Seasonal, spatial and gear-related influences on relationships between retained and discarded catches in a multi-species gillnet fishery

A scientific observer program was used to quantify relationships among the compositions and rates of retained and discarded catches taken in a temperate estuarine commercial gillnet fishery in southeastern Australia. Sampling was stratified across six estuaries and three fishing seasons that corresponded to different permitted setting practices (set and immediate retrieve versus overnight set). A total of 265 fishing trips was sampled throughout 2001, yielding 57 species (52 finfish, 3 invertebrate, 1 bird and 1 tortoise), of which 42 and 45 species were retained and discarded, respectively. More species and a greater mean number and weight of total individuals were retained than discarded during each fishing season. Throughout the entire survey, 6.2% by number and 3.3% by weight of catches were discarded. Average retained catches ranged from 37 to 609 kg fisher-day−1 and discarded catches from 1 to 10 kg fisher-day−1. Mugil cephalus and Girella tricuspidata accounted for 85% by number of total observed catches, with a further 10% being contributed by Acanthopagrus australis, Platycephalus fuscus and Portunus pelagicus. G. tricuspidata, A. australis and P. pelagicus below the minimum legal length collectively accounted for 69% by number and 49% by weight of all discards observed. Discarding was greatest in the smallest mesh sizes and during winter when nets can be set overnight. Increasing the minimum permitted mesh size as well as decreasing the maximum soak time of nets set in winter will further reduce the low levels of discarding in this fishery.