Alewife (Alosa pseudoharengus) Contributions to Lake Phosphorus Budgets: Implications for Management

As human-made dams are removed and fish passage at dams is improved in support of restoration efforts, anadromous alewives (Alosa pseudoharengus) gain access to historic spawning grounds. As they migrate to spawn, adult alewives import marine derived nutrients to lakes and impoundments. Young of year alewives (juveniles) export nutrients as they emigrate to the sea. These nutrients support primary production and are incorporated into freshwater food webs. However, many lakes in New England are mesotrophic or eutrophic. Additional nutrients, specifically phosphorus (P), may exacerbate water quality issues. To examine these issues, I compared outputs of an alewife nutrient and population model to background lake P data from seven lakes in New England. My objective was to provide a nutrient analysis as an example for stakeholders, communities and organizations considering dam removal or improved fish passage and the restoration of alewife populations. Results demonstrated that alewives’ impact on P levels was minimal under most scenarios. In 2017, alewives contributed less than 5% of mean epilimnetic P in four of seven lakes studied (China Lake, Highland Lake, Togus Pond, and Pawtuckaway Lake). Alewives contributed more P in Warwick and Webber Ponds, which translated to 3.6 – 11.19% of mean summer epilimnetic total phosphorus (TP) in Warwick Pond and 8.67 – 23.86% in Webber Pond. In Carr Pond, however, alewives contributed 11.43 – 93.67% of summer epilimnetic TP, which is potentially a large portion of the in-lake P budget. Alewife P import increased as adult escapement increased, and eventually adult import outweighed juvenile export, relative to lake size. Although the scale of P contributed byiv alewife was not extensive in the majority of the study lakes, it could be instructive to include alewife-derived P as part of the flux of nutrients in management documents such as total maximum daily load (TMDL) reports.