Designing and evaluating length–frequency surveys for trap fisheries with application to the southern rock lobster
Journal article, Peer reviewed
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A survey design for estimating the length distribution of harvested southern rock lobsters (Jasus edwardsii) was developed for the South Australian fishery. Experimental sampling was carried out by volunteer fishers in spring 1996 and autumn 1997 to test three proposed survey designs. A variance components analysis indicated that it would be more efficient to sample one pot per trip from all trips rather than the previous design of sampling multiple pots from a few trips. The variation among licenses (fishers) accounts for most of the remaining sample variance. Onboard research sampling by scientists, who in the past measured from all pots on selected trips, was shown to be the least efficient design option in comparison with volunteer sampling by fishers. A sampling protocol where fishers measure one to three pots per trip has been adopted by the South Australian rock lobster fishers. Estimators, based on a three-level sampling hierarchy of pot, day, and license, are presented for estimating the mean and sample variance of the numbers harvested overall and within each length category.