Developing techniques to estimate the age of bigeye tuna and broadbill swordfish off eastern Australia: a pilot project

Funded Activity Summary

The BET and BBL swordfish fishery is expanding rapidly off the east coast of Australia and is now a significant fishery. The warning 'trigger', set by AFMA, of 800t of BBL caught this year has been exceeded. There is now an urgent need to gain an understanding of the stock structure of this fishery. There are now grave concerns, both within the Pacific and the Indian Ocean, on the possibility of over exploitation of these species.

Very little is known scientifically on these species (Whitelaw and Unnithan. 1997). Critically there is no verifiable information on the size at maturity and age-structure of populations of BET and BBL in the western Pacific.

Stock assessments require knowledge of size at maturity, size at age, growth rate and estimates of the variability in these parameters within the stock.

For management plans to be devised and implemented it is necessary to expand our biological knowledge. A first step in a structured stock assessment of a fishery is to determine whether ages of individuals can be estimated from their bony parts (otoliths and spines). There is a need to develop verifiable age estimation techniques for stock assessment studies.

Refs;
Whitelaw, A.W. and Unnithan, V.K. 1997. Synopsis of the distribution, biology and fisheries of the bigeye tuna, with a bibliography. CSIRO Marine Laboratories Report 228. 62pp.

Objectives:
1. To collect hard parts (otoliths and spines) from broadbill swordfish and otoliths from bigeye tuna (much of this has been completed).
2. Assess a range of standard age estimation techniques using otoliths, vertebrate and spines of BET and BBL. This will be carried out in collaboration with SPC and NMFS.
3. Compare age estimates derived using these techniques with those of the SPC and NMFS using other techniques.
4. Using marked (strontium chloride) BET otoliths from previous SPC/CSIRO tagging studies, as well as tag release/recapture growth data from other tagging programs, attempt to validate our age estimation methods and techniques.
5. Make recommendations to Eastern Tuna MAC on the feasibility of an extended ageing project to provide biological information to stock assessment studies.

Funded Activity Details

Start Date: 29-06-1998

End Date: 09-03-2001

Funding Scheme: Funding Scheme not available

Funding Amount: $26,793.90

Funder: Fisheries Research and Development Corporation

Research Topics

ANZSRC Field of Research (FoR)

There are no FoR codes available for this funding activity

ANZSRC Socio-Economic Objective (SEO)

There are no SEO codes available for this funding activity

Other Keywords

Ageing | Otolith | Population Dynamics | Stock Assessment

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