Biomass and commercial catch estimates for abalone stocks in areas proposed as sanctuary zones for the Capes Marine Park

A. Hesp; N.R. Loneragan; N. Hall; H. Kobryn; A.M. Hart; F.P. Fabris; J. Prince

This study was undertaken to estimate the biomasses, biologically sustainable catches and current average annual commercial catches of three fished species of abalone, Haliotis roei (Roei), Haliotis laevigata (Greenlip) and Haliotis conicopora (Brownlip) in the proposed sanctuaries of the Capes Marine Park, south-western Australia. The current annual, catch estimates represent the catches that would be foregone by commercial fishers if the sanctuaries are implemented and will be used to evaluate the potential compensation to fishers (not part of this study). The biomass and catch estimates for each species in the proposed sanctuaries were estimated from a combination of scientific survey data and commercial catch information (provided by fishers) for the proposed sanctuaries. It should be noted that the design, field surveys, analyses of data and writing of this report had to be completed in less than a year, which limited the scope of this study. Commercial abalone fishers who operate in the Capes area were consulted to identify areas where commercial quantities of abalone were known to occur within the proposed sanctuaries. Of the 12 proposed sanctuaries, three were identified as containing commercial stocks of Roei, with one of those zones, i.e. Cape Naturaliste, having two optional configurations. Four sanctuaries were identified with commercial stocks of both Greenlip and Brownlip. Roei, which occur over intertidal and shallow, subtidal reefs, were sampled using 0.5 m2 quadrats along 34 transect lines (136 quadrats) set perpendicular to the shore. Greenlip and Brownlip, which are found in deeper waters over reefs, were sampled using 30 m2 transects (2 transects per site) at 116 randomly selected sites (232 transects) within the areas identified by commercial fishers. The numbers and shell lengths of all abalone were recorded, and length-weight (total and bled meat weight) relationships were determined for each species from sub-samples taken from a range of sites, which thereby enabled estimation of the weights of all individual abalone recorded in the surveys. For all three abalone species of abalone, industry harvests abalone at lengths above the minimum legal length (MLL) for capture. The minimum size at which Roei is harvested commercially in the Capes region is 70 or 75 mm, depending on location within the region (cf. 60 mm MLL); minimum sizes for Greenlip and Brownlip in the region range from 150 to 153 mm (cf. 140 mm MLL for Greenlip and Brownlip). Between 15 and 39% of Roei measured in the proposed sanctuaries surveyed were above the respective minimum size at which it is harvested commercially in those areas. In comparison, nearly half of the Greenlip and Brownlip in the proposed sanctuaries were above the minimum size at which these species are harvested in those areas.

Biomass and commercial catch estimates for abalone stocks in areas proposed as sanctuary zones for the Capes Marine Park

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