The effects of commercial exploitation on orange roughy (Hoplostethus atlanticus) from the continental slope of the Chatham Rise, New Zealand, from 1979 to 1997

Orange roughy (Hoplostethus atlanticus) is a recently exploited species, fished by trawling at depths of 700-1200 m on the continental slope around New Zealand. In this paper, changes in the major New Zealand orange roughy fishery on the Chatham Rise during a 19-year period are examined. Data from research trawl surveys and commercial fishing returns from 1979 to 1997 were analysed, and changes in the population described. The distribution of orange roughy showed a marked contraction, and aggregations became largely centred around seamounts or very localised areas of the slope. The biomass of orange roughy, measured by trawl survey and commercial catch-ger-unit-effort indices, declined substantially, and in 1997 was estimated to be about 20% of virgin levels. Most bycatch species also declined in abundance, with no indication of species replacement. Size structure of the population did not change markedly over the period. Timing of spawning in July, and the pattern of gonad development, were also consistent over the years. There was no change in size or age at maturity. Prey composition remained similar. Biological changes may not have been apparent because orange roughy is a long-lived, slow-growing species, with low productivity. There could be a long response time of the population to fishing pressure. (C) 2000 Elsevier Science B.V. All rights reserved.