Baie de Somme

50.201, 1.651

Study A

Study A

Birds

Oystercatcher, Haematopus ostralegus

Modelling

Non-MORPH

Abstract

In a number of extensive coastal areas in northwest Europe, large numbers of long-lived migrant birds eat shellfish that are also commercially harvested. Competition between birds and people for this resource often leads to conflicts between commercial and conservation interests. One policy to prevent shellfishing from harming birds is to ensure that enough food remains after harvesting to meet most or all of their energy demands. Using simulations with behaviour-based models of five areas, we show here that even leaving enough shellfish to meet 100% of the birds’ demands may fail to ensure that birds survive in good condition. Up to almost eight times this amount is needed to protect them from being harmed by the shellfishery, even when the birds can consume other kinds of non-harvested prey.

Funding and Collaboration

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Study B

Study B

Birds

Oystercatcher, Haematopus ostralegus

Modelling

Non-MORPH

Abstract

Reproduced with permission from Elservier

Intertidal areas support during the non-breeding season many wading birds Charadrii thatmay often take flight in response to the presence of people or of birds of prey on their intertidal feeding and roosting grounds. Disturbance can cause birds to spend energy flying away and to lose feeding time while relocating to different feeding areas, where the increased bird densities may intensify competition from interference and, if of sufficient duration, from prey depletion. Until now, there has been no method for establishing how frequently birds can be put to flight before their fitness is reduced. We show how individual-based behavioural models can establish critical thresholds for the frequency with which wading birds can be disturbed before they die of starvation. It uses oystercatchers Haematopus ostralegus in the baie de Somme, France where birds were put to flight by disturbance up to 1.73 times/daylight hour. Modelling shows that the birds can be disturbed up to 1.0–1.5 times/h before their fitness is reduced in winters with good feeding conditions(abundant cockles Cerastoderma edule and mild weather) but only up to 0.2–0.5 times/h when feeding conditions are poor (scarce cockles and severe winter weather). Individual based behavioural models enable critical disturbance thresholds to be established for the first time.

Funding and Collaboration

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Study C

Study C

Birds

Oystercatcher,Haematopus ostralegus

Curlew, Numenius arquata

Dunlin,Calidris alpina

Modelling

MORPH

Abstract

Reproduced with permission

Conservation managers need to be able to assess and prioritize issues that may affect their target habitats and species. In the Baie de Somme, France, conservation issues affecting overwintering shorebirds include hunting pressure, cockle fishing, recreational disturbance, Spartina encroachment, and changing sediment levels. We used an individual-based model to predict the effect of these issues on the survival of three shorebird species: dunlin Calidrisalpina, oystercatcher Haematopus ostralegus and curlew Numenius arquata. In the model, removing hunting from the mudflats in the eastern part of the estuary had the greatest positive effect on shorebird survival. Oystercatcher survival decreased markedly when stocks of large cockles were reduced to ,250 m-2 or numbers of fishermen per day were doubled. Short-term disturbance events, such a swalkers, had more effect on shorebird survival than long term events, such as fishermen. Dunlin, as a protected species, were able to feed outside the Re´serve Naturelle andwere unaffected by disturbance within the Re´serve. Oystercatcher survival decreased when the number of disturbance events within the Re´serve exceeded one h-1, and curlew survival when disturbance events exceeded six h-1.Spartina encroachment caused dunlin survival to decline steadily as feeding habitat was lost. Dunlin were also the species most affected by changes in sediment levels, likely to occur through either sedimentation or sea level rise.

Funding and Collaboration

European Commission. Project number: EVK2-2000-00612 (extracted from Stillman et al 2005 report)

 

 

Related Paper:

Study A

Goss-Custard, J.D., Stillman, R.A., West, A.D., Caldow, R.W.G., Triplet, P., le V dit Durell, S.E.A. and McGrorty, S., 2004. When enough is not enough: shorebirds and shellfishing. Proceedings. Biological sciences, 271(1536): 233-237.

 

Study B

Goss-Custard, J.D., Triplet, P., Sueur, F. and West, A.D., 2006. Critical thresholds of disturbance by people and raptors in foraging wading birds. Biological Conservation, 127(1): 88-97.
 

Study C

Durell, S. E. A. le V. dit, Stillman, R. A., Triplet, P., Desprez, M., Fagot, C., Loquet, N., Sueur, F. & Goss-Custard, J. D. (2008) Using an individual-based model to inform estuary management in the Baie de Somme, France. Oryx, 42, 265-277.