Postrelease movements of captive-reared adult Atlantic Salmon in two Maine rivers

Objective

Atlantic Salmon Salmo salar remain at critically low levels in the United States, with the last remaining populations located in the state of Maine. In 2021, a pilot captive-rearing program, similar to a smolt-to-adult supplementation, was implemented to boost naturally spawning adults in support of recovery goals.

Methods

We conducted a 2-year acoustic telemetry study to track a subset of captive-reared salmon (N = 270) that were released into the Penobscot and Machias rivers. We evaluated their postrelease movement patterns, dam passage, and site fidelity between the two rivers, years, and seasons.

Results

Atlantic Salmon that were released into the Penobscot River tended to overwinter, but their movement patterns varied between release years. In contrast, the Atlantic Salmon that were released into the Machias River were more likely to move directly downstream to the river exit. In addition, the fish that were released into the dammed Penobscot River frequently made multiple attempts to pass dams in both directions, often with passage delays and failures. Atlantic Salmon that were released during the summer displayed more exploratory movements than those that were released in the fall. Most Atlantic Salmon either left the river shortly after release (5–30 d) or the following spring (>120 d). Site fidelity was greater for the fall-released Atlantic Salmon (76%) than for the summer-released Atlantic Salmon (23%).

Conclusions

Overall, releasing salmon in the fall as sexually mature adults may increase site fidelity to the release reach, thereby enhancing the chances of successfully spawning in the wild.