The biomass of snapper in SA shows considerable inter-annual variation resulting from changes in 0+ recruitment. To understand inter-annual recruitment variation, temporal patterns of reproduction, aspects of early life history and the relationship of these to water temperature were studied in Spencer Gulf, the region that contributes 70% of South Australia’s snapper catch.

0+ snapper distribution and abundance were assessed by a trawl survey undertaken in April of each year since 2000. Reproductive samples of snapper were collected from northern Spencer Gulf during the spawning seasons of 2005/06 and 2006/07, and analysed macro- and microscopically. Aspects of the early life history of snapper were interpreted from otolith microstructure.

Inter-annual abundance of 0+ snapper was highly variable but distribution was consistent between years, with one small nursery contributing the majority of the catch. Spawning was continuous from November to early February but peaked in December. From otolith microstructure, birth dates showed that most successful recruits were spawned from mid-December to mid-January. Thus, whilst spawning occurred over a prolonged period, windows of opportunity for recruitment were limited. Periods of spawning when water temperature was between 22 and 24ºC were particularly important and thus may be a key determinant of 0+ recruitment dynamics.