Population Structure , Ageing , and Fishing Mortality of the New Zealand Abalone Haliotis iris

Ministry of Agriculture and Fisheries. Fisheries Research Centre P.O. Box 297. Wellington, New Zealand Present address: Department of Zoology. University of Canterbury Christchurch J. New Zealand Population Structure, Ageing, and Fishing Mortality of the New Zealand Abalone Haliotis iris Abstract. Populations of the New Zealand (NZ) black-footed abalone Haliotis iris were examined in two important fishing areas. Sizefrequencies were compared among three regions around Stewart Island in the extreme south of NZ, three regions of the Marlborough Sounds in the northern part of the South Island, and a site closed to commercial fishing in the North Island. Von Bertalanffy growth parameters were estimated from shell growth rings of subsamples from all regions. Markrecapture data were available for two regions, and independent estimates of von Bertalanffy parameters were calculated. Total mortality was estimated from catch curves and also from length-frequencies using the method of Fournier and Breen (1983). Yield-per-recruit (YPR) and egg-per-recruit (EPR) were calculated and two reference levels of fishing mortality, FO.1 and F25%. were estimated. Analyses showed that, despite previous evidence to the contrary, rings are not laid down annually in the regions we examined. For two fishing regions, the estimated current fishing mortality rates are greater than both F0.1 and F25%, suggesting that the current fishery is more intense than can be sustained in the long term. YPR and EPR do not appear to be greatly affected by changing the minimum legal size. By decreasing F to F0.1' however, equilibrium egg production would increase from 18% to a more satisfactory level with little change in YPR. We discuss management strategies and argue that it would be prudent to decrease fishing mortality, thereby maintaining higher egg production at little sacrifice of YPR.