Publication Abstract

Importance of benthic habitat complexity for demersal fish assemblages

M.J. Kaiser, S.I. Rogers and J.R. Ellis

Major amendments in 1996 to the Magnuson-Stevenson Act require fisheries managers to define "essential" fish habitat and address the impact of fishing gear in their management plans. However, before considering what might qualify as "essential" fish habitat, it is necessary to first understand the association between fish and their habitat. Some studies have already revealed subtle relationships between fishes and sediment-type, however this approach does not quantify habitat complexity. We undertook a large-scale survey of demersal fish populations and benthic communities in the southern North Sea and eastern English Channel. As in other studies, water depth was closely linked to the main dichotomy in assemblage composition. Flatfishes occurred in shallow water, whereas roundfishes and small shark species were found in deeper habitats. Within each of these two sample station groupings the assemblages dichotomised further on the basis of habitat type and benthic faunal associations. Three further groupings were identified within the deep water habitat. These were characterised by the presence of rocks, broken shells and/or a large biomass of sessile epibenthos. Small shark species were almost exclusive to habitats with shelly substrata. In contrast, the shallow water habitats were topographically less complex with a smaller biomass of sessile epibenthos. Flatfishes that were visual predators were most closely associated with habitats with some sessile epibenthos, whereas sole, which largely locate their prey using chemosensory cues, were more closely associated with the least complex habitat. Although these flatfish habitats are intensively fished by bottom trawls, the characteristic sessile epifauna are relatively fast growing and are probably able to withstand such disturbance. In contrast, the deep water sessile communities had a greater biomass of sessile epifauna with some slow-growing species which would be more vulnerable to fishing disturbance. However, these habitats are seldom fished using invasive techniques.

Reference:

M.J. Kaiser, S.I. Rogers and J.R. Ellis, 1999. Importance of benthic habitat complexity for demersal fish assemblages. Proceedings of the American Fisheries Society, 22: 212-223