Diel vertical migration and interaction of zooplankton and juvenile walleye pollock (Theragra chalcogramma) at a frontal region near the Pribilof Islands, Bering Sea
The diel vertical migration of age-0-walleye pollock ( Theragra chalcogramma Pallas) and their principal prey organisms were examined at a productive frontal region in the Bering Sea using 38 kHz acoustic measurements and net samples. Small copepods dominated the catch of depth-stratified plankton t...
| Published in: | ICES Journal of Marine Science |
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| Main Authors: | , , , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
2000
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| Subjects: | |
| Online Access: | http://icesjms.oxfordjournals.org/cgi/content/short/57/4/1283 https://doi.org/10.1006/jmsc.2000.0814 |
| Summary: | The diel vertical migration of age-0-walleye pollock ( Theragra chalcogramma Pallas) and their principal prey organisms were examined at a productive frontal region in the Bering Sea using 38 kHz acoustic measurements and net samples. Small copepods dominated the catch of depth-stratified plankton tows. Two copepod species ( Calanus marshallae and Metridia pacifica ), euphausiids and chaetognaths, exhibited strong diel vertical migrations, although the magnitude and timing of the migrations varied among taxa. Age-0 pollock dominated midwater trawl catches (92% by number) that targeted layers of strong acoustic backscatter. Distributions of target strengths (TS) recorded within the layers corresponded well with predicted values based on empirical length/TS relationships for age-0 walleye pollock. Juvenile pollock in these layers migrated from daytime maxima at 40 m depths to less than 20 m at night. The proportion of large copepods, euphausiids, and chaetognaths in the diet of juvenile pollock increased with increasing fish size, but prey composition did not change significantly throughout the diel period. |
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