Well-founded and supposed negative effects of cockle dredging on tidal-flat sediment and fauna: a review of contributions of ecological research
Beukema, J.J. (2023). Well-founded and supposed negative effects of cockle dredging on tidal-flat sediment and fauna: a review of contributions of ecological research. J. Sea Res. 194: 102408. https://dx.doi.org/10.1016/j.seares.2023.102408
In: Journal of Sea Research. Elsevier/Netherlands Institute for Sea Research: Amsterdam; Den Burg. ISSN 1385-1101; e-ISSN 1873-1414, more
Published studies on effects of mechanical dredging on tidal flats for cockles (Cerastoderma edule) are critically reviewed, with special emphasis on studies in the Dutch Wadden Sea. The evidence on fishery-caused changes in sediment composition is contradictory, but some loss of silt and coarsening of the sediment was found in part of the fished areas. However, the part of the tidal flats touched annually in the Wadden Sea was invariably small (mostly only a few percent) and recovery was rapid. Generally, negative effects on bivalve recruitment following fishing were not established. Negative effects on non-target fauna were always present but variable. Recovery of the fauna was generally rapid. The stocks of adult cockles were thinned, but high proportions were caught only in a small minority of the years when cockle abundance was low. Food supply for shellfish-eating birds on the tidal flats, notably Oystercatchers, was reduced in fished areas, but not seriously so in most years. Evidence for negative effects of mechanical cockle fishing on bird condition and survival was present, but scarce. Such effects depended on the availability of alternative food, particularly mussels (Mytilus edulis). Overall-negative reports on consequences of cockle fishery were published only by a group of Dutch ecologists. These reports are judged questionable. Though the effects of mechanical cockle dredging appear to be not all so bad as sometimes supposed and the reasons to close this fishery are partly open to question, resumption of this (since two decades forbidden) fishery in the Wadden Sea is not recommended.
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