Study

Post-capture survival of whale sharks encircled in tuna purse-seine nets: tagging and safe release methods

  • Published source details Escalle L., Murua H., Amande J.M., Arregui I., Chavance P., Delgado d.M.A., Gaertner D., Fraile I., Filmalter J.D., Santiago J., Forget F., Arrizabalaga H., Dagorn L. & Merigot B. (2016) Post-capture survival of whale sharks encircled in tuna purse-seine nets: tagging and safe release methods. Fisheries Research, 26, 782-789.

Actions

This study is summarised as evidence for the following.

Action Category

Establish handling and release protocols in non-recreational fisheries

Action Link
Marine Fish Conservation
  1. Establish handling and release protocols in non-recreational fisheries

    A study in 2014 in pelagic waters of the eastern Atlantic Ocean off the African continent (Escalle et al. 2016) reported that tracked whale sharks Rhincodon typus released using an enhanced protocol from purse-seine nets targeting tuna Thunnus spp. survived for at least 21 days and movements showed no unusual behaviour. Of six satellite-tagged whale sharks, data were transmitted only from five (the fate of the other was unknown) for a period of at least 21 days following shark release. Three tags detached at the programmed 30 days after release, and two at 21 and 71 days (programmed to 30 and 90 days respectively). The detachment after 21 days was due to a deep dive, and the cause of the detachment after 71 days was unknown, although all sharks were assumed to have survived post-release from the purse-seine nets. Movement patterns, including vertical dives, were considered within normal behaviour (data presented graphically). Six whale sharks were tagged after capture in tuna purse-seine nets in the eastern Atlantic in 2014. Sharks were released using an improved version of a previously proposed method involving a cable being first fed through the net, then attached to the opposite edge of the net near the whale shark’s head. The net is then slackened, and the cable tightened to position it underneath the whale shark’s head, which rolls over the float line of the net as the cable is tightened. The float line then sinks with the weight of the shark, which rolls out of the net as the cable is alternately tightened and slackened. Full details of the handling methods are provided in the original study.

    (Summarised by: Leo Clarke)

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