Foreign trawling off NW Australia (1960-1980s) caused extensive impact on benthic and fish communities reflected in a 2-orders of magnitude reduction in sponge bycatch and high value emperor fish stocks giving way to low value lizard fish and threadfin bream. This process was investigated in the largest ever adaptive management experiment on a commercial fishery using a series of closures in the 1980s-early 1990s. This gave rise to the current management arrangements for the Pilbara Trawl Fishery which has protected some previously heavily trawled areas in long term closures. A quarter century on, this situation and the awarding of 4 weeks RV Investigator time in late 2017 provides the opportunity to quantitatively examine >35 years recovery of trawled habitat and to determine whether the climax community of large sponges and the fish communities they supported ever fully recovered. NW Australia is uniquely able to provide long term information for VME habitats that is directly applicable to several trawl fisheries in northern Australia and is potentially the only source of such information internationally for adoption by FAO/MSC. Further, NW Australia is uniquely able to test new methods proposed for Ecological Risk Assessment of seabed impacts and validate their reliability. Lastly, both the Pilbara Trawl and Trap Fisheries are looking towards Fishery Improvement Plans and/or MSC certification and will require the information obtained in this project.
Final report
This project investigated the extent to which trawled communities of Australia’s North-West Shelf have recovered from high levels of trawling before the exclusion of foreign fleets in 1990 and after the imposition of tight controls on trawl and trap fishing in the early 1990s. The results suggest the region has largely recovered from the effects of heavy foreign trawling and that the existing trawl effort is not impacting on habitat-forming filter feeder benthic habitats or fish stocks to a level that affects the health of either. The overall aims of the adaptive management experiment in the 1980s and 1990s and the fisheries management arrangements were achieved. The project also supported the premise that filter-feeder habitats support, or are at least associated with, a higher biomass and diversity of demersal fish species. There is little evidence that fishing effort since 2005 has prevented continued recovery of filter feeder habitats.
More information: john.keesing@csiro.au
