Effects on individual level behaviour in mackerel (Scomber scombrus) of sub-lethal capture related stressors: Crowding and hypoxia.

Neil Anders,Nils Olav Handegard,Bjørn Totland,Maria Tenningen,Kirsten Howarth,Michael Breen,Antonio Medina Guerrero

doi:10.1371/journal.pone.0213709

Neil Anders, Nils Olav Handegard + Show 5 more

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https://doi.org/10.1371/journal.pone.0213709

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Abstract

Stress to fish during harvest in wild capture fisheries is known to negatively influence subsequent survival in catches that are released. Therefore, if fisheries are to be conducted sustainably, there is a need to promote good fish welfare during the capture process. Purse seine fishing is a widespread and efficient fishing method. However, capture and release of fish from purse seines (a process called “slipping”) can result in extremely high mortality in small pelagic schooling species. The objective of this study was to establish behavioural indicators of sub-lethal stress in Atlantic mackerel (Scomber scombrus) that may be used to set safe threshold limits for use in commercial purse seine fishing, in order to ensure good fish welfare and thereby minimise slipping mortality. Controlled mesocosm scale experiments with schools of mackerel in net pens were undertaken to determine behavioural responses to simulated purse seine capture stressors of “crowding”, “hypoxia” and “crowding & hypoxia”. Crowding (at 30 kg.m-3) was achieved by reducing the volume of the net pen, while hypoxia (to 40% oxygen saturation) was achieved by surrounding the net pen with a tarpaulin bag to prevent water exchange. Using video analysis, we investigated behavioural responses in nearest neighbour distances, nearest neighbour angular deviations, tail beat amplitude and tail beat frequency (TBF). Of the metrics considered, only TBF showed a response; a significant increase to “crowding” (42% increase) and “crowding & hypoxia” (38% increase) was found. The increase in TBF in response to “hypoxia” alone (29% increase) was not significant. We therefore conclude that increases in tail beat frequency may be used as an indicator of sub-lethal purse seine capture stress in mackerel that may have utility in minimising post slipping mortality.

Highlights

Stress prior to the escape, release or slaughter of wild fish caught by fishing gear has been shown to reduce subsequent fitness [1], survival [2,3,4] and resulting product quality [5,6,7,8,9]
We report on mesocosm scale experiments to determine individual level behavioural stress indicators in response to simulated sub-lethal purse seine capture stressors in schools of Atlantic mackerel (Scomber scombrus)
No response in nearest neighbour distance (NND), angular deviation in pitch (ADP) or angular deviation in yaw (ADY) could be detected and likewise we detected no response in tail beat amplitude (TBA) to either “crowding” or “crowding and hypoxia” treatments

Summary

Introduction

Stress prior to the escape, release or slaughter of wild fish caught by fishing gear has been shown to reduce subsequent fitness [1], survival [2,3,4] and resulting product quality [5,6,7,8,9]. The minimisation of stress to promote good fish welfare during capture should be of paramount concern for ethical, sustainable and profitable wild capture fisheries. In order to promote good welfare, objective and measurable indicators of stress are required. Physiological measures may be used [10] and have been widely applied in studies examining stress responses to fisheries capture [7,11,12]. Behavioural indicators of stress are, relatively easy to observe, non-invasive to record and potentially non-intrusive [15]. They are a more holistic and often more immediate expression of the stress response, reflecting underlying neurological and physiological changes [16,17,18,19]

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