Populations Demographics, Distribution, and Seasonal Movement Patterns of Atlantic and Shortnose Sturgeons in the Penobscot River Estuary, Maine

Stephen J. Fernandez

Thesis Advisors: Dr. Gayle B. Zydlewski and Dr. Michael T. Kinnison
Thesis Committee: Dr. Gayle B. Zydlewski, Dr. Michael T. Kinnison, Dr. Joseph Zydlewski

An Abstract of the Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science (in Ecology & Environmental Science)
August, 2008

There is historical evidence of the Penobscot River supporting an Atlantic (and likely shortnose) sturgeon population. Historically, the Penobscot River supported a population of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and likely shortnose sturgeon (Acipenser brevirostrum). Aside from fishery landings prior to the early 1900s, the status of these populations is largely unknown. This study was initiated in 2006 to address the presence, abundance, distribution, and movement patterns of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and shortnose sturgeon (Acipenser brevirostrum) in the Penobscot River system using capture and acoustic telemetry.

Thirty-five Atlantic sturgeon and 151 shortnose sturgeon were captured with stationary gill nets, measured, tagged, and released. A subset of 8 Atlantic and 40 shortnose sturgeon were implanted with acoustic transmitters and tracked using a passive array of acoustic receivers throughout the river, estuary and bay from June 2006 to November 2007 to examine movement patterns. Atlantic sturgeon moved into the estuary in the summer and concentrated into a 1.5 km reach until emigrating in the fall; Atlantic sturgeon did not overwinter in the estuary. Shortnose sturgeon were present year-round in the estuary. An overwintering aggregation of shortnose sturgeon formed in the upper Penobscot estuary each year. They remained in this area from mid-October, 2006 to mid-April, 2007. In the spring fish all shortnose sturgeon left the overwintering site, moved downstream, and aggregated in the lower estuary. Many of these individuals moved upstream slowly as a group over the course of the summer to about 2 km downstream of the lowest dam in August before moving into the overwintering site. In the spring/early summer, shortnose sturgeon also immigrated and emigrated; emigration also occurred during a short window in the fall. In 2007 two Atlantic and ten shortnose sturgeon that had been acoustically-tagged in the Penobscot River system were detected by an acoustic array operated by the Maine Department of Marine Resources in the Kennebec River. Additionally, several shortnose sturgeon that had been tagged with PIT tags in the Kennebec River in 1998 and 1999 were recaptured in the Penobscot estuary in 2007. Since shortnose sturgeon are not known to make wide coastal migrations, this new information has important implications for management of populations throughout their range. For example, this is particularly important with reference to currently used abundance estimation techniques using closed system models. The information gathered in this study has provided previously unknown information regarding Atlantic and shortnose sturgeons in an unstudied part of their range. This is critical to listing/delisting decisions of both species, and also offers baseline data on these populations prior to a planned large-scale dam removal project that will make historical habitat available.