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FIELD COMPARISON OF EEL-LADDER-STYLE AND TRADITIONAL SEA LAMPREY TRAPS
We tested if an eel-ladder-style trap (ELST) can be used to trap adult sea lampreys, Petromyzon marinus, in routine trapping operations over two spawning seasons. The ELST consisted of a wetted inclined ramp with vertical pegs arranged in a regular pattern, leading to a vertical drop into a collection box. We assessed catch rate of ELST compared to traditional funnel traps with “fingers” at three locations, the St. Marys River (2012 only), Cheboygan River, and Ocqueoc River. At the Brule River in 2013, we tested if the ELST ccould be used in sorting adult sea lampreys from fin-fish. In addition, at the Cheboygan and Ocqueoc rivers we observed lamprey behavior on the ELST using PIT tags and video and tested for any trap bias using a differential marking scheme. We found sea lamprey capture rates of ELSTs to be lower than that of the traditional funnel traps at the Ocqueoc River, but higher at the Cheboygan River. However, unlike the funnel trap, the ELST did not trap any fin-fish. Using an ELST at the St Marys River did not improve the overall capture rate at the test locations. At the Brule River, the spawning run was small, but all sea lampreys entered the ELST, effectively sorting them from hundreds of fin-fish. ELSTs were 100% effective at retaining captured sea lampreys, while the funnel trap at the Cheboygan River allowed considerable escapement. Fish caught in the ELST, marked and released showed trap happiness, i.e. returned to the ELST in preference over the paired funnel trap. The success rate of fish attempting to enter the ELSTs varied between years and locations between 16% to 79% probability of finishing an attempt. Particularly in the Ocqueoc River, many climbing attempts were aborted early in the climbing phase. The visual impression was that most aborted attempts were voluntary, i.e. not due to fatigue. No physical differences between lampreys retrieved from the ELST and paired funnel trap were found at the Ocqueoc location, while at the Cheboygan location, smaller males, more females and females with lower GSI were found in the ELST. Due to their perfect selectivity and retention, eel-ladder style traps can become a valuable tool for sea lamprey management. With further research on attraction flow and ELST ramp substrate, the entry and success rate of the ELST can be increased to match or surpass the catch rate of the traditional funnel traps.