Timing is Everything during Salmon Migration in Estuaries

smoltAs an anadramous species, Atlantic Salmon Salmo salar have a complex life history that includes spending part of their lives in freshwater, estuarine, and marine habitats. In recent years, the decline of Atlantic Salmon has been attributed to their poor marine survivorship, due in large part to climate change. However, factors contributing to their marine mortality do not operate independently of factors acting in estuarine and fresh waters. Therefore, an understanding of all the factors that influence mortality could help to enhance Atlantic Salmon management. In a new study in Marine and Coastal Fisheries, Daniel S. Stich of the University of Maine and his colleagues examined the behavior and survival of Atlantic Salmon smolts during estuary migration in the Penobscot River, using surgically implanted acoustic tags, between 2005 to 2013. They examined three main categories of potential drivers for behavior and survival: (1) individual fish characteristics (fork length, mass, condition factor), (2) migratory history (number of dams passed, migratory route), and (3) environmental variability (cumulative temperature experienced). Of all the drivers tested, the one that most affected a smolt’s chances of survival was the number of dams it passed during its estuary migration. For every dam a salmon passed, its survival decreased by 6-7%, and the effects were cumulative. In the study, most salmon passed between two and nine dams. The authors also found that smolt survival during migration increased by up to 25% if they entered the estuary at their peak physiological preparedness (i.e, fish with the highest gill Na+, K+ -ATPase activity). These findings can help hatchery mangers decide when to release their smolts in order to increase survival.

REFERENCE

Stich, D. S., G. B. Zydlewski, J. F. Kocik, and J. D. Zydlewski. 2015. Linking behavior, physiology, and survival of Atlantic Salmon smolts during estuary migration. Marine and Coastal Fisheries 7:68-86. dx.doi.org/10.1080/19425120.2 015.1007185

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