Distribution of Eastern Scotian Shelf Cod (Gadus morhua) With Respect to Age, Depth and Temperature*
The two factors important in determining the age-specific exploitation pattern of the fishery, commonly referred to as partial recruitment (PR), are the selectivity of the fishing gear and the availability of different aged fish to the fishery. Regulation of mesh and hook size in commercial fisherie...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.502.9744 http://archive.nafo.int/open/studies/s18/sinclair.pdf |
| Summary: | The two factors important in determining the age-specific exploitation pattern of the fishery, commonly referred to as partial recruitment (PR), are the selectivity of the fishing gear and the availability of different aged fish to the fishery. Regulation of mesh and hook size in commercial fisheries tends to limit the importance of selectivity changes in interannual variations in PR. However, if the fish are segregated by age, then the fishery could target large year-classes thus making availability an important component in PR variation. The objectives in this study were to investigate whether age groups of cod (Gadus morhua) are spatially segregated and see how this may be related to PR, and also to examine the relationship of depth and temperature with cod distribution at age. The cod management unit on the eastern Scotian Shelf area (NAFO Subdiv. 4Vs and Div. 4W) was used for the study. The depths of the study area were highly variable with many areas deeper than 200 m, and several shallow banks less than 100 m in depth. With respect to temperature, the area forms three layers in summer; a warm surface layer, a cold intermediate layer, and warmer deep water. Data were obtained from stratified-random groundfish abundance surveys (Halliday and Koeller, 1981), conducted on the Scotian Shelf during the summer between 1970–89. Catch-at-age of cod were calculated on a tow-by-tow basis. Catches were weighted by the ratio of stratum area and the number of tows in each stratum on an annual basis. Cumulative frequencies were calculated for ages 1 to 12. Cumulative frequencies of temperature (Smith et al., 1991) and depth were used as an indication of the distribution of the fish in relation to these environmental variables. The median temperature or depth was defined as the 50 % point of the cumulative frequency and the first and third quartiles were defined as the 25 and 75 % points. There was a distinct tendency for cod of older ages to be distributed at greater depths. The medians and quartiles of the depth ... |
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