Spatio-temporal variability in reproductive ecology of sand flathead,Platycephalus bassensis, in three Tasmanian inshore habitats: potential implications for management

Temporal and spatial variability in gonad development, duration of spawning period, and size/age at maturity were investigated in sand flathead, Platycephalus bassensis. A 3-year study (2001–2003) revealed that variation in gonad weight with somatic weight was a function of an interaction between season and study location (Coles Bay, Georges Bay, and Tamar River estuary). Highest gonad weight was recorded in Coles Bay in early summer, which in comparison to Georges Bay, was approximately 50% higher and occurred 3 months later. Tamar River mature individuals were reproductively inactive during the spawning season. The proportion of mature individuals at different stages of maturity differed significantly among the three locations across all times. Coles Bay individuals were reproductively active from October to March, while in Georges Bay females with hydrated oocytes were seen in September but were absent from the population by November. Interannual variation in initiation and duration of spawning activity was evident in each location. Apart from male size at maturity, for both sexes the size and age at maturity (L50) was higher in Georges Bay compared to Coles Bay. The results emphasize the necessity of temporal and spatial management based on population differences in reproductive ecology.