MORPHOLOGICAL FEATURES USED TO IDENTIFY CHINOOK SALMON SEX DURING FISH PASSAGE

We compared several external morphological features for determining sex of adult fall-run chinook salmon (Oncorhynchus tschawytscha) migrating to spawning grounds in the Central Valley of California. Adult fish carcasses of known sex were measured at fish hatcheries or during angler surveys. These data were used to develop predictive morphometric discriminant function models for potential incorporation in an automated monitoring system. The best predictor for determining sex of handled fish was snout length to fork length ratio, which correctly classified 96% of individuals tested. In contrast, adipose fin length to fork length ratio was the best predictor of sex when measurements were obtained from video images at a fish passage facility. Of these fish, 86% were correctly identified. Combining both ratios with a third (head length) increased model accuracy to 92% for video images.