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Variability in Biological Characteristics of Northern Squawfish in the Lower Columbia and Snake Rivers
Author(s) -
Parker Robert M.,
Zimmerman Mark P.,
Ward David L.
Publication year - 1995
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1995)124<0335:vibcon>2.3.co;2
Subject(s) - fecundity , population , ecology , fish measurement , biology , population density , fishery , fish <actinopterygii> , demography , sociology
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 impoundments. Snake River populations had the highest mortality rates but exhibited intermediate values for other population parameters. None of the biological characteristics were strongly correlated with density of northern Squawfish except relative fecundity. Differences in life history traits of northern Squawfish among reservoirs and between free‐flowing and impounded reaches underscore the ability of northern Squawfish to adapt to altered conditions. Spatial heterogeneity in population characteristics creates uncertainty regarding the effects and relative benefits of a northern Squawfish management program to reduce predation on juvenile salmonids.