Age and growth estimates for the tiger shark, Galeocerdo cuvier, from the east coast of South Africa

Abstract

Growth rings (GR) in sagitally sectioned vertebral centra of 69 female tiger sharks (102–300 cm precaudal length; 6–412 kg) and 32 males (123–301 cm; 16–396 kg) were counted. In vertebrae from three sharks injected with oxytetracyline (OTC) and recaptured after 18, 389 and 791 days of liberty, respectively, OTC was visible and there was evidence of annual GR deposition. Centrum analyses of the entire vertebral sample failed to confirm this GR periodicity. Assuming annual GR deposition, the youngest female and male aged were 1 year (102 cm) and 2 years (123 cm), and the oldest were 11 years (293 cm) and 8 years (301 cm) respectively. von Bertalanffy parameters for the combined sexes based on back-calculated values were L• 301 cm, k 0.202 year⁻¹ and t₀ −1.11 years. Ages calculated for length at 50% maturity were 11 years (274 cm) and 8 years (250 cm) for females and males, respectively. Calculated growth in length decreased from 44 cm (0–1 year) to 4 cm (12–13 years). Gompertz parameters were w₀ 14 kg, G 3.73 and g 0.172 year⁻¹. Calculated growth in mass increased from 12 kg (0–1 year) to 38 kg (7–8 years), then decreased to 29 kg (12–13 years). Back-calculated length and mass values were similar to observed values and Lee’s phenomenon was not evident in either case.