Decreasing shrimp (Pandalus borealis) sizes off Newfoundland and Labrador -: environment or fishing?

During the 1990s, carapace length statistics including minimum size caught (L-min), mean male and female lengths, size at sex transition (L-50) and maximum size (L-max) of northern shrimp (Pandalus borealis) decreased in commercial and survey catches off Newfoundland and Labrador. Decreased growth rates caused by decreases in per-capita food availability due to large population increases, exacerbated by increased metabolic demands from higher water temperatures in the mid-1990s, appear to be the main cause of the size decrease. Fishing could have had an accelerating effect on environmentally driven decreases in shrimp growth and size by 'cropping' the largest shrimp from the population. The greatest decreases in shrimp size occurred in Hudson Strait and the adjacent northern shelf, the area which also has the highest densities and largest shrimp. We hypothesize that the greater size decrease here resulted from decreased primary production from decreased nutrient flux into the euphotic zone, caused by increased atmospheric warming, freshwater runoff and stratification during the warming trend of the 1990s.