ALBERT

Description: 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 large 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., that 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 lesser importance at smaller spatial scales.

Description: Flatfishes have been the subject of scientific research since the beginning of the 19th century but information on the specific habitat requirement of the adult life stages is largely anecdotal. Detailed knowledge of flatfish habitats however is a precondition for a more ecosystem orientated approach to fisheries management. Here the association between benthic habitat and the adult life stage of three flatfish species plaice (Pleuronectes platessa), sole (Solea solea) and lemon sole (Microstomus kitt) was investigated in the English Channel. Data from groundfish surveys spanning a period of 9 years was used to identify three distinct site groups: sites where a species occurred in consistently high abundances, sites of variable or low abundance and sites at which none were caught. Following the supposition of habitat selection theories such as the ideal free distribution theory these three sites groups should represent a gradient in habitat suitability from highly suitable to less suitable and unsuitable respectively. Habitat parameters and features for the three site groups and species were described and analysed. In particular sediment type and the importance of structuring epifauna for adult flatfish was investigated. Overall plaice and sole showed very similar trends for abiotic environmental parameters such as depth, temperature, salinity and tidal currents. Lemon sole was found over distinctly different habitats which may indicate a stronger niche partitioning of this species. Sediment associations differed between the three species with plaice predominantly occurring over sandy substrates with little mud and gravel content, while sole was found over a wider range of muddy to sandy substrates. Lemon sole was predominantly found over sand however containing a higher percentage of gravel than plaice. Structuring emergent epifauna was related positively to plaice and lemon sole abundances. These structures might be important as they tend to harbour larger numbers of epibenthic species upon which adult plaice and lemon sole prey. No such trend was found for the tactile feeding sole which mainly forages on infaunal polychaetes and molluscs.

Description: Fishers have often complained that standard United Kingdom groundfish survey data do notadequately reflect the grounds targeted by commercial fishers, and hence, scientists tend to make overcautiousestimates of fish abundance. Such criticisms are of particular importance if we are to make acreditable attempt to classify potential essential fish habitat (EFH) using existing data from groundfishsurveys. Nevertheless, these data sets provide a powerful tool to examine temporal abundance of fishon a large spatial scale. Here, we report a questionnaire-type survey of fishers (20012002) that invitedthem to plot the location of grounds of key importance in the Irish Sea and to comment on key habitatfeatures that might constitute EFH for Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus,and European whiting Merlangius merlangus. Plotted grounds were cross-checked using records ofvessel sightings by fishery protection aircraft (19851999). A comparison of the areas of seabedhighlighted by fishers and the observations made on groundfish surveys were broadly compatible forall three species of gadoids examined. Both methods indicated important grounds for cod and Europeanwhiting off northern Wales, the Ribble estuary, Solway Firth, north of Dublin, and Belfast Lough. Themajority of vessel sightings by aircraft did not match the areas plotted by fishers. However, fishingrestrictions, adverse weather conditions, and seasonal variation of fish stocks may have forced fishersto operate outside their favored areas on the (few) occasions that they had been recorded by aircraft.Fishers provided biological observations that were consistent among several independent sources (e.g.,the occurrence of haddock over brittle star [ophiuroid] beds). We conclude that fishers knowledge isa useful supplement to existing data sets that can better focus more detailed EFH studies.

Description: Patches of a very dense tube mat biotope were found during fish habitat studies in the eastern English Channel. At three locations in the lows between linear sand banks off the French coast an un-described small Chaetopterus sp. occurred with small Lanice conchilega as an enriched sediment stabilizing biotope. This biotope was distinct though having similarities to other tide swept sub-tidal biotopes dominated by L. conchilega. Using cameras and side-scan sonar it was seen to overlay heterogeneous cobbles and shell hash with intermittent rippled sand veneer. The patchiness of this enriching biogenic feature contributed to the variability in trawl catches of fish.