Underwater observations of seal-fishery interactions and the effectiveness of an exclusion device in reducing bycatch in a midwater trawl fishery

Interactions between seals and midwater trawl operations in the Australian Small Pelagic Fishery are common and can be lethal. The nature of interactions and effectiveness of a seal exclusion device (SED) in mitigating lethal interactions was assessed using underwater video. Recent fishing activity and the phase of the trawl operation significantly influenced interaction rates; interactions increased with the amount of recent trawl activity and were highest while the trawl was being set. Most seals accessed the trawl via the net entrance and exited via an escape opening located at the base of the SED. The size of the escape opening was the only operational factor that influenced mortality rates - simply enlarging the escape hole reduced lethal interactions by 79%. However, since all deceased seals dropped out of the net before they were brought on board, they would have gone unobserved without video monitoring. Limiting the concentration of fishing activity in space and time and refinement of the SED design, in particular to address dropouts, is recommended if mortality rates are to be reduced.