Ontogenetic shifts in the distribution and reproductive patterns of Australian anchovy (Engraulis australis) determined by otolith microstructure analysis

Upwelling systems can provide ideal conditions for survival and growth of larval fishes. However, these unstable environments are highly dispersive and mortalities can be high. Anchovies (Engraulis spp.) utilise a range of behavioural strategies to increase egg and larval survival. Ontogenetic shifts in distribution have been proposed for Australian anchovy (Engraulis australis), but no supporting otolith-based age studies have been published to date. The present study used otolith increment counts to age larval, juvenile and adult Australian anchovy, which spawn throughout South Australian gulf and shelf waters. Only fish up to 1 year of age occurred in the northern Spencer Gulf, where eggs and larvae in high densities are retained in a nursery area favourable to anchovies. The southern gulf area was inhabited by 1, 2 and 3 year olds. Older anchovy were found in offshore shelf waters, where upwelling occurs and larval survivorship may be high. We hypothesise that Australian anchovy move offshore with age to utilise the wide range of environments that provide suitable spawning and nursery areas for this species.