Localised spawning omission in snapper, Chrysophrys auratus (Sparidae)

Abstract

Failure to spawn in a significant proportion of adult fish may greatly decrease the reproductive output of a population and lead to overestimates of recruitment to the fish stock. Reproductive output of the commercially important sparid, Chrysophrys auratus, around the Kaipara Harbour, New Zealand, is particularly important as this harbour is the primary source for the C. auratus population along the west coast of the North Island of New Zealand. We tested the hypothesis that C. auratus do not spawn inside the Kaipara Harbour by comparing monthly gonad and otolith samples from fish caught within the harbour with those of fish from surrounding coastal waters. Fish from coastal waters showed normal gonad development with peak spawning in spring. By comparison, almost all adult fish from the harbour had underdeveloped gonads, with mean gonadosomatic indices <= 1. Histological gonad analyses of C. auratus caught in the harbour showed vitellogenic oocytes were reabsorbed before spawning. Therefore, recruitment to the harbour must originate from spawning that occurs outside the harbour. This first record of spawning omission in C. auratus has important implications for fisheries management, as it may lead to overestimation of the spawning stock and increase the risk of broad-scale population depletion, through the targeted fishing of spawning aggregations.