Effects of mechanical cockle harvesting on intertidal communities

摘要: Summary 1. Shellfish of marketable size can be harvested much more quickly and efficiently using mechanical methods such as tractor-powered harvesters suction dredgers than by traditional methods. The adverse effects machines on non-target organisms need to considered carefully before licensing activities. 2. A tractor-towed cockle harvester was used extract cockles from intertidal plots muddy sand clean in order investigate the other benthic invertebrates their predators. 3. Harvesting resulted loss a significant proportion most common both areas, ranging 31% Scoloplos armiger (Polychaeta) (initial density 120 m−2) 83% Pygospio elegans 1850 m−2). Significant could not detected populations with less 100 m−2. 4. Populations Hydrobia ulvae (Gastropoda) remained significantly depleted area for 100 days after harvesting, Nephtys hombergi (Polychaeta), Bathyporeia pilosa (Amphipoda) 50 days. 5. Invertebrate relatively few Cerastoderma edule (Pelecypoda) recovered those structured community, which included several tube-dwelling species Lanice conchilega (Polychaeta). 6. Bird feeding activity increased at first gulls waders taking advantage made available harvesting. Subsequently, sand, level bird declined compared control areas. It reduced curlews Numenius arquata 80 days harvesting oystercatchers Haematopus ostralegus 50 days. 7. It is concluded this study that tractor dredging high areas causes sufficiently large mortality should excluded conservation importance communities invertebrates, fish birds.