Ovarian development and the potential annual fecundity of western stock hoki (Macruronus novaezelandiae)

Abstract

Hoki (Macruronus novaezelandiae) form two of New Zealand's largest spawning fisheries, one centred off the west coast of the South Island (WCSI), the other in Cook Strait. Research data collected during surveys 1983–96 show that ovarian development begins on the feeding grounds between March and April, whereas spawning occurs mainly in July and August. Research has also shown that a significant proportion of adult hoki do not develop to spawn in a given year. Plans to estimate the absolute abundance of the western spawning stock off the WCSI using an egg production method require estimates of total annual fecundity and proportion spawning. Although determinate spawners, hoki are capable of multiple spawning in one season, and it is difficult to differentiate between fish about to spawn and fish that have already begun to spawn on the WCSI. In this study, we applied a modified stereological technique to samples of western stock hoki obtained from the feeding grounds south of New Zealand in May to determine the feasibility of estimating fecundity, at the same time as estimating the annual proportion developing to spawn. Mean fecundity estimates ranged from 0.4 million to 3.0 million oocytes and compare favourably with previous unpublished estimates of fecundity in early spawners on the west coast. We concluded that samples collected from the Southern Plateau during surveys of pre‐spawning hoki in May could provide useful estimates of fecundity.