Fishing and Natural Mortality of Adult Largemouth Bass in a Tropical Reservoir

Abstract

Largemouth bass Micropterus salmoides, an intensively studied sport fish of temperate North America, has been introduced into tropical regions, but with little evaluation of fishing or natural mortality rates. Previous research in Puerto Rico suggested that annual mortality rates are high, but whether the extended spawning season (nearly 6 months annually), high angler harvest, or a combination was the cause of the elevated mortality was unresolved. Using ultrasonic telemetry, we tracked 44 adult largemouth bass over an 18-month period to quantify patterns of natural, fishing, and total mortality. Using a general capture–recapture model, we estimated the annual instantaneous rates of fishing (0.584, SE = 0.164) and natural mortality (0.310, SE = 0.122). Natural mortality varied seasonally and generally increased during periods of spawning activity; however, fishing mortality was fairly consistent throughout the study. Given the relatively high fishing mortality rate, restrictions on harvest could probably be used to alter the age and size distribution of this population.