Summary

This report documents the results of a FRDC funded study into the commercial fishery for kingfish in New South Wales.

Since the 1980's, landings of kingfish by commercial fishers have declined from around 600 tonnes to less than 100 tonnes. During this time there have been 2 controversial management changes: (i) the introduction of a minimum legal length of 60 cm total length and (ii) the banning of kingfish traps. The debate about the appropriateness of these management measures has been ongoing, but has been limited by a lack of understanding of the status of the fishery. The research described in this report assists this debate by detailing the sizes and ages of kingfish in commercial landings, refining estimates of growth rates, estimating mortality rates, modeling the yield per recruit for a range of mortality rates and minimum legal lengths and discussing future monitoring of the kingfish fishery in NSW.

Forty seven tonnes of kingfish, representing 16% of total commercial landings, were measured during the study. The results showed that the fishery was dominated by fish smaller than 65 cm fork length. The sizes of kingfish larger than the current minimum legal length which are available to the fishery do not appear to have changed since the late 1980's. Estimated ages ranged up to 21 years, but the fishery was dominated by 2 and 3 year old fish, for example, in 1999/00 78% of the fishery consisted of 2 and 3 year old fish. There were no differences in the growth rates of kingfish along the NSW coast, from Lord Howe Island, or between males and females. The results showed that kingfish grow rapidly and reach their minimum legal length of 60 cm total length at around 2 years of age.

Estimates of yield per recruit showed that the kingfish stock can be considered to be growth overfished. Removing the minimum legal length on kingfish would reduce the yield per recruit by around one third and may increase fishing effort and mortality. Setting the minimum legal limit at the estimated size at sexual maturity (approximately 70 cm fork length) may significantly increase the yield per recruit. The availability of larger kingfish to the fishery is unknown and setting a size limit based on sexual maturity may not be appropriate for the fishery, as up to 90% of the commercial fishery were observed to be smaller than this size during the study. The yield per recruit calculations suggest that if the minimum legal length is to be changed in order to reduce the bycatch of small kingfish, that it should be increased.

Ongoing monitoring of the status of the kingfish stock is essential. It is suggested that the fishery for kingfish in NSW be monitored through a combination of assessing the annual reported landings and the average sizes of kingfish being captured. A daily fisher logbook may provide a cost-effective method for assessing (i) the abundance of undersized kingfish, and (ii) any changes in the mean sizes of kingfish landed.