The importance of marine derived nutrients delivered to Atlantic rivers by four species of anadromous fishes

Returns of anadromous fish have declined dramatically in the past century throughout Atlantic Canada, reducing the delivery of marine-derived nutrients (MDN) to rivers. The loss of these fishes could have had profound effects on stream nutrient dynamics and aquatic production, particularly in nutrient-poor systems. The role of MDN transport in coastal rivers is a function of net nutrients transferred by all anadromous fish. Although many Atlantic anadromous fish, such as salmon, smelt, and alewives, do not die after spawning, collectively their release of excretory by-products and gametes may result in marine nutrient subsidies equivalent to those delivered by Pacific salmon and, therefore, are of importantance to the productivity of Atlantic Canada streams. The objective of this study is to identify the pathway of incorporation and transfer of MDN to biofilm, invertebrate and fish communities, using stable isotope analysis of nitrogen, carbon, and sulfur, in Atlantic rivers. These MDN inputs could drive a positive-feedback mechanism that will increase freshwater productivity, and, in turn, the production of future generations of anadromous fish. By examining the relative importance of marine and freshwater nutrients, we may learn that the impact of spawning by multiple anadromous fish species is larger in scope that previously understood.