Analysis of Sea-Run and Freshwater Fish Abundance Trends in the Penobscot River 2000-2019

The Penobscot River flows to the Atlantic Ocean through central Maine providing essential habitat for freshwater and sea-run fish that utilize the river to complete their life cycle. Dams can obstruct access to this habitat, but with their removal, fish abundance changes and can be studied. Two dams were removed from the Penobscot River by 2013 and a new fish lift became operational at the Milford Dam. We compiled data from the most downstream fish trapping sites pre and post dam removal in order to quantify trends in catch rates for several sea run and freshwater fish species. Pre-removal fish species abundance data was collected at the Veazie Dam (2000 -2013) and post-removal data from the Milford Dam fish lift (2014-2019). Our graphical analysis of seven of the most abundant species suggests an overall increase in Penobscot sea-run fish populations. American shad catches increased from only one or two annual sightings to over 3,500 on average. Both species of river herring (Alewife and Blueback herring) showed a 10,000 fold increase in catch following dam removal. In addition, smallmouth bass and striped bass exhibited a significant increase in catch. Due to differences in facility efficiency, catch rates are only an approximation of abundance but are suggestive of both increased numbers of returning fish and higher passage rates for some species. The Penobscot River restoration project is finding success in restoring fish populations, with average catch rates increasing 34 percent per species and habitat access improvements ranging from 31-100% of historic ranges estimated by Trinko et al. (2012).