Publication Abstract

The Burry shellfishery and oystercatchers: using a behaviour-based model to advise on shellfishery management policy

The Burry shellfishery andoystercatchers: using a behaviour-based model to advise on shellfishery management policy.

A.D. West, J.D. Goss-Custard, S. McGrorty, R.A. Stillman, S.E.A.leV.dit Durell, B. Stewart, P. Walker, D.W. Palmer and P.Coates

The Burry inlet,South Wales, supports a licensed cockle Cerastoderma edule fishery and occasional musselMytilus edulis fishery. It is also an important overwintering ground for oystercatchersHaematopus ostralegus. In recent years mussels have settled over parts of some cocklebeds, preventing cockle fishery there and leading to a request by shellfishers to removethis 'mussel crumble'. Conservation managers, however, were concerned that the musselcrumble might be providing a high-quality food source for the oystercatchers, making itsremoval detrimental to the birds. A behaviour-based model of oystercatcher feeding oncockles and mussels was parameterised for the inlet and its predictions tested against thedistribution of birds across the shellfish beds and the amount of time they spent feeding.The model was then used to explore whether the birds were currently food-limited and whatwould be the effects on their mortality rate and body condition if the mussel crumble wereto be removed, thereby re-exposing underlying cockle beds. The model predictedsuccessfully the proportion of birds feeding on the different types of food and the numberof hours birds spent feeding on neap tides. It was predicted that, at current birdpopulation sizes, there would have to be a 50 % reduction in shellfish stocks and theareas of shellfish beds from 2000-01 levels to cause noticeable extra emigration ormortality. A given area of mussel bed was predicted to be able to support more birds thanthe same area of cockle bed, but the greater area of the cockle beds meant that they weremore important than mussels in determining the number of birds supported by the inlet, Thesimulated removal of mussel crumble to expose underlying cockles had no effect onpredicted bird mortality and body condition at 2000-01 shellfish stock levels. However,there were circumstances under which the mussel crumble was predicted to increase theinlet's capacity to support birds, particularly when the area of existing cockle andmussel beds was substantially reduced.

Reference:

A.D. West, J.D. Goss-Custard, S. McGrorty, R.A.Stillman, S.E.A. leV.dit Durell, B. Stewart, P. Walker, D.W. Palmer and P.Coates (2003). The Burry shellfishery and oystercatchers:using a behaviour-based model to advise on shellfishery management policy. MarineEcology-Progress Series, 248: 279-292

A.D. West, J.D. Goss-Custard, S. McGrorty, R.A. Stillman, S.E.A. leV.dit Durell, B. Stewart, P. Walker*, D.W. Palmer* and P.Coates,

Marine Ecology Progress Series, 248: 279-292