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Assessing the distribution and relative abundance of wobbegong sharks (Orectolobidae) in New South Wales, Australia, using recreational scuba-divers

Published online by Cambridge University Press:  23 October 2009

Charlie Huveneers ,
Kehui Luo ,
Nick M. Otway  and
Robert G. Harcourt
Charlie Huveneers
Affiliation:
Graduate School of the Environment, Macquarie University, Sydney, NSW 2109, Australia School of Biological Sciences, Flinders University, Adelaide, SA 5043, Australia
Kehui Luo
Affiliation:
Department of Statistics, Macquarie University, Sydney, NSW 2109, Australia
Nick M. Otway
Affiliation:
NSW Department of Primary Industries, Port Stephens Fisheries Centre, Taylors Beach Road, Taylors Beach, NSW 2316, Australia
Robert G. Harcourt
Affiliation:
Graduate School of the Environment, Macquarie University, Sydney, NSW 2109, Australia
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Abstract

Wobbegongs are benthic sharks that are commercially targeted in New South Wales (NSW), Australia. Given a dramatic reduction of more than 50% in landed catch in a decade, there is a clear need to ensure that basic ecological data such as distribution and abundance are available for management use. Opportunistic sightings of wobbegongs collected by recreational scuba-divers were used to assess the distribution and relative abundance of wobbegongs in NSW. From July 2003 until January 2005, 304 dives were undertaken by recreational divers and 454 wobbegongs were reported. Larger numbers of wobbegongs were sighted in northern compared to southern NSW. Spotted and ornate wobbegongs were sighted in similar numbers, but species composition was highly variable across locations. Only a few juvenile and newborn spotted wobbegongs were sighted, whereas small ornate wobbegongs were mostly sighted north of central NSW. The latter were possibly the third, cryptic species, the dwarf ornate wobbegong. The paucity of sightings of small wobbegongs suggests that juveniles and newborns are inconspicuous to divers or that small wobbegongs are found in areas not visited by divers. Potential species and size segregation suggest that closing areas to fishing may enable populations to sustain current levels of commercial exploitation. The cost-effectiveness of using recreational scuba-divers to opportunistically collect distribution and relative abundance data was apparent from this study. However, the lack of spatial and temporal homogeneity in diving effort suggests that future studies should consider incorporating organized surveys and a facilitator, rather than using opportunistic records of sightings.

Keywords

Orectolobus ornatusOrectolobus maculatusOrectolobus haleiSurveyTasman sea
Type
Research Article
Information
Aquatic Living Resources , Volume 22 , Issue 3 , July 2009 , pp. 255 - 264
Copyright
© EDP Sciences, IFREMER, IRD, 2009

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