Ardea
Official journal of the Netherlands Ornithologists' Union

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Goss-Custard J.D., McGrorty S. & Durell S.E.A. le V. dit (1996) The effect of Oystercatchers Haematopus ostralegus on shellfish populations. ARDEA 84 (A): 453-468
This paper discusses the contrasting effect of Oystercatchers, in combination with other predators, on the dynamics of a mussel Mytilus edulis and a cockle Cerastoderma edule population. On the Exe estuary, a plentiful supply of young (spat) Mussels seem only able to settle successfully, and survive their first winter, amongst the byssus threads of already established adults (> 1-year olds), where they are probably protected against predation by crabs Carcinus maenas. So more spat reach adulthood where adults are already numerous. By removing up to 30% of the large Mussels in winter, Oystercatchers may reduce the protected space available to young Mussels, unless the growth rates of the remaining Mussels are thereby sufficiently enhanced to compensate for the loss. In direct contrast, a study by Hancock (1971, 1973) of Cockles in the Burry Inlet showed that settlement of a plentiful supply of spat was reduced at high densities of adults. Although this association may have arisen, in part, because crab predation is lower in years of low adult density, the effect of Oystercatchers on spat settlement in this shellfish was directly opposite to that which they had on Mussels in the Exe estuary, enabling more spat Cockles to settle and survive. In other populations of both species, where spat shellfish settle in different places to adults, Oystercatchers will have little influence on recruitment. On the other hand, Oystercatchers are likely to affect in most populations the abundance of the large shellfish, upon which both they and commercial shellfisheries mainly depend.


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