Nursery grounds of the orange roughy around New Zealand

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Abstract

The orange roughy (Hoplostethus atlanticus) is a deep-sea species with a centenarian lifespan, a life-history feature that may enable the stocks to withstand prolonged periods of recruitment failure. Most stocks have been substantially depleted, however, so estimating recruitment has become a priority in setting catch quotas to ensure future sustainability of the fisheries. A description of the nursery grounds of the species off New Zealand is provided, using extensive research-survey data from 12 541 bottom trawls and 713 midwater trawls. The juveniles were initially caught on the seabed, near known spawning grounds, and towards the shallower end of the species' distribution, and not in midwater or the shallower or deeper bottom tows. Densities were greatest at 850-900 m. As juveniles grew, their spatial and depth distribution expanded, both shallower and deeper, with a skew towards deeper water, such that by the onset of maturation, densities were relatively high in 850–1300 m of water. The early nursery grounds were in relatively warm water, but on the south Chatham Rise, appeared to be bounded by the presence of a cold-water front.

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