Juvenile Alewife (Alosa pseudoharengus) Movement and Residency in a Northern Temperate Estuary

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Estuaries and Coasts Journal of the Coastal and Estuarine Research Federation


Information on juvenile alewife use of estuaries is limited on the east coast of North America. In this study, we collected juvenile alewife from the Penobscot River estuary, Maine, and measured stable isotope values from their muscle and liver tissues, which have a low and high turnover rate (respectively). These values were compared to the stable isotope values of preferred prey taxa collected from three distinctly different isotopic habitats within the Penobscot River watershed to estimate the amount of time fish had spent in the estuary. Fish were collected in spring, summer, and autumn in 2013 and 2014 at seven fixed collection sites in the estuary, from four freshwater lakes, and from five bay locations. Based on the δ13C values of muscle and liver tissue, estuarine caught juvenile alewife were assigned to one of the following distinctly different isotopic habitat groups: freshwater transient (recently from freshwater), bay transient (recently from the bay), or estuarine occupant (spent extended time in the estuary). Stable isotope ratios of nitrogen (for all samples) and sulfur (in muscle tissues of a subset of 17 samples) were analyzed to confirm habitat group designations. Bay transients had 37% and 15% higher sulfur and nitrogen isotope ratio values than estuarine occupants and five times more sulfur and almost two times more nitrogen isotope ratio values than freshwater transients. Of 88 juvenile alewife analyzed for carbon isotopes, 32% were identified as estuarine occupants that had spent extended time periods in the estuary, whereas 68% of juvenile alewife had recently moved from bay or freshwater habitats. Mean number of days that juvenile alewife spent in the estuary was highest in spring and declined over time, with more movement occurring in autumn. This result suggests that movement of juvenile alewife between bay and estuary occurs frequently from May to October. Juvenile alewife may use estuarine and nearshore habitats for extended time periods, and migration between estuarine and bay habitats may not follow typical life history strategies.