Assessing Food Availability and Growth Rate as Emigration Triggers for Juvenile River Herring.

Farrell, Abigail* ¹, Meghna Marjadi¹, Allison Roy¹, Matt Devine¹, Faith Perez¹, Dulani Sandanayaka¹, John Sheppard², ¹U.S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Environmental Conservation, University of Massachusetts, Amherst, MA, ²Massachusetts Division of Marine Fisheries, New Bedford, MA

The emigration of juvenile river herring (alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)) is a vital and complex milestone in the species’ lifecycle. Adults of both species migrate to freshwater in the spring for spawning, and, after a few months, juveniles will emigrate to their marine habitat. This emigration may be initiated by several factors, including environmental factors and characteristics of the fish. One potential cue for emigration is individual river herring growth rate, which has only been researched in a limited number of studies. We investigated temporal patterns of lake food resources (zooplankton) and juvenile river herring growth rate to assess the role of these biotic factors in triggering juvenile emigration. Zooplankton samples were collected on four dates (6/12, 6/29, 7/9, and 7/23) in 2019 from Great Herring Pond (Plymouth, MA) and will be used to assess food availability as a trigger for emigration. We also extracted otoliths from both emigrating and non-emigrating juvenile river herring that were sampled within the same week at the beginning and end of July 2019 from Great Herring Pond and the Monument River (Bourne, MA). The otoliths will be used to determine the age and growth rates of the individuals, and we will link growth to food availability. The growth rates will also be compared for emigrating and non-emigrating fish to determine if growth rate seems to be a factor in emigration. These results will contribute to our understanding of potential triggers for river herring emigration.