Lines snag spines! A field test of recreational angling gear ensnarement of Bythotrephes

Branstrator DK, Dumke JD, Brady VJ, Wellard Kelly HA. 2021. Lines snag spines! A field test of recreational angling gear ensnarement of Bythotrephes. Lake Reserv Manage. 37:391–405. Recreational angling gear is a high-risk pathway of dispersal for the invasive spiny water flea (Bythotrephes cederströmii). We measured the number of Bythotrephes individuals ensnared on trolled shallow angling lines (3 line materials), a trolled downrigger angling line, a trolled downrigger steel cable, a trolled simulated livewell, a trolled bait bucket, and stationary anchor ropes (3 rope materials) in 2 Minnesota (United States) lakes. The shallow angling lines and the downrigger angling line had the greatest mean ensnarement rates (number of Bythotrephes individuals ensnared/transect transit), followed by the downrigger cable and the livewell, followed by the bait bucket and the anchor ropes. Added together, the shallow angling lines (as a mean of the 3 line materials) and the downrigger angling line accounted for 87–88% of the mean total ensnarement rate. Among the shallow angling lines, monofilament and fluorocarbon lines had greater mean ensnarement rates than braided line but the distinction was only statistically significant in one of the 2 lakes. The ensnarement rate of all angling gear combined was positively related to the density of Bythotrephes in the water column at the time of study (ambient density). On the downrigger angling line (monofilament), instar-3 Bythotrephes were ensnared at a relative frequency disproportionately greater than ambient density would predict, while instar-1 Bythotrephes were ensnared at a relative frequency disproportionately less than ambient density would predict. Our results suggest that education and outreach messaging should include instructions on removing Bythotrephes from angling lines in addition to the reminder to drain all water.