Dynamics in 0+ recruitment and early life history for snapper (Pagrus auratus, Sparidae) in South Australia

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Abstract
The population dynamics of snapper (Pagrus auratus) relate to interannual variation in 0+ recruitment. The focus of the present study was to improve our understanding of this variation for snapper in northern Spencer Gulf, South Australia. The objectives of this study were to describe the distribution and abundance of 0+ juveniles annually from 2000 to 2002 and to determine early life history characteristics through retrospective analysis of otolith microstructure from captured fish. The environmental characteristics differed between years, with 2001 being extremely hot and 2002 the coldest summer recorded. Sampling was undertaken in April after spawning and settlement were complete. The estimates of recruitment were relatively low, suggesting a complex relationship with sea surface temperature. Each year new recruits occurred at the same places that were bare and flat with muddy substratum, suggesting nursery areas are actively selected by the recruits. The sagittae from juveniles had clear daily increments and settlement mark, allowing age and presettlement duration to be determined. Growth rates varied considerably both within and between years, and were related to water temperature, which affected the presettlement duration. Based on spawn dates, successful recruitment resulted from specific periods through the reproductive season that appeared to relate to the specific water temperature regimen in each year.

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