Behaviour, resource use, and condition of demersal age 0 Atlantic cod (Gadus morhua) in coastal Newfoundland : components of survival risk in the nearshore environment
It is well established, that following a pelagic phase age 0 Atlantic cod (Gadus morhua) settle to the bottom to assume a demersal habit. However, risks to juvenile cod survival in the coastal zone of the northwest Atlantic are not well understood. A better knowledge of factors affecting survival of...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
2000
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| Online Access: | https://research.library.mun.ca/1143/ https://research.library.mun.ca/1143/1/Grant_ScottMichael.pdf https://research.library.mun.ca/1143/3/Grant_ScottMichael.pdf |
| Summary: | It is well established, that following a pelagic phase age 0 Atlantic cod (Gadus morhua) settle to the bottom to assume a demersal habit. However, risks to juvenile cod survival in the coastal zone of the northwest Atlantic are not well understood. A better knowledge of factors affecting survival of age 0 cod during the transition to a demersal habit in shallow (< 10 m deep) nearshore regions of Newfoundland has broad ecological applications and will improve our understanding of the role of coastal habitats to the rebuilding of north Atlantic cod stocks. In this thesis, I investigated the importance of nearshore regions in coastal Newfoundland as rearing grounds for age 0 cod by examining their behaviour, resource use, and condition in relation to diet for the first several months post-settlement. -- Day-night differences in catch and diet of age 0 and age 1 cod were examined to delineate the diel peak in foraging activity and resource use in eelgrass (Zostera marina) habitat. Cod exhibited a size-related shift (age 0 to 1) from feeding predominantly on zooplankton by day to benthos at night. Intercohort cannibalism occurred when age 1 cod were approximately three times larger than their prey. Diet composition and catch data revealed that concentrations of age 0 cod foraged in the water column during the day, ceased feeding at night, and appeared to move to the bottom. Seasonally decreasing day length and prey size contributed to a decline in daily ration, yet age 0 cod maintained a strictly diurnal foraging cycle. The nocturnal decrease in feeding coincided with an increase in the catch of older conspecifics (age 2 and 3) and increased foraging activity of age I cod suggesting that avoidance of older conspecifics is an important factor influencing the survival of age 0 cod in the nearshore. -- Capture-mark-recapture experiments and seasonal sampling were conducted to examine the movement levels, spatial distribution, behaviour, and abundance of age 0 cod in eelgrass and no-eelgrass habitat over two years. ... |
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