Hydrodynamic modelling of snapper Pagrus auratus egg and larval dispersal in Shark Bay, Western Australia: reproductive isolation at a fine spatial scale

Snapper is an important commercial and recreational target species in the Shark Bay region of Western Australia. The present study aimed to define the range of movements of snapper by tagging in the two inner gulfs of Shark Bay and on oceanic fishing grounds adjacent to the Bay. Recaptures by fishers fell to low levels within 4 years after tagging, but small numbers of recaptures were still being made up to 15 years after release. There was no mixing of snapper populations between the two inner gulfs nor was there any movement between the ocean and the inner bay. This supports genetic and other evidence for the existence of several separate stocks in the region. Snapper of the ocean stock were mostly recaptured within 20 km of their release point, although a few fish moved long distances of up to 370 km southwards along the continental shelf. The tagged snapper tended to become more dispersed along the shelf with increasing years at liberty. Yet, an empirical model indicated that of the snapper recruiting to the main oceanic fishing grounds near Koks Island, which have a mean life expectancy in the fishery of 1.5 years, 76% would remain within 93 km (50 nautical miles), even after 6 years. The distinct stocks and their movement characteristics are significant for snapper fishery management in the Shark Bay region.

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Sexual and local variation in head morphology of snapper, Pagrus auratus, Sparidae, in the Shark Bay region of Western Australia

Marine and Freshwater Research ◽

10.1071/mf98031 ◽

1999 ◽

Vol 50 (1) ◽

pp. 27 ◽

Cited By ~ 14

Author(s):

M. Moran ◽

C. Burton ◽

N. Caputi

Keyword(s):

Western Australia ◽

Stock Assessment ◽

Local Variation ◽

Export Market ◽

Canonical Variate ◽

Shark Bay ◽

Incomplete Mixing ◽

Genetic Stocks ◽

Pagrus Auratus ◽

Head Morphology

Sexual dimorphism is demonstrated in pink snapper, Pagrus auratus (Sparidae), from the Shark Bay region of Western Australia, by canonical variate analysis of 13 morphometric measurements of the head. Snapper of both sexes develop a prominent hump on the forehead as they grow to large size, but the males do so to a greater extent than the females. Males also develop a bulge on the snout which was not found in females. Snapper with humps are less well accepted in an export market and this may result in high-grading problems in the quota-managed commercial fishery. Morphometric differences between localities were also found, with three regions previously recognized as containing separate genetic stocks being clearly distinct. Snapper from four areas within one of these stocks, the widespread ocean stock, were compared and found to show lesser differences. These four population samples fell into two groups, interpreted as a resident inshore group and an offshore group which migrates inshore for spawning. The local differences indicate incomplete mixing which has implications for fisheries management and stock assessment.

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