The presented methodological notes address the question of sampling accuracy when sample-based data collection operations are performed under operational constraints, a frequent concern of fishery administrations with limited budget and human resources. Such a question is directly related to the frequency and extent of field operations for data collection. The paper focuses on an a prioridetermination of safe sample size using classical statistical methods appropriately adjusted to respond to specific target populations. The concepts and methods included in the paper apply equally to both marine and inland capture fisheries and are presented in a manner that is generic enough to make them adaptable in commonly used data collection systems.