Abstract
Biotelemetry is a central tool for fisheries management, with the implantation of transmitters into animals requiring refined surgical techniques that maximize retention rates and fish welfare. Even following successful surgery, long-term post-release survival rates can vary considerably, although knowledge is limited for many species. The aim here was to investigate the post-tagging survival rates in the wild of two lowland river fish species, common bream Abramis brama and northern pike Esox lucius, following their intra-peritoneal double-tagging with acoustic transmitters and passive integrated transponder (PIT) tags. Survival over a 2-year period was assessed using acoustic transmitter data in Cox proportional hazards models. Post-tagging survival rates were lowest in the reproductive periods of both species, but in bream, fish tagged just prior to spawning actually had the highest subsequent survival rates. Pike survival was influenced by sex, with males generally surviving longer than females. PIT tag detections at fixed stations identified bream that remained active, despite loss of an acoustic transmitter signal. In these instances, loss of the acoustic signal occurred up to 215 days post-tagging and only during late spring or summer, indicating a role of elevated temperature, while PIT detections occurred between 18 and 359 days after the final acoustic detections. Biotelemetry studies must thus always consider the date of tagging as a fundamental component of study designs to avoid tagged fish having premature end points within telemetry studies.
Highlights
Biotelemetry has developed into a central tool for fisheries management, providing valuable information on population dynamics, fish behaviours and movements, habitat connectivity, and even interspecific relationships (e.g., Halfyard et al, 2017; Hussey et al, 2015)
As the diversity of tracking technologies and tracked fish species expands, including a wider range of fish sizes and morphologies, such as Anguillids and flatfish (Neves et al, 2018; Thorstad et al, 2013), knowledge gaps surrounding the effects of telemetry are potentially widening
The duration of acoustic tracking of “Lost” fish, prior to a signal becoming inactive or stationary, ranged from 37 to 215 days, and final detections all occurred during late spring or early summer (Table 3), which corresponds with the trend described in the bream Cox proportional hazards (CPH) model (Figure. 3b)
Summary
Research objectives, study design, and data interpretation are driven by knowledge of the impacts of tagging on fish survival and behaviour (Donaldson et al, 2014) This includes the planning of sampling and release protocols, tagging procedures and timeframes of subsequent telemetry (Bolland et al, 2019). As the diversity of tracking technologies and tracked fish species expands, including a wider range of fish sizes and morphologies, such as Anguillids and flatfish (Neves et al, 2018; Thorstad et al, 2013), knowledge gaps surrounding the effects of telemetry are potentially widening This can be especially problematic for researchers studying species where information is more limited, as it constrains their ability to optimize tagging procedures in relation to maximizing fish welfare and survival or draw robust conclusions from the resulting data. The study objectives were to (a) assess the survival rates of the two fishes in relation to their individual characteristics, and the timing and location of tagging; and (b) for those fish that did not survive within the study, assess their fate (death, leaving the study area, or loss of the acoustic tag signal, such as through tag failure or tag expulsion)
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