Fetal growth and the condition of pregnant northern fur seals off western North America from 1958 to 1972
Annual estimates of the condition of pregnant northern fur seals (Callorhinus ursinus) and the size of their fetuses were determined from over 2600 samples collected in the North Pacific from 1958 to 1972. A condition index related the observed mass of pregnant females (adjusted for fetal mass) to t...
| Published in: | Canadian Journal of Zoology |
|---|---|
| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1992
|
| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/z92-286 http://www.nrcresearchpress.com/doi/pdf/10.1139/z92-286 |
| Summary: | Annual estimates of the condition of pregnant northern fur seals (Callorhinus ursinus) and the size of their fetuses were determined from over 2600 samples collected in the North Pacific from 1958 to 1972. A condition index related the observed mass of pregnant females (adjusted for fetal mass) to their predicted mass (calculated from body length). It showed that females carrying male fetuses were in poorer condition than those carrying female fetuses. It also showed that the mean condition of pregnant females improved from 1958 to 1964, but dropped sharply in 1965. Body condition remained poor until 1972, when it plunged again. Fetal mass declined throughout the 1960s, unlike body length, which changed very little. It is suggested that fetal growth, particularly mass, is a sensitive indicator of feeding conditions during the last trimester of pregnancy while pregnant females are in the Gulf of Alaska and Bering Sea. It is further speculated that the condition index for adults reflects overall feeding conditions experienced throughout the annual migration. |
|---|