A STRATEGY FOR SIMULATING BROWN TROUT POPULATION-DYNAMICS AND HABITATQUALITY IN AN URBANIZING WATERSHED

A mathematical model was developed to simulate the population dynamics of an allopatric brown trout Salmo trutta population in the Paint Bra nch of Montgomery and Prince Georges counties, Maryland. The model rel ates land disturbing activities and imperviousness in the watershed to trout habitat quality through generalized relationships involving sed iment transport, hydrology, and water temperature. Habitat quality the n influences population dynamics. The model operates in three sectors: watershed, habitat, and population. The sectors are replicated at six sites along the longitudinal gradient of the stream. Watershed effect s related to hydrology and sediment transport are accumulated from one sub-watershed to the next. The habitat sector is the Habitat Suitabil ity Index (HSI) for brown trout (Raleigh et al., 1986, Habitat suitabi lity index models and instream Row suitability curves: brown trout. US Fish Wildl. Ser., Biol. Rep. 82 (10.124)). The author collected field measurements on 18 HSI parameters for input to the model. The HSI val ues then are dynamically adjusted through time according to impacting factors from the watershed sector. These adjusted HSI values determine population growth by affecting probabilities of reproduction, recruit ment through the life stages, and mortality. The model was verified by comparing modelled and actual population data from a single site over the past 17 years. Simulations represent various watershed developmen t strategies for the next 20 years. General trends in the modelled adu lt population suggest that population recovery after a construction ev ent is achieved in watersheds of moderate imperviousness (<15%) but no t in more densely developed watersheds. (C) 1998 Elsevier Science B.V. All rights reserved.