We addressed the problems of recall and nonresponse biases in self-report angling participation surveys. While each source of bias has been recognized as problematic, previous research has not addressed the interaction effects of these biases. Recall bias was assessed by comparing immediate, 3-month, and 6-month recall periods. A diary format was used for the immediate recall period and mail surveys for the 3-month and 6-month recall periods. Nonresponse bias was assessed by conducting telephone interviews with subjects who did not respond to the mail or diary surveys. The dependent variable was total number of days fished over two separate 3-month periods. Analysis showed significant first-order interactions (P ≤ 0.05), suggesting that recall bias and nonresponse bias are not independent factors. Respondents are more likely to report higher levels of participation and nonrespondents lower levels of participation as the length of recall period increases. Findings indicate that studies which use l...