CHARACTERIZING FISH ASSEMBLAGE STRUCTURE IN THE PENOBSCOT RIVER PRIOR TO DAM REMOVAL

CHARACTERIZING FISH ASSEMBLAGE STRUCTURE IN THE PENOBSCOT RIVER PRIOR TO DAM REMOVAL

By Ian A. Kiraly

Thesis Advisor: Dr. Stephen Coghlan, Jr.

A Lay Abstract of the Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science (in Wildlife Ecology) August, 2012

Keywords: Fish; Dams; River; Restoration; Electrofishing

The Penobscot River drains the largest watershed in Maine, and once provided spawning and juvenile rearing habitats to at least 11 species of sea-run fish. Many of these species, such as Atlantic salmon, alewife, and American shad, provided important commercial and recreational fisheries. The construction of dams blocked migrations of these fish and likely altered fish communities throughout the river. Further alteration to fish communities occurred as a result of habitat fragmentation and modification. The proposed removal of two main-stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on dam obstructing a major tributary is anticipated to increase passage of many species of fish. To sample fish communities within the lower 70 kilometers of the Penobscot River prior to dam removal, we used boat electrofishing methods during both summer and fall in 2010 and 2011. Major tributaries were also sampled. In total, we captured 61,837 fish of 35 species while sampling 114 kilometers of river and tributary shoreline. Fish communities differed among river sections delineated by dams, indicating that dams were a major driver of differences in fish community structure along the river. Alewife and blueback herring, two historically abundant sea-run species, were captured frequently within the tidal river section, but at no locations upriver. Smallmouth bass and pumpkinseed sunfish were most prevalent in the Orono area, within and above the Veazie Dam impoundment. Further upriver, warm-water species such as chain pickerel, brown bullhead, and yellow perch, along with minnow species such as common shiner and fallfish were most prevalent. Fish communities did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability. We predict that many sea-run fish will migrate further upriver after dam removal, potentially causing changes to fish communities. Improved habitat connectivity might also change the distribution or abundance of many species. While it is difficult to predict specific changes to fish communities in this large river, such predictions can be tested by future studies to evaluate river restoration success and the recovery of historically important fish species.