No abstract

Girella tricuspidata is widely distributed and harvested by recreational and commercial fishers along the coastline of eastern Australia. The present study examined variability in the reproductive biology and growth of individuals within populations of G. tricuspidata across 3 estuaries (Clarence, Tuggerah and Tuross) and assessed population connectivity via a large-scale tagrecapture study in which fish were tagged across 9 estuaries. Spawning occurred predominantly between June and September in the Clarence River and between October and January in the Tuross River, suggesting that spawning occurs later in the year at higher latitudes. The recruitment of young to nursery grounds was spatially and temporally variable. G. tricuspidata are group-synchronous spawners, and the estimated batch fecundity was positively correlated with fish length. The estimated length and age at which 50% of G. tricuspidata attained reproductive maturity was similar for both sexes: ~286 mm fork length (FL) and 4.1 yr for males and 295 mm FL and 4.5 yr for females. G. tricuspidata were aged using otoliths to > 26 yr, whereas the reading of scales consistently underestimated the age of fish older than 5 yr. Growth was flexible but varied significantly between sexes and among estuaries; females grew faster than males and attained a larger asymptotic length in the Clarence and Tuross Rivers but not in Tuggerah Lake. Growth was rapid for both sexes until 4 to 5 yr of age, after which it slowed. Of the 6871 G. tricuspidata tagged, 15% were recaptured, with 96% of these fish recaptured in the estuary in which they were initially tagged. The recaptured individuals that migrated between estuaries predominantly displayed a northward movement into the prevailing coastal current, which is probably a life-history tactic to facilitate wide dispersal of eggs and larvae along eastern Australia.

This study examined the spatio-temporal reproductive patterns, population structure, maturity and growth of Acanthopagrus hybrid complexes, which comprise mainly black bream Acanthopagrus butcheri and the hybrids they form with yellowfin bream Acanthopagrus australis, in two Australian estuaries (Coila and Brou Lakes, NSW). There were no differences between pure A. butcheri and hybrids in terms of their population structure, growth and maturity, suggesting that these two breeds have similar life histories and may therefore be managed as single, naturally cohesive units. Sexual variation in size structure was only observed for the complex in Coila Lake. Although there was significant variation in age structure between estuaries, both complexes exhibited dominance of only a few year classes indicating episodic recruitment and high fishing mortality. Acanthopagrus eggs occurred in higher numbers within upstream creek habitats compared to lake habitats, thereby highlighting the need to protect these spawning habitats. Although maturity in the complexes was not influenced by gender or estuary, differences in growth were detected between the genders and estuaries.