Dataset Information

Behavioural and welfare implications of a new slipping methodology for purse seine fisheries in Norwegian waters.

ABSTRACT: The release of unwanted fish from purse seines whilst still in the water is termed slipping and may lead to significant mortality following release. The objective of this study was to determine the fish welfare implications of a new slipping methodology in which fish are released via a discharge opening formed in the bunt end of the purse seine net. Video analyses of collective and individual level fish behaviour were undertaken in the Norwegian mackerel and herring purse seine fisheries, to quantitively describe slipping behaviour and to determine its driving factors. The majority of fish escaped the purse seine with the schooling structure intact as part of large groups towards the end of slipping process, increasing their speed following escape. However, there was also a tendency (24% of all escapes) to escape in a manner likely to impact negatively upon their welfare, with a breakdown in schooling structure and physical contact with the fishing gear and conspecifics. The tendency to express such welfare compromising behaviour was higher for mackerel than for herring, but was also influenced by the vessel releasing the fish, the amount of fish being slipped, how long the discharge opening had been open and the particular slipping event. These results provide important information for future science-based development of welfare friendly slipping practises.

SUBMITTER: Anders N

PROVIDER: S-EPMC6411124 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Behavioural and welfare implications of a new slipping methodology for purse seine fisheries in Norwegian waters.

Anders Neil N Breen Mike M Saltskår Jostein J Totland Bjørn B Øvredal Jan Tore JT Vold Aud A

PloS one 20190311 3

The release of unwanted fish from purse seines whilst still in the water is termed slipping and may lead to significant mortality following release. The objective of this study was to determine the fish welfare implications of a new slipping methodology in which fish are released via a discharge opening formed in the bunt end of the purse seine net. Video analyses of collective and individual level fish behaviour were undertaken in the Norwegian mackerel and herring purse seine fisheries, to qua ...[more]

PMID: 30856224

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Project description:Tuna fisheries catch over three million tonnes of skipjack tuna (Katsuwonus pelamis) each year, the majority of which come from purse-seine vessels targeting fish associated with man-made fish aggregating devices (FADs). A significant challenge for fisheries management is to maximize the efficiency of skipjack tuna catches whilst minimizing the bycatch of small and immature bigeye (Thunnus obesus) and yellowfin (T. albacares) tuna, for which long-term sustainability is uncertain in 75% of the world's stocks. To better manage the issues common with this fishing method, an improved understanding of tuna behaviour around FADs is necessary. We probabilistically classified the vertical behavioural patterns of 50 bigeye and 35 yellowfin tuna (mean fork length 72cm and 70cm, respectively) electronically tagged throughout the western and central Pacific Ocean into shallow and deep states, using a state-space modelling approach. The occurrence of surface-association behaviours, defined as an individual remaining in a shallow state for 24-hours, was examined in relation to known capture events and FAD density. In general, surface-association events for both species were short and lasted on average less than three days, although events as long as 28 days were observed, and were more common in yellowfin when in archipelagic waters. Events were longest immediately following tagging in 62% and 17% of bigeye and yellowfin, respectively. Surface-association behaviour was not generally estimated just prior to recapture, being either non-existent or shorter than two days for 85% of bigeye and 74% of yellowfin. Current management measures in purse-seine tuna fisheries involve periodic or spatial closures for FAD use. If the chief benefit to purse-seine fishers of surface-association around floating objects is in locating schools in horizontal space at short-term time-scales, rather than holding fish near the surface for extended periods, controlling the number of sets made on FADs should be explored further as an additional management tool.

Project description:A proposition addressed here is that, although bitted horses are viewed by many equestrians as being largely free of bit-related mouth pain, it seems likely that most behavioural signs of such pain are simply not recognised. Background information is provided on the following: the major features of pain generation and experience; cerebrocortical involvement in the conscious experience of pain by mammals; the numerous other subjective experiences mammals can have; adjunct physiological responses to pain; some general feature of behavioural responses to pain; and the neural bases of sensations generated within the mouth. Mouth pain in horses is then discussed. The areas considered exclude dental disease, but they include the stimulation of pain receptors by bits in the interdental space, the tongue, the commissures of the mouth, and the buccal mucosa. Compression, laceration, inflammation, impeded tissue blood flow, and tissue stretching are evaluated as noxious stimuli. The high pain sensitivity of the interdental space is described, as are likely increases in pain sensitivity due to repeated bit contact with bruises, cuts, tears, and/or ulcers wherever they are located in the mouth. Behavioural indices of mouth pain are then identified by contrasting the behaviours of horses when wearing bitted bridles, when changed from bitted to bit-free bridles, and when free-roaming unbitted in the wild. Observed indicative behaviours involve mouth movements, head-neck position, and facial expression ("pain face"), as well as characteristic body movements and gait. The welfare impacts of bit-related pain include the noxiousness of the pain itself as well as likely anxiety when anticipating the pain and fear whilst experiencing it, especially if the pain is severe. In addition, particular mouth behaviours impede airflow within the air passages of the upper respiratory system, effects that, in their turn, adversely affect the air passages in the lungs. Here, they increase airflow resistance and decrease alveolar gas exchange, giving rise to suffocating experiences of breathlessness. In addition, breathlessness is a likely consequence of the low jowl angles commonly maintained during dressage. If severe, as with pain, the prospect of breathlessness is likely to give rise to anxiety and the direct experience of breathlessness to fear. The related components of welfare compromise therefore likely involve pain, breathlessness, anxiety, and fear. Finally, a 12-point strategy is proposed to give greater impetus to a wider adoption of bit-free bridles in order to avoid bit-induced mouth pain.

Dataset Information

Behavioural and welfare implications of a new slipping methodology for purse seine fisheries in Norwegian waters.

Publications

Behavioural and welfare implications of a new slipping methodology for purse seine fisheries in Norwegian waters.

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