MEPS 411:137-148 (2010)  -  DOI: https://doi.org/10.3354/meps08668

ABSTRACT: Harvesting of intertidal invertebrates for use as fishing bait is a global problem for estuary and coastal managers, with significant effects on sediments and associated infauna. Crab-tiling is a method of collection for the shore crab Carcinus maenas, which is then used as angling bait. This fishery operates in estuarine mudflats at a commercial scale, yet its impact on infaunal assemblages has not been quantified. The fishery involves laying hard man-made structures, known as ‘crab-tiles’, to attract pre-ecdysis C. maenas. Moulting shore crabs are harvested from underneath the tiles during low tide. Infauna surrounding these tiles, which are important prey for over-wintering wading birds and estuarine fishes, are therefore subjected to disturbance from crab-tiling activity. We experimentally manipulated sites on mudflats in 3 previously non-tiled estuaries to determine the impact of crab-tiling on macro-infaunal diversity. In addition to crab-tiled and control plots, treatments were incorporated in order to discriminate between the effects of the tiles and trampling disturbance. Response variables used were sediment penetrability, grain size and organic content as habitat-related variables, and number of taxa and abundance of individual animals as diversity estimators. The effects of crab-tiling on the sediment were contingent on the estuary; those with a greater proportion of fine particles were most affected. Simultaneously, crab-tiling reduced diversity (number of taxa and abundance of macro-infauna) and altered assemblage structure. The trampling aspect of crab-tiling was found to have the most impact on the sediment and infauna, and so crab-tiling could be managed via control of access and approaches to minimise sediment disturbance.

KEY WORDS: Bait collection · Carcinus maenas · Disturbance · Trampling · Anthropogenic effects