Trawl operations in the South East Fishery, Australia: spatial distribution and intensity

Abstract

Trawl areas and intensities were mapped at coarse (22 km 1986–99)and fine (1 km 1995–99)scales, and statistics reported by area and depth stratum. Total effort in hours was relatively stable to 1992, then increased substantially to 1999. The total distance trawled from fine-scale analysis showed a similar trend for the 1995–99 period. Coarse-scale analysis from 1986–99 indicated effort increases in north-east Bass Strait in particular, and also off western Tasmania and west of Bass Strait. There was little change in the total area of the fishery from 1995 to 1999, but grid cells on the periphery showed considerable interannual variation in the presence or absence of fishing. Increased or redistributed effort tended to further concentrate in the relatively small high-effort areas, rather than increasing equally across the grounds, or spreading to new grounds. In the total management area, a small proportion of the 1 km grids was fished. However, in 200–1000 m depth strata, ≥50%of the grids were fished with some intensity. The consequences and compromises of spatial scale are discussed in terms of data quality, the use of trawl effort as a surrogate for marine disturbance, and the interpretation of catch rates.