Growth and life history variability of the grey reef shark (Carcharhinus amblyrhynchos) across its range.

Kydd Pollock,Douglas J. McCauley,Jennifer E. Caselle,Bruce E. Kendall,Steven D. Gaines,Yannis P. Papastamatiou,Darcy Bradley,Eric Conklin

doi:10.1371/journal.pone.0172370

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.

Highlights

Intraspecific variation has been observed in many life history traits for a number of elasmobranchs [1,2,3,4,5,6,7,8,9,10,11,12,13], but the drivers of this variability are often unclear
Consistent with findings from studies on other elasmobranch species, we found significant variation in life history traits of C. amblyrhynchos across its geographic range
Growth at length was highest in the highest latitude location (NWHI, 23.1–28.2 ̊ N) [43], but was relatively large in Papua New Guinea (PNG) (2–11 ̊ S) [45], a low latitude location (Table 3; Fig 4)

Summary

Introduction

Intraspecific variation has been observed in many life history traits (e.g. growth, maximum size, size at maturity, fecundity) for a number of elasmobranchs (sharks and rays) [1,2,3,4,5,6,7,8,9,10,11,12,13], but the drivers of this variability are often unclear. For broadly distributed species such as elasmobranchs, conservation management would benefit from understanding how life history traits change in response to local environmental and ecological contexts. Understanding how fishing has altered life history traits requires knowledge of populations in the absence of fishing, which is rarely possible

Methods

Results

Conclusion