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Marine Ecology Progress Series

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MEPS 417:249-261 (2010)  -  DOI:

Highly variable recruitment in an estuarine fish is determined by salinity stratification and freshwater flow: implications of a changing climate

Gregory P. Jenkins1,2,*, Simon D. Conron1, Alexander K. Morison1,3

1Marine and Freshwater Fisheries Research Institute, Department of Primary Industries, Queenscliff, Victoria 3225, Australia
2Department of Zoology, University of Melbourne, Parkville, Victoria 3010, Australia
3Morison Aquatic Sciences, Nelly Bay, Queensland 4819, Australia

ABSTRACT: 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.

KEY WORDS: Year-class strength · Salinity · Population dynamics · Estuary · Black bream · Acanthopagrus butcheri · Gippsland Lakes

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Cite this article as: Jenkins GP, Conron SD, Morison AK (2010) Highly variable recruitment in an estuarine fish is determined by salinity stratification and freshwater flow: implications of a changing climate. Mar Ecol Prog Ser 417:249-261.

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