2 results

Determination of the diets of Snapper and Silver Trevally and construction of a food web for the demersal fish community in south-western Australia

Project number: 2009-006
Project Status:
Completed
Budget expenditure: $74,288.75
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 30 Jun 2009 - 29 Sep 2011
Contact:
FRDC

Need

Implementation of ecosystem-based fishery management requires sound knowledge of food webs if the indirect effects of fishing on trophic structure are to be understood. There is an urgent need to construct a quantitative food web so that we can understand the ways in which the marked declines in the abundances of important fish species off the lower west coast of Australia, which led to the recent closure of the metropolitan commercial fishery, are likely to have impacted on the ecosystem. While there are sound dietary data for most of the more abundant and important species in this region, no such data are available for Snapper (Pagrus auratus) and Silver Trevally (Pseudocaranx dentex). Snapper was a primary target species for commercial fishers, and Snapper and Silver Trevally both continue to be of great importance to recreational fishers. Sound dietary data for these species, which take into account the ways in which their diets change with body size and season, are essential for the construction of a reliable food web. There is a need to combine the new dietary data for these species with those that were collated in the database developed in FRDC 2002/016 and with the results from more recent studies, converting them into common dietary categories, size categories and a common format before they can be used to construct a reliable food web. The opportunity exists, while Ian Potter remains actively involved in research, to apply the experience and knowledge that he and Margaret Platell possess (noting that these two biologists have been involved in collecting much of the available dietary data for the demersal fish species of south-western Australia) to bring together the results of approximately 15 years of research to create a food web for this region that will be invaluable for future research and management.

Objectives

1. To determine the diets of Snapper and Silver Trevally on the lower west coast of Australia and how they change with body size and season
2. To construct a reliable food web derived from quantitative dietary data for a wide range of demersal fish species off the lower west coast of Australia

Final report

ISBN: 978-1-921877-06-3
Author: Ian Potter

Determination of biological parameters for managing the fisheries for mulloway and silver trevally in Western Australia

Project number: 2002-004
Project Status:
Completed
Budget expenditure: $214,217.00
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 29 Jun 2002 - 30 Mar 2006
Contact:
FRDC

Need

The progressive rise in the number of recreational fishers in Western Australia is increasing the fishing pressure on the most sought-after recreational fish species in this State. The potential thus exists for these species to become exploited at levels that exceed those that are sustainable. The absence of biological data for mulloway, an icon recreational species, and silver trevally, the third most frequently-caught recreational fish species, has meant that the existing and proposed regulations, that were aimed at conserving and managing the stocks of these very important species, were not based on appropriate biological criteria. There is thus a strong need to develop a sound database for these species, which encompasses such crucial features as size and age compositions, growth, length and age at first maturity, fecundity and the location and time of spawning. Since the sand trevally, which is also fished recreationally, is morphologically so similar to silver trevally that it is very frequently confused with this species, and indeed is currently considered collectively with this species for management purposes, there is a need to understand the significance of those differences that are likely to exist between the habitats and biology of these two species.

The urgent need to acquire biological data on mulloway and silver trevally to underpin management plans has been highlighted by both RFAC and RecFishWest.

Objectives

1. To obtain the biological data that are required by managers to develop plans to conserve the stocks of mulloway and silver trevally in Western Australia. This will thus require determining the following characteristics of both of these species:
2. Size and age compositions, growth rates and the sizes and ages at which maturity is first reached.
3. Locations and periods of spawning, and whether they are multiple spawners.
4. Batch fecundity.
5. Estimates of mortality.
6. To elucidate the patterns of distribution of the silver and sand trevally, and thereby determine the ways in which they differ.

Final report