based census at Point Barrow, Alaska, during spring migrations from 1978 to 1988 is estimated from the visual census data. The trend in the annual numbers yields an estimated rate of increase of 3.1% per year with a 95% confidence interval ranging from 0.1% to 6.2% for the Bering‐Chukchi‐Beaufort Seas bowhead stock during this period. Alternative treatments of the data suggest less precise or somewhat lower estimates, but all results indicate that the stock was incre

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00558.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPredation on ringed seals (Phoca hispida) was examined in Barrow Strait between March and May 1984 to 1986. Polar bears were the most important predator. Evidence of bear predation was observed at 18–30% of the ringed seal subnivean structures we located. Ten to 24% of predation attempts were successful, with pups making up 75% to 100% of the seals killed. Bears killed an average of 0.08 to 0.51 seals/km2, which comprised 8 to 44% of the estimated annual pup production. Bears were successful on average in 11.3% of their attempts to kill pups hidden inside birth lairs. On southeast Baffin Island where snow was soft and pups were exposed, bears were successful in 33.5% of their attempts to kill a seal. Negative correlations were found between mean snow depth and predation by polar bears (r= ‐0.896,P= 0.04,n= 5) in 1985, and between snow depth and the number of predation attempts (r= ‐0.613,P= 0.02,n= 14) in

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00559.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThirteen Weddell seals (Leptonychotes weddellii) were collected at Vestkapp, eastern Weddell Sea coast, in austral spring 1986. All stomachs contained partially digested food. The mean wet weight of stomach contents was 7.5 kg, 3.3% of the. mean body weight of the collected seals. Twelve fish species and three cephalopod species were identified from 372 left otoliths and 25 lower beaks, representing 58.4% of 679 total prey items obtained. Composition by number of total prey was:Chionodraco myersi(15.8%),Trematomus eulepidotus(10.0%),Pagetopsis maculatus(9.7%),Racovitzia glacialis(9.6%) andCryodraco antarcticus(4.1%). Otoliths of the seven other fish species and beaks of the three cephalopod species together represented 9.1% of total prey numbers. The pooled wet weights calculated from 13 prey species (regressions for two octopod species were not available) amounted to 43.5 kg food mass and represented 44.7% of the combined food mass in all stomachs. Composition by mass was:C. myersi(44.5%),T. eulepidotus(19.8%), squidPsychroteuthis glacialis(8.5%),P. maculates(7.9%),C. antarcticus(7.1%) andR. glacialis(6.2%). The remaining 7 fish species together represented 5.8% by mass. Temporal variation in food availability was apparent. Midwater fishPleuragramma antarcticumwas the staple food of Weddell seals from the same area during the 1985 summer, whereas it was absent in the samples taken in spring 1986. Estimates of fish biomass from net hauls demonstrate a highly variable availability of pelagic food resources for top predators in the Vestkapp area.

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00560.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe absolute and relative precision of birth timing was assessed in 27 captive harbor seals and 30 captive California sea lions. Data were obtained from zoos and aquaria and only adult females with at least three live births were selected for analysis. Individuals of both species demonstrated very high absolute precision with narrow ranges of birth dates and small standard deviations of the individual mean birth dates. In addition, with the exception of one sea lion, no temporal trends for earlier or later birthing were found. Whereas marked differences in birth timing were found among individual harbor seals, these relative differences tended to disappear when subspecies affiliation and location were taken into account. Moderate inter‐individual differences were also found among the California sea lions, but these differences persisted following the partitioning of adult females by location.The absolute precision in birth timing strongly suggests that environmental regulation of birth timing occurs via a highly precise cue, such as photoperiod. The relative differences among individuals may indicate that birth timing in pinnipeds has a heritable component, and hence may evolve in response to natural selection, thus allowing adaptation of the pupping season to specific seasonal environment

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00561.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFifty‐two male elephant seals were weighed and photographed at Año Nuevo State Reserve, California, to establish a predictive relationship between photographically measured morphological variables (length, side area, and girth area) and body mass. Regression of mass on these variables revealed that side area, roughly equivalent to a longitudinal cross‐section, was the most useful single variable for predicting mass, and that adding the other two variables to side area slightly improved the accuracy of the photogrammetric technique. Curvilinear regressions based on a power model provided the best predictive relationships. This technique may prove useful for estimating body mass of other pinni

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00562.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractOver a 10‐wk period in early 1982, 39 Florida manatees (Trichechus manatus latirostris) were found dead in the lower Caloosahatchee River and nearby waters of southwestern Florida. Two were killed by boats. The remainder showed no evidence of trauma. Lesions indicative of infectious agents were not identified, and bacteriological and contaminant residue findings were unremarkable. Nonspecific lesions of congestion and hemorrhage were identified in brain tissue. Numerous reports were also received of manatee morbidity. Some distressed manatees showed no biochemical lesions in clinical analyses of blood samples and recovered quickly. Timing of manatee illnesses coincided with fish and double‐crested cormorant (Phalacrocorax auritus) mortality and morbidity. A widespread bloom of the dinoflagellate red tide organism (Gymnodinium breve) also coincided with these incidents.G. breveproduces potent neurotoxins (brevetoxins). Circumstantial evidence links these events, and possible routes of exposure may include ingestion of filter‐feeding ascidians. Ecological conditions that magnified the extent of the epizootic included an early dispersal of manatees into the area from a nearby winter aggregation site and unusually high salinities that facilitated the inshore spread of the red tide bloom. Management responses to future episodes of red tide in manatee areas are sugg

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00563.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPhotographs of distinctively scarred manatees (Trichechus manatus) were taken at aggregation sites throughout Florida and assembled into a catalog for identifying individuals. Resightings of known manatees in different years or at different locations enabled us to document site fidelity and long‐distance movements. Of the 891 individuals included in the catalog as of August 1986, 470 (53%) were resighted at least once. We documented 219 cases of seasonal returns to specific aggregation sites and 98 instances of movements between areas. Movements in excess of 820 km were documented for individuals on the east coast of Florida. Rapid movements south during early winter, as well as northerly spring movements, verify a seasonal migration pattern for many individuals along Florida's east coast. The wide‐ranging migratory habits of manatees in Florida must be considered if meaningful management strategies are to be developed and implemen

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00564.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00565.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00566.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00567.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY