Predicting food requirements of overwintering shorebird populations on the Solway Firth. A report to Scottish Natural Heritage and Marine Scotland

• Main Authors: Stillman, Richard A., Wood, K.A.
• Format: Book
• Language: English
• Published: Bournemouth University 2013
• Subjects: Calidris canutus; Red Knot
• Online Access: http://eprints.bournemouth.ac.uk/21908/; https://eprints.bournemouth.ac.uk/21908/3/Stillman%2520%2526%2520Wood%25202013%2520-%2520Predicting%2520food%2520requirements%2520of%2520overwintering%2520shorebird%2520populations%2520on%2520the%2520Solway%2520Firth%2520-%2520pdf%2520compatible.pdf

In this report we use a recently-developed spreadsheet model to predict the overwinter food requirements of two shorebird species, oystercatcher (Haematopus ostralegus) and red knot (Calidris canutus), within the Solway Firth. The model is based on the energy requirements of the birds together with the energy value of their shellfish food. The model predicts the quantity of shellfish required to maintain high survival rates, and hence avoid significant mortality events within the oystercatcher and knot populations. Knot were assumed to consume 5-14mm cockles (Cerastoderma edule L.), 5-24mm mussels (Mytilus edulis L.) and 8-16 mm tellin (Macoma balthica L.). Oystercatcher were assumed to consume >15mm cockles, 30-60mm mussels and >12mm tellin. The biomasses of invertebrate prey were derived from intertidal surveys of the site. The population sizes of the bird species were derived from Wetland Bird Survey (WeBS) core counts. Predictions were for the winter of 2013-2014. Shellfishing was assumed to exploit >28mm cockles. The food requirements of oystercatcher and knot were predicted for different combinations of food supply. All scenarios assumed that the birds could consume cockles, mussels and tellin. Alternative scenarios assumed that knot and oystercatcher could consume other food from upshore areas, or that oystercatcher could consume food from terrestrial habitats. Cockle and tellin biomasses were estimated within Solway Firth, and at Wigtown Bay, a site outside the area in which bird population sizes were estimated. Further scenarios therefore assumed that birds either could, or could not, consume food from Wigtown Bay. In each scenario the model initially predicted the amount of shellfish biomass not required by the birds. This was then converted into the biomass potentially available for fishing, accounting for the fact that the size range exploited by fishing did not overlap completely with that consumed by the birds. In the case of knot there was no overlap, and so the amount available to ...