Research Document 1997/119
Temperature, catch rate and catchability during the spring lobster fishery off eastern Cape Breton Island
By M.J. Tremblay and K.F. Drinkwater
Abstract
Seasonal changes in catchability (q) and temperature are investigated for the spring lobster fishery in eastern Cape Breton (Aspy Bay - Petit de Grat). Two approaches are used: analysis of spatial and temporal coherence in temperature and catch rate; and analysis of seasonal tag returns. Lobster catch rate trends along the northeast Cape Breton (Aspy Bay - Main-a-Dieu) were similar with relatively large declines occurring over the season. Catch rates along the Atlantic coast of Cape Breton (Louisbourg-Petit de Grat) were flat or showed a much lower rate of decline. Temperature variability along the northeast coast was highly coherent between stations for periods > 2 days and wind-dependent. In agreement with Ekman theory, winds from the south produced upwelling (and lower temperatures) while winds from the north resulted in downwelling (and higher temperatures). No significant relationships between temperature and catch rate were found but further analyses are required to confirm this. Tagged lobster recaptures showed no trend relative to the capture of untagged lobsters in most cases, suggesting the q of unmarked lobsters could be inferred from that of tagged lobsters. Seasonal catchability did not increase with temperature, probably because lobsters become less catchable as they prepare to molt. The increased catchability with increasing seasonal temperature shown in an earlier study (Paloheimo 1963) may be due to an artifact of tagging
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