Fish larvae of the Wellington Harbour and South Coast 1997-1998

Abstract

Studies on the larval ichthyofauna of the Wellington region have largely concentrated on the Harbour itself. Only one author has described the early life history of species on the south coast of Wellington, and these studies were restricted to several species of small rocky intertidal fishes from the families Tripterygiidae and Gobiesocidae. The present study was carried out with the primary aim of describing as many species that occur as larvae on the south coast as possible, and extending the descriptions of larvae that already exist in the literature. Samples were collected from three study sites: at Kau Bay in Wellington Harbour, and Lyall Bay and Island Bay on Wellington's south coast. Over a one-year study period, 19 samples were collected from each of the sites, and the larval teleosts in each were identified to the greatest extent possible and quantified. Thirty-three species from 21 families were positively identified over the course of the study, including the first record of a larva of Jack Mackerel, Trachurus declivis. Twenty species were recorded on the Wellington south coast for the first time, as were two species in Wellington harbour. Wellington's southern coastline is characterised by very different hydrological and geological features to the harbour. With this in mind, the hypothesis was examined that the two south coast sites are likely to be more closely related to one another in terms of species composition and abundance than either is to the harbour site. Three indices were used to compare between and among the sites. All three returned evidence that the two south coast sites were more similar to each other than either one was to the harbour site. Comparisons on a basic level were made between data collected in an earlier study of Frentzos (1980) from a similar depth contour in Kau Bay. While these sites were found to have similar species richness, few of the species in the current study were present in similar proportions to those described by Frentzos (1980). Possible causes of the differences between the two studies are discussed. These include El Niño-induced warm water temperature, and the possibility that these conditions triggered both an episode of very high salp density, and possibly a bloom of the toxic phytoflagellate Gymnodinium brevisulcatum. Comments are made on the difficulty of quantifying larval fishes because of the highly variable nature of larval assemblages in response to physical or temporal variables. Long term monitoring of ichthyoplankton is recommended as the only way of minimising the effects of high larval variability on short and medium term temporal scales.