摘要:

Abstract:At least four morphologically distinct forms of common dolphins are found in the eastern Pacific, We compared length data for common dolphins photographed from the northern, central and southern regions as defined by Perrinet al.(1985) and found significant differences in average length for adult animals (>150 cm) and for “adult females” defined for our purposes as animals accompanied by calves. Analyses of calculated birth dates for calves demonstrated differences in timing of reproduction between the geographically adjacent forms. Length distributions from aerial photographs and samples collected from the purse seine fishery were strikingly similar. This work demonstrates a new, non‐invasive method for obtaining unbiased life history and morphological

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) were used to test for population subdivision in the bottlenose dolphin(Tursiops truncatus).Atlantic and Pacific dolphin mtDNA samples exhibited distinctly different haplotypes (approximately 2.4% sequence divergence), indicating a lack of gene exchange. Within the Atlantic Ocean, mtDNA samples from the Gulf of Mexico and the Atlantic Coast were also found to be distinct, with a sequence divergence of approximately 0.6%. The Atlantic Coast–Gulf of Mexico dichotomy is consistent with patterns of genetic variation from other marine and coastal organisms from this region, and supports the hypothesized role of bio‐geographic events in promoting the divergence of these and other forms. Regional differentiation was identified along the Atlantic Coast, whereas low sequence divergences among haplotypes and consistent haplotype frequencies across populations suggested considerable gene exchange among Gulf of Mexico populations. A highly divergent haplotype found in two individuals from two localities in the Gulf of Mexico is best explained by dispersal from either a distinct offshore Gulf stock or an unsampled Atlantic Coast stock. Additional samples are required to test for the existence of a distinct offshore race and, if it exists, to identify its distribution and contribution to population struct

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Several important aspects of reproduction in the female sea otter, such as gestation, pupping frequency, period of pup dependency, and annual pupping rate, were unclear when this study was begun. We present data from 75 tagged adult females that indicate gestation is variable, but on average is about 6 months, the length of pup dependency is 6 mo, thus the pupping interval is usually 12–13 mo. Most females breed for the first time in their fifth year of life. About 85–90% of adult females pup in a given y

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Direct observations of feeding sea otters (Enhydra lutris) at 11 sites in southeast Alaska showed infaunal clams to be the primary prey utilized by otters throughout the region. Foraging dive times associated with clam and sea urchin prey were significantly longer than those for more easily captured prey (crabs and mussels). Dive times and surface intervals were also generally correlated with water depth or apparent difficulty in obtaining buried prey. Male otters, which fed more extensively on clams than females, made significantly longer foraging dives than females. Foraging success remained high, even at sites where prey numbers were found to be very low during a related study. The very deeply burrowing geoduck clam (Panope abrupta), while common at several otter feeding sites, was rarely captured by otters. These results, combined with those of a companion study on prey numbers, indicate that butter clams (Saxidomus giganteus) account for the majority of the sea otter diet in southeast Alaska, and that sea urchins may represent relatively short‐term prey in comparison to infaunal bivalves in regions where both prey types co‐exist. Furthermore, the importance of butter clams in the sea otter diet and the tendency for this bivalve to retain chronically high levels of paralytic shellfish poisoning toxins in southeast Alaska increases the probability that toxic phytoplankton blooms influence sea otter distribution in this reg

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00441.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:The transmission losses with distance of four pure tones (0.5, 1, 2, 4 kHz) were measured in the air 9 cm above the surface of the coastal waters in the Bay of Fundy. The study was conducted between May and July 1992, on warm days with low winds. The measured transmission losses were as much as 11 dB less than predicted by spherical spreading (6 dB/distance doubled), at 400 m (0.5 kHz). This enhanced sound transmission is probably due to the air temperature profile which increases with height above the water's surface. Such a profile causes sound waves to refract towards the water, thereby reducing spreading losses. High‐frequency sound absorption negates enhanced transmission at 4 kHz, at distances over 500 m. On days with low winds and low ambient noise levels, a seal pup calling at 90 dB re 20, μPa at 0.5 kHz should be detectable by the mother up to 1 km away, and may be audibly recognizable up to 140 m aw

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00442.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00446.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1993.tb00447.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY