Longevity of Atlantic Sharpnose Sharks Rhizoprionodon terraenovae and Blacknose Sharks Carcharhinus acronotus in the western North Atlantic Ocean based on tag-recapture data and direct age estimates.

Bryan S Frazier,William B Driggers Iii,Glenn F Ulrich

doi:10.12688/f1000research.4767.2

Abstract

Longevity of Rhizoprionodon terraenovae and Carcharhinus acronotus in the western North Atlantic Ocean was examined using direct age estimates from vertebral sections and tag-recapture data. Time-at-liberty ranged from 7.7-14.0 years (mean =10.1) for R. terraenovae and 10.9-12.8 years (mean =11.9) for C. acronotus. Maximum estimated longevity was determined to be 19.8 years through tag-recapture data and 18.5 years from direct age estimates for R. terraenovae and 22.8 years through tag-recapture data and 20.5 years through direct age estimates for C. acronotus. These longevity estimates represent a large increase over previous estimates and may have significant effects on analyses that depend on longevity including lifetime fecundity, mortality rates, demographic analyses and stock assessments.

Highlights

Tag-recapture data grant researchers the opportunity to synthesize a vast array of information for species they are studying
Longevity estimates for sharks are generally derived from von Bertalanffy Growth Function (VBGF) parameter estimates; VBGF parameter estimates can be heavily affected by low sample sizes, incomplete sampling among size classes and/or difficulties associated with age estimation of large individuals (Goldman, 2004; Francis et al, 2007)
Obtaining accurate longevity estimates can be hampered by the low probability of catching older individuals as they represent a small portion of the entire population, difficulty associated with capturing large specimens that are more capable of escaping gear than smaller conspecifics, and the reduction of older individuals in the population due to fishing pressure (Bishop et al, 2006)

Summary

Introduction

Tag-recapture data grant researchers the opportunity to synthesize a vast array of information for species they are studying. In particular, are well suited for tagging studies due to their migratory behavior, longevity, and relatively large size, which allows tagging at all life stages (Bonham et al, 1949). Valuable information gained from recapture data includes greater understanding of species-specific migratory patterns, stock structure, spatial and temporal distribution, site fidelity/residence times, and life histories (Kohler & Turner, 2001). Among life history parameters needed to best manage populations of fishes, robust longevity estimates are of paramount importance, for iteroparous species, such as sharks. Longevity estimates for sharks are generally derived from von Bertalanffy Growth Function (VBGF) parameter estimates (i.e. growth constant); VBGF parameter estimates can be heavily affected by low sample sizes, incomplete sampling among size classes and/or difficulties associated with age estimation of large individuals (Goldman, 2004; Francis et al, 2007). Based on tag-recapture data and direct age estimates, we report on the longevity of Atlantic Sharpnose Sharks Rhizoprionodon terraenovae (Richardson, 1836) and Blacknose Sharks Carcharhinus acronotus (Poey, 1860), both of which are common in the coastal waters off the southeastern United States

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