R-14-04 Variation in Habitat Use by Juvenile River Herring

Karen A. Wilson
Department of Environmental Science
University of Southern Maine
Email Karen Wilson

Theodore Willis
University of Southern Maine

Karin Limburg
College of Environmental Science & Forestry
State University of New York

Alewife and blueback herring are sea-run (diadromous) fish that migrate between the ocean and Maine rivers. Once present in large numbers, river herring provided food for humans, other fish, and many wildlife species. Today, while river herring populations are declining throughout their range, in Maine they continue to support local commercial fisheries, primarily for lobster bait. As a result of restoration efforts, the numbers of river herring in the Penobscot have gone from a few thousand fish to more than one million in just two years.

However, not much was known about juvenile stages of alewives and blueback herring. What happens to juvenile fish after they leave freshwater can influence growth, behavior, and ultimately whether or not they come back as adults. Limited studies, including preliminary research funded by Sea Grant, suggested that river herring use estuaries and coastal waters much more than previously assumed, and that individual river herring from the same population may use different habitats.

Using otolith microchemistry, diet analysis, and stable isotope signatures of alewife and blueback herring, Wilson and graduate students Greg Labonte and Amy Webb showed the estuarine transition zone as a dynamic habitat, full of juvenile river herring attracted by food sources such as copepods, mysid shrimp, and barnacle larvae.

“No one thought they [the herring] were hanging out in the estuary,” said Wilson. “The estuary is a significant feeding area for these fish. They are staying there longer than people thought, moving back and forth, yet we don’t always think of the estuary as critical habitat.”

Read more about the project in Maine Boats, Homes & Harbors Magazine.

Two-year project, 2014-2016
Total Sea Grant funds: $76,569