Atlantic Sturgeon Use of the Penobscot River and Marine Movements within and beyond the Gulf of Maine

Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus were recently listed as threatened in the Gulf of Maine and endangered in the rest of their U.S. range. Continued research priorities include long‐term population monitoring, identifying the species’ spawning and nursery grounds, and determining its use of estuaries and marine coastal waters. Although recent and ongoing research is filling in knowledge gaps, the Atlantic Sturgeon's life history and its severely depleted populations make this a challenging species to fully characterize. Our goal was to compile data collected over 7 years from fish captured in the Penobscot River estuary, Maine, to inform management decision making. Atlantic Sturgeon were captured (n = 199), recaptured (n = 16), and passively telemetered (n = 32 that were analyzed here) from 2006 to 2013. Captured individuals were predominantly subadults, and data from telemetry indicated repeated use of a 5‐km reach of the mesohaline portion of the estuary. Subadults predictably emigrated from the river each fall (mean date ± SD, August 31 ± 43.5 d) and immigrated back each spring to early summer (May 15 ± 27.8 d), with most individuals (>95% [31 of 32]) returning one or more years after tagging. Marine detections of these subadults were common (81.25% [26 of 32]) and spanned the geographic extent of both the threatened and endangered U.S. distinct population segments and into international waters, e.g., from the Hudson River, New York, to Minas Basin, Nova Scotia. However, they were more typically detected by receivers in the Gulf of Maine; 77% (20 of 26) were only detected in the Gulf of Maine when not in the river. These data indicate that, based on the temporal and spatial predictability of habitat use, the estuary of the Penobscot River is important for subadult Atlantic Sturgeon of the Gulf of Maine. The wider movement patterns emphasize the need for conservation and management across regions and international boundaries.