Trends in age-composition, growth and reproductive parameters of Barents Sea harp seals, Phoca groenlandica
We examined age-compositions by sex in samples from Norwegian catches of moulting harp seals ( Phoca groenlandica ) in the East Ice (southeastern Barents Sea pack ice) from 1978 to 1993. Recruitment to the stock during the late 1980s was poor, mainly due to the nearly complete absence of year-classe...
| Published in: | ICES Journal of Marine Science |
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| Main Authors: | , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1995
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| Subjects: | |
| Online Access: | http://icesjms.oxfordjournals.org/cgi/content/short/52/2/197 https://doi.org/10.1016/1054-3139(95)80035-2 |
| Summary: | We examined age-compositions by sex in samples from Norwegian catches of moulting harp seals ( Phoca groenlandica ) in the East Ice (southeastern Barents Sea pack ice) from 1978 to 1993. Recruitment to the stock during the late 1980s was poor, mainly due to the nearly complete absence of year-classes 1986, 1987 and 1988. Data from reproductive organs of Barents Sea harp seals, with corresponding age determinations, were analysed in combined samples collected during three periods: 1963–1972, 1976–1985 and 1990–1993. The available size-at-age data suggest decreased growth rates and reduced maximum lengths for both sexes in 1990–1993. Testes weights and volumes indicate that males attained sexual maturity in age-groups 6–9 years during 1990–1993. Testes volumes also indicate an apparent increase in age at sexual maturity for males from age-groups 4–7 years in the combined 1963–1972 sample. Cumulative maturity frequencies, based on ages at first ovulations as indicated by corpora lutea and albicantia formed within the two years prior to the year of capture, show that the apparent mean age of maturity for females increased significantly from 5.5 years in the 1963–1972 sample to 6.7 years in 1976–1985 and 8.1 years in 1990–1993. A limited number of mature females, sampled after implantation in September–October 1990–1993, indicate a rate of early pregnancies of about 0.84. Indirect analyses of fertilities (using size-sequences of corpora in the ovaries) suggest an appreciable reduction in fecundity of females during the past 30 years. The observed changes in life history parameters are discussed. |
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