摘要:

ABTRACTIt has long been assumed that the heavy bones and horizontal lungs of sirenians are adaptations for maintaining neutral buoyancy and horizontal trim. These assumptions are examined in the light of detailed measurements of skeletal weight distribution in the Florida manatee (Trichechus manatus latirostris), measurements of the positions of body and skeletal centers of gravity in the Amazonian manatee (T.inunguis), and available data on lung morphology in sirenians. The detailed arrangement of bones, muscle masses, and viscera in a sirenian (T. inunguis) is illustrated in cross sections for the first time. The hypotheses that skeletal weight is appropriately distributed to serve as hydrostatic ballast, and that the lungs are properly designed to help maintain horizontal trim, are confirmed. We suggest that selection for maintenance of trim and maximization of turning moments of the flippers may help account, respectively, for hindlimb loss and shortening of the neck in both sirenians and cetaceans. We recommend that the term “pachyostosis” be used to refer only to thickening of bones regardless of their density; that “osteosclerosis” be used for the replacement of cancellous with compact bone; and that “pachyosteosclerosis” be used for the joint occurrence of these conditions. Pachyosteosclerosis in sirenians, which may be brought about during ontogeny by mechanisms involving thyroid and parathyroid hormones, is fully normal and adaptive in this order and in no sense “

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00111.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe used small microprocessor‐based, time‐depth recorders to document the diving patterns of six adult male northern elephant seals (Mirounga angustirostris) from San Miguel Island, California. The recorders stored measurements of hydrostatic pressure every 30 or 60 set while the seals were at sea for 107 to 145 d in spring and early summer; collectively, over 36,000 dives were recorded. Seals dove continually while at sea, most often to depths of 350–450 m although two seals had secondary modes at about 700–800 m; maximum depths for two seals of 1,333 m and 1,529 m are the deepest yet measured for air‐breathing vertebrates. Seals were submerged about 86% of the time they were at sea, rarely spending more than 5 min at the surface between dives; 99% of all post‐dive surface intervals were shorter than 10 min. Dives averaged 21–24 min, the longest was 77 min. The uninterrupted patterns of long dives punctuated by brief surface periods suggest that most if not all dives were well within these seals’aerobic limits. Dives of bulls were, on average, about 18% longer than those published earlier for cows, evidently because of the substantially greater body mass of bulls and allometric scaling of dive endurance. Dive depths and dive durations varied seasonally; depths were greatest in spring, durations greatest in early summer. During each season dives were deepest during the day and shallowest at night except for the sixth seal whose consistently shallow dives (50–150 m) in spring were independent of time of day. Prey remains recovered by lavage from seals’stomachs were primarily of vertically migrating, epi‐ and meso‐pelagic squid. The die1 patterns in dive depths suggest that five seals dove to and foraged in the offshore mesopelagic zone, pursuing those vertically migrating prey. The sixth seal behaved similarly in early spring and early summer but may have foraged in nearshore epiben

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00112.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMale southern sea lion,Otaria byronia, pups born at Peninsula Valdés, Argentina, were significantly heavier (13.7 ± 1.6 kg, n = 37 vs 12.3 ± 1.4 kg,n= 38) and longer (0.82 ± 0.04 m,n= 29vs. 0.79 ± 0.03 m,n= 29) than females. The rate of mass and length gain during the first month of life did not differ between the sexes (males: 0.21 kg/d, 0.003 m/d; females: 0.20 kg/d, 0.004 m/d). Sex differences in pup body size were not reflected in female nursing behavior, attendance patterns, and duration of feeding trips. These results suggest that southern sea lion mothers invest more energy in sons than in daughters during gestation, a difference consistent with the importance of large body size to the reproductive success of males in a polygynous spe

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00113.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractDiet of sea otters (Enhydra lutris) using a haulout site on the north side of the Alaska Peninsula was determined from 50 scats. Dominant prey species were mussels (Mytilus edulis), followed by three species of clams (Siliquaspp.,Spisula polynyma, andTellina lutea), sand dollars (Echinarachnius parma), and helmet crabs (Telmessus cheiragonus). Our results support preliminary findings by Cim‐berg et al. (1984) that this sea otter population preys heavily on mussels and that the presence of low caloric value sand dollars in their diet is significant. Coupled with population estimates, our results also provide evidence that this population of sea otters may be declining due, in part, to overdepletion of food resource

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00114.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractNarwhals (Monodon monoceros) are known to frequent the waters of the Norwegian arctic archipelago of Svalbard. An attempt is made to summarize narwhal observations from the Svalbard area, and from this to deduce their distribution. Observations have been gathered from the literature, sealing vessel log books and official statistics. Interviews have also been conducted with residents of Svalbard. I con&de that narwhals are most frequently observed in the area off the north‐west corner of Spitsberge

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00115.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.tb00116.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.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Book review in this ArticleWHALING COMMUNITIES. North Atlantic Studies 2(1‐2). E. Vestergaard, ed.THE BOTTLENOSE DOLPHIN. Stephen Leatherwood and Randall R. Reeves, ed

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Book review in this ArticleWHALING COMMUNITIES. North Atlantic Studies 2(1‐2). E. Vestergaard, ed.THE BOTTLENOSE DOLPHIN. Stephen Leatherwood and Randall R. Reeves, ed

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY