Implications of the effects of trawling on sessile megazoobenthos on a tropical shelf in northeastern Australia

Abstract

Pitcher, C. R., Poiner, I. R., Hill, B. J., and Burridge, C. Y. 2000. Implications of the effects of trawling on sessile megazoobenthos on a tropical shelf in northeastern Australia. – ICES Journal of Marine Science, 57: 1359–1368. We estimate the possible overall status of populations of attached seabed fauna after 20 years of trawling in Australia’s Great Barrier Reef (GBR), based on the key results of a five-year experimental study that provided an understanding of faunal resilience, in terms of removal rates per trawl. The removal rates of most seabed fauna were between 5 and 20% per trawl (range 0–40%). In attempting to estimate population status, it was also necessary to review patterns of trawl effort intensity and add a simple model for possible recovery dynamics of fauna. Large areas of the GBR are subject to trawling. In 1996, effort was recorded in 1300 statistical grids, each 66 minutes, an area equivalent to 153 000 km 2 .E ffort was highly aggregated among the grids, with about 20% concentrated into 2000–3000 h of effort. More fauna will be removed from grids with higher effort. Though 50–70% of trawled grids have been trawled only lightly (<700–1000 h) each year, over the last 20 years there has been a cumulative effect. A generalized depletion across all trawled grids is likely, but fauna with low vulnerability may be depleted by only 3% overall; medium vulnerability fauna may be depleted by about 20%; and highly vulnerable populations may be depleted by about 55% overall. Because of differential vulnerability, the composition of the faunal community will be substantially altered in most grids, with a shift to less vulnerable species.