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Shelf spawning habitat of Emmelichthys nitidus in south-eastern Australia – Implications and suitability for egg-based biomass estimation

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Neira, FJ and Lyle, JM and Keane, JP (2009) Shelf spawning habitat of Emmelichthys nitidus in south-eastern Australia – Implications and suitability for egg-based biomass estimation. Estuarine, Coastal and Shelf Science, 81 (4). pp. 521-532. ISSN 0272-7714

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Abstract

The spawning habitat of Emmelichthys nitidus (Emmelichthyidae) in south-eastern Australia is described from vertical ichthyoplankton samples collected along the shelf region off eastern through to southwestern Tasmania during peak spawning in October 2005–06. Surveys covered eastern waters in 2005 (38.8–43.5S), and both eastern and southern waters in 2006 (40.5oS around to 43.5oS off the southwest). Eggs (n = 10,393) and larvae (n = 378) occurred along eastern Tasmania in both years but were rare along southern waters south and westwards of 43.5oS in 2006. Peak egg abundances (1950–2640 per m-2) were obtained off north-eastern Tasmania (40.5–41.5oS) between the shelf break and 2.5 nm inshore from the break. Eggs were up to 5-days old, while nearly 95% of larvae were at the early preflexion stage, i.e. close to newly emerged. Average abundances of aged eggs pooled across each survey declined steadily from day-1 to day-5 eggs both in 2005 (97-18) and 2006 (175-34). Moreover, day-1 egg abundances were significantly greater 2.5 nm at either side of the break, including at the break, than in waters -5 nm both inshore and offshore from the break. These results, complemented with egg and larval data obtained in shelf waters off New South Wales (NSW; 35.0–37.7oS) in October 2002–03, indicate that the main spawning area of E. nitidus in south-eastern Australia lies between 35.5oS off southern NSW and 43.5oS off south-eastern Tasmania, and that spawning activity declines abruptly south and westwards of 43.5oS around to the south-west coast. In addition, quotient analyses of day-1 egg abundances point to a preferred spawning habitat contained predominantly within a 5 nm corridor along the shelf break, where waters are 125–325 m deep and median temperatures 13.5–14.0 oC. Spawning off eastern Tasmania is timed with the productivity outburst typical of the region during the austral spring, and the temperature increase from the mixing between the southwards advancing, warm East Australian Current and cooler subantarctic water over the shelf. Overall, ichthyoplankton data, coupled with reproductive information from adults trawled off Tasmania, indicate that E. nitidus constitutes a suitable species for the application of the daily egg production method (DEPM) to estimate spawning biomass. This finding, together with evidence in support of a discrete eastern spawning stock extending from southern NSW to southern Tasmania, strengthens the need for DEPM-based biomass estimates of E. nitidus prior to further fishery expansion.

Item Type: Article
Keywords: Emmelichthys nitidus, Emmelichthyidae, ichthyoplankton, shelf spawning habitat, Tasmania, south-eastern Australia
Journal or Publication Title: Estuarine, Coastal and Shelf Science
Page Range: pp. 521-532
ISSN: 0272-7714
Identification Number - DOI: 10.1016/j.ecss.2008.12.012
Additional Information: The definitive version is available at http://www.sciencedirect.com
Date Deposited: 05 Feb 2009 03:22
Last Modified: 18 Nov 2014 03:55
URI: http://eprints.utas.edu.au/id/eprint/8292
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