Trends in condition factors for 40 finfish stocks off the northeast U.S. continental shelf

One of the unintentional effects of fishing is enhanced natural selection towards smaller fish, where declines in individual fish weights often indicate heavy fishing pressure.  Alternatively, changes in fish weight can be due to competition or environmental changes.  In this study, trends in condition factors were analyzed for 40 finfish stocks caught during the 47 years of the Northeast Fisheries Science Center’s autumn bottom trawl survey.  A mixed model analysis of covariance was used to test if fish length, year, local species abundance or bottom temperature predicted individual fish weight.  Genders were analyzed separately for species known to have sexually dimorphic growth rates.  We found that fish length significantly predicted weight in all cases, and that 64% of the stocks declined in weight over the time series, whereas only 1.5% increased in weight.  However, local abundance of the stock being tested as well as local bottom temperature were only significant in predicting fish weight in 15-30% of cases, with similar numbers of cases indicating that abundance and temperature were positively correlated with fish weight as negatively correlated.  Therefore, on a community scale, density dependence and bottom temperature do not appear to be driving the observed decreases in fish weight.