Changes in shorebird behaviour and distribution associated with an intertidal crab fishery

Abstract

Harvesting green crabs Carcinus maenas for bait is a popular fishery in south-west UK estuaries that are important habitats for shorebirds. The fishery involves laying roof tiles or PVC guttering into sediments; crabs seeking refuge bury beneath the tiles and are collected by fishers during low tide. By observing foraging birds in tiled and non-tiled sites the general model that this fishery modified shorebird diversity, distribution, and behaviour was tested. No evidence was found for a relationship between shorebird species richness, abundance or assemblage composition and the presence of tiles. To measure distributional and behavioural changes of shorebirds to crab-tiles, the focus was on two shorebird species: curlew Numenius arquata and redshank Tringa totanus. The crab-tiles affected the shorebird distribution and feeding patterns but this was dependent on species, time, and scale of observation. Redshank spent more time next to tiles than away and dedicated similar feeding effort between treatments. Curlew did not spend proportionally more time next to tiles but did spend more time feeding when they were next to tiles than away from tiles. Curlew and redshank spent proportionally more time probing than pecking when they were next to crab-tiles, but overall spent similar times exhibiting the two feeding behaviours compared with conspecifics in a non-tiled site, although this was dependent on time. It is suggested that crab-tiles may influence the spatial distribution of potential prey, thereby aggregating the birds and relieving predation pressure elsewhere. As both species (curlew and redshank) were observed ‘standing not feeding’, i.e. resting or preening, when next to tiles we also suggest that the structure created by the tiles provides some shelter to reduce negative effects of wind on thermoregulation. Copyright © 2012 John Wiley & Sons, Ltd.