Session B8- Monitoring changes in diadromous populations resulting from fish passage improvements on the Acushnet River, Massachusetts

The Acushnet River has been the focus of much diadromous fish passage restoration work in recent years. A cooperative effort between the Massachusetts Division of Marine Fisheries, the National Marine Fisheries Service, and the U.S. Fish and Wildlife Service focused on fish passage improvements beginning in 2002 with the construction of a state-of-the-art Denil fishway at the New Bedford Reservoir dam. Restoration efforts continued in 2007 with improvements to fish passage at two downstream obstructions (the Acushnet Sawmill dam and the Hamlin Street dam), in which both sites were fitted with innovative nature-like fishways, including a stone flow-constrictor/step pool system at the former and a stone step-weir system at the latter. To measure the success of the fish passage restoration activities, monitoring of river herring and elver populations was conducted pre- and post-construction. Adult river herring returning to the reservoir from 2005 through 2007 (the pre-construction phase) were low (N2005 = 395, N2006 = 202, N2007 = 371) and elver counts declined significantly (N2005 = 1,285; N2006 = 475; N2007 = 192) during this period. Post-construction monitoring of river herring commenced in the spring of 2008 using a combination of census and electronic counting. Results indicated an increasing trend of spawning adults (N2008 = 977; N2009 = 1,700; N2010 = 2,703) as well as increased numbers of elvers returning to the reservoir (N2008 = 5,421; N2009 = 6,078; N2010 = 3,388). Results from this monitoring program, including results from 2011, will be presented and suggest that the fish passage improvements to the three dams on the river are successful and have significantly improved passage for both juvenile American eels and river herring, greatly increasing the probability of restoring healthy populations of diadromous fish to the Acushnet River system