Distribution And Genetic Diversity Of Rhincodon Typus In Coastal Waters Of China

The whale shark (Rhincodon typus Smith,1829), is alomst the largest fish in the ocean, belongs to Orectolobiformes, Rhincodontidae, Rhincodon, is the only member in Rhincodontidae and Rhincodon. The whale shark has been considered as "vulnerable to extinction" in the IUCN Red List of Threatened Species and in the CITES Appendix Ⅱ, also listed as secondary protection animals in China. The population of whale shark around the world reduced sharply over the past ten years, the excessive intervention of human activities, the deregulation of marine climate and the destruction and pollution of habitat mainly caused whale sharks to extinction. Effective conservation strategies would benefit from an accurate and comprehensive understanding of the genetic diversity of the species. Whale shark’s life cycle is complex, the huge span on the time and space makes it difficult to use traditional methods to provide the whale sharks’exhaustive information about the life history and the diversity of species. Effective conservation strategies would benefit from an accurate and comprehensive understanding of the genetic diversity by the field investigation, molecular genetics experiment along with satellite tracking technology. In recent ten years, there have been some scholars began to study whale shark’s genetic diversity in the world, compared to other countries, genetics research of whale shark in China is still blank and in its infancy. Few domestic experts and scholars systematically collect and analyze the data of whale sharks in coastal areas of China. This study, with the investigation of a total of eight China’s coastal provinces, collected 30 whale sharks’muscle samples, including the four seas as the South China Sea, the East China Sea, the Yellow Sea and the Bohai Sea, obtained the following innovative results:1.Through the questionnaire survey, interviews survey and follow-up survey by the fishermen in major fishing ports and the fishery enforcement officers, preliminarily evaluate the distribution situation and the main habitat of China’s whale shark, predict whale shark’s activity regularity and the main factors to influence their activities, roughly determine the key conservation areas of China’s whale shark, master the first-hand information about the whale shark’s population distribution and quantity, provide valuable information to build global whale shark’s information database and network platform. Whale sharks were often caught or stranded in China’s coastal areas, the coastal waters near Zhejiang and Hainan were the most areas where whale sharks appeared, the waters near Hainan Island exist a considerable size of the whale shark habitat. Through the investigation of the whale shark’s population resources, it can be predicted that whale shark’s seasonal migration along the coastal waters of China. They main inhabited in the waters off Hainan between winter and spring, began to appear in east China area in May and June, in north China area in July and August, and in the whole Chinese coast in September, then before December migrated to the East China Sea and the South China Sea.2.In China’s main fishing ports we collected 30 whale sharks’muscle samples, through the research and analysis on the whale shark’s mitochondrial DNA, such as cytochrome oxidase subunit I gene, cytochrome b gene and control region gene. This is a preliminary study on whale shark’s genetic diversity in coastal areas of China, fill the blank of China’s whale shark’s genetics research in the world. Through the genetic distance analysis, assess the phylogeographical relationships between China’s whale sharks and whale sharks in other areas. Compared with other sharks, explore the whale shark’s evolutionary status in elasmobranchs. The experiment mainly obtained the following results:(1) We got a total of 13 control region haplotypes,7 COI haplotypes and 7 Cyt b haplotypes in 30 whale shark samples. The haplotype polymorphism was in a high level, but the nucleotide polymorphism was low. Overall, the genetic diversity was in a low level. (2) Constructed phylogenetic trees based on the three gene sequences and found that there were two main migration routes of the whale shark in the coastal areas of China, they had the closest relationship with Japan’s whale sharks, the genetic relationship was relatively close to the whale sharks in Australia and the East Indian Ocean. Whale shark’s phylogenetic relationship between China and the Atlantic, the Gulf of Mexico and the Caribbean was far, there was less gene exchange. It is close to the zebra shark (Stegostoma fasciatum) and spot bamboo shark (Chiloscyllium plagiosum) in Chondrichthyes. It is evolved by Orectolobidae, appeared comparatively late in Orectolobiformes. At the same time, the evolution status of Orectolobiformes is also relatively primitive, and is close to Carcharhiniformes. (3) Analysis of three gene sequences showed that whale sharks in the coastal areas of China had experienced recent population expansion.3.Through this study, we clear the international conservation status of China’s whale sharks, provide scientific information that can inform the strategy for the protection of whale shark resources in China, get the knowledge and protect their genetic diversity, biological diversity and evolution capacity, change our utilization of whale sharks, excavate the whale shark tourism resources in China, explore the balance between rare marine animal protection and the economic development.