CLIMATE-CHANGE AND SALMONID LIFE-HISTORY VARIATION

A model is developed to predict some effects of climate change on anadromous fish. A review the relevant biology of salmonids, focusing on three species of Pacific salmon and on Atlantic salmon, shows that there is sufficient commonality to this biology that we can conceive of a ''general salmon'' model, which is then tailored to consider a particular species in a particular situation. Such a model is developed for the Atlantic salmon (Salmo salar L.) and is used to study the effects of climate change on its patterns of development and maturation. The main variables in this model are the weight and length of the fish (assumed to be related allometrically), the metabolic rate of the fish (a measure of how potential growth is converted into realized growth) and environmental properties such as food availability and water temperature. The main predictions are the pattern of development (maturation and smoltification) and feeding behavior in the stream. Given these predicted patterns of development and behavior, we can address the response to climate change. For example, if climate change leads to an overall decrease in the availability of food, then returning fish will be smaller (as expected). However, the return timing may change too, depending upon the metabolic rate. Similarly, assuming that streams are warmed by climate change, leads to a clear prediction about switches in the patterns of smolting as a function of size of the fish and metabolic rate. Methods for testing the proposed models are described.