Evaluation of habitat use by adult plaice (Pleuronectes platessa L.) using underwater video survey techniques

Large-scale spatial surveys of fish species in relation to habitat have tended to focus on depth, sediment type and temperature as descriptors of fish habitats. At a smaller scale, habitat parameters such as the relief of the sea floor, the presence of structuring fauna and prey availability may have a considerable influence on fish distribution, but often are not considered. In the present study we used video survey techniques to study habitat components in areas of the English Channel that were known to support consistently high densities of adult plaice. Habitat features were quantified and related to the density of adult plaice caught within the same study areas. To focus the study on habitat components other than sediment type all sites chosen had sandy substrata. The scale and spatial distribution and heterogeneity of physical and biological structures were quantified for each site and correlated to plaice densities. Plaice densities correlated with the abundance of benthic fauna recorded. In particular the emergent tube-dwelling polychaetes Lanice conchilega and Cheatopterus spp., which are a valuable food source for plaice, dominated some sites. Abiotic habitat features and habitat heterogeneity showed no clear relationships with respect to plaice densities at the scale of our surveys. This indicated that prey availability might be the driving force for habitat selection of adult plaice within sandy habitats and that other habitat descriptors assume less importance at smaller spatial scales.