Comparing fishery-independent measures of snapper (Pagrus auratus) abundance in inner Shark Bay; daily egg production method vs. mark-recapture

Document Type

Conference Proceeding

Publication Date

7-2005

Conference Title

Monitoring Fish Stocks and Aquatic Ecosystems: Proceedings of a workshop conducted by the Australian Society for Fish Biology in Darwin, Northern Territory

Place of Publication

Darwin

Disciplines

Aquaculture and Fisheries

Abstract

Snapper (Pagrus auratus) comprise about 50% of the catch landed by recreational boats in the inner gulfs of Shark Bay, Western Australia, and have been attracting large numbers of recreational fishers for many years, mostly during the winter tourist season when snapper are aggregated to spawn at predictable locations. Anecdotal information in the mid 1990s suggested recruitment overfishing in the Eastern Gulf, but no estimate of snapper abundance was available at that time. The daily egg production method (DEPM), where snapper eggs were collected in plankton surveys, has generated spawning biomass estimates annually since 1997. To confirm these estimates, a fishery-independent mark-recapture study was undertaken in 2004 (4,285 snapper tagged, 200+ recaptured), providing a biomass estimate (86 t, 95% ci 59 to 112) that was not significantly different to a comparable, concurrent DEPM estimate (38 t, 95% ci 22 to 73). The tagging study was assisted by about 70 volunteer fishers in 21 recreational vessels, who were trained in fish handling and tag application. Tagging generated an abundance estimate more quickly than the DEPM (one month v. six months, approx.), was relatively well received and understood by stakeholders, and helped foster a sense of custodianship of the resource and acceptance of management arrangements in the fishery. DEPM was less expensive, although tagging costs should decrease in future. The results help to develop a future research and management framework for inner Shark Bay snapper.

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