Disturbance of intertidal soft-sediment benthic communities by cockle handraking

Recent awareness of the ecosystem effects of fishing activities on the mari ne environment means that there is a pressing need to evaluate the direct a nd indirect effects of those activities that may have negative effects: on non-target species and habitats. The cockle, Cerastoderma edule (L.) is the tat get of a commercial and artisanal fishery that occurs in intertidal an d estuarine habitats across Northern Europe. Cockles are harvested either m echanically using tractor dredges or suction dredges or by large numbers of individual fishers using hand rakes. This study examined the effects of ha nd raking on the non-target species and under-sized cockles associated with intertidal cockle beds and the effects of size of the parch of sediment di sturbed on subsequent recolonisation. Hand raking led to an initial three-f old increase in the damage rate of under-sized cockles compared with contro l plots. The communities in both small and large raked plots showed communi ty changes relative to control plots 14 days after the initial disturbance. The small raked plots had recovered 56 days after the initial disturbance whereas the large raked plots remained in an altered state. Samples collect ed over a year later indicated that small-scale variations in habitat heter ogeneity had been altered and suggest that while: effects of hand raking ma y be significant within a year, they are unlikely to persist beyond this ti me-scale unless there are larger long-lived species present within the comm unity. (C) 2001 Elsevier Science B.V. All rights reserved.