Biomathematics & Statistics Scotland
The British Isles are internationally important for breeding seabirds, and for many species an important element in the diet of their chicks is the lesser sandeel Ammodytes marinus. We have been working with collaborators at CEH and NERI to develop a method for combining two distinct time series on sandeel size, namely data on small fish from the SAHFOS Continuous Plankton Recorder and data collected later in the year from fish caught by adult Atlantic puffins Fratercula arctica to feed their chicks. Our method uses a novel statistical model with parameter estimation implemented by Markov Chain Monte Carlo sampling. The core of this method is a common underlying growth curve for sandeels during each year, with year-specific parameters for mean hatching date, the shape of the growth curve, and the length of fish at a fixed point during the puffin breeding season . Coherence of the two data sets is achieved by a model for length-specific selectivity. Modelling the year-specific parameters as a function of year-specific environmental covariates has allowed us to assess the evidence for environmental impacts on different aspects of sandeel growth.
The lengths of sandeels captured by puffins
provide information on an important part
of the food chain. (Photo: CEH, Aki Takahashi)
Further details from: David Elston
