Migration and Histologic Effects of Visible Implant Elastomer (VIE) and Passive Integrated Transponder (PIT) Tags in the Marine Toad (Rhinella marina)

Passive integrated transponder (PIT) and visible implant elastomer (VIE) tags are commonly used to identify reptiles, amphibians, and fish. Despite reports of good retention rates and little to no negative effect on survival time, migration remains a concern and histologic changes have not been widely evaluated. Fifty-six wild-caught marine toads (Rhinella marina) were marked with a PIT tag in the left caudal thigh and a VIE tag over the right gastrocnemius muscle prior to transport to the North Carolina Zoo. Fourteen toads were then humanely euthanized on day 9, 15, 32, and 62 for postmortem examination and histopathology which were compared to 10 control toads with no tags. All PIT tags were functional and 95% remained at the insertion site with minimal to no histologic changes. Externally, 48% of VIE tags were visible through the skin at the original site of injection under fluorescent or UV light. Upon gross examination of the tissues, VIE tags had an overall retention rate of 62% at the injection site, with similar retention rates across time points. Migrated VIE material was visible grossly and histologically in the kidneys of 98% of toads and along the right leg, proximally and distally, in 25% of toads. VIE material was also found sporadically in mesentery, colon, and free in the coelomic cavity. Histologically, VIE material in the skin was surrounded by minimal to mild granulomatous inflammation while in the kidney it was associated with dilation of the small vessels, edema, and granulomatous nephritis that progressed in severity over time. Based on these findings, the authors recommend the use of PIT tags over VIE tags for identification of adult anurans, when feasible.

Incorporating antenna detections into abundance estimates of fish

Autonomous passive integrated transponder (PIT) tag antennas are commonly used to detect fish marked with PIT tags but cannot detect unmarked fish, creating challenges for abundance estimation. Here we describe an approach to estimate abundance from paired physical capture and antenna detection data in closed and open mark-recapture models. Additionally, for open models, we develop an approach that incorporates uncertainty in fish size, because fish size changes through time (as fish grow bigger) but is unknown if fish are not physically captured (e.g., only detected on antennas). Incorporation of size uncertainty allows for estimation of size-specific abundances and demonstrates a generally useful method for obtaining state-specific abundances estimates under state uncertainty. Simulation studies comparing models with and without antenna detections illustrate that the benefit of our approach increases as a larger proportion of the population is marked. When applied to two field data sets, our approach to incorporating antenna detections reduced uncertainty in abundance substantially. We conclude that PIT antennas hold great potential for improving abundance estimation, despite the challenges they present.

Turning Pools in Stepped Fishways: Biological Assessment via Fish Response and CFD Models

With the aim of building more compact fishways and adapting them to field conditions to improve their location by fish, it is common to use turning pools, reducing the longitudinal development of the construction. However, depending on their design, turning pools may affect the hydraulic performance of the fishway and consequently the fish passage. To study these phenomena, turning pools in a vertical slot and in different configurations of submerged notches with bottom orifice fishway types were assessed. Both types of fishways were studied using numerical 3D models via OpenFOAM, a computational fluid dynamics software, in combination with fish responses, assessed with PIT (Passive Integrated Transponder) tag telemetry for three different species of potamodromous cyprinids in several fishways. Results show differences between the hydrodynamics of straight and turning pools, with lower values in the hydrodynamic variables in turning pools. Regarding fish behavior, the ascent was slower in turning pools but with no effect on passage success and without being a problem for fish migration. This information validates the use of turning pools as a key design component for fishways for studied species.