Cross-channel distribution of small fish in tropical and subtropical coastal wetlands is trophic-, taxonomic-, and wetland depth-dependent

Abstract

Although understanding the spatial distribution of fish is crucial to effective management of estuaries and coastal wetlands, there has been little systematic study of fish distribution at the cross-sectional scale in tropical estuaries. We tested the generality of a model for the cross-channel distribution of small fish (<200 mm fork length), extrapolated from temperate studies, for tropical and sub-tropical estuaries and coastal wetlands. We used cast nets, which could be deployed across a wide variety of habitats, to directly compare fish abundance between channel edges and adjacent mid-channel areas across a variety of coastal floodplain wetlands, including fully estuarine, brackish and freshwater sites. Cross-channel distribution of fish was more complex than the original model suggested. The original model reliably predicted the distribution of benthic feeding fish in most locations when mean mid-channel depths were >0.83 m. However, the model was less effective for predicting distributions of benthic feeders in shallow locations or in locations lacking shallow water edges. In those locations there was little difference in the abundance of fish between edges and midchannels. Distributions of planktivores and detritivores in estuarine and brackish areas were not consistently predicted by either of these models, but varied unpredictably over space and time. An additional model was needed for detritivores in freshwater wetlands with highest abundances in deeper mid-channel areas.