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

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.

Fig 1. Map of sampling locations for sharks on the eastern coast of the Peninsular Malaysia (West Malaysia) and the western coast of Borneo Island (East Malaysia).

All study sites face to the SSCS in Malaysia territorial waters (blue shades) covering the four states of Kelantan, Terengganu, Pahang and Johor in West Malaysia and the two states, Sabah and Sarawak, in East Malaysia. Base map is downloaded from the USGS National Map Viewer (open access) at http://viewer.nationalmap.gov/viewer/.

Fig 2. Shark diversity landed in six states in the southern South China Sea.

Fig 3. Seasonal occurrence and diversity of sharks landed in Terengganu State in the southern South China Sea.

Eleven species were found in monthly observations for approximately four years from 2014 to 2017. Three species, the brownbanded bamboo shark Chiloscyllium punctatum, the spot-tail shark Carcharhinus sorrah and the Indonesian bamboo shark Chiloscyllium hasseltii, were the dominant species constituting 90% of sharks of a total of 11 shark species in the Terengganu State.

Fig 4. Monthly size distributions of three dominant species, the brownbanded bamboo shark Chiloscyllium punctatum, the Indonesian bamboo shark Chiloscyllium hasseltii and the spot-tail shark Carcharhinus sorrah, landed in Terengganu State in the southern South China Sea.

Monthly size distributions were recorded for approximately four years from 2014 to 2017.

Fig 5. Size distributions of sharks landed in the southern South China Sea.

Twelve shark species with more than 20 specimens landed at various growth stages from newborn juveniles and/or to mature adults^22-26. LB (black arrow), LMM (green arrow) and LMF (red arrow) indicate the length at birth, length at maturation of male and length at maturation of female, respectively.

Fig 6. Size distributions of sharks landed in the southern South China Sea.

Sixteen shark species with less than 5 specimens were landed at various growth stages from the newborn juveniles and/or to mature adults^22-26. LB (black arrow), LMM (green arrow) and LMF (red arrow) indicate the length at birth, length at maturation of male and length at maturation of female, respectively.

Fig 7. Sharks landed in the southern South China Sea.

Piked spurdog Squalus altipinnis at various growth stages from the newborn to mature adults were landed (a). Sharks with fins cut off at landing ports in southern South China Sea (b). Shark finning practice at landing ports in southern South China Sea (c).