Elevated salinity and isotopic composition of fish otolith carbonate: stock delineation of pink snapper, Pagrus auratus, in Shark Bay, Western Australia

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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An evaluation of the daily egg production method to estimate spawning biomass of snapper (Pagrus auratus) in inner Shark Bay, Western Australia, following more than a decade of surveys 1997–2007

Fisheries Research ◽

10.1016/j.fishres.2010.12.009 ◽

2012 ◽

Vol 117-118 ◽

pp. 22-34 ◽

Cited By ~ 12

Author(s):

G. Jackson ◽

Y.W. Cheng ◽

C.B. Wakefield

Keyword(s):

Western Australia ◽

Egg Production ◽

Production Method ◽

Shark Bay ◽

Pagrus Auratus ◽

Spawning Biomass

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Parameter estimation with egg production surveys to estimate snapper, Pagrus auratus, biomass in Shark Bay, Western Australia

Journal of Agricultural Biological and Environmental Statistics ◽

10.1198/108571101750524580 ◽

2001 ◽

Vol 6 (2) ◽

pp. 243-257 ◽

Cited By ~ 19

Author(s):

Gary Jackson ◽

Yuk W. Cheng

Keyword(s):

Parameter Estimation ◽

Western Australia ◽

Egg Production ◽

Shark Bay ◽

Pagrus Auratus

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The uranium isotopic composition of modern stromatolites forming in Shark Bay, Western Australia

10.5194/egusphere-egu21-14810 ◽

2021 ◽

Author(s):

Ashley N. Martin ◽

Monika Markowska ◽

Allan R. Chivas ◽

Stefan Weyer

Keyword(s):

Isotopic Composition ◽

Western Australia ◽

Earth Metal ◽

Uranium Isotopes ◽

Seawater Chemistry ◽

Shark Bay ◽

Microbial Carbonate ◽

Microbial Carbonate Precipitation ◽

Local Water ◽

Co Precipitation

Stromatolites represent some of the earliest evidence for life and are valuable geochemical archives for understanding the rise of oxygen on early Earth. Metal redox proxies in carbonates, such as stable uranium isotopes (238U/235U), are useful for assessing the oxidation state of ancient waterbodies, but may also be sensitive to local water chemistry and early sedimentary diagenesis. This requires the validation of such proxies in modern environments before applying them to ancient carbonates. Here we measure the U isotopic composition of modern stromatolites forming in Hamelin Pool in Shark Bay, Western Australia &#8211; a large hypersaline marine embayment and the largest modern example of stromatolite development globally. Actively-growing stromatolite tops from Shark Bay exhibited a narrow range of &#948;238U from -0.30 to -0.33&#8240;, corresponding to an offset of ca. +0.1&#8240; from seawater. Such an offset has not been found in other biotic marine carbonates, which exhibit seawater-like &#948;238U (ca. -0.4&#8240;), but is consistent with findings from carbonate co-precipitation experiments. One hypothesis for our measured +0.1&#8240; offset is the elevated Ca concentration of the hypersaline Shark Bay seawater relative to open seawater. This results in a greater proportion of dissolved U present as Ca2UO2(CO3)3, which is expected to be isotopically lighter than other U species and not incorporated during carbonate mineral formation. Higher &#948;238U up to +0.11&#8240; were measured in the deeper stromatolite laminae, consistent with the expected U isotope signatures for U reduction. Stromatolite radiocarbon ages show that the diagenetic modification of U occurs within ~1 ka and may be considered syndepositional on geological timescales. These results from the deeper stromatolite laminae support the application of a ca. -0.4&#8240; correction factor to the &#948;238U of stromatolites formed in oxic waterbodies, similar to other biotic carbonates. It is unclear whether the additional +0.1&#8240; offset found in stromatolite tops is particular to seawater chemistry of Shark Bay or a general feature of microbial carbonate precipitation. This warrants investigation of the &#948;238U proxy in other modern environments where stromatolites proliferate.

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