Predicting the factors influencing the inter‐ and intraspecific survival rates of riverine fishes implanted with acoustic transmitters

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.

Acoustic telemetry reveals strong spatial preferences and mixing during successive spawning periods in a partially migratory common bream population

“…After applying data restrictions, the 2018 dataset comprised the movements of 13 resident and nine migrant bream (of 76 tagged), while the 2019 dataset comprised 30 residents and 22 migrants (of 181 tagged), and the 2020 dataset comprised 20 residents and 13 migrants (of 181 tagged; Table 1). Loss of bream from the study was higher than expected by natural mortality alone, but we provide evidence to suggest tagging date and tag expulsion were contributing factors (Winter et al 2020). For fish detected in multiple years, including those classified 'other' (n = 40), 88% were consistent in their type of movement behaviour (resident/migrant/other) across years.…”

Movements of common bream Abramis brama in a highly connected, lowland wetland reveal sub‐populations with diverse migration strategies

“…Of the remaining fish used in analyses, 116 transitioned to the Lost state during the study period (of which 2 bream emigrated from the monitored area), while 57 were detected within 3 months of the study end‐date and therefore considered living at the end of the study. The loss rate was considered higher than expected from natural mortality alone; however, evidence suggested that acoustic tag expulsion contributed to the loss of some bream from the study (Winter et al., 2020). Bream were recorded at 53 of the 56 acoustic receivers in the study area, including all receivers placed in the mainstem Bure, Ant, and Thurne across approximately 60 km of river length (Figure 1).…”

“…Season was defined as: spring (1 March–31 May); summer (1 June–31 August); autumn (1 September–30 November); and winter (1 December to 28 February). Covariate effects (β) were explored only for movements between the river reaches and not for transitions between the reaches and the Lost state (see Winter et al., 2020 for an analysis of bream post‐tagging survival). Hazard ratios (HR; exp(β)) indicated the strength of covariate effects; HR < 1 indicated a negative effect, HR = 1 was no effect, and HR > 1 indicated a positive effect.…”