Early postlarval fish in the hyperbenthos of the Dutch Delta (south-west Netherlands)

Early (post)larval fish constitute a significant part of the temporary hyperbenthos, i.e. of the fauna living in the lower reaches of the water column close to the substratum. Information on the densities and spatial and temporal variations of these stages, as well as on their lengths at the moment of occurrence, can be an important contribution to the knowledge of their dispersion, migrations and to the identification of possible bottlenecks in their recruitment. Therefore the hyperbenthos of the Voordelta, a shallow coastal zone in front of the Dutch Delta, as well as that of the subtidal channels and the intertidal brackish marsh creeks of the Westerschelde Estuary, was sampled monthly during one year by means of a sledge and a stow net. A total of 37 taxa were recorded from 410 samples. Densities often exceeded 400 ind 1000 m(-2) in the Voordelta and 300 ind 1000 m(-2) in the Westerschelde, including the tidal marshes of Waarde and Saeftinghe. The dominant taxa were clupeid larvae (predominantly herring Clupea harengus and sprat Sprattus sprattus), Pomatoschistus spp. (a mixture of sand goby P. minutus and Lozano's goby P. lozanoi), common goby Pomatoschistus microps, Syngnathus spp, (probably almost exclusively Nilsson's pipe fish S. rostellatus), plaice Pleuronectes platessa; sole Solea solea and flounder Pleuronectes flesus. Most species were found at a larger size in the Westerschelde (and in the tidal marshes) suggesting migration from the shallow coastal area into the estuary. Several species utilize the tidal marshes in the brackish reaches of the Westerschelde. The nursery value of these areas however, is restricted to specific early life history stages of a few species, especially flounder, bass Dicentrarchus labrax and the common goby. The estuary itself seems to function as a nursery for other species like sole and plaice. The hyperbenthic sledge was found to sample specific Life history stages of postlarval flatfish (early settlement stages at the onset of asymmetry), which are not easy to sample with other types of sampling gear.