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Feasibility of using oviduct tagging with acoustic transmitters to determine spawning time and habitat of lake trout in the Drummond Island Refuge
Thomas R. Binder1, Scott M. Miehls2, Charles C. Krueger3
1 Michigan State University, Hammond Bay Biological Station, 11188 Ray Rd., Millersburg MI 49759
2 United States Geological Survey, Hammond Bay Biological Station, 11188 Ray Rd., Millersburg MI 49759
3 Center for Systems Integration and Sustainability, Michigan State University, 1405 South Harrison Road, 115 Manly Miles Building, East Lansing, MI 48823
Oviduct-inserted transmitters have shown promise as a tool for determining precise location of spawning in fishes. However, use of manual tracking to locate expelled oviduct-transmitters is laborious and without frequent surveying, it is difficult to accurately estimate the time at which transmitters were expelled. We tested the feasibility of pairing oviduct-inserted transmitters with positional telemetry to estimate time and location of spawning in lake trout (Salvelinus namaycush). Three assumptions were tested: (1) oviduct transmitters remain within the fish until spawning, (2) oviduct transmitters are expelled with the eggs during spawning, and (3) time and location of oviduct transmitter expulsion can be accurately determined. In the laboratory, 39 of 44 (89 %) lake trout that received an oviduct transmitter retained it until the end of the spawning period (~ 10 weeks). Premature transmitter expulsions occurred during the first two weeks after tagging, well before the spawning period. Natural spawning in the laboratory was not feasible, but 31 of 35 (89 %) ripe trout that retained transmitters until spawning expelled them with eggs during manual stripping. The ability of the Vemco Positioning System (VPS) to calculate positions for oviduct transmitters placed by hand in the substrate at known spawning sites in the Drummond Island Refuge (Lake Huron) was greatly reduced relative to transmitters suspended 1 m above substrate – 78 % of transmitters were not positionable in substrate. Therefore, using a VPS system with only an oviduct inserted transmitter was not a viable approach for determination of time and location of spawning. Most transmitters in the substrate were still heard on some receivers, but at a lower rate compared to suspended transmitters. Thus, manual tracking remains an alternative strategy to determine location but not time of spawning. Low detection probability of oviduct transmitters in substrate does, however, increase the amount of effort required to locate expelled oviduct transmitters using manual tracking. A promising alternative (tested using random walk simulations) was the use of a paired-transmitter experimental design where each fish receives two transmitters, one small transmitter that is expelled with eggs during spawning and a second larger transmitter that remains within the fish after spawning. Accuracy of estimated time and location of transmitter separation, identified with changepoint analysis, varied with degree of spawning site residency and swimming speed, and was dependent on transmitter signal delay. Overall, our results validated the first two assumptions of the oviduct tagging technique. The third assumption appeared feasible using a paired-transmitter design but not using only an oviduct-inserted transmitter. Use of oviduct transmitters in conjunction with positional telemetry has potential to be a powerful tool for studying spawning behavior in lake trout, as well as other fishes. Nonetheless, we recommend that researchers conduct feasibility studies like this one before using oviduct transmitters in a new species.