title: Growth and life history variability of the grey reef shark (Carcharhinus amblyrhynchos) across its range.
abstract: For broadly distributed, often overexploited species such as elasmobranchs (sharks and rays), conservation management would benefit from understanding how life history traits change in response to local environmental and ecological factors. However, fishing obfuscates this objective by causing complex and often mixed effects on the life histories of target species. Disentangling the many drivers of life history variability requires knowledge of elasmobranch populations in the absence of fishing, which is rarely available. Here, we describe the growth, maximum size, sex ratios, size at maturity, and offer a direct estimate of survival of an unfished population of grey reef sharks (Carcharhinus amblyrhynchos) using data from an eight year tag-recapture study. We then synthesized published information on the life history of C. amblyrhynchos from across its geographic range, and for the first time, we attempted to disentangle the contribution of fishing from geographic variation in an elasmobranch species. For Palmyra's unfished C. amblyrhynchos population, the von Bertalanffy growth function (VBGF) growth coefficient k was 0.05 and asymptotic length L∞ was 163.3 cm total length (TL). Maximum size was 175.5 cm TL from a female shark, length at maturity was estimated at 116.7-123.2 cm TL for male sharks, maximum lifespan estimated from VBGF parameters was 18.1 years for both sexes combined, and annual survival was 0.74 year-1. Consistent with findings from studies on other elasmobranch species, we found significant intraspecific variability in reported life history traits of C. amblyrhynchos. However, contrary to what others have reported, we did not find consistent patterns in life history variability as a function of biogeography or fishing. Ultimately, the substantial, but not yet predictable variability in life history traits observed for C. amblyrhynchos across its geographic range suggests that regional management may be necessary to set sustainable harvest targets and to recover this and other shark species globally.
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Darcy
authors.initials: D
authors.lastname: Bradley
authors.affiliation: The Nature Conservancy, Honolulu, Hawaii, United States of America.
authors.forename: Eric
authors.initials: E
authors.lastname: Conklin
authors.affiliation: Department of Biological Sciences, Florida International University, North Miami, Florida, United States of America.
authors.forename: Yannis P
authors.initials: YP
authors.lastname: Papastamatiou
authors.affiliation: Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.|Marine Science Institute, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: McCauley
authors.affiliation: The Nature Conservancy, Honolulu, Hawaii, United States of America.
authors.forename: Kydd
authors.initials: K
authors.lastname: Pollock
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Kendall
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Gaines
authors.affiliation: Marine Science Institute, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Caselle
mesh_terms: D000818:Animals; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005260:Female; D008018:Life Cycle Stages / Q000502:physiology*; D008297:Male; D011156:Population Density; D012754:Sharks / Q000254:growth & development*