Variability in Biological Characteristics of Northern Squawfish in the Lower Columbia and Snake Rivers

Abstract

Abstract We described and compared population structure, growth, mortality, and reproduction of northern Squawfish Ptychocheilus oregonensis among four reservoirs of the lower Columbia River and among four reservoirs of the lower Snake River. We also pooled data for comparisons among three larger areas: Columbia River reservoirs, Snake River reservoirs, and the unimpounded Columbia River downstream from Bonneville Dam. Females made up 76–100% of northern squawfish 380 mm fork length or greater in individual reservoirs, and 87–99% of fish 380 mm or greater in the three combined areas. Females lived longer and grew faster than males in all reservoirs and areas and had lower annual mortality rates in all but two reservoirs. Proportional stock density was highest and annual mortality rates were generally lowest in Columbia River reservoirs. Northern Squawfish downstream from Bonneville Dam had a lower mean relative weight and higher relative fecundity (eggs per unit fish weight) than populations in impoundmen...