Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa

Booth, Anthony J; Foulis, Alan J; Smale, Malcolm J

Title: Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa
Creator: Booth, Anthony J
Creator: Foulis, Alan J
Creator: Smale, Malcolm J
Date Issued: 2011
Date: 2011
Type: text
Type: article
Identifier: http://hdl.handle.net/10962/123630
Identifier: vital:35466
Identifier: https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/2011/1091/booth.pdf
Description: This study documents validation of vertebral band-pair formation in spotted gully shark (Triakis megalopterus) with the use of f luorochrome injection and tagging of captive and wild sharks over a 21-year period. Growth and mortality rates of T. megalopterus were also estimated and a demographic analysis of the species was conducted. Of the 23 OTC (oxytetracycline) -marked vertebrae examined (12 from captive and 11 from wild sharks), seven vertebrae (three from captive and four from wild sharks) exhibited chelation of the OTC and f luoresced under ultraviolet light. It was concluded that a single opaque and translucent band pair was deposited annually up to at least 25 years of age, the maximum age recorded. Reader precision was assessed by using an index of average percent error calculated at 5%. No significant differences were found between male and female growth patterns (P>0.05), and von Bertalanffy growth model parameters for combined sexes were estimated to be L∞=1711.07 mm TL, k=0.11/yr and t0= –2.43 yr (n=86). Natural mortality was estimated at 0.17/yr. Age at maturity was estimated at 11 years for males and 15 years for females. Results of the demographic analysis showed that the population, in the absence of fishing mortality, was stable and not significantly different from zero and particularly sensitive to overfishing. At the current age at first capture and natural mortality rate, the fishing mortality rate required to result in negative population growth was low at F>0.004/ yr. Elasticity analysis revealed that juvenile survival was the principal factor in explaining variability in population growth rate.
Format: 12 pages
Format: pdf
Language: English
Relation: Fishery Bulletin
Relation: Booth, A.J., Foulis, A.J. and Smale, M.J., 2011. Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa. Fishery Bulletin, 109(1), pp.101-112.
Relation: Fishery Bulletin volume 109 number 1 101 112 2011 0090-0656
Rights: Fishery Bulletin
Rights: Use of this resource is governed by the terms and conditions of the NOAA Open Access Statement (https://spo.nmfs.noaa.gov/fb.htm)

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RU Department of Ichthyology and Fisheries Science

SDG 14. Life Below Water

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