Nekton use of salt marsh creeks in the upper Tejo estuary

The use of the Tejo estuary, Portugal, salt marsh creeks by nekton was examined based on sampling surveys with a fyke net from September 1998 until August 2001. From the 20 taxa (14 fish species, 5 decapod crustacean species, and 1 cephalopod species) identified in the studied creeks, 16 were regularly caught throughout the sampling period. The shrimp Palaenionetes varians was the most numerically abundant species in the creeks, while the biomass was dominated by the mullet Liza ramada. The nekton assemblage was mainly represented by marine-estuarine opportunist species, comprising 85% of the total number of species; when the number of individuals was considered, estuarine residents accounted for 96% of the total. A high seasonality was detected on the species abundance patterns: the most abundant species (P varians, Crangon crangon, L. ramada, Pomatoschistus microps, Syngnathus sp., and Anguilla anguilla) occurred throughout the sampling period, Sardina pilchardus, Dicentrarchus labrax, and Atherina boyeri were particularly abundant in spring and summer, and Engraulis encrasicholus, Liza aurata, Gambusia holbrooki, Palaemon longirostyis, and Palaemon serratus were most abundant in autumn and winter. L. ramada occurred in the tidal creeks in high numbers during neap tides, while the majority of the remaining taxa were most abundant during spring tides, suggesting a differential pattern of habitat use according to species.