Comparison of Interval and Aerial Count Methods for Estimating Fisher Boating Effort

Abstract

Interval and aerial angler creel survey counting methods were compared for a statistical district of Lake Michigan (MM‐6) to evaluate potential underestimation of the interval method. Two 0.5‐h boat (i.e., interval) counts were made per sample day at five access ports within MM‐6, and on the same day, boats in 3 out of 18 MM‐6 grids were counted from aircraft. Seasonal and monthly day‐type (weekday or weekend day) estimates of boating effort by count method were compared. Seasonal boating effort estimates during open‐water periods were not significantly different for aerial versus interval counts: 250,387 versus 247,117 in 2000 and 177,532 versus 219,097 in 2001. Similarly, comparisons of boating effort by monthly day type (i.e., weekday or weekend day) within each year did not indicate significant differences. Aerial precision estimates (2 SEs/estimate; 14.84% in 2000 and 15.53% in 2001) were more precise than interval estimates (21.42% in 2000 and 24.54% in 2001). Similarly, predicted power (1 − β) was greater for aerial estimates than for interval estimates. The potential power of future interval estimates to detect a 25% change in boating effort with α = 0.05 was 0.38 for 2000 data and 0.30 for 2001 data. Aerial estimates provided power estimates of 0.66 for 2000 data and 0.62 for 2001 data. At least four interval counts per sample day are needed to match the precision and power of three aerial counts. Although both count types were made on the same sample days and at approximately the same (random) times each sample day, each method relied on unique estimation methods. Comparable, independent estimates establish the reliability of these two methods.