Thirty Years of Merrimack River Herring Restoration: Inadvertent Restoration, Crash, and Lessons Learned

Restoration efforts for river herring often center on increasing habitat connectivity (fish passage or dam removal) and transportation of fish upstream.  Upstream stocking is often used to jump start natural recolonization processes or to provide access to juvenile rearing habitat that is otherwise underutilized.  The Merrimack River is a heavily dammed river in New England with a 30+ year modern history of efforts to restore river herring.  The largest runs (100,000’s) occurred in the 1990’s and were attributed to the stocking of a large upstream lake to provide forage for a cold water fishery.  These efforts provided an inadvertent boost to restoration efforts, but the annual run quickly dropped to pre-stocking levels (<10,000) when stocking ceased even with concurrent efforts to increase habitat connectivity.  Contrasting management efforts and responses in run counts between the Merrimack, Connecticut and coastal New Hampshire rivers provide insight and comparisons that can help identify causative versus correlative population responses.  In the case of the Merrimack River, it appears that stocking efforts produced the large run sizes rather than the improvements to fish passage.  This should be considered when looking at other ‘successful’ restorations that are still heavily stocked.