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This paper presents a novel approach for fitting length data to the Schnute growth model. Cohorts were fitted manually to a time series of length distributions from two stocks (Clarence and Hunter Rivers) of Metapenaeus macleayi and considered analogous to individuals from tag–recapture data, in order to estimate growth parameters. Data for Clarence males best fitted the three-parameter Schnute Model (L∞ = 21.3 mm CL, κ = 0.025 day–1 and γ = –1.35), whereas those for Hunter males were best fitted to a two-parameter version of the model (L∞ = 33.5 mm CL, κ = 0.009 day–1 and γ = 0 fixed). The equivalent to the von Bertalanffy growth function was the best fit to female data from both stocks (L∞ = 36.6 and 40.2 mm CL, κ = 0.004 and 0.005 day–1 and γ = 1 fixed for Clarence and Hunter respectively). Females grew larger than males and took longer to achieve their maximum size. No significant differences in female growth were found between stocks; however, males from the Hunter grew to a longer mean maximum length but at a slower rate than those from the Clarence. This study shows how the Schnute Model can be fitted to length based data and thus include the flexibility of comparing fits between asymptotic and non-asymptotic growth functions.

This study investigates the effects of increasing the lateral mesh openings in codends on the size and species selectivity of lagoon and river seines and a stow net used to target penaeid prawns (eastern king (Penaeus plebejus), school (Metapenaeus macleayi) and greasyback prawns (M. bennettae)) in Wallis Lake, New South Wales, Australia. Compared with conventional codends made from 36-mm diamond-shaped mesh, new designs made from 25- and 29-mm mesh hung on the bar (i.e. square-shaped mesh) significantly reduced the catches of non-target fish (by between 58 and 95%) and improved size selection for the targeted penaeids in the stow net and lagoon seine. In contrast, owing to gear-specific operational characteristics such as a slower hauling speed, there were few detectable effects of altering mesh openings in the codend of the river seine. The results are discussed in terms of the differences in the gears used and their particular selection mechanisms. We conclude that, pending further trials, codends made from a mesh size approaching 29 mm, hung on the bar, would provide appropriate size- and species-selection for Wallis Lake stow nets and lagoon seines. Further research is required, however, to examine the utility of operational changes to river seines and/or alterations to mesh size and configuration in the wings and body to improve selectivity.

Movement and growth of M. macleayi in the Clarence River region were investigated during tagging studies using Atkins-type tags. Although some tagged prawns released into the estuary showed a marked susceptibility to developing lesions and skeletal necroses at the tag wound site, the majority were able to moult, bury and behave normally. Movement of tagged prawns suggested that M. macleayi from the Clarence River undertake limited northwards migrations which are possibly assisted by currents. Such movement may therefore contribute to the Evans Head fishery. Growth of tagged prawns appeared to be unusually rapid in the first 2 weeks after release but in subsequent weeks was found to be comparable with that recorded in other similar studies.