Relationship Between Largemouth Bass Recruitment and Water Level Dynamics in a Puerto Rico Reservoir

Abstract

Recruitment of largemouth bass at age-1 in a Puerto Rico reservoir can be predicted from water level variables of the previous year. Age-1 largemouth bass electrofishing catch-per-unit-effort (CPUE) as an index of year-class strength varied five fold between 1994 and 2001 in Lucchetti Reservoir, Puerto Rico. The CPUE of age-1 largemouth bass was higher in years when the water level of the previous years (1993–2000) remained high during the spawning period (January-June). The greatest water level drop (11.2 m) during the spawning period was observed in 1999, resulting in a water volume decrease of 66.5%, which corresponded to the lowest recruitment (CPUE 24.2 fish·h⁻¹). With only 2.6 m of water level drop and 18.3% water volume decrease during the spawning period, the 1995 largemouth bass cohort was the strongest (CPUE 128.3 fish·h⁻¹). The effect of these hydrological variables on largemouth bass recruitment appeared to be exponential rather than linear. Age-1 largemouth bass comprise the majority of the fishable stock in Lucchetti Reservoir, and the stock is typically below carrying capacity. Thus, the potential exists to adopt a water level management plan during the spawning period of largemouth bass to ensure successful largemouth bass recruitment into the next year's fishable stock.

Key Words:

• tropical reservoir
• hydrology
• water level
• largemouth bass
• recruitment