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

• Published in: Fisheries research Vol. 231; p. 105692
• Main Authors: Watson, L. Cynthia, Stewart, Donald J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2020
• Subjects: Age structure; Conservation; Essequibo River basin; Management; Osteoglossidae; Osteoglossidae; Essequibo River basin; Management; Age structure; Conservation
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/j.fishres.2020.105692

•Length-mass relations reveal Guyanese Arapaima at a given length will be much heavier than those from Central Brazil.•Size-selective harvests may have led to slower growth and delayed maturity by two years.•Annual total mortality was 62 72%, which precludes opening a commercial harvest without further population recovery. 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 (20208 cm total length, TL), including ages 08. Rings on scales were annuli, and the scale radius versus total length relation was cubic. Theoretical maximum TL (∼192 cm) was less than maximum observed length (∼240 cm), but that estimate may have been biased downward by size-selective removal of faster-growing juveniles. Back-calculated TL 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 6272 % (ages 25 or 6), a rate that precludes notable harvests and that may suggest ongoing illegal harvests.