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Habitat quality for a given fish species is determined by factors that enhance survival, growth and reproductive success of its individuals. As such fish growth rate can be used to estimate the quality of essential fish habitats like estuaries. If food is not limiting, then temperature is likely to be the main controlling factor for growth. A multivariable bioenergetics model was constructed for the European flounder to generate spatially-explicit estimates of growth in theScheldt estuary. Digital maps of abiotic variables (temperature, oxygen concentration and salinity) for March, July and October were used as model inputs to evaluate spatial and temporal effects of water quality on growth rate potential. The model was run for two years (1998 and 2003) in order to describe any effect of improvement of the water quality on the estuarine-wide distribution of flounder. The model predicted that in March, when 0-group flounder is known tomigrate upstream, growth is highest in the upper freshwater reaches of the estuary. This suggests that freshwater migration of flounder may be, at least partly, temperature driven. In July and October, low oxygen concentrations near the mouth of the main tributary probably prevent upstream migration. In summer and autumn, growth rate in the brackish part of the estuary was higher compared to the marine part. Field data on the distribution of flounder in theestuary showed that flounder abundance throughout the year was highest in the brackish part, where suitable prey items are readily available. Our results indicate that abiotic variables may be useful to predict the habitat use of diadromous species in estuaries. Given the importance of food in habitat selection, the model should be expanded with a foraging compartment to account for prey availability. |
