Development of a Crowded Largemouth Bass Population in a Tropical Reservoir

This case study examines the development of an overcrowded largemouth bass population following initial stocking in a tropical reservoir and efforts to correct crowding with a protected slot length limit. Cerrillos Reservoir is a relatively new impoundment (filled 1996) in Puerto Rico and is one of only two reservoirs that have been stocked exclusively with pure Florida largemouth bass (Micropterus salmoides floridanus). Largemouth bass were first stocked in Cerrillos Reservoir in 1997 and the population quickly expanded. Within three years, relative weight declined from above 100 to about 80 and the population displayed characteristics of overcrowding, with much of the population composed of fish ≤ 350 mm. This condition was most likely the result of limited harvest, as angling was not allowed during the first three years of the fishery. In 2000, the reservoir was opened to angling, but access remained limited and unpredictable. A protected slot limit (356-508 mm) was implemented in 2003 to encourage harvest of smaller largemouth bass, to protect the intermediate-sized bass, and allow for occasional harvest of a trophy bass. Population sampling in 2010 indicated that overcrowding persists in Cerrillos Reservoir, with 91% of stock-size largemouth bass less than 400 mm, and 81% of those below the protected slot. The failure of the protected-slot limit in reducing largemouth bass crowding is believed to be due to limited angling pressure and unwillingness of anglers to keep smaller fish. The slot has since been removed and research has begun to address best management strategies for this reservoir.

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