Title:

Habitat modification and its influence on prawn and crab fisheries

Project Number:

1998-208

Organisation:

SARDI Food Safety and Innovation

Principal Investigator:

Jason E. Tanner

Project Status:

Completed

FRDC Expenditure:

$344,550.00

Program(s):

Environment

Need

This project addresses a need for information on the effects of human-induced disturbance on important coastal habitats. Aims of the public and of the fishing industry have congruence in seeking to maintain healthy aquatic ecosystems. Ecological sustainable development is a frequently expressed aim of modern fisheries management but management objectives relating to the ecological consequences of commercial fishing are rarely underpinned by defensible quantitative information. It is therefore difficult, if not impossible, to determine if fisheries are being prosecuted in an ecological, sustainable manner. So little is known of processes structuring sub tidal ecosystems that is difficult to formulate coherent and meaningful policies governing activities in Australian aquatic habitats. More importantly, it is difficult to identify environmental performance indicators to assess the status of individual fisheries. In reality, the interactions of harvesting on marine species and co-occurring boita are poorly understood. This is particularly the case for inshore fisheries in which harvesting occurs within the euphotic zone and the potential for significant alteration in the food chain, mediated by fishing, is real. There is a clear need to identify human-induced processes that may damage coastal ecosystems and that may affect the viability of nearshore fisheries. Fisheries in Gulf St Vincent claim that the productivity of fisheries is being affected by changes to the habitat. This project is one of a suite of research programs aimed at evaluating the ecological consequences of fishing. Other research programs on prawn fishing discards and of the consequences of abalone fishing are proposed for South Australian ecosystems and address similar needs. The linkages and common focus on coastal ecosystems will reinforce the outcome and the utility of the proposed research. A key outcome will be the identification of quantitative yardsticks of performance in relation to reasonable standards of ecological sustainable fishing practices. This outcome is needed to reinforce management plans with the quantifiable performance indicators relating to ecological sustainable development that are presently lacking for Australian fisheries.

Objectives

1. To determine and correlate the distribution and relative abundance of prawns, crabs, encrusting epibiota in the vicinity of prawn and crab grounds in relation to coastal discharge sites in the Gulf St Vincent.

2. To measure and compare the outcome of controlled trawling on the epifaunal composition of prawn/crab habitats and bryozoan dominated habitats

3. To provide an understanding of the consequences of habitat modification on the productivity of important commercial and recreational fisheries

Habitat modification and its influence on prawn and crab fisheries

Final Report
ISBN:0 7308 5286 5
ISSN:
Author(s):Jason Tanner
Date Published:March 2003
Experimental trawling in Gulf St Vincent indicated that epifaunal assemblages experienced substantial trawling mortality, which varied depending on sediment characteristics.  Locations with strong currents and coarse sediments experienced minimal effects, whereas those with weak currents and fine sediments experienced larger effects.  Overall, trawling caused a 36% reduction in the number of large epifaunal organisms.  However, recruitment into trawled sites was higher than into untrawled sites, suggesting that recovery may be relatively rapid.  Examination of infauna showed that they did not experience any effect, although there was some indication that at the location with fine sediments infaunal abundance was reduced.

 

Keywords:  Effects of trawling, habitat fragmentation, habitat selection, western king prawn, blue swimmer crab, seagrass.