Duluth WRS Seminar

Lines Snag Spines! A field test of angling gear ensnarement of Bythotrephes


Dr. Donn Branstrator
UMD Dept. of Biology

September 14, 2020


Recreational angling gear is a high-risk pathway for the dispersal of spiny water flea (Bythotrephes cederströmii), a nonindigenous invasive zooplankter. We measured the number of
Bythotrephes ensnared on trolled shallow and downrigger angling lines, a trolled downrigger steel cable, a trolled bait bucket, a simulated livewell, and stationary anchor ropes in 2 Minnesota (United States) lakes. The shallow and downrigger angling lines had the greatest mean ensnarement rates (number of individuals ensnared/transect), followed by the downrigger cable and livewell, followed by the anchor ropes and bait bucket. Taken together, the shallow and downrigger angling lines accounted for 87-88% of the mean total ensnarement rate of Bythotrephes. Among shallow angling lines, monofilament and fluorocarbon lines had greater mean ensnarement rates than braided line but the distinction was only statistically significant in 1 of 2 lakes. Ensnarement rate of all gear combined was positively related to the ambient density of Bythotrephes. There was no effect of time of day (daytime versus twilight) on ensnarement rate. In Lake Mille Lacs (which supports cisco [Coregonus artedi]) the mean ensnarement rate of Bythotrephes was greater on the shallow angling lines (as a mean of 3 lines deployed) than on the downrigger angling line, but this pattern was reversed in Island Lake Reservoir (which lacks cisco). Our results offer empirical evidence relevant to education and outreach messaging around human-assisted dispersal of Bythotrephes.

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