Self-Reporting Bias in Chinook Salmon Sport Fisheries in Idaho: Implications for Roving Creel Surveys

Abstract

Self-reporting bias in sport fisheries of Chinook Salmon Oncorhynchus tshawytscha in Idaho was quantified by comparing observed and angler-reported data. A total of 164 observed anglers fished for 541 h and caught 74 Chinook Salmon. Fifty-eight fish were harvested and 16 were released. Anglers reported fishing for 604 h, an overestimate of 63 h. Anglers reported catching 66 fish; four less harvested and four less released fish were reported than observed. A Monte Carlo simulation revealed that when angler-reported data were used, total catch was underestimated by 14–15 fish (19–20%) using the ratio-of-means estimator to calculate mean catch rate. Negative bias was reduced to six fish (8%) when the means-of-ratio estimator was used. Multiple linear regression models to predict reporting bias in time fished had poor predictive value. However, actual time fished and a categorical covariate indicating whether the angler fished continuously during their fishing trip were two variables that were present in all of the top a priori models evaluated. Underreporting of catch and overreporting of time fished by anglers present challenges when managing Chinook Salmon sport fisheries. However, confidence intervals were near target levels and using more liberal definitions of angling when estimating effort in creel surveys may decrease sensitivity to bias in angler-reported data.

Received January 3, 2013; accepted May 20, 2013

ACKNOWLEDGMENTS

We thank N. Porter, W. Field, J. Hansen, C. Smith, J. Walrath, C. Watkins, S. Whitlock, J. Yates, and IDFG creel clerks for assistance with data collection; IDFG management biologists with expertise on sampling locations; and F. Wilhelm, C. Williams, K. Pope, and three anonymous reviewers for providing comments on earlier versions of this manuscript. Funding for this project was provided by the IDFG through Federal Aid in Sport Fish Restoration. The Idaho Cooperative Fish and Wildlife Research Unit is jointly sponsored by the University of Idaho, U.S. Geological Survey, IDFG, and Wildlife Management Institute. The use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.