Introduction & Objectives

This telemetry monitoring study was initiated in May 2021 to collect year-round occurrence data for Atlantic and shortnose sturgeon in the lower Kennebec River (including Bath Iron Works) and also to collect data during recurrent Naval activities. This study will also implement monitoring stations offshore of Popham Beach to capture coastal movements of sturgeon and other species, including white sharks. This area encompasses a curtain between Fox-Seguin Islands and the Jack Knife Ledge Dredge Disposal area. Additionally, an additional 55 total Atlantic and shortnose sturgeon will be tagged in the Kennebec River to increase the population of tagged fish.

Project objectives are: 1) monitor sturgeon activity in the proximity of Bath Iron Works; 2) Document coastal movements of fish offshore from Popham Beach: ESA sturgeon species, striped bass, white sharks, and other highly migratory species; 3) Monitoring year-round presence and migration of Atlantic sturgeon in the lower Kennebec River; 4) Monitoring year-round presence and migration of shortnose sturgeon in the lower Kennebec River; and 5) add additional acoustically tagged species to the Kennebec River system. Collaborators on this project include State of Maine Department of Marine Resources, University of Maine, U.S. Geological Survey, Portsmouth Navy Yard, University of Maryland (data analytics).

Technical Approach

The technical approach is to deploy year-round telemetry monitoring stations in the Lower Kennebec River including Bath Iron Works area to capture timing and movement through these areas, and also offshore stations to assess movements of ESA-listed sturgeon between river systems.  Locations and habitat of deployments are chosen carefully to maximize detection of sturgeon and also to minimize potential loss of equipment.  Data analysis will include summaries of number of unique sturgeon detected at each station for each month, and number of days per month sturgeon detected.  Also, finer scale telemetry data for the array will be reviewed for metrics such as likelihood of detection for different areas across seasons, and comparative rates of movement. 

With many previously deployed sturgeon tags expiring, the approach is also to surgically tag a minimum of 55 new Atlantic and shortnose sturgeon.  Biometrics are collected during tagging including inter-orbital and mouth width, a PIT tag inserted, and a fin clip collected for DNA analysis.

Progress & Results

There are 15 year-round telemetry monitoring stations from Courthouse Point in Dresden to Fort Popham (including one in the Eastern River offshoot), and 5 stations offshore. Downloads of telemetry stations occur twice a year.

For the time period representing the last two download cycles (November 2023 – October 2024), 478,938 matched detections were recorded across all stations, with the exception of Courthouse Point that is pending retrieval by divers in Spring 2025. Detections of fish tagged by other organizations were recorded from several different tagging projects in the Mid-Atlantic Acoustic Telemetry Observation System (MATOS; https://matos.asascience.com).

The addition of new Navy-tagged sturgeon to the Kennebec system in 2022 significantly increased the dataset in-river. Of all detections matched in the MATOS database (tagged by Navy and/or other projects), the vast majority were Atlantic sturgeon (river: 430,321), followed by shortnose sturgeon (river: 37,400), striped bass (river: 9,190), and white shark (ocean [FS stations]: 182). However, the frequency of tag observations should not be interpreted as a proxy for population distribution or abundance, as the proportion of tagged individuals for each species is not equivalent. Notably, a higher percentage of Atlantic sturgeon are tagged in the Gulf of Maine region, as compared with shortnose sturgeon.

Mid-River stations are those located north of Bath, lower river stations are from Bath to Fort Popham, and ocean stations from Fox to Seguin Island. These data provide a unique comparison for the winter/early spring months compared to the warmer months leading up to fall. For Atlantic sturgeon, there were noticeably higher detections on mid-river stations during cooler months, consistent with data from prior years and where a portion of this species is known to overwinter. The opposite trend was found to be true for warmer months with greater detections in the lower river, when fish move further downstream (and offshore) with warmer temperatures. For tagged shortnose sturgeon, the abundance of detections was, again, higher mid-river during the warmer months, typical of this species known to overwinter in the vicinity of Merrymeeting Bay and not as resident to the Eastern River. As with prior years, there was a fairly event split between mid- and lower-river detects for shortnose sturgeon during the two time periods, highlighting the widespread movement of this species in the Kennebec.

Notably, there were 17 unique white sharks detected that were tagged by Massachusetts Division of Marine Fisheries, an increasingly important dataset showing movements for this highly migratory species. These white shark detection data were recently included in a manuscript titled "Insights into the Habitat-Use Patterns of White Sharks (Carcharodon carcharias) Along the Maine Coastline" for consideration of publication in Frontiers in Marine Science, section Marine Megafauna.

Finally, 2024 represents the first year of Atlantic salmon detects of captive-reared fish tagged in the Penobscot River (75-80km distance from mouth of Kennebec River to Penobscot Bay). One of these fish was detected at station FS06 offshore Seguin in February 2024, while another was detected on five stations between Abby Point (ABBYPT) and Mill Cove (MILL) during April 2024 (moving south over a period of two days).