摘要:

AbstractRe‐sightings of photographically identified individuals were used to estimate survival rates for a free‐living population of Hector's dolphinsCephalorhynchus hectori, a species endemic to New Zealand waters. Most individuals were identified from injuries to the dorsal fin. Consequently, the photographic catalog contained very few young individuals. Our analysis included no newborn calves or yearlings, and provided estimates of survival rates only after the first year of life. We used two complementary methods for calculating survival rates: a modified Jolly‐Seber model, and a simpler method which corrects in a more explicit way for individual dolphins being alive but not sighted. Selection of the most reliable subset of the data had a greater effect on computed survival rates than did the difference between the two methods. We conclude that careful inspection of resighting data before analysis, and, if necessary, selection of a subset, is very important in studies of this kind. Survival rate estimates came from a population which was subject to relatively heavy mortality from gillnet entanglement. Standard errors of the survival rate estimates have been used to assess the conditional probability of population decline given three fertility scenarios. The high probability that the Banks Peninsula Hector's dolphin population was decreasing during the study period (0.78 to 0.99) suggests that gillnet entanglement constituted a serious risk to this popul

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMethods for estimating tag loss and sightability of tags are presented. Rates of tag loss were estimated for metal and several varieties of plastic cattle ear tags in a long‐term population study of Weddell seals. Tags were lost at a higher rate in the first year after application than in subsequent years, and pups lost tags at a higher rate than older seals given the same tag types. Medium‐sized plastic tags (Dalton, Allflex and Fearing) were retained at higher rates and were overlooked less frequently than metal tags on adult seals. Dalton Jumbo Rototags showed the lowest loss rates on pups in comparison to larger, flexible plastic tags, but were harder to read in the fi

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractObservations were made on 11 brains from bowhead whales subsistence‐harvested by Alaskan Eskimos under International Whaling Commission guidelines. This study is part of a larger project to determine the basic morphology of this endangered species. The bowhead brain is similar to other cetacean brains, particularly that of the southern right whale. Long olfactory peduncles are reflected upon the rostrodorsal surface of the cerebral hemispheres. Olfactory bulbs have not been recovered but are presumed to exist since nerve fibers have been identified histologically in the olfactory peduncles. The induseum griseum is evident on the corpus callosum. The hippocampus proper is small but protrudes into the lateral ventricle. The cruciate sulcus runs diagonally across the rostral surface, limiting a small frontal lobe. The structure of the floor of the sylvian fissure varies from a few short gyri radiating toward the circular sulcus to a more extensive and complex two‐tiered arrangement including numerous gyri perpendicular to the gyrus bordering the paleocortex. Pineal‐body‐like tissue was present in one specimen. There is no interthalamic adhesion. The lateral geniculate body is elevated but smaller than the large medial geniculate body. The neurohypophysis was adherent on most brain specimens r

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractDetails of the lenses of eyes in two livingTursiops truncatusand oneGrampus griseuswere photographed. In the laboratory the lens cortex could be retro‐illuminated by a fundus camera and spatially periodic stria could be visualized, in large part because of the highly developed tapetum of the cetacean eye. Varying spaces were present between the stria. On a three‐dimensional basis, the best analogy is the layering of an onion. One photograph was digitized giving good quantification of the sizes of the layers and their number. Similar, but less easily resolved, lens cortex organization has been described frequently in humans as “zones of optical discontinuity.” These have been explained as a periodic temporal consequence of normal aging with layer thickness depending on general health. We found that young cetaceans have few “zones” and older cetaceans have many. Lens zones measurement may be developed to Provide objective data on history of cetacean hea

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn contrast with most southern elephant seal,Mirounga leonina, colonies, births at Península Valdes, Argentina, increased from 7,455 in 1982 to 9,636 in 1990. Colony size during the 1990 breeding season, including pups, was estimated at 19,000. Colony growth may respond to abundant food resources and lack of competitors. The range of distribution of elephant seals in Patagonia has not changed since at least 1972 but the spatial distribution of births along the coastline of Peninsula Valdes has varied. In 1982, 58% of the births occurred in the northeast portion of the Peninsula versus 36% in 1990. Females may prefer to give birth on broad, sandy beaches. In 1982, 56% of the females gave birth on pebble beaches and 44% on sandy beaches. In 1990, 24% bred on pebbles versus 76% on sand. Sand substrate may be preferred by females because it may confer thermoregulatory advantages in relieving heat stress

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00056.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00057.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1992.tb00058.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY