Research On The Biology And Ecology Of Several Pelagic Sharks In The Eastern Pacific Ocean

As the top predators in the oceanic food web, shark is the one of the most important compositions in marine ecosystem, which greatly contribute to diversity. During recent decades, catches of Chondrichthyan continue to increase and reach more than 800,000 mt in 2001. Due to incomplete statistics and discards at sea, actual catches are probably far more than those of reported, which make great uncertainty to shark stock assessment. Some shark populations actually are deteriorated and undetected. Therefore, it is urgent that shark conservation should be conducted. Pelagic fish stock in IATTC waters is mainly exploited by Japan, Korea, Mainland China, Taiwan China as well as coastal countries of South American. Pelagic tunas are main target species and sharks as by-catch. The status of pelagic sharks shall relate to marine ecosystem stability and sustainable utilization of pelagic fish stocks in IATTC waters.During July-November, in 2003(141 days), pelagic fish survey was conducted by longliner covering areas of 03癝~17癝 , 96癢~146癢. Sampling gear was longline fishing. Oceanic sharks caught by longline fishing were identified and analysized on their biology and reproductive biology. Furthermore, shark habitat and marine environment factors were measured with STD(for measuring Salinity, Temperature and Depth) and DST Milli(for measuring hook Temperature and Depth).The main contents of this research are as following:The horizontal and vertical change of Temperature(T) and Salinity(S) in the surveyed areas were measured with STD and marine environment factors from 0m to 300m were obtained. The depth of hook position was measured with DST Milli and shark habitat depth was determined.Catch rates of shark were analyzed and shark catch by individual vessel were estimated. So, total shark catch by tuna longline fishery in the EPO can be estimated. The HSI and TGSI of main shark species were analyzed. And research on fecundity and reproductive biology of main shark were conducted in detail.At present, no research on shark biology of EPO is conducted in domestic andfew in abroad. The results of this research are presented as following.1. Marine EnvironmentDuring surveyed period, atmospheric temperature fluctuated between 32.8-36.9 C, highest temperature is in November. The area blew Southeast wind, with scale 3-5. The sea surface current is controlled by Peru Current and Southern Equatorial Current. The most of wave height is about 2-3m.2. Habitat of sharksThe survey areas covered long distance. There are considerable horizontal changes of environment factors. Temperature of 0m and 300m in east part (14 30' S 9648' W) are measured with 21.6C and 10.3C respectively, but in west part (10 20' S, 13209' W) are measured with 26.6C and 10.9C respectively. The salinity of 0m and 300m in the east part are measured with 35.95 and 34.71 respectively. But in west position are measured with 36.00 and 34.80 respectively.Vertical variations of environment factors (T & S) are obvious in the surveyed areas. There are thermoclines between 100m and 200m water layer at surveyed east areas, but existed 100m to 250 in the west. Water mass have low T and S in the surveyed east part, but high T and S in the west part. The salinity of water layer of 0 ~ 250 m in the east part fluctuated between 35.96-34.74, with few variations. But in the west part, fluctuated between 36.00-34.80, with a high salinity of water mass between 50 and 150m water layer going to eastward.The habitat layers of blue shark and crocodile shark are measured and analyzed. The habitat depth of blue shark is mainly located at 100-150m, average 149.7m, with 24.3-17.9C. But the habitat depth of crocodile shark is mainly 150-200m, average depth 172.4m, with 22.2-13.3C.3. Shark species and catch rateIn total, nine shark species appeared in the surveyed areas: blue shark, oceanic whitetip shark, silky shark, scalloped hammerhead shark, crocodile shark, shortfm mako, bigeye thresher and velvet dogfish respectively. The catch number of nine shark specie...