Effects of Trawling Subprogram: dynamics of large sessile seabed fauna important for structural fisheries habitat and biodiversity of marine ecosystems, and use of these habitats by key finfish species
CSIRO Oceans and Atmosphere Hobart
Roland C. Pitcher
Predicting the response of megabenthos to the establishment of refuge/replenishment areas and acquiring an understanding of the ecological interactions between trawled and refuge areas are both essential steps in the effective design of refuges for fisheries habitat and the stocks they support. They are also necessary for the development of alternative fishing strategies that have less impact on habitat. To achieve these goals, it will be necessary first to obtain information on the recovery rates of habitat and then the processes which link trawled areas and refuges. We propose to investigate the population dynamics (recruitment, growth, mortality, reproduction) of structurally dominant megabenthos habitat organisms and document the relationship between benthic habitat and ecological usage by important commercial finfish species. These issues — habitat dynamics and processes — have also been identified at FRDC workshops as high priority areas for future research. Also identified as high priority, especially by managers of tropical finfishes, is the need for finfish resource monitoring. To this end, we also propose to examine environmentally-friendly, fishery-independent techniques for measuring finfish abundance, including remote (baited) video stations and acoustics. Documentation of fish-megabenthos associations is the first step toward mapping the spatial distribution of snapper and emperor grounds on the basis of key habitat proxies, a process now underway in the development of an Interim Marine and Coastal Regionalisation of Australia. Alternative fishing strategies which have less impact on habitat and lead to increased productivity among commercial species will, by preserving critical habitat in refuges, in turn help reduce conflict between commercial extractive activities and conservation. It will also improve the public perception of trawling. Two possible alternative strategies include: changing from fish-trawl to non-trawl methods; and changing trawling strategies to corridor trawling, in order to allow former trawling grounds to recover and resume their role as fisheries habitat supplying stock to the trawl corridors, whilst maintaining or even enhancing catch rates. In either case, the recovery time frames for the seabed habitat — and hence fisheries resources — are important, because they will influence the economic feasibility of switching to alternative fishing strategies. The results of this study will become increasingly important as the requirement for ecologically sustainable fisheries management is implemented in trawl fisheries from the temperate zone to the tropics. The lessons learned from this study in the form of knowledge of habitat dynamics, and methods for monitoring habitats and commercial stocks will contribute to a rational balance between ecologically sustainable fishing, biodiversity and conservation when ESD related management changes are implemented in those Australian fisheries dependent on seabed habitat.
1. To determine the dynamics (recruitment, growth, mortality, and reproduction) of structurally dominant large seabed habitat organisms (ie. megabenthos = sponges, gorgonians, and alcyonarians and corals etc) important for demersal fisheries habitat and biodiversity of the seabed environment, in a tropical region (ie. GBR).
2. To model the dynamics of seabed habitat and predict the potential of trawled grounds to recover and resume their role as prime fisheries habitat.
3. To document the ecological usage of living epibenthic habitat by key commercial finfish species, in terms of species micro-distribution, shelter requirements, and food chain links.
4. To assess three fishery-independent and "environmentally-friendly" techniques for surveying tropical finfish resource abundance in inter-reefal areas, including fish-traps, remote (baited) video stations and quantitative acoustics.
Principal Investigator: C.R. Pitcher, T.J. Wassenberg, M.C. Cappo, G.P. Smith, M. Austin, S.R. Gordon, R.H. Bustamante, C.H. Moeseneder, P.J. Speare, J.A. Kennedy, P.J. Doherty, J.N.A. Hooper