3 results

Age and growth of broadbill swordfish (Xiphias gladius) from Australian waters

Project number: 2001-014
Project Status:
Completed
Budget expenditure: $267,183.00
Principal Investigator: Jock Young
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 13 Jul 2001 - 30 Sep 2004
:
SPECIES

Need

The swordfish fishery has expanded rapidly in the past few years off eastern Australia with an annual catch now of ~2400 tonnes. When the fishery first began AFMA set a ‘trigger’ point of 800 tonnes, after which they would review the amount of fish taken. Similar rapid growth has been reported for the fishery for swordfish off Western Australia where the catch is now at ~1000 tonnes. Added to this is the developing New Zealand fishery now also reaching 1000 tonnes. This last point is relevant in that recent genetic evidence indicates a single stock encompassing all three fisheries (Reeb et al 2000). There is an urgent need, therefore to determine whether these catches are sustainable. However, the population parameters from which accurate stock assessment can be made have not yet been determined for the Australian region. To this end Eastern Tuna MAC and SWTBF MAC listed age and growth determination as priorities three and one respectively in their list of ten priority research issues. The latest meeting of the Standing Committee on Tuna and Billfish (SCTB 13) held in Noumea noted the increase in swordfish fishing in the Western Central Pacific Ocean. They listed age and growth as a priority research issue for this species.

Assessments require input data on mortality, longevity and age structure; estimates that can be obtained from age and growth studies. There is a clear need therefore, for an age and growth study of this species. However, without validation over a number age classes, incorrect interpretations have lead to the wrong decisions by management. Therefore, before such an ageing study is begun the first priority is validation of the annual cycle of growth. With appropriate validation a length at age key, which is presently lacking, could be provided.

Objectives

1. Collect sufficient samples from at least five age classes of broadbill swordfish so that a validation study can be completed
2. Collect spine samples for known-sex fish from a representative sample of the size range of the fishery
3. Determine whether the cycle of increment deposition at the margin of the anal fin spine is annual thus providing a validation that bands are laid down annually
4. Dependant on successful validation, provide a sex-separated estimate of mean size-at-age for the east coast swordfish population.

Final report

Defining regional connections in Southwestern Pacific broadbill swordfish

Project number: 2007-036
Project Status:
Completed
Budget expenditure: $135,187.00
Principal Investigator: Chris Wilcox
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 28 Jun 2007 - 30 Jun 2009
:
SPECIES

Need

Knowledge of the stock structure and migration patterns is fundamental to ensuring effective stock assessment and management of a fishery. While this knowledge is scanty for many Commonwealth fisheries, swordfish structure and movements are particularly poorly known. The stock harvested by the ETBF is locally depleted, suggesting population structure, but there are no direct data on movement or distribution available. Parameterizing a model of movement for swordfish would clarify the stock structure and provide a mechanism for incorporating their movements into spatial management or assessment models.

The recent Ministerial Directive to AFMA has highlighted the lack of knowledge regarding swordfish. Key initiatives in the directive are 1) develop harvest strategies for its fisheries to ensure sustainable management; 2) recover overfished stocks; and 3) end overfishing on stocks. Furthermore, the directive urges AFMA to move to spatial management. Critical to the design of harvest strategies, determination of stock status, and development of spatial management measures is a sound knowledge of the connectivity between stocks fished locally and in other parts of the Pacific basin. In order to ensure equity in limitations due to management arrangements, Australia will need to pursue policies that ensure other nations protect shared stocks within the context of the Western Central Pacific Fisheries Commission - requiring clear evidence of the amount of movement between locally and regionally harvested stocks and empirically validated assessment models.

The March 2005 AFMA/ComFRAB Research Gap Analysis and Priority Setting Workshop, held jointly by AFMA and ComFRAB underlined the needs outlined above for swordfish in the ETBF specifically – identifying both spatial management measures to rectify the localized depletion and provision of science and policy advice into the WCPFC. The ETBF research priorities and FRDC’s strategic challenges both identify these same issues, as discussed in the Background section.

Objectives

1. Collect swordfish movement data and habitat preferences on the Coral Sea spawning grounds and during subsequent migration using electronic tags
2. Collate data from this study with data from ongoing studies on swordfish movement in the Tasman Sea, east of New Zealand, and in the central South Pacific spawning area.
3. Refine existing analysis methods to incorporate electronic tag data and oscillatory movements such as annual migrations
4. Parameterize a regional movement model which describes retention times on the spawning grounds and migration patterns
5. Provide a succinct description of stock structure and movement that can be incorporated into other analyses
Environment