New Zealand Journal of Marine and Freshwater Research abstracts
Utility of morphological data for key fish species in southeastern Australian
beach-seine and otter-trawl fisheries: predicting mesh size and configuration
Matt K. Broadhurst
NSW Department of Primary Industries
Fisheries Conservation Technology Unit
P.O. Box J321 Coffs Harbour
NSW 2450, Australia
email: mbroadhurst@nmsc.edu.au
Koenraad K. P. Dijkstra
National Marine Science Centre
P.O. Box J321 Coffs Harbour
NSW 2450, Australia
Dennis D. Reid
Charles A. Gray
NSW Department of Primary Industries
Cronulla Fisheries Centre
P.O. Box 21 Cronulla
NSW 2230, Australia
Abstract Samples of 16 key fish species targeted by oceanic
prawn trawlers and oceanic and estuarine beach seiners in southeastern Australia
were measured for up to 10 morphological dimensions that included: total (Wt)
and eviscerated weights (EWt); total (TL), fork (FL), natural (NL), standard
(SL), dorsal standard (DSL), and anal standard lengths (ASL); and maximum body
height (MH), width (MW), and girth (MG). All partial lengths were indexed against
TL to provide linear relationships and, where there were sufficient data, tested
for intra-specific sexual dimorphism. Nearly all species that were sexed demonstrated
at least some morphological divergence, and especially for transverse measures;
probably owing to different reproductive conditions. Sex-specific or combined
regressions of DSL and ASL and transverse measures versus TL were used to identify
the most appropriate: (1) partial length for compliance purposes; and (2) mesh
sizes and configurations for the different fishing gears used. Using relevant
data describing the smallest commercial-sized fish species (stout, Sillago
robusta and red spot whiting, S. flindersii—150 mm TL) retained
in prawn trawls, a new square-mesh codend (made from 35-mm mesh hung on the bar)
was designed and constructed. The selectivities of this square-mesh codend and
a conventional diamond-mesh design (40-mm mesh) were then modelled and compared
in a case study. The conventional codend was demonstrated to be non-selective
for the sizes of eastern king prawns and red spot whiting targeted. In contrast,
the square-mesh codend selected red spot whiting across narrow selection ranges
(18.88–15.67 mm) and at lengths of 50% retention (143.39–146.32 mm
TL) that closely corresponded to the estimated maximum mesh opening. The square-mesh
codend also improved selection for eastern king prawns, without impacting on
commercial catches. Based on these results, similar predictions were made for
appropriate mesh sizes and configurations in oceanic and estuarine beach seines;
both of which were demonstrated to comprise minimum mesh sizes that would be
non-selective for the sizes of all targeted fish.
Keywords selectivity; trawl; seine; bycatch reduction; mesh
size; fisheries management
New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40:
259–272
0028–8330/06/4002–0259 © The Royal Society
of New Zealand 2006
M05052; Online publication date 10 April 2006. Received 10 August 2005;
accepted 3 October 2005
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