Trends in the maternal investment of harbour porpoises are uncoupled from the dynamics of their primary prey

Harbour porpoises in the Bay of Fundy and Gulf of Maine feed primarily on A tlantic herring. Herring stocks have undergone dramatic fluctuations in abu ndance over the past three decades due to changes in fishing intensity. In order to understand the effects of these changes in prey abundance on the p atterns of maternal investment, I examined interdecadal variation in the si ze of porpoise calves measured in August prior to weaning. Female harbour p orpoises exhibited significant variation in maternal investment between 197 0 and 1999. During the 1980s, females consumed more herring and produced la rger calves. Surprisingly, however, this increased maternal investment occu rred during the period of lowest prey abundance, perhaps because the herrin g stock assessment does not reflect the availability or quality of prey to female porpoises.