EXTREME-VALUE ANALYSIS OF A FISH TEMPERATURE-FIELD DATABASE

Extremes of water temperatures limit the presence of various fishes in streams and lakes. Upper extreme water temperatures and their uncerta inties are determined by several statistical methods from a large fiel d database. There are over 140 000 weekly mean fish/stream temperature matched pairs in the database. Three different techniques are employe d to estimate upper extremes of habitat temperatures for 12 fish speci es. To quantify the uncertainty of the estimated extremes the bootstra p method, the method of moments and the residual method are applied. T he data above the maximum growth temperature are matched well by a typ e III extremal or a three-parameter lognormal distribution. Standard e rror of the estimated extreme habitat temperatures depends on species and varies from 0.1 degrees C to 0.6 degrees C at the 95% cumulative p robability of occurrence.