Empirical estimates of discard survival are difficult to obtain due to the complex logistics of survival studies, either by accommodating organisms in holding tanks or by tagging. There are few studies on the survival of discards in beam trawl fisheries (Table A 1 in APPENDIX for an overview until 2013), and up till today (March 2014) most of them have focused on the short-term survival using holding facilities in on-board tanks (Depestele et al., 2014; Revill et al., 2013) or underwater cages (Uhlmann et al., 2014; van Marlen et al., 2013). To our knowledge only very limited information is available on successful tagging studies in beam trawl fishery. As a consequence of the complex methodology, there are only a very limited number of species and/or individuals investigated, thus leading to the investigation of yet another modest number of influential factors. The complex logistic nature of onboard survival tank studies, especially when conducted on-board commercial vessels, resulted in a narrow focus of potential key aspects, such as haul duration, number of tickler chains (van Beek et al., 1990), catch weight (Depestele et al., 2014), or maturity (Revill et al., 2013), etc. Major influential factors could nevertheless be numerous. Beam trawl fisheries, as many other fisheries, disturb fish throughout the catching process, starting by the encounter of the chains (or pulses), followed by a stressing period (e.g. fish trying to escape the net) and culminating in a physical and internal damaging process during retention in the codend, release on deck, and subsequent sorting. |
