Search

ABSTRACT Monitoring wildlife population trends often involves indices assumed to correlate in proportion to abundance. We used aerial count data and harvest statistics for moose ( Alces alces) populations in 16 hunting districts of Montana, USA, spanning 32 years (1983-2014) to assess population trends, drivers of uncertainty about those trends, and the relationship between aerial counts and hunter catch-per-unit-effort (CPUE). We found a great deal of statistical uncertainty surrounding population trends of moose measured with aerial minimum-count data, despite time series averaging >15 annual counts/district. State-space models of count-based trends suggested declining populations in 11 of 16 districts, yet 95% credible intervals overlapped 0 in all cases. The precision of count-based trends improved with increases in the number of years spanned by the time series (β = −0.003, P < 0.001) and average number of moose counted per survey (β = −0.0006, P = 0.002). Calibration of CPUE with count data showed positive correlations in only 5 of 16 (31%) districts and a catchability exponent (β) significantly <1. This indicated a generally poor level of agreement between these 2 indices, and evidence of 'hyperstability,' wherein declines measured by aerial counts were not reflected by proportionate declines in CPUE. Additionally, long-term trends measured with CPUE were not correlated to those in aerial counts ( P = 0.61). We encourage explicit attention to the precision of trend estimates and local calibration of population indices to ensure both positive and proportionate relationships to underlying patterns of abundance. © 2016 The Wildlife Society. [ABSTRACT FROM AUTHOR]