Growth and mortality of the giant arapaima in Guyana: Implications for recovery of an over-exploited population

摘要

Arapaima are endemic to tropical South America and are among the largest freshwater fishes in the world. Although their populations have been harvested intensely for more than a century they are poorly studied. Here, we estimated for the first time, age, growth, and mortality rates for a Guyanese population of arapaima. Analyses were based on growth ring deposition on scales for 223 individuals (20-208 cm total length, T-L), including ages 0-8. Rings on scales were annuli, and the scale radius versus total length relation was cubic. Theoretical maximum T-L (similar to 192 cm) was less than maximum observed length (similar to 240 cm), but that estimate may have been biased downward by size-selective removal of faster-growing juveniles. Back-calculated T-L at first annulus increased 18.6 cm between early and later year-classes, indicating removal of fast-growing juveniles in earlier years. Size-selective harvests may have delayed maturity of average survivors by two years. Comparison of length-mass relationships indicate that, for a given length, Guyanese arapaima will be much heavier than those from central Brazil. Annual total mortality was 62-72 % (ages 2-5 or 6), a rate that precludes notable harvests and that may suggest ongoing illegal harvests.