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Determining routes of adult sea lamprey escapement to the upper Cheboygan River and impacts on adult abundance estimates with acoustic telemetry
2Hammond Bay Biological Station, 11188 Ray Road, Millersburg, MI
3USFWS, Marquette Biological Station, 3090 Wright St., Marquette, MI 49855
The Cheboygan River is an important sea lamprey producing tributary to Lake Huron. The trap near its mouth captures more adult sea lampreys than any other in the Great Lakes. Despite having an efficient trap and refurbished dam, the upper river (upstream of lock and dam) remains infested with sea lampreys and has been treated with lampricides on a 3-year cycle for nearly 50 years at an average treatment cost of $500,000 per treatment. Upstream escapement of sea lampreys through a navigational lock near the dam has been hypothesized to be the source of infestation in the upper river. Here, we used telemetry data to estimate reach-specific probabilities of movement, including trap capture and dam passage, for sea lampreys in the lower Cheboygan River, MI by fitting the data to a Bayesian state-space model (BSSM). Movement probabilities through individual river reaches were combined to estimate of the proportion of the population present at each telemetry receiver and trap location, and further expanded by the trap catch to estimate abundance at each location. Of an estimated 22 104 to 29 683 (95% credibility interval) adult sea lampreys that entered the river, we estimated that 46-61% were caught in the trap (i.e. exploitation). Although no tagged lampreys passed the above the dam (0/148), the structure could not be considered a complete barrier to sea lamprey migration because we estimated that 0-2% of the population, or 0 to 513 sea lamprey, passed upstream of the dam . The BSSM provided a rigorous framework for inferring spatial dynamics and allowed sampling variability to be considered when estimates were 0 or 1. Given our results, enhanced trapping at existing sites in the Cheboygan River may have greater potential to increase exploitation than adding traps at new locations because an estimated 82-95% of the population reached the trap site, but only 51-68% of those were caught. Furthermore, given the low estimated rate of escapement upstream of dam (fewer than 513 sea lampreys), yet consistent yearly recruitment success, determining if the upper river supports a sea lamprey population that completes its life cycle without entering Lake Huron (landlocked) should be a priority before management actions are taken at the lock and dam to ensure 100% sea lamprey blockage. If a landlocked population resides in the upper river, plans to eradicate sea lampreys from the upper river should be formulated prior to rebuilding the lock (a project currently being explored). Otherwise, continued lampricide treatments in the upper river would be necessary.