Interstate comparisons of river otter harvest data

Abstract

River otter (Lutra canadensis) harvest and biological data from 1970 to 1989 for 10 northeastern states were examined to determine temporal and spatial characteristics, assess utility for ascertaining population trends, and provide guidelines for subsequent data collection and analyses. Analysis of river otter harvest data from several states in the northeastern United States allowed us to examine relationships that may otherwise be constrained by limited data within any single state or year. There was no directional bias among states in assigning otters to 3 age classes (juvenile, subadult, and adult) based on cementum annuli and radiographs. Use of radiographs improved the consistency of age classifications as juvenile or nonjuvenile compared to cementum annuli alone. Otter harvests were positively correlated with beaver (Castor canadensis) harvest and with average beaver pelt price from the previous year throughout most northeastern states. Thus, otter and beaver management practices are not independent. Females and juveniles composed a greater proportion of the harvest early in the season. Because the proportion of juveniles in the harvest of river otters was related to age estimation technique, aging procedures should be standardized throughout a region. Counts of corpora lutea and embryos provided consistent estimates of litter size in reproductively active females. However, embryo counts provided better estimates of pregnancy rate than corpora lutea counts. Subadults may contribute more to recruitment than previously believed. Catch/unit effort indices should be developed to assess otter population status in northeastern states. Combined with juvenile to nonjuvenile ratios, catch/unit effort may provide managers with the minimum information necessary for evaluating river otter population trends in their jurisdictions.