Freshwater Habitat Quantity and Coho Salmon Production in Two Rivers: an Initial Study to Support the Development of Habitat-Based Escapement Goals in Norton Sound, Alaska
Matthew J. Nemeth, Benjamin C. Williams, Robert C. Bocking, and Simon N. Kinneen
Abstract.—Data were collected in Norton Sound from 2002 through 2006 to support the development of habitat-based models of coho salmon smolt production and adult escapements. Length of stream rearing habitat available to juvenile coho salmon in the summer was estimated at 83 km on the Nome River and 277 km on the North River, using a combination of a priori predictions of fish distribution and subsequent field sampling. The likely range of smolts produced by this habitat was modeled using three different relationships of habitat quantity and smolt production developed elsewhere. The estimated escapement of adult salmon needed to produce this range of smolts resulted in counts from 2,632 to 3,649 fish in the Nome River and from 8,766 to 10,481 fish in the North River, using various literature values of production, survival, and fecundity. A field study conducted in the next two years to estimate actual smolt abundance in the Nome River yielded estimates of 92,820 (95% CI = 84,615 – 101,026) in 2005 and 122,079 (95% CI = 112,612 – 131,546) coho salmon in 2006; these smolt abundances were within the range estimated by the a priori models. Through 2007, average adult coho salmon escapement to both rivers had also been within the 95% confidence interval predicted from two of the three smolt models, within 2% and 18% of the point estimate of one model, and within 27% and 32% of the second. Overall, models based on production estimates and life history variables developed outside of the region were relatively accurate for predicting coho salmon rearing distributions, smolt production per km of total rearing habitat, and adult spawner abundance. Based on this, habitat-based models used to help develop escapement goals in other regions may be similarly useful in the Norton Sound region.