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ESR 52:149-161 (2023)  -  DOI:

Characteristics of east Australian demersal trawl elasmobranch bycatch as revealed by short-term latitudinal monitoring

Thomas C. Barnes1,2,3,*, Daniel D. Johnson1

1NSW Department of Primary Industries, Port Stephens Fisheries Institute, Locked Bag 1, Nelson Bay, NSW 2315, Australia
2Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania 7001, Australia
3Present address: National Institute of Water & Atmospheric Research, 301 Evans Bay Parade, Wellington 6021, New Zealand
*Corresponding author:

ABSTRACT: Elasmobranchs are being depleted on a global scale, caused mainly by fisheries. Demersal trawling is a component of mortality but is often not assessed. This could pose risk to benthic/demersal elasmobranchs which are often endemic and therefore vulnerable to fisheries when species ranges are within (or mainly within) trawl footprints. Northern New South Wales (NSW) is an area with endemism but also an area with fisheries such as the ocean prawn trawl (OPT) (penaeid sector). The OPT may interact with elasmobranchs, but this has never been comprehensively studied. To identify high assessment-priority species, determine spatiotemporal stratification for designing future monitoring, and to report catch rates of individuals caught during a trip (i.e. form baseline), we implemented an observer programme (2017 to 2019). To test for stratification of assemblages, we used model-based multivariate analysis. On 435 trawl trips, observers identified elasmobranchs from ~54 species, 13 orders and 34 families from variable catches. Only 2 elasmobranchs were protected in NSW, ~7% qualified for conservation listing, and ~33 and ~17% were endemic and lifeboat (listed elsewhere) species, respectively. Models suggested common elasmobranch assemblages were significantly affected by all strata (geographic zone, season and depth). Elasmobranch catch rates were low compared to other taxonomic groups (e.g. teleost fish), with 2 species captured at >10, 5 species at >2, and the remaining species <2 individuals per trip. The occurrence of endemism and spatiotemporal assemblage variation was explained by mesoscale climate transitions and oceanography. This study forms a timely baseline which can be used to assess the impact of the OPT on elasmobranchs in the future.

KEY WORDS: Commercial fisheries monitoring · Conservation · Penaeid trawling · Benthic · Multivariate modelling · Endemic · Biodiversity · CPUE · Stratification

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Cite this article as: Barnes TC, Johnson DD (2023) Characteristics of east Australian demersal trawl elasmobranch bycatch as revealed by short-term latitudinal monitoring. Endang Species Res 52:149-161.

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