Shortnose Sturgeon (Acipenser brevirostrum) Spawning Potential in the Penobscot River, Maine: Considering Dam Removals and Emerging Threats
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Master of Science (MS)
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Dam removals from the Penobscot River in Maine restored access to freshwater habitat critical for the life cycle of endangered shortnose sturgeon. Prior to the dam removals, shortnose sturgeon spawning activity had not been documented. Instead, evidence suggested that individuals emigrated from the Penobscot River to spawn in the Kennebec complex, 140 km away. A central question of this thesis was whether spawning activity would commence in the first two years following dam removal. Consistent with pre-dam removal movement patterns determined using acoustic telemetry, the majority (78%) of tagged individuals emigrated from the Penobscot River at some point over the study period and, of these, 71% were found on spawning grounds in the Kennebec complex. The high degree of connectivity with other coastal Maine rivers, along with the lack of documented spawning activity, suggests that shortnose sturgeon remain dependent on spawning in the Kennebec complex. For all individuals occupying the Penobscot River, seasonal distributions within the river were consistent among years and similar to those observed pre-dam removal, with upstream/freshwater river use predominating in fall and winter and estuarine/downriver use dominating in spring and summer. In the fall of 2015, individuals were detected in the first 5 km made available by the Veazie Dam removal, offering evidence that shortnose sturgeon could return upstream during future springs to spawn.
Shortnose sturgeon require a suite of habitat characteristics to be present to spawn. Habitat suitability modeling was performed to assess the quality of the newly available habitat in the Penobscot River. Using a two-dimensional hydrodynamic model and ArcGIS, the first 5 km reach made available by the Veazie Dam removal was examined based on velocity, depth, and bottom substrate. Results indicate that at any discharge likely to occur during the spring spawning season, at least 40% of the area is usable for spawning. Velocity is the most limiting habitat characteristic at any simulated discharge. The habitat suitability maps generated could be useful for planning spawning sampling in future years.
Lessons learned from the first two studies were used to suggest future steps for research concerning shortnose sturgeon in the Penobscot River. To more fully describe how this endangered species responds to the recent dam removals, more acoustic tags should be deployed and further examination of habitat suitability should occur. In addition to continued telemetry and habitat assessments, researchers should consider how the emerging threat of climate change could impact shortnose sturgeon recovery. For example, how increased saltwater intrusion affects available habitat for spawning and juvenile rearing. Tracking the behavior and use of newly available habitat will help researchers and managers address threats to the species in the Penobscot River and to the wider population in the Gulf of Maine.
Johnston, Catherine, "Shortnose Sturgeon (Acipenser brevirostrum) Spawning Potential in the Penobscot River, Maine: Considering Dam Removals and Emerging Threats" (2016). Electronic Theses and Dissertations. 2480.