Effects of Including Misidentified Sharks in Life History Analyses: A Case Study on the Grey Reef Shark Carcharhinus amblyrhynchos from Papua New Guinea.

Jonathan J Smart,Andrew Chin,William T White,Andrew J Tobin,Leontine Baje,Colin A Simpfendorfer,Sharon A Appleyard,Madeline E Green,Heather M Patterson

doi:10.1371/journal.pone.0153116

Abstract

Fisheries observer programs are used around the world to collect crucial information and samples that inform fisheries management. However, observer error may misidentify similar-looking shark species. This raises questions about the level of error that species misidentifications could introduce to estimates of species’ life history parameters. This study addressed these questions using the Grey Reef Shark Carcharhinus amblyrhynchos as a case study. Observer misidentification rates were quantified by validating species identifications using diagnostic photographs taken on board supplemented with DNA barcoding. Length-at-age and maturity ogive analyses were then estimated and compared with and without the misidentified individuals. Vertebrae were retained from a total of 155 sharks identified by observers as C. amblyrhynchos. However, 22 (14%) of these were sharks were misidentified by the observers and were subsequently re-identified based on photographs and/or DNA barcoding. Of the 22 individuals misidentified as C. amblyrhynchos, 16 (73%) were detected using photographs and a further 6 via genetic validation. If misidentified individuals had been included, substantial error would have been introduced to both the length-at-age and the maturity estimates. Thus validating the species identification, increased the accuracy of estimated life history parameters for C. amblyrhynchos. From the corrected sample a multi-model inference approach was used to estimate growth for C. amblyrhynchos using three candidate models. The model averaged length-at-age parameters for C. amblyrhynchos with the sexes combined were = 159 cm TL and = 72 cm TL. Females mature at a greater length (l50 = 136 cm TL) and older age (A50 = 9.1 years) than males (l50 = 123 cm TL; A50 = 5.9 years). The inclusion of techniques to reduce misidentification in observer programs will improve the results of life history studies and ultimately improve management through the use of more accurate data for assessments.

Highlights

Life history information such as growth and maturity are fundamental prerequisites for many demographic and population dynamics models [1]
As C. amblyrhynchos is caught in larger numbers in Papua New Guinea (PNG), life history information is needed from the local population to form the basis of effective fisheries management and conservation
Vertebrae from Carcharhinus amblyrhynchos were collected from commercial longline operations operating in Papua New Guinea by an observer placed on the vessels by the National Fisheries Authority (NFA), the governing fisheries authority in Papua New Guinea

Summary

Introduction

Life history information such as growth and maturity are fundamental prerequisites for many demographic and population dynamics models [1]. Producing accurate life history information is crucial to inform fisheries management and conservation. The production of accurate life history estimates or a quantifiable uncertainty around them is imperative for sustainable fishing and effective population management. Carcharhinus amblyrhynchos are caught in tropical fisheries throughout their range [5, 6] and are often landed as incidental catch in some commercial fisheries [7, 8]. Despite being susceptible to fisheries across much of its range, life history information for C. amblyrhynchos is only available from Australia [10, 11], with some limited data available from Hawaii [12, 13] and Indonesia [5]. As C. amblyrhynchos is caught in larger numbers in PNG, life history information is needed from the local population to form the basis of effective fisheries management and conservation

Methods

Results

Conclusion