The fib-model. Modelling fish in recovery from acidification

We propose here to extend a response model for brown trout populations in Norwegian lakes undergoing recovery from acidification, the FIB model ("Fisk I Bedring" = "Fish in Recovery"), as dynamic models for biological response are lacking, and there is an urgent need for such models to evaluate when, where and to what extent biological recovery can be expected. This model, aimed to explain age structure in a fish population in response to variations in recruitment. The mathematical basis for the initial m odel is the "Fibonacci-numbers", using a defined value for the presence of a defined year-class. The first version is manual, and uses presence of at least one single specimen of a certain year class as score input in the model. We plan in this proposal t o extend and evaluate the FIB model using test-fishing and water chemistry data for lakes in Norway, and link FIB to MAGIC to provide a tool by which the recovery of fish populations can be predicted given changes in acid deposition. We will extend FIB to a population dynamic model, where the demographic variables are under influence of ANC along with lake- and catchment characteristics. The model will be developed in close co-operation with the originators of MAGIC. The new model will be evaluated using catch- and water chemistry data from 42 lakes. A similar approach for analysing the dynamic interplay between ANC and fish abundance under environmental stochasticity has never, to our knowledge, previously been undertaken.