Establishing Size-Based Mortality Caps

Abstract

Mortality limits are seldom identified as management objectives in freshwater fisheries. I present two simple models for establishing approximate mortality caps that reflect threshold objectives about fish mean size or size structure. The deterministic caps would take the form of intervals to account for uncertainties caused by measurement error, model assumption violations, and environmental fluctuations. The intervals represent danger zones that trigger intensified monitoring and reductions in harvest. Monitoring the status of the population relative to a mortality cap would require frequent estimates of fish size and less frequent estimates of mortality. The methods can be used with data obtained from angler harvest surveys and routine population sampling.