Alewives are an integral part of and link between freshwater and marine ecosystems in the Gulf of Maine. Little is known about the life history and distribution of alewives during their time at sea. However, bycatch and unfavorable ocean conditions during the marine phase have been suggested as contributing factors to the decline and lack of recovery of some stocks. Our research on alewives focuses on understanding alewife stock structure. Our study involves structural analysis of otoliths (fish ear bones) from major rivers in Maine to identify unique stocks of alewife, and the development of a sophisticated simulation model that explores the consequences of stock structure throughout New England and the impact of mixing at sea.