Benthic Habitats and the Effects of Fishing

Symposium Abstract: Structure and Use of a Continental Slope Seascape: Insights for the Fishing Industry and Marine Resource Managers

A. Williams, B. Barker, R. J. Kloser, N. J. Bax, and A. J. Butler

doi: https://doi.org/10.47886/9781888569605.ch129

Benthic habitats of the upper continental slope seabed (~300-700 m depth) off SE Australia are being surveyed for the first time in response to the needs of regional, ecosystem-based, marine management plans being developed under Australia’s Oceans Policy, and increased commercial fishery reliance on fishes that inhabit the slope seascape. We developed substratum maps of the Big Horseshoe Canyon – one of the region’s prime fishing grounds – using multi-beam acoustic backscatter data, and targetsampled with video cameras and a range of physical samplers. In upper-slope depths, a patchy mosaic of habitats is formed of sloping terraces of muddy substrata and rubble patches that support a sparse benthic epifauna, together with low-relief rocky ridges formed by outcropping claystones and limestones that support communities of erect epifauna dominated by sponges. Many sedentary adult individuals of two key commercial species (pink ling and ocean perch) shelter in a range of microhabitats provided only by the rocky habitats. Video shows that bottom trawls ‘hook-up’ on rocky substratum, turning and moving loose pieces – an observation acknowledged by commercial fishermen who also report that boulders and ‘slabs’ are removed and redistributed. This is evidence of a fishing impact that is, at least in part, irreversible. The question then is, how much impact will adversely affect long-term fishery productivity and conservation values? We discuss this question with respect to managers needs for both the detailed understanding and fine-scale mapping of habitats provided by scientific survey, and the fishing industry’s knowledge of broad-scale habitat distributions that enables extrapolation to a regional fishery scale.