Oceanographic, Watershed and Anthropogenic Drivers of River Herring Productivity

River herring consist of two species of anadromous and iteroparous clupeids, alewives (Alosa pseudoharengus) and blueback herring (Alosa aestivalis). Both species have a long history of impacts from habitat loss, directed and non-directed fishing mortality, and other physical, chemical, biological and climate-driven changes. Currently, river herring are federally listed as “Species of Concern”  after experiencing a sharp decline in coast-wide landings in the 1980s and 1990s, and a default ban on directed harvested will go into effect in 2012. Interestingly, not all populations have demonstrated declines and a variety of trajectories are evident in river-specific measures of productivity, including landings, counts at fishways, and young-of-year surveys.  The 2008 river herring stock status report by the Atlantic States Marine Fisheries Commission (ASMFC) used cluster analysis to identify patterns in the river productivity data, which suggest some rivers have common patterns. Further, while some of the productivity trends were seen in adjacent systems, others were distant, suggesting that trends were not entirely controlled by proximate factors.  We synthesize previous studies examining environmental drivers of river herring productivity and expand upon the ASMFC cluster analysis by incorporating watershed, estuarine and oceanographic variables, and human demographic trends in pursuit of a more holistic understanding of the causes of decline.  The amount of accessible spawning and nursery habitat is clearly an important factor, but other watershed attributes such as flow, water quality, directed harvest pressure, and the extent of urbanization in the watershed are all contributing factors as well.  Salmon returns have shown good correlations with oceanographic variables, and testing of similar patterns for river herring is a priority next step for this study, especially to better gauge climate impacts.  Ultimately, our work aims to complement ongoing stock assessments by adding insights on broader environmental drivers, and to assist prioritization of impacts for mitigation and development of conservation strategies.