Biological and Environmental Requisites for a Successful Trap Fishery of the Northern Shrimp Pandalus Borealis
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A permanent trap fishery for northern pink shrimp (Pandalus borealis) was established in Chedabucto Bay, Nova Scotia in 1996 after several years of experimental trapping by one fisherman. Despite extensive experimental trapping projects elsewhere in Nova Scotia, only in one other area, Mahone Bay, has a long-term fishery been successfully established. The successful trapping of shrimp from small vessels off the coast of Nova Scotia appears to be dependant on a number of requisite conditions, including the presence of soft mud habitat and low temperatures in large, relatively deep coastal embayments. Catch rates for the established inshore trap fisheries increase in late summer-fall and decrease in spring, suggesting that an inshore migration occurs in the fall from adjacent “feeder” populations. In addition to the seasonal pattern of trap catches, cyclical changes at a finer temporal scale were observed that appear to be related to tidal cycles, with higher catch rates associated with greater tidal ranges. Coupled with known diurnal vertical migratory behaviour, this pattern could arise as more water, and the shrimp within it, pass horizontally over the trap and come into contact with its bait plume during greater tidal ranges. More complex, selective vertical migration coupled with tidal drift may result in net movement into areas such as Chedabucto Bay. Analysis of length at sex transition and maximum size suggests that shrimp trapped in Chedabucto Bay come from the same population as those caught by trawlers inshore and offshore on the eastern Scotian Shelf. Shrimp trapped in Mahone Bay and St. Margaret’s Bay have significantly different growth characteristics and are probably from a different population. Thus the Mahone Bay and St. Margaret’s Bay population appears to be more locally confined than the widespread shrimp population on the eastern Scotian Shelf, possibly originating from areas within and immediately adjacent to these bays.