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REFINEMENT OF A NEW TRAPPING TOOL FOR MIGRATING ADULT SEA LAMPREY
Ulrich Reinhardt1; Peter Hrodey2, Scott Miehls3
1Dept. of Biology, Eastern Michigan University, 403 A Science Complex, Ypsilanti,
2USFWS Marquette Biological Station, 3090 Wright St, Marquette, MI 49855
3USGS Hammond Bay Biological Station, 11188 Ray Road, Millersburg, MI 49759
The main aim of the study was to determine the impact of three operational parameters on the effectiveness of eel-ladder-style traps for sea lamprey (ELST). At two rivers, ELST with different parameters were fished side by side and the effectiveness of the traps monitored via catch analysis, PIT tag detection and video recordings of lampreys climbing the ELST ramp. Both attraction flow to the ELST and the flow rate down the ELST ramp strongly influenced the rate at which sea lampreys attempted to climb the ELST ramp and completed or aborted the climb. In 2014, cutting off the attraction flow to the ELST at the Ocqueoc site, lead to low rates of approaches, attempted climbs and retained catch. Only about 10% of the catch was found in the trap without attraction flow. In 2015, 50%- reduced and full attraction flow were compared and no difference in nightly catches was found. Three levels of pumped flow down the ELST ramp were established, ranging from 38 to 152 l/minute. Higher ramp flow led to significantly greater completion rates of attempted climbs, with a low of 16% completion rate at the lowest ramp flow and a high of 65% at observed at the highest flow. Between-year variations in the completion rate were also observed. The second trap parameter we modified was the angle of the ELST ramp, which we did at the Cheboygan River. There was little difference in catch rates between ramps that were angled at 30 and 45 degree from horizontal, but potential differences were masked by daily fluctuations in catch and by an overriding effect of trap position. Analysis of video recordings on matched days showed that in both years a greater percentage of attempted climbs were completed on the steeper ramp. The 30-degree ramp had a completion rate of 26% (2014) and 42% (2015) while the 45-degree ramp had a rate of 44% (2014) and 51% (2015). Finally, we tested if addition of synthetic mating pheromone (3kPZS) to the ramp flow would improve the efficiency of the ELST. Addition of the male pheromone did not increase the catch or frequency of attempts to enter the trap. Added pheromone did lower the completion rate of the climb up the ramp (in 2015) and led to a somewhat more female-skewed catch. This was possibly due to a repelling effect of concentrated male pheromone on male lampreys. As observed in previous years, the ELST at the Cheboygan, River caught on average smaller sea lampreys compared to a nearby funnel trap with a sex ratio that was heavily biased toward females. While the smaller average weight of the lamprey catch in the ELST suggests that the physical challenge of climbing an ELST ramp deters some individuals, the bulk of our observations suggest that motivation is the greatest determinant of ELST entry. Ample attraction and ramp flow and a fairly steep ramp angle appear to be key parameters for an effective ELST. Observation of behavior at three spatial scales suggested a bias toward lampreys approaching and entering traps from the left when facing upstream. An experiment at the Brule River fishway and lamprey trap confirmed that a combination of ELST and smooth wetted ramps can be helpful in sorting migrating finfish from adult lampreys, but the sorting was incomplete and skewed toward mostly smaller finfish passing the smooth ramp.