Assessment of seal fishery interactions in the South East Trawl Fishery (SETF) and the development of fishing practices and seal exclusion devices (SEDs) in the winter blue grenadier fishery to mitigate seal bycatch by SETF trawlers
With the continuing recovery in the size of Australian-based fur seal populations post-sealing, a corresponding increase in seal interactions with domestic fishing vessels is occurring and will continue. There is an urgent need to develop effective seal bycatch prevention procedures to prevent fishing operations from being severely curtailed, or closed down, under the Environment Protection and Biodiversity Conservation Act 1999.
Following the 1999 winter blue grenadier season, incidental seal mortalities emerged as a major issue that threatened the continuation of this fishery; at least that part of the fishery harvested by factory trawlers. These trawlers had successfully developed the fishery, increasing the total grenadier catch from about 3000 t in 1996 to over 9000 t in 1999. The processed value of the factory trawler catch is now around $20 million per year (ASIC 2003) at first sale. The seal deaths in 1999 resulted in significant pressure from some environmental groups to prevent factory trawlers access to this fishery in 2000. This action would have caused significant loss of income in this sector and possibly jeopardised the future participation of factory trawlers in the fishery. There is a strong need for such vessels to demonstrate that seal bycatch can be reduced by adopting appropriate fishing procedures and gears.
It is also likely that pressures will be brought to bear on the ‘wet boats’ fishing for blue grenadier and possibly the rest of the SEF trawl fleet to take measures to reduce incidental seal captures. The study by Knuckey et al. (2002) indicated seal bycatch to occur virtually across the whole multi-species trawl fishery. Some of the results of the development and testing of SEDs and other mitigation measures by the factory trawlers in the targeted ‘single-species’ fishery under this project may be transferable to other vessel operators in the wider multi-species fishery, helping them to avoid many potential operational problems and costs. Increasing the effectiveness of SEDs in both reducing seal mortalities and minimising fish losses would be an important step in helping to gain wider industry acceptance of the potential use of these devices.
Final report
Introducing a Code of Fishing Practice aimed at avoiding seals appeared to halve the incidence of seal bycatch in this fishery. In SED trials, the problems of fish-loss via the SED escape hatch and net blockage via the SED grid were solved by changes in SED design. Although the effectiveness of most SED designs in reducing seal bycatch could not be quantified, the forward facing, ‘top-hatch’ SED design used in 2002 significantly lowered the incidence of seal bycatch in midwater trawl nets. Trials with this design are continuing. Some of the major factors that influence the probability of seal bycatch occurring in this fishery were delineated. Biological sampling of seal fatalities showed the dominant seal bycatch to be sub-adult male Australian fur seals habituated to foraging from trawl nets. Seal tracking studies developed a novel method of tagging seals at sea and indicated that a comparatively small and intransient sub-set of their population interacted with this fishery.
The following recommendations were made in the winter grenadier fishery: use open, forward-facing, ‘top-hatch’ SEDs (or a more effective design if one is developed) in all midwater net shots (or as directed for research purposes); continue the Code of Fishing Practice; continue the shot-by-shot recording of seal bycatch in the SEF1 logbook and maintain a level of scientific observer coverage and biological data collection; and, continue trials of the ‘top-hatch’ SED and gather more information by using underwater filming on the timing and depth–frequency of net entry by seals, and the circumstances of net entry that place seals at risk.
The following recommendations were made in the rest of the SEF trawl fleet: Priority should be given to assessing the nature and extent of seal-fishery activities across the fishery; The Code of Fishing Practice should be followed where practicable; and, At this juncture, SED use should be confined to large midwater trawl nets in areas where seals are known to be common, as more assessment of SED effectiveness is needed before extending their usage.
Project results also assisted the goal of obtaining accreditation for the SEF under a Section 33 determination under this Act.
Keywords: Blue grenadier trawl fishery, seal bycatch mitigation, Seal Exclusion Devices, Australian fur seal biology.
