Project number: 1998-154
Project Status:
Completed
Budget expenditure: $31,608.00
Principal Investigator: Stephen J. Newman
Organisation: Department of Primary Industries and Regional Development (DPIRD) WA
Project start/end date: 21 Jun 1998 - 30 Dec 2000
Contact:
FRDC

Need

The Northern Territory Fisheries Division and the Fisheries Department of Western Australia are currently formulating management plans for the demersal fisheries off their respective coastlines and are concerned about current levels of exploitation and the potential for over-exploitation. A key issue in the formulation of these plans is whether there is a single shared stock between WA and NT or distinct isolated stocks. Under a single stock assumption, overfishing in any one sector of the fishery could lead to depleted catches in other sectors. There is presently little information on the stock structure of Pristipomoides multidens across northern Australia, nor is there any information on migration patterns within the region (genetic differences are currently being investigated in FRDC Project 96/131). This important issue needs to be resolved before appropriate management plans can be determined.

Furthermore, the resolution of stock structure between WA and NT will allow informed decisions on the likelihood of shared demersal fishery resources with Indonesia across international maritime boundaries (NT Fisheries have collected some samples from Indonesian waters).

See also original Need in FRDC Project 96/131.

Objectives

1. To investigate the stock structure of Goldband Snapper (Pristipomoides multidens) across northern Australia using otolith microchemistry and stable isotopic composition in order to assist in the sustainable development of appropriate management plans for the deepwater snapper fisheries of the Northern Territory and Western Australia.

Final report

ISBN: 0-7309-8444-3
Author: Stephen Newman
Final Report • 2000-08-08 • 491.49 KB
1998-154-DLD.pdf

Summary

Measurement of stable isotope ratios of oxygen (18O:16O) and carbon (13C:12C) in the earstone (sagittal otolith) carbonate from assemblages of goldband snapper, Pristipomoides multidens, from waters off northern and western Australia revealed location-specific signatures and indicated that fish from all sites sampled within Australia (Exmouth, Rankin Bank, Broome, Vulcan Shoals, Timor Sea, Arafura Sea), Indonesia (Kupang) and Papua New Guinea (Pommern Bay) were different.

The significant differences in the isotopic signatures of goldband snapper demonstrated that there is unlikely to be substantial movement of fish among these distinct adult assemblages. The stable isotopic signatures for the fish from the different locations was persistent through time, and therefore it could be concluded that they comprise separate stocks for many of the purposes of fisheries management.

The ratios of the stable oxygen isotopes in goldband snapper were significantly related to sea surface temperatures (r2 = 0.797) and latitude (r2 = 0.783). This study has provided further evidence that measurement of the stable isotope ratios in teleost earstone (sagittal otolith) carbonate can be a valuable tool in the delineation of fishable stocks, or fishery management units, of vulnerable age classes where the range of distribution of the species in question covers waters with different temperature regimes.

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