Tidal marshes as habitat for juvenile fish in the Zeeschelde estuary (Belgium)

Little is known about the use by fishes of tidal marshes located in the mesohaline, oligohaline and freshwater tidal zone of an estuary. Two different fishing protocols were applied in order to assess: 1) spatial and temporal effects and 2) the influence of creek characteristics on the fish assemblages. In 2007 fish were sampled monthly from creeks in four tidal marshes, located in different salinity zones in the Zeeschelde. In 2008 nine creeks within one tidal marsh but each with different characteristics were sampled in spring, summer and autumn.Fish were caught in the creeks with winged fyke nets (1.5 cm mesh size in the cod end). For each creek we measured mouth width, level of bottom (versus mean low water level of the main river) and slope of the bank. Creek volume was calculated using cross section data, creek length and number of adjacent creek branches. In addition we recorded the presence of debris and permanent pools in both creeks and tributaries. In total we recorded 24 different fish species between 2007 and 2008 and catches were dominated by juveniles. The most abundant species was flounder. Multivariate analyses examined the variations of the fish assemblage in relation to position in the estuary and also to creek characteristics within one marsh. The influence of the salinity gradient is reflected in the different fish assemblages present in the four marshes. The highest number of fish tidal frame and containing permanent pools. The study emphasizes the importance of creeks in tidal marshes as habitats for juvenile fish