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.