Abstract
Catch-per-unit-effort (CPUE) is often used to monitor wildlife populations and to develop statistical population models. Animals caught and released are often not included in CPUE metrics and their inclusion may create more accurate indices of abundance. We used 21 years of detailed harvest records for bobcat (Lynx rufus) in Wisconsin, U.S.A., to calculate CPUE and ‘actual CPUE’ (ACPUE; including animals caught and released) from bobcat hunters and trappers. We calibrated these metrics to an independent estimate of bobcat abundance and attempted to create simple but effective models to estimate CPUE and ACPUE using harvest success data (i.e., bobcats harvested/available permits). CPUE showed virtually no relationship with bobcat abundance across all years, but both CPUE and ACPUE had stronger, non-linear, and negative relationships with abundance during the periods when the population was decreasing. Annual harvest success strongly predicted composite ACPUE and CPUE from hunters and trappers and hunter ACPUE and CPUE but was a poorer predictor of trapper ACPUE and CPUE. The non-linear, and sometimes weak, relationships with bobcat abundance likely reflect the increasing selectivity of bobcat hunters for trophy animals. Studies calibrating per-unit-effort metrics against abundance should account for population trajectories and different harvest methods (e.g., hunting and trapping). Our results also highlight the potential for estimating per-unit-effort metrics from relatively simple and inexpensive data sources and we encourage additional research into the use of per-unit-effort metrics for population estimation.
Highlights
Quantifying and estimating trends in wildlife abundance is critical for wildlife management and conservation, but many species are cryptic leading to innate difficulties in estimating abundance [1, 2]
Bobcat abundance increased during 1993–2003 and decreased from 2005–2013 [27], and our preliminary analyses indicated that the relationship between CPUE and abundance varied over time as a function of the population trajectory
We found that hunter/trapper success, generally an inexpensive metric that is readily available from harvest data without requiring annual questionnaires, can serve as a proxy for per-unit-effort metrics in population models for effective management and conservation
Summary
Quantifying and estimating trends in wildlife abundance is critical for wildlife management and conservation, but many species are cryptic leading to innate difficulties in estimating abundance [1, 2]. Population indices, including harvest-based indices, are often used as surrogate indices for wildlife populations [1, 3]. Harvest records may span multiple decades, and may provide the only long-term data source for certain species or populations in a given management unit [4,5,6].
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