Coastal habitats (e.g. estuaries, lagoons) provide vital winter feeding grounds for large populations of shorebirds (e.g. sandpipers, plovers, oystercatchers), but are also an important resource for humans (e.g. for recreation, shellfishing, industry). Coastal managers face the often difficult problem of assessing whether existing or proposed human activities will have an adverse effect on the birds. Conservation objectives for these birds are often determined in terms of population size, and so methods are required to accurately predict the effect of human activities on either population size, or a demographic rate (e.g. mortality) that determines population size. Developing such methods has been a long-running difficulty for shorebird ecologists.
I present the latest results from a research programme that has been designed to produced such predictions, and so provided the information required to make evidence-based decisions. The research is within the conceptual framework of individual-based ecology, in which ecological populations are viewed as systems with properties (e.g. population size) that arise from the traits (e.g. decisions, behaviour, physiology) and interactions of their constituent individuals. The link between individuals and populations is made through individual-based models (IBMs), that follow the fitness-maximising decisions of individuals, and predict population-level processes (i.e. mortality) from the fates of individuals.
Results/Conclusions
If IBMs are to successfully advise coastal management they need to produce accurate predictions, and so I initially describe how these models have been parameterised and tested. Models have been developed for over 15 European sites, and have generally been successful at predicting the underlying behaviour (e.g. feeding location, diet selection, proportion of time spent feeding) from which mortality predictions are derived. Models have also accurately predicted observed overwinter mortality rates on the lesser number of sites on which mortality has been measured. I briefly discuss the range of issues to which coastal bird IBMs have been applied, and then focus on predicting the impact of shellfishing on the birds. I show how recent IBMs have been used to predict the maximum stock of shellfish that can be harvested without adversely effecting the birds, and how general rules for the management of fisheries can be derived from the model outputs. The conflicts that these models are designed to address occur worldwide and the principles on which they are based apply to many species other than shorebirds, and so I finally discuss the wider applicability of the approach.
