Some consequences of unreported fishing on the results of simple fish stock assessment

Abstract

Unreported fishing received less attention than illegal fishing but the later contributed the problem of data availability. Among various data needed for fish stock assessment, catch and fishing effort are popular for some preliminary analysis to describe annual trends of catch, fishing effort and catch per unit effort. Surplus production models can be used to determine the status of fish stock, maximum sustainable yield (MSY) and optimum annual fishing effort. Fisheries authorities then can determine some management measure promoting sustainability of the fisheries, such as total allowable catch. This study exercised some consequences of unreported fishing effort and catch data on the outputs of the assessment by a simulation with different levels of data using the model. The estimates of both MSY and optimum fishing effort were lower when catch and fishing effort were not fully reported. When the authority should firmly use the best available but limited data, their decision on the maximum annual catch and fishing effort will be more conservative. In contrast, their decision can be risky if over-estimated catch and fishing effort were used. If fishers expected fair levels of catch and fishing effort, the authorities can firmly ask them to provide data completely.