APPLICATION OF AN IN-SITU GROWTH-MODEL - INFERRED INSTANCE OF INTERSPECIFIC TROPHIC COMPETITION BETWEEN ANADROMOUS FISHES OF PRUDHOE BAY, ALASKA

A previously described in situ growth model was used to predict the su mmer growth of age-1 and age-2 broad whitefish Coregonus nasus in the Sagavanirktok River delta near Prudhoe Bay, Alaska, during 1990-1992. Comparisons of observed versus predicted weekly growth increments over the entire 9-year study (1982 and 1985-1992) yielded r = 0.789 (N = 7 7; P < 0.01) for age-1 fish and r = 0.522 (N = 70; P < 0.01) for age-2 fish. Based on daily comparisons of observed versus predicted mean fo rk length, the model was able to predict growth in 1991 and 1992 with mean squared errors (MSE) of 3.0 and 1.8 mm for age-1 fish and 6.5 and 21.2 mm for age-2 fish. Results were similar to those previously desc ribed for 1982 and 1985-1989. The model failed noticeably in 1990 for age-1 fish (MSE = 48.6), and model fit for age-2 fish (MSE = 29.9) was the poorest of the 9 years examined. Poor model fit for both year-cla sses in 1990 was attributed to a divergence of observed from predicted growth; observed growth began lagging predicted growth about the thir d week of July. By the end of August, predicted mean length exceeded o bserved length by 13.6 mm for age-1 fish and 12.8 mm for age-2 fish. D ata suggest that the divergence in growth began at the time of a massi ve immigration of least ciscoes C. sardinella into the delta. We specu late that the presence of least ciscoes may have overtaxed the trophic carrying capacity of the delta, thereby curtailing the growth of youn g broad whitefish.