Application of angler-supplied data to estimate population rate functions for Mountain Whitefish

Objective Demographic data provide insight into the ecology and dynamics of fish populations and are crucial for fisheries managers to make informed management decisions. Collection of demographic data using traditional sampling techniques (e.g., electrofishing) may not be possible for a variety of reasons, including the presence of fishes protected by the Endangered Species Act. The objective of this study was to compare population characteristics and trophic status of Mountain Whitefish Prosopium williamsoni sampled using angling and electrofishing in the Clearwater River, Idaho. Specifically, we sought to describe length and age structure, growth, and mortality as well as isotopic indicators of trophic ecology. Lastly, we evaluated whether management decisions would differ depending on the data source using population models. Methods Population structure and dynamics data were quantified using standard fisheries techniques and compared between data sources. Additionally, trophic status was assessed using stable isotopes (i.e., 13C and 15N) and compared between data sources. Differences in various estimates (e.g., length structure, body condition) were tested using Kolmogorov–Smirnov and Wilcoxon’s signed rank tests. Relationships between total length and isotopic values were examined using linear regression. Finally, Beverton–Holt yield-per-recruit models were used to evaluate how data source may influence fisheries management decisions. Results Collection methods produced differences in both length- and age-frequency distributions. Mountain Whitefish collected using electrofishing gear were generally smaller and had a broader distribution of lengths compared with those collected by angling. Mean back-calculated lengths at age indicated that angled Mountain Whitefish exhibited slightly faster growth rates than those sampled by electrofishing; however, parameter estimates for von Bertalanffy growth models showed only minor differences between collection methods. Estimates of total annual mortality of Mountain Whitefish were comparable between angling (15.3%) and electrofishing (16.9%). Stable isotope analysis suggested that Mountain Whitefish not only exhibited piscivory, but those collected by angling were at a higher trophic level than those collected by electrofishing. Yield and spawning potential ratio estimates from the yield-per-recruit models typically differed by less than ∼5% between collection methods. As such, management decisions would likely be similar regardless of the data source. Conclusions Results of this study suggest that angler-supplied data can be useful for monitoring Mountain Whitefish population dynamics. Although standardized sampling techniques remain an important component of population assessments, angler-supplied data may expand sampling opportunities where logistical limitations exist. Consequently, angler-supplied data may be particularly useful for increasing the spatial and temporal extent of demographic monitoring without expending substantial agency resources.