Biological changes in the ecosystem of the Northeast Newfoundland Shelf during the late-1980s and 1990s included a collapse in the biomass of cod (Gadus morhua), a substantial increase in the biomass of northern shrimp (Pandalus borealis), and an expansion in the area fished for shrimp. The timing and magnitude of changes in cod biomass and the quantity of shrimp consumed by cod were explored to determine if they were consistent with the hypothesis that the increase in shrimp biomass was a consequence of a reduction in predation pressure from cod. Results are equivocal because the timing of both the increase in the shrimp stock and the decline in the cod stock remain unclear and there is considerable uncertainty in the estimates of consumption of shrimp by cod. Nevertheless, it appears that an initial increase in shrimp biomass must have occurred during the early to mid-1980s and was not related to changes in the cod, whereas a larger increase in shrimp biomass in the 1990s was related at least in part to the collapse of the cod.
Recent stock assessments for Atlantic Canadian shrimp (Pandalus borealis) stocks, including the Scotian Shelf, the Gulf of St. Lawrence and the Labrador-Newfoundland Shelf, were conducted using the checklist or "Traffic Light" method. Results were viewed positively by many scientists, fisheries managers and industry, and the method has since been adopted by the Northwest Atlantic Fisheries Oganization (NAFO) for "data poor" stocks. It is also being considered by other stock assessment/management organizations. A major drawback of the method in its current form is that it does not link assessments to TACs or other management controls. Modeling results suggest that "Traffic Light" scores can be linked to simple harvest control rules in a way that is consistent with shrimp stock dynamics and management requirements, creating an integrated management framework that could be useful for "data rich" as well as "data poor" stocks.
Modal analyses of carapace length frequencies and interpretation of biological data for the northern shrimp (Panda/us borealis) indicate variation in both age at sex change and growth rate for some Northwest Atlantic populations. The first female age (the species is protendrous) varied from 6 in the southernmost area to 7 and possibly 8 in more northerly areas. The observed differences could not be related to differences in environmental temperature. Overlapping of modes in the length frequency data was severe in many cases, possibly obscuring an additional mode (age group) in the Davis Strait data. The assumption that sex change occurs at a specific age and the choice of appropriate models and statistical analyses to describe growth require further study.
A sedimentation model was used to map the distribution of particulate organic carbon (POC) in the Labrador Sea in relation to shrimp (Pandalus borealis) distribution. The model was based on information from sediment traps and ice regimes defined by: ice concentration, duration of ice cover and distance from an ice edge. Initial results from a subset of POC-binned commercial shrimp fishing data resulted in linear regression coefficients between catch per hour and POC of r 2 = 0.926 for 1989 and 0.964 for 1996. Binning the data according to depth resulted in r 2 = 0.995 and 0.948, respectively. Shrimp catch data from research surveys binned by (1) POC, (2) depth and (3) temperature resulted in corresponding r 2 of (1) 0.304, (2) 0.763, (3) 0.745 and (1) 0.535, (2) 0.897 (3) 0.954 for 1996 and 1997, respectively. The results validate the sedimentation model and confirm the importance of POC as food for shrimp. Information on POC distribution determined by sedimentation models has potential applications in shrimp fisheries and research.
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