White Sturgeon in the Lower Columbia River: Is the Stock Overexploited/

Abstract

We used computer simulation to examine potential yields and sustainable exploitation rates for white sturgeon Acipenser transmontanus in the lower Columbia River. Simulated yields varied with assumptions used for mortality, growth, and stock–recruitment relationship, and with size restrictions imposed on harvest. The stock-recruitment function had the greatest influence on our results. Maximum yields (sustained or at 100 years) ranged from 0.2 to 2.9% of unexploited biomass. Maximum yields were produced with exploitation rates ranging from 0.02 to 0.20, and yields declined or collapsed at higher rates. Size restrictions (sport and commercial harvest of fish only between 92 and 183 cm or 122 and 183 cm, respectively) resulted in higher yields and higher supportable exploitation than no size restrictions. However, size windows did not prevent collapse of the fishery under higher exploitation rates when a stock-dependent recruitment function was used. The fishery on the Columbia River has expanded dramatically in recent time. Most recent yields were about 30% of the peak yield realized when the stock was overfished before 1890, and were at least three times the sustained yields expected from our most optimistic simulations. Cultural development of the river could have reduced the productivity of the stock and made it vulnerable to overexploitation. The present fishery appears to be overexpanded. Current yields probably cannot be sustained, and current harvest risks eventual collapse of the fishery.