摘要:

AbstractWe observed 40 California sea otters,Enhydra lutris, that were instrumented with implanted radio transmitters and flipper‐tagged, and obtained additional data on the reproduction of tagged female otters from the California Department of Fish and Game.The proportion of instrumented females accompanied by a pup peaked in the spring, with a secondary peak in the fall. Two methods of estimating the annual reproductive rate gave comparable values of 0.90 and 0.94. The average inter‐birth interval was 389 d. Two methods of estimating pup survival to weaning gave values of 0.46 and 0.58. Pups either remained with a female less than 80 or more than 120 d. Early mortality of dependent pups appears to be more frequent in California than in Prince William Sound, Alaska.Two methods of estimation indicated that adult females had the highest survival rates and adult males the lowest. Juvenile females had lower survival rates than adult females but juvenile males had higher survival rates than adult males. The survival rate of juvenile females was lower than that of juvenile males.The estimated annual loss rate for flipper‐tags, based on the instrumented individuals, was 0.26. More individuals lost two tags than would be expected by chance. It is unlikely that accurate estimates of sea otter survival rates can be derived from observations of tagged indivi

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00099.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractData from the North Pacific sperm whale(Physeter catodonLinnaeus, 1758) fishery were examined for a possible density dependent change in growth during 40 yr harvesting after World War II. Early in this period males from the eastern stock were 16.8 m or less in length. By the early 1970s the largest males in the catch exceeded 16.8 m in length and reached 18.9 m in the late 1970s. The proportion of males measuring over 16.8 m, among sexually mature males (≥14.0 m), increased from 0 to>20% during the 1970s. Increases in the maximum size of males were possibly preceded by a change in the frequency distribution of body lengths in the middle 1960s when only 10% of the postwar catch had been taken. Testis weights suggested an increase in body length at sexual maturity. Two of the three putative North Pacific stocks showed similar growth changes. Adult males taken in the Bering Sea did not show such changes during the exploitation which ended in 1972 because of overfishing. Females showed no detectable change in body size. It is concluded that: (1) density dependent effects on male growth are greater before sexual maturity than after it, (2) males may show density dependent changes even at a population level above 90% of the carrying capacity, (3) polygynous males acquire more mates and realize higher reproductive success because of increased body size, and (4) females appear to maximize production by maturing earlier and shortening calving intervals in response to density chang

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00100.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSonar target strength measurements of several types of nets and associated gear were made using simulated dolphin echolocation signals. The different types of nets included (a) standard commercial monofilament gillnet used in the salmon mothership fishery, (b) prototype hollow core monofilament net, (c) Macah tribal cord setnet, and (d) multifilament nets. Target strength measurements were made at four angles of incidence, 0° (normal to net), 15°, 30°, and 45°. The standard gillnet had the smallest target strength which was relatively independent of the angle of incidence. The target strength based on the peak‐to‐peak values of the echoes varied from –59 to – 62 dB. Using echo energy within the integration time ofTursiops truncatus, the target strength was found to be between – 54 and –59 dB. Biosonar detection ranges for different sea state conditions were estimated using the noise‐limited form of the sonar equation and target detection data obtained forTursiops truncatusin Kaneohe Bay, Oahu, Hawaii. The results suggest that an echolocating dolphin should be able to detect a gillnet at ranges long enough to avoid entanglement, even in sea state 6 conditions. Several possibilities for the seeming inability of dolphins to detect gilln

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00101.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTo reduce the number of cetaceans caught incidentally in gillnets, two forms of acoustic modifications have previously been proposed. These modifications seek to make gillnets more obvious to cetaceans so they can avoid them, and include making gillnets more reflective to cetacean sonar and placing active sound emitters in the nets. I discuss the relationship between sonar and net entanglement, and address the assumptions and logic of net modification strategies. I argue that neither strategy is likely to be effective, and that reductions in the number of cetaceans killed in gillnets are best achieved through the closure of specific areas to gillnetting.

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00102.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe incidental catch of Hector's dolphins(Cephalorhynchus hectori)in gillnets in Pegasus Bay and Canterbury Bight, New Zealand is assessed. From 1984 to 1988, at least 230 Hector's dolphins were killed in groundfish gillnets by commercial and amateur fishermen. Approximately 91% of entanglements occurred from November to February. Seasonality of catch corresponded to increased commercial gillnetting inshore in spring and summer. Most entanglements (89%) occurred within 4 nautical miles (7.4 km) of the shore, and most dolphins (86%) were caught in water less than 20 m deep. The dolphin's summer inshore movement also coincided with high levels of inshore gillnetting by amateur fishermen. The age‐frequency of net‐caught dolphins suggested that young animals were particularly vulnerable to entanglem

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00103.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.tb00104.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.tb00105.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.tb00106.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.tb00107.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBook review in this ArticleTHE PINNIPEDS: SEALS, SEA LIONS, AND WALRUSES. M. Riedman. University of California Press, Berkeley. ISBN O‐520‐06497‐6. 439 pp. 1990. Price $29.95 (U.S.) (hard

ISSN:0824-0469    

DOI:10.1111/j.1748-7692.1991.tb00108.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY