THE INFLUENCE OF ANADROMOUS ALEWIFE ON MAINE LAKES AND STREAMS: USING NUTRIENT LIMITATION ASSAYS AND STABLE ISOTOPES TO TRACK MARINE-DERIVED NUTRIENTS

Sea-run fish can act as nutrient subsidies to freshwater ecosystems when they return there to spawn. However, relatively few studies have quantified the role of sea-run alewives (Alosa pseudoharengus) as an ecologically important source of marine-derived nutrients (MDN) to lakes and streams. Primary producers (photosynthesizing organisms) in lakes and streams are often limited in their growth by nutrients, such as nitrogen and phosphorus. If alewife bring nutrients to lakes and streams, then the nutrient limitation of primary producers in those systems should be alleviated. Nutrient limitation experiments were used to examine the effects of alewife MDN on Maine lakes and their outlet streams. There was less of an alewife effect on freshwater nutrient limitation than was expected, but the current densities of alewife runs were relatively low compared to historical counts and to other areas of the northeastern U.S. This study has relevance in Maine given the current and proposed dam removals and diadromous fish restoration, which will restore access to historical freshwater habitat for native anadromous alewife.