Changes in body size in five commercially exploited Scotian Shelf groundfish populations from 1970 to 2003

Fisheries scientists are increasingly interested in marine population parameters beyond abundance. One parameter, body size, appears to be important in maintaining reproductive success, productivity and stability in fish populations and may therefore play an important role in maintaining ecosystem health. While changes in the range of body sizes within communities and ecosystems have been well documented, size changes within populations has received less attention. Using data collected from 1970 to 2003 as part of the Canadian Department of Fisheries and Oceans' summer groundfish surveys, my research tests whether there has been a change in size spectra within five commercially important western Scotian Shelf groundfish populations. Results indicate that mean length and length of the largest quarter (third quartile) of four out of the five study populations has decreased significantly. While cause of these changes is difficult to ascertain definitively, changes to growth rates appears to be affecting average length in haddock.