Diversity, occurrence and conservation of sharks in the southern South China Sea.

Takaomi Arai,Azie Azri,Ismael Aaron Kimirei

doi:10.1371/journal.pone.0213864

Abstract

Sharks constitute a vital sector of marine and estuarine nekton and are of great commercial importance all over the world. International concern over the fate of shark fisheries has grown recently. However, information concerning the species diversity, geographic distribution and life histories of sharks in the Indo-Pacific region is highly limited. Comprehensive research on the species composition, distribution and seasonal occurrence of sharks in the southern South China Sea (SSCS) was conducted for four years. A total of 4742 sharks belonging to 10 families and 28 species were recorded from 6 fishing ports in SSCS. The families recorded included Squalidae, Heterodontidae, Orectolobidae, Hemiscylliidae, Alopiidae, Scyliorhinidae, Triakidae, Hemigaleidae, Carcharhinidae and Sphyrnidae. Seventeen of 28 shark species were landed at various developmental stages from in the ranges of or even less than the length at birth and from newborn juveniles to fully-mature. The results suggest that these sharks were born just before fishing and landing, and reproductive-stage sharks were also fished and landed. In total, 15 species, four species and one species in 28 shark species were categorized as Near Threatened, Vulnerable and Endangered species, respectively, on the IUCN Red List. Sharks are not targeted by fisheries practices in the SSCS, but are caught as bycatch throughout the year in various developmental stages. Thus, current fisheries practices in the SSCS area might lead to further decline to critical levels and lead to extinction of some of species in the future. These results suggest that the need for gear selectivity of the commercial fishing gears in order to reduce mortality and to conserve shark stocks.

Highlights

Sharks are an evolutionarily conservative group, comprising approximately 250 species, ranging in size from 30 cm tiny pygmy shark, Euprotomicrus bispinatus, to 12 m plankton-feeding whale shark, Rhincodon typus, that have functioned successfully in diverse ecosystems for 400 million years [1]
The scalloped hammerhead shark, Sphyrna lewini, which is listed as an Endangered species on the IUCN Red List [22] (Table 1), was abundant (184 specimens, 4%)
Alopias pelagicus, Hemigaleus microstoma, Hemipristis elongata and Carcharhinus plumbeus are listed as Vulnerable species, while 15 of the 28 shark species are listed as Near Threatened on the IUCN Red List [22] (Table 1)

Summary

Introduction

Sharks are an evolutionarily conservative group, comprising approximately 250 species, ranging in size from 30 cm tiny pygmy shark, Euprotomicrus bispinatus, to 12 m plankton-feeding whale shark, Rhincodon typus, that have functioned successfully in diverse ecosystems for 400 million years [1]. Sharks constitute an important predator group in marine ecosystems and play an essential role in energy exchange within the highest trophic levels [2]. Despite their evolutionary success, a number of sharks are threatened with extinction as a result of overfishing over recent decades in all oceans [3,4,5]. Collection and analysis, decision to publish, or preparation of the manuscript

Methods

Results

Conclusion