Population size and exploitation rate of snapper, Chrysophrys auratus, in the Hauraki Gulf from tagging experiments, 1975–76

The results of three snapper tagging cruises in the Hauraki Gulf area to estimate population size and annual exploition rate are presented. Eight hundred and thirty‐two snapper were tagged around Great Barrier Island in August 1975; in the inner Hauraki Gulf 1743 were tagged in June 1976 and 2685 in October 1976. Estimates of tag loss due to the combined effect of shedding of tags and tagging mortality were made, and the crude tag return rates were adjusted accordingly. The combined returns from commercial and amateur fishermen for the first year after tagging, adjusted for tag loss, were: Great Barrier Island, 19 (2.3%); inner Hauraki Gulf, June tagging, 98 (5.7%), October tagging, 179 (6.8%). Tag return rates from different parts of the study area varied considerably.

Calculations of the population size for the inner Hauraki Gulf (fishery statistical areas 006 and 007) were made from tag returns of longline and set net fishermen and their catch statistics taken from the monthly fishing returns; Petersen's method gave population sizes of 43 million (returns from June tagging) and 36 million (October). The catch statistics are thought to considerably under‐record the real landings, and better estimates of the population size may be 71 million and 60 million respectively.

Keywords:

• Chrysophrys auratus
• tagging
• population number
• exploitation
• Hauraki Gulf