Fish that migrate between freshwater and sea ecosystems play a multitude of ecological roles. In the centuries since Europeans first colonized the Americas, damming and other disruptions to river connectivity have greatly decreased the migration opportunities of these species. Recent BioScience author Steven Mattocks of the University of Massachusetts, in Amherst, joins us on this episode of BioScience Talks to discuss the effects of lost habitat and river connectivity for these crucial fish. In particular, he explains that because of a dearth of information on pre-1950 conditions, past estimates of lost biomass may drastically underestimate the ecological harm of damming.   Read the article discussed on the show. Subscribe on iTunes. Subscribe on Stitcher. Catch up with us on Twitter.