Aspects of the reproductive biology of some demersal fish species in Wellington Harbour, New Zealand

Abstract

Aspects of the reproductive biology of fish species commonly caught by otter trawl in Wellington Harbour were investigated by monthly samples from March 1973 to June 1974 to determine which of them spawn in the area. The most important criteria used in the study were: the seasonal abundance of individuals with ripe gonads in relation to the total number of fish in the catch; the seasonal fluctuations of the maturity coefficient of the fish; and the seasonal fluctuations of its mean condition factor. Of the 31 species comprising the trawl catch in the Harbour, 10 spawn in the area; two utilize the Harbour as a nursery/"staging" ground, where they grow to maturity and then migrate out of the harbour to spawn; and the majority of the species in the catch use the area as a feeding ground. Most of the species which spawn in the Harbour begin their spawning cycle at the approach of winter, some lasting until spring. A study of the total fecundity in some of these species showed that the number of eggs in the ovary increases with the size of the fish. Ova measurements were used to identify the species which are partial spawners. The relationship of gonad development to maturity coefficient and condition factor for all the species studied is discussed. Mean length and mean age at first maturity of the species were determined. Comparisons with the seasons of occurrence of fish larvae and juveniles of the species concerned in the plankton collections from the same area made by previous workers, confirmed the observed spawning periods of the various species studied.