Identifying barriers to the detection of passive integrated transponder (PIT) tags in southern brook lamprey ammocoetes (Ichthyomyzon gagei, Hubbs & Trautman, 1937)

Caleb A. Aldridge, Bradley M. Richardson, David A. Schumann, and Michael E. Colvin

Southern Brook Lamprey Research Group Department Wildlife, Fisheries & Aquaculture, Thompson Hall Box 9690 Mississippi State University, Mississippi State, MS, 39762

Abstract for an upcoming talks at the Southeastern Fishes Council meeting at McCormick, South Carolina November 8-9, 2018

The southern brook lamprey (Ichthyomyzon gagei) is a primitive, nonparasitic, filiform fish that inhabits streams of the Southeastern USA. Little is known about the species, especially in their cryptic larval form (i.e., ammocoetes) which burrow into fine sediment. The presence of southern brook lamprey populations suggest good stream quality; they may also help maintain stream integrity (e.g., nutrient cycling). As part of a comprehensive study of southern brook lamprey ecology in Mississippi, we surgically implanted passive integrated transponder (PIT) tags into the peritoneal cavity of ammocoetes. Although short-term survival and tag retention was high (100%), the percentage of released individuals detected in subsequent sampling efforts was low compared to hidden PIT tag analogs (5.36 ± 0.04 % and 66.07 ± 0.10 %, respectively). To understand, in part, this discrepancy, we varied sediment depth (0–30 cm; 3 cm intervals) above analogs in laboratorium. At each interval we measured the response of each analog, detected (1) or not (0), with a PIT tag reader. The analogs were then measured at the same depth intervals but without sediment (i.e., control). We modeled analog detection as a function of substrate type and depth to describe the influence of ammocoete burrowing behavior on the detections of tagged individuals. Substrate type (eß = 0.04 , Wald’s χ2 = 17.84, p = <0.01) and depth (eß = 0.64, Wald’s χ2 = 37.75, p = <0.01) affected the detection probability of analogs. The estimated detection probability of analogs at 12 cm (typical ammocoete length) in sand was estimated at 41.7% compared to 95.2% in no substrate. Further investigation into ammocoete burrowing habits will improve expected detection probabilities and sampling approaches. This experiment provides a small but needed piece of information when using PIT tags in studying and conserving this unique species.