Negative feedback concept in tagging: Ghost tags imperil the long-term monitoring of fishes

Abstract

Wildlife monitoring using passive telemetry has become a robust method for investigating animal migration. With increased use, this method progressively pollutes the environment with technological waste represented by so called ghost tags (PIT tags ending in the environment due to reproductive expulsions, shedding or animal mortality). However, their presence in the environment may lead to failed detections of living individuals. We used tagging data from studies of the asp Leuciscus aspius and the bleak Alburnus alburnus collected from 2014 to 2018 and located ghost tag positions on the monitored spawning site using portable backpack reader for their detection. We modelled virtual river-wide flat-bed antennas (widths 0.2, 0.4, 0.6 and 0.8 m) representing monitoring effort and estimated the probability of the presence of ghost tags within the antenna field. Of 3724 PIT tags used in the study, we detected on the spawning ground 173 ghost tags originating from long-term monitoring. The ghost tags accumulated in the environment in time, suggesting insufficient degradation rate or shift downstream from the research site. Number of ghost tags present on the spawning ground led to high probability of disabled readings of tagged fish passing through the antenna electromagnetic field. We demonstrate how accumulated ghost tags may cause detection failures for focal species and incomplete data acquisition. We infer that intensive long-term monitoring using PIT tag technology may encumber future data acquisition or entail additional costs for clean-up.

Using PIT‐tags and portable antennas for quantification of fish movement and survival in streams under different environmental conditions

“…Movement patterns can be used to discriminate ghost tags (Stout et al ., 2019), although ghost tag displacements can mimic fish movements (Bond et al ., 2019), as ghost tags can be displaced downstream by currents and carcasses can be carried over large distances both upstream and downstream by scavengers (Havn et al ., 2017). In addition, accumulation of ghost tags can decrease the detection efficiency when tracking because of ‘tag collision’ and generate a source of error for future studies (Šmejkal et al ., 2020).…”

Does Fish Conditioning in Aquaculture Increase Survival Success in the Wild? A Case Study on a Cyprinid Fish

“…In 2021, the fish were two years old and will be mature in two to three years. Their detection by passive telemetry arrays during reproductive migration [67,68] may shed more light on the survival among groups and verify the current significance of the data. Assessing survival to adulthood by detecting spawning individuals could therefore be more accurate than the methods used to collect the currently available data.…”

Movement and mortality of invasive suckermouth armored catfish during a spearfishing control experiment

“…This project is not without limitations and caveats that could be explored in the future. One potential limitation is the presence of ghost tags , or tags that were expelled, shed, or left after fish mortality that could potentially be interpreted as tagged fish (Šmejkal et al 2020 ). To combat the potential effects of ghost tags, we made note of individuals that remained entirely stationary across multiple tracking events and removed those individuals from the analysis.…”

“…To combat the potential effects of ghost tags, we made note of individuals that remained entirely stationary across multiple tracking events and removed those individuals from the analysis. We also retrieved shed tags from the river as suggested by Šmejkal et al ( 2020 ). A second limitation is that the scope of our study only included relocation events near the site of tagging, which likely biased movement and space use towards stationary fish that used little space (Gowan et al 1994 ).…”