Winter and summer trawl surveys of hoki south of New Zealand, 1990 / R.J. Hurst, K.A. Schofield.

20 references; 20 figures; 17 tables; 2 appendices.

Random trawl surveys of the Southland and sub-Antarctic areas of New Zealand were carried out in July-August (winter) and November-December (summer) 1990. The main aims were: to estimate the proportion of hoki which remain in the southern area during the winter spawning season; to determine if there are spawning grounds in the southern area (winter survey); to determine if there is significant hoki biomass deeper than 800 m by extending the usual survey depth of 300-800 m down to 1000 m (summer survey); and to derive estimates of relative changes in abundance since previous comparable surveys in Oct.-Nov. 1983 and 1989. The estimated biomass is given for the 15 most abundant species and catch data are given for another 10 major species. The biomass of javelinfish, rattails (all species combined), pale ghost shark, hake, and all species combined decreased significantly between winter and summer. The adult hoki biomass doubled between winter and summer. Extension of the survey depth range in summer, from 800 to 1000 m, resulted in a small (4%) increase in the hoki biomass, and significant increases in the biomass of hake, rattails and smooth oreo. Comparison of biomass estimates with those from earlier surveys is difficult because different vessels and gear were used. However, seasonal and annual comparisons of the biomass distribution by area and depth are made for hoki, ling, southern blue whiting, and hake. Detailed biological data (including length, sex, weight, reproductive state, and feeding) are presented for hoki, ling, southern blue whiting, and hake. Survey comparisons of fish size distribution and other biological data are also made for these species, where appropriate data are available. No new hoki spawning grounds were found. (auths.)