Effects of catch composition on the fate of European plaice (Pleuronectes platessa) discarded from Belgian beam trawlers

Uhlmann, Sven Sebastian; Ampe, Bart; Goley, Joanna Marie; Savina, Esther; Broadhurst, Matt K.

doi:10.1016/j.fishres.2023.106616

Cited by 4 publications

(2 citation statements)

References 31 publications

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“…This study has implications for commercially trawled plaice that are exempt from the European landing obligation to not discard any less than MCRS plaice ( STECF, 2023 ). Arguably, as previous research had indicated, discarding plaice that have gone through a commercial beam-trawl capture event in summer is likely to be fatal ( Uhlmann et al., 2016 , 2021 , 2023 ). Accordingly, it can be sensible to grant an actionable exemption in those seasons and regions when release survival can be maximized and routinely collect vitality-relevant parameters during at-sea monitoring campaigns ( Falco et al., 2022 ).…”

Section: Discussionmentioning

confidence: 99%

“…It is likely that under current climate change scenarios, warming seawater temperatures will only further compromise the reasoning behind the existing high survival exemption for plaice. It is reasonable to assume that prolonged summer seasons will occur with more frequency, leading to near-0% survival of commercially discarded plaice ( Uhlmann et al., 2023 ). A northward shift in distribution seems inevitable for plaice ( Townhill et al., 2023 ).…”

Section: Discussionmentioning

confidence: 99%

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The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa)

Uhlmann,

Paoletti,

Ampe

et al. 2024

Conservation Physiology

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Thermal stress can influence the recovery of fish released after capture. Vitality assessments using reflex and behavioural responses require that responses can be observed reliably, independent of temperature. Here, we tested whether reflex and behavioural impairment and survival of beam-trawled and discarded European plaice (Pleuronectes platessa) are independent from seasonal air and water temperature deviations. In total, 324 beam-trawled plaice (n = 196 in summer and n = 128 in winter) were exposed to two air temperature treatments and two water treatments (i.e. modified and ambient temperatures for both). The modified treatments (i.e. cooled in summer, warmed in winter) represent the thermal shock a fish may experience when being returned to the water. All reflexes and tested behaviours were affected by ambient temperature, with high impairment noted in summer. None of the reflexes were affected by temperature shocks alone, only body flex was. Body flex was highly impaired under every exposure combination. Fish size and duration of air exposure further influenced impairment of reflexes such as head complex and tail grab. More generally, post-release survival was assessed as 21% [95% CI: 16–28%] in summer and 99% [97–100%] in winter. Beam trawling in summer is likely to induce high reflex impairment and mortality in discarded plaice, and therefore spatial–temporal mitigation approaches should be prioritized over control of on-board temperatures.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa)

Uhlmann,

Paoletti,

Ampe

et al. 2024

Conservation Physiology

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Short-term discard survival and catch-related trauma in European plaice (Pleuronectes platessa) caught in the Baltic Sea by Danish seine during summer

Ern,

Faber,

Madsen

2025

Fisheries Research

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Optimizing the prediction of discard survival of bottom-trawled plaice based on vitality indicators

Uhlmann,

Savina,

Karlsen

et al. 2024

Conservation Physiology

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Predicting the discard survival of aquatic animals after fisheries capture using vitality indicators (i.e. individual scores or indices of physical condition) is a resource-efficient approach compared to estimating discard survival from captive observation. But such indicators do not always lead to accurate and robust predictions. Individual scores of reflex impairments and injuries are typically given the same weight when being aggregated into an index, while some reflexes or injuries may contribute to mortality more than others. This study established an analytical methodology and created an index based on differential contributions of individual reflexes and injuries to optimize the prediction of discard survival of bottom-trawled European plaice (Pleuronectes platessa). The optimization procedures were applied to a dataset from vitality assessment of 1122 undersized plaice caught during 16 commercial fishing trips and 58 gear deployments in Belgium and Denmark. As welfare indicators, we considered and evaluated against post-capture survival of plaice: original vs. optimized reflex impairment and injury (R&I) index, number of absent reflexes, number of present injuries, number of absent reflexes and present injuries, categorical vitality score and individual reflex and injury scores. These were used in eight candidate generalized linear models (one without any vitality indicator) as explanatory variables to predict survival, with or without biological, environmental, technical and operational covariates, either at the individual fish or trip level. Bruising to the head and body were the most relevant predictors. The optimized R&I index did not perform better than any other vitality indicator, and all the indicators performed poorly in predicting survival probability both at the fish and trip levels without information on air exposure and seawater temperature. This means that they cannot be considered to be independent measures. The categorical vitality score provided a viable alternative to the more labour-intensive, scoring method of reflex responsiveness. Use of reflexes as proxies may not be accurate when they are not independent of environmental, biological or technical variables.

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Effects of catch composition on the fate of European plaice (Pleuronectes platessa) discarded from Belgian beam trawlers

Cited by 4 publications

References 31 publications

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa)

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa)

Short-term discard survival and catch-related trauma in European plaice (Pleuronectes platessa) caught in the Baltic Sea by Danish seine during summer

Optimizing the prediction of discard survival of bottom-trawled plaice based on vitality indicators

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