Species Diversity And Biology Of Fish In Coral Reef Waters Of Xisha, Zhongsha And Nansha Islands, South China Sea

Coral reef is marine ecosystem with high productivity. Dongsha, Xisha, Zhongsha and Nansha Islands in South China Sea (hereinafter referred to as'SCS') are typical coral reef ecosystem, which belong to one of ten global coral reef reserves partitioned in 2002. SCS's reef-fishery is a unique fishery type among Four Seas—Bohai Sea, Yellow Sea, East China Sea and South China Sea, and it has its own special position and plays an important role both in marine fishery and maintenance of state sea right and benefit.There are few study on coral reef fishery resources in Dongsha, Xisha, Zhongsha and Nansha Islands because on-site survey is subject to many constraints such as remote distance, bad sea condition, special fishing method, given fishing season, as well as complicated geopolitics with neighbouring countries. Based systematic collection and document of historical data from different surveys of coral reef fishery resources in SCS, the study analyses large-scale distribution pattern of species diversity of fish in coral reef waters of the sea, addresses ecological distribution and catch distribution of some typical associated-reef fishes, in addition, it also examines reproduction, age and growth of some main commercial species and evaluates their population dynamics. And on the basis, the paper calculated optimum catchable size taking advantage of Y/R iso-catch curve of Beverton-Holt model and combining fish biological characteristics, which provide scientific references for development and sustainable utilization of associated-reef fish resources in SCS.(1) The analysis on large scale distribution pattern shows that there are 514 species recorded in Dongsha Islands,620 species in Xisha and Zhongsha Islands, and 548 species in Nansha Islands respectively. However, the number is lower than the expected one, also less than number of other reef waters where there are similar hatibats with SCS. Taxonomic diversity index of fish species was calculated. Average taxonomic distinctness index△+ in Dongsha, Xisha & Zhongsha and Nansha Islands is 55.1,60.2,56.6, respectively; and correspondingly, variation in taxonomic distinctness index∧+ is 121,164,150 in the three islands, respectively. All△+ values in three islands are less than that of the Northern Continental Shelf Waters of South China, but, on the contrary, all∧+ values are more than the Northern Continental Shelf Waters.(2) Considering comprehensively weight and individual composition proportion, catch rate in all survey sites, and index of relative importance (IRI) given by Pinkas, the paper introduces 10 species of Chondrichthyes—Carcharhinus limbatus, Hexanchus nakamurai, Sphyrna lewini, Triaenodon obesus, Hexanchus griseus, Isurus oxyrinchus, Squalus megalops, Carcharhinus longimanus, Galeocerdo cuvier and Taeniura meyeni, and 9 species of Osteichthyes—Plectorhinchus flavomaculatus, Plectorhinchus pictus, Lethrinus miniatus, Caranx stellatus, Ruvettus pretiosus, Caranx ignobilis, Etelis carbunculus, Pristipomoides filamentosus, Gymnosarda unicolor and Arothron stellatus, addressing their ecological distribution, and CPUE's distribution in Xisha, Zhongsha and Nansha Islands waters.(3) Gonadal maturation data from 306 individuals of 21 species of Chondrichthyes and 1048 individuals of 93 species of Osteichthyes were examined. The result shows that the Chondrichthyes sex ratio is close to 1:1. The fact that stageⅡdominates in gonadal samples indicates reproduction time of most Chondrichthyes is not in the survey months, and that of a few species such as Carcharhinus limbatus and Centrophorus tessellates should be between May to July. According to available information and data collected in the survey, most of Chondrichthyes reproduce by means of ovoviviparity or zoogony with 1 to 10 embryos or even more than 100 ones, their pregnancy duration from 5 through 10 months or more time.The sex ratio of 15 species of Osteichthyes is 13:1. The statistics shows that stageⅢaccounting for 37.4%, stageⅣ16.6% for male, but to female, stageⅡamounting 35.9%, stageⅢ28.4%,Ⅳ21.4%,Ⅴ11.4%,Ⅵ2.9%, respectively. Some species such as Plectorhinchus flavomaculatus and Lethrinus miniatus reproduce in spring, another some like Plectorhinchus pictus in between late spring and early summer, and other most in summer or in autumn. Absolute fecundity of these species can reach at 300 to 4 500 thousand eggs, relative fecundity being 80 to 850 eggs per gram of body weight. Serranidae has lower fecundity, while Lutjanidae has higher reproductivty.(4) Age of 13 species of Osteichthyes and 2 species of Chondrichthyes were observed. Age distribution of the observed samples is 2 to 12 yr (with no 1 yr sample), and dominant age group of each species is more than 3 yr, which implies that there exist old populations in coral reef waters of SCS. According to fitting of Length-Weight relationship, B values of most of these species are between 2.5 to 3.5, indicating their growth is uniform or close to uniform. Growth equations of 15 species are fitted. The mapped growth speed (dL/dt and dW/dt) and accelerate speed (d2L/dt2 and d2 W/dt2) curves indicates that their absolute growth rates increase first and then decrease with age, but, on the contrary, relative growth rate and instantaneous growth rate decrease constantly at all times.(5) According research findings from "Age and Growth", population dynamics for 13 species of Osteichthyes are evaluated taking advantage of Beverton-Holt model. Catchable age tc and length Lc is calculated by Y/R iso-catch curve of B-H model and combining growth, gonadal development and maturation, and utilization of resources. The result shows that tc and Lc for Plectorhinchus flavomaculatus is 3.5 yr and 428 mm; Plectorhinchus pictus 3.0 yr and 319 mm, Lethrinus miniatus 4.8 yr and 513 mm, Lethrinus rubrioperculatus 2.4 yr and 188 mm, Lethrinella variegates 2.1 yr and 329 mm, Acanthopagrus latus 3.2 yr and 387 mm, Lutjanus bohar 3.0 yr and 384 mm, Lutjanus stellatus 2.6yr and 315 mm, Lutjanus argentimaculatus 2.2 yr and 366 mm, Aphareus rutilans 1.9 yr and 384 mm, Pristipomoides auricilla 2.3 yr and 224 mm, Pristipomoides filamentosus 3.5 yr and 355 mm, and Etelis carbunculus 3.5 yr and 433 mm.