Published since 1946
American Shad in a Changing River in Maine
The Maine Cooperative Fish and Wildlife Research Unit is studying American shad in the Penobscot River in Maine. Throughout their life history, American shad provide an important food source for a number of organisms in the river. For anglers, American shad support a popular fishery built around the strong fight they muster and the fine table fare they provide.
Graduate student Kevin Job is using cutting-edge microchemical analysis of juvenile American shad prior to dam removal. A small ?bone? found in the ear, the otolith, is central to his work. Otoliths form throughout the life of a fish and lay down rings, like a tree, that are chemical records of where a fish spent its time ? and when.
American shad are a large herring species native to the marine waters along the East Coast of North America. As anadromous fish, adult American shad migrate upstream into freshwater to spawn and, if they survive, move back to the marine waters where they feed and grow. After hatching, juvenile shad feed and grow in freshwater until fall, when dropping water temperatures prompt a seaward migration.
American shad were historically abundant in the Penobscot River drainage in Maine, with annual landings of over 2 million adults prior to dam construction in the 1830s. Until recently, upstream adult shad migration was cut off by Veazie Dam, the seaward-most dam on the river. Together with dams, a combination of habitat loss and overexploitation reduced the run to the point where some feared the population had disappeared entirely. Work performed through the USGS Maine Coop Unit at the University of Maine by Ann Grote demonstrated that there were large numbers of American shad below Veazie Dam, but these fish could not pass.
As of late 2013, the Veazie and Great Works Dams have been removed, leaving Milford Dam as the downstream-most dam on the Penobscot River. Upstream fish passage at Milford Dam is now accomplished with an upstream fish elevator and adult American shad passage numbers have increased. For the first time in nearly 200 years, these improvements allowed thousands of American shad to reach upstream habitat. Effective American shad passage, however, is challenging.
In addition to the otoliths research, the Maine Unit is leading an effort with the Penobscot River Restoration Trust and NOAA to better understand American shad passage through the modified Milford Dam fish passage facilities. In the last three years, doctoral student George Maynard has tagged hundreds of American shad with radio transmitters in the lower Penobscot River and tracked them through the summer.
American shad were historically an important fish, not just to those who use the river, but also to the ecosystems in which they inhabited. Continuing research efforts such as these provide information for managers to make informed on-the-ground decisions that can improve the odds for a species that is making its return to a changed river.
The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by Joseph Zydlewski, USGS Research Scientist and Assistant Unit Leader, Maine Cooperative Fish and Wildlife Research Unit at the University of Maine.