New Zealand Journal of Marine and Freshwater Research abstracts

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Atypical size selection of captive school prawns, Metapenaeus macleayi, by three recreational fishing gears in south-eastern Australia

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

Russell B. Millar

Department of Statistics
University of Auckland
Private Bag 92 019
Auckland, New Zealand

Damian J. Young
Michael E. L. Wooden

NSW Department of Primary Industries
Fisheries Conservation Technology Unit
P.O. Box J321
Coffs Harbour
NSW 2450, Australia

Stuart Rowland

NSW Department of Primary Industries
Grafton Aquaculture Centre
PMB 3, Grafton
NSW 2460, Australia

Abstract  Three manipulative experiments were done to estimate the selectivity of conventional and new sizes and configurations of mesh for school prawns, Metapenaeus macleayi, in three south-eastern Australian recreational fishing gears (haul, push, and scoop nets). The treatment meshes examined were: (1) conventional-sized, diamond-shaped mesh used in all gears (20 mm in scoop nets and 30 mm in push and haul nets); (2) 30 mm in scoop nets; and (3) 40-mm diamond- and (4) 23-mm square-shaped mesh in all gears. In all experiments, known quantities of school prawns (6Ð24 mm carapace length (CL)) were placed in purpose-built enclosures, monitored to ensure no experimental-induced stress (as measured by changes in l-lactate in their haemolymph) and the replicate treatments of the various gear configurations deployed. Escapees from the various treatment nets were collected from the enclosures using fine-meshed nets. Logistic selection curves were derived for all treatment nets and specific comparisons made within and among gears. All nets had 50% retention lengths (L50) comparable to other penaeid-catching gears with similar mesh sizes, but most had selection ranges (SRs) that were atypically inflated. The large SRs were attributed to a combination of factors that included the mesh geometry and towing speed of the gears and the behaviour of school prawns. The 20-mm scoop net had the smallest selection parameters, retaining >99% of individuals larger than 13 mm CL. Mesh size in this gear would need to be increased to at least 30 mm to allow some maturing prawns (>18 mm CL) to escape.

Keywords  selectivity; shrimp; prawn; bycatch reduction; mesh size; Metapenaeus macleayi; lactate

M04055; Online publication date 24 November 2004 Received 5 March 2004; accepted 30 August 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 755–766
0028–8330/04/3805–0755 © The Royal Society of New Zealand 2004

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