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Estuarine-dependent fish live in a complex and dynamic environment that is primarily influenced by the salinity structure resulting from the mixing of fresh and marine waters. In response to this variable environment, the recruitment of estuarine-dependent fish can also be highly variable. Recruitment variability in black bream Acanthopagrus butcheri in Gippsland Lakes, southeastern Australia, was determined both from annual recruitment monitoring and the age structure of the population. Recruitment was found to be episodic, with the population dominated by a few year classes. For the 2 methods of estimating recruitment and associated time periods, we found a consistent linear relationship between water column stratification (difference between surface and bottom salinity) and recruitment. There was also a significant, non-linear (dome-shaped) relationship between freshwater flow and recruitment. This relationship suggested that the highest recruitment occurred at intermediate flows greater than ~3000 Ml d -1 in the main tributary rivers. The combination of stratification and freshwater flow in a multiple regression model improved the variability in recruitment explained to 71 and 79%, respectively, for the 2 methods. Analysis of age structure of bream from other Victorian estuaries showed that, as in Gippsland Lakes, recruitment was highly variable and episodic; however, the timing of strong and weak year classes varied between estuaries. This suggests that freshwater flow and salinity structure, and consequent recruitment variability, are unique to each estuary based on characteristics of catchment, channel topography, and entrance opening and closing. Climate change predictions for the Gippsland Lakes region include less rainfall and higher evaporation, potentially leading to higher salinities and lower stratification in Gippsland Lakes. The bream population is therefore likely to be negatively affected, and these effects may be exacerbated by any human activities in the catchment that further reduce freshwater flows or increase marine incursion.

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Snapper, Pagrus auratus (Forester), is an important recreational species in marine waters of Victoria, Australia. This study estimated survival for compulsorily released undersized P. auratus by holding fish in cages and tanks for 3 days. In all, 620 P. auratus caught by angling were assessed for post-release survival and 200 additional fish were used as controls. The survival rate was greater for shallow-hooked (97%) than deep-hooked (48%) P. auratus. Post-mortems showed that hooking injuries to the throat and/or gill area caused most deaths, while piercing of the heart also caused mortalities. Removing deeply ingested hooks decreased survival. To estimate survival of P. auratus across the Victorian fishery, this studyÕs results should be combined with estimates of shallow-hooking rates in the fishery. Shallow-hooking rate estimates would quantify the impact of the low survival rate found for deep-hooked fish.

Estuarine fish live in a highly dynamic environment where recruitment variability is a key determinant of population trajectory. Environmental requirements for successful recruitment may differ between co-occurring species, and therefore species may be advantaged or disadvantaged under climate change. Recruitment variability in black bream Acanthopagrus butcheri and estuary perch Macquaria colonorum in estuaries along the coast of western Victoria, southeastern Australia, was determined from the age structure of the populations. Recruitment was found to be episodic in both species, with the populations dominated by a few year classes; however, abundant year classes differed between species. Historical freshwater flows were found to be similar across estuaries, reflecting broad-scale rainfall. In contrast, water column stratification (difference between surface and bottom salinity) over a 7 yr period varied widely amongst estuaries. In general, recruitment of black bream was negatively correlated with freshwater flow and positively correlated with the level of stratification. In contrast to black bream, significant correlations for recruitment of estuary perch were negatively related to stratification and positively related to flows. Thus, although both species spawn in the spring and early summer, they have different environmental requirements in terms of flow and stratification for successful recruitment. This means that high inter-annual variability in flow is required for both species to experience favourable environmental conditions over time. Furthermore, the climate change scenario of significantly reduced flows in the Victorian region may mean that in many estuaries the conditions will be more favourable for the recruitment of black bream than for estuary perch.