Application of Genetic Markers to Determine the Impacts of Marine Bycatch on River Herring Spawning Stocks

Anadromous alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis) are species of conservation concern across their ranges. Many populations are at historically low abundances, and bycatch in marine fisheries has been identified as a major threat to recovery efforts. Our prior research revealed that, for both species, genetically distinguishable local spawning populations are nested within distinct regional stocks. This population genetic structure provides an opportunity to identify the natal origins of individuals incidentally captured as bycatch in marine fisheries. We applied a Bayesian genetic stock identification method to identify the natal origins of alewife and blueback herring individuals (n≈1600) captured in marine fisheries from 2011-2013. We then used total bycatch estimates going back to 2005 to determine the potential impacts of marine bycatch on the alewife and blueback herring spawning stocks over this time period. Our results suggest that bycatch has been an important factor in driving population declines and needs to be addressed in order for populations to recover.