Age and growth estimates for the Zambezi shark, Carcharhinus leucas, from the east coast of South Africa

Abstract

Growth rings (GR) were counted in vertebrae of 69 female (56–221 cm precaudal length; 3–238 kg) and 54 male (57–216 cm; 3–180 kg) C. leucas. Annual GR deposition could not be confirmed by centrum edge analyses but was assumed on the basis of ‘mark–recapture’ analysis of 10 sharks held captive for between 2.2 and 20 years in an aquarium. GR counts indicated that the largest female and male were 32 years (221 cm) and 29 years (216 cm), respectively and the smallest mature female and male were 14 years (197 cm) and 25 years (196 cm). Length at 50% maturity was 193 cm (21 years) and 190 cm (20 years) for females and males, respectively. Maximum age is >50 years, and the two specimens (216, 217 cm) that have been held in the aquarium for 20 years are both estimated to be >29 years. Von Bertalanffy parameters for the combined sexes were L∞ = 230 cm, k = 0.071 year–1, t0 = –5.12 years, and Gompertz parameters were w0 = 24 kg, G = 2.86, g = 0.046 year–1.

Similar life history traits in bull (Carcharhinus leucas) and pig-eye (C. amboinensis) sharks

“…Current estimates of juvenile growth rates within northern Australia reinforce predictions by Thorburn and Rowland (2008) and suggest that juvenile bull sharks have similar growth rates to those estimated from other populations (Branstetter and Stiles 1987). However, as they mature, Australian bull sharks appear to grow at a high rate, similar to those in South African waters, but mature earlier than individuals from the Gulf of Mexico (Branstetter and Stiles 1987;Wintner et al 2002;Cruz-Martinez et al 2004). Despite Australian bull sharks obtaining larger sizes than in other locations, individuals from all populations are equally longlived (Branstetter and Stiles 1987;Wintner et al 2002;Neer et al 2005).…”

“…The notoriety of the bull shark as one of the most aggressive sharks in the world, and the high frequency of human interactions with this species, has increased public awareness of it and the pressure to quantify species resilience. For this reason, multiple age and growth studies are available from different locations within its distribution (Branstetter and Stiles 1987;Wintner et al 2002;Cruz-Martinez et al 2004;Neer et al 2005). Our estimates of age and growth parameters confirm that bull sharks in northern Australia obtain greater total lengths than conspecifics from other locations, and like pig-eye sharks, they have also evolved slow vital rates.…”

“…Deposition of annual bands in bull shark vertebrae has been verified by earlier studies from several different regions (Branstetter and Stiles 1987;Wintner et al 2002;Cruz-Martinez et al 2004;Neer et al 2005). Consequently, we assumed that growth bands were deposited annually in the bull sharks we examined.…”

“…Between-reader consensus age estimates were attained for all samples for both species; consequently, all individuals were deemed readable. IAPE for individual vertebrae were consistently less than 20% (Wintner et al 2002) (see Accessory Publication for age-specific within-and between-reader variability). Confidence levels were moderate (two) to high (three) consistently across all total lengths for both species.…”

“…For bull sharks, age and growth estimates are available from South Africa and the northern and southern regions of the Gulf of Mexico (Branstetter and Stiles 1987;Wintner et al 2002;Cruz-Martinez et al 2004;Neer et al 2005). These suggest that bull sharks, like many other carcharhinids, are long-lived, attaining maximum ages from 30 to .50 years.…”