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

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. T otal effort in hours was relatively stable to 1992, then increased substant ially 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 i ndicated effort increases in north-east Bass Strait in particular, and also off western Tasmania and west of Bass Strait. There was little change in t he total area of the fishery from 1995 to 1999, but grid cells on the perip hery showed considerable interannual variation in the presence or absence o f fishing. Increased or redistributed effort tended to further concentrate in the relatively small high-effort areas, rather than increasing equally a cross the grounds, or spreading to new grounds. In the total management are a, a small proportion of the 1 km grids was fished. However, in 200-1000 m depth strata, greater than or equal to 50% of the grids were fished with so me intensity. The consequences and compromises of spatial scale are discuss ed in terms of data quality, the use of trawl effort as a surrogate for mar ine disturbance, and the interpretation of catch rates.