Age, growth and reproductive biology of the spot-tail shark, Carcharhinus sorrah, and the Australian blacktip shark, C. tilstoni, from the Great Barrier Reef World Heritage Area, north-eastern Australia

Abstract

Understanding the life history of an exploited fish species is an integral part of successful fisheries management and this information can be used in quantitative population assessments. The present study describes the quantitative relationships among age, growth and reproductive biology of two commercially exploited sharks from the Great Barrier Reef World Heritage Area (GBRWHA), namely, the spot-tail shark, Carcharhinus sorrah (n = 659) and the Australian blacktip shark, C. tilstoni (n = 512). Longevity estimates based on vertebral ageing were 9 and 14 years for male and female C. sorrah and 13 and 15 years for C. tilstoni. However, an age-validation study failed to validate annual banding in larger individuals, suggesting that maximum age may be underestimated by vertebrae. C. sorrah grew to adult size relatively fast, reaching maturity at 2.3–2.4 years, whereas C. tilstoni grew slower, reaching maturity at 5.2–6.1 years. For both species, however, reproduction did not commence until approximately a year after maturity, at 3.4 years for C. sorrah and 7.2 years for C. tilstoni. The results of the present study suggest that in the GBRWHA, C. tilstoni, in particular, begins reproducing at an older age and lives longer than previously thought.