Live fast and die young: On the growth and mortality of largemouth bass in Puerto Rico.

摘要

In Puerto Rico, largemouth bass (Micropterus salmoides) growth and survival are unlike that observed in its native temperate regions. Juvenile growth is linear and rapid (≥1 mm/day), attributed in part to a continuous growing season near optimum temperature year-round, but slows to near 0 mm/day at maturity, and few surpass age 3. I hypothesized that the slow growth of adult fish results from excessive energy allocation to reproduction. Largemouth bass in Puerto Rico reach sexual maturity in 1 year, spawn over a six-month period, and individual fish spawn multiple times. The diversion of energy from growth to reproduction causes growth rates to decline, and the risk of disease, parasites, predation, or other means of natural mortality increases. I used three approaches to address this hypothesis: (1) empirical assessment of population dynamics, (2) theoretical modeling of bioenergetics processes, and (3) direct experimentation to compare reproductive and non-reproductive largemouth bass.; Overall, empirical data on largemouth bass population dynamics supported the reproductive energetics hypothesis. Adult mortality coincided with spawning period, and condition was seasonal and declined with fish age, suggesting a cumulative effect with no recovery period. Bioenergetics simulation using a conservative mean daily ration of 2% body weight predicted that a non-reproductive, female 500-g largemouth bass would grow to 1,140 g in six months (182 d), the maximum spawning season duration. The actual size from tagging studies was 740 g, yielding a 400-g discrepancy between observed and predicted weight. This discrepancy in observed and predicted growth was explained for females using a range of spawning frequency-magnitude combinations, and for males by accounting for lost consumption.; To experimentally test the reproductive energetics hypothesis, the growth, condition, and reproductive development of diploid and triploid largemouth bass were compared through age 1 in Lucchetti Reservoir. Growth rates up to the size of maturity (275 mm) were similar for both groups, and maturity was not reached until midway into the spawning season, preventing extensive spawning of diploid bass, and resulting in growth rates similar to triploid bass. Diploid largemouth bass exhibited higher GSI values than triploids, and no triploid females had GSI values consistent with maturation, suggesting that the triploids do not invest significant energy into reproductive development. Specific research needs and management recommendations are discussed along with ecological implications of this research.