中东太平洋鲨鱼生物多样性时空分布格局

Spatiotemporal pattern of shark biodiversity in the Eastern and Central Pacific Ocean

利用2012—2019年中国金枪鱼延绳钓渔业观察员计划获取的数据,采用α多样性指标分析了中东太平洋海域鲨鱼的物种多样性,并利用广义加性模型分析了其栖息地偏好。结果表明,中东太平洋金枪鱼延绳钓渔业兼捕鲨鱼共20种,主要种类为大青鲨(Prionace glauca)和镰状真鲨(Carcharhinus falciformis)。中东热带太平洋和东南太平洋海域的鲨鱼物种组成相似,但中东热带太平洋鲨鱼物种均匀度更高,且热带海域的鲨鱼生物多样性高于温带地区。鲨鱼的物种丰富度和Shannon多样性指数受栖息地环境影响,存在较大的时空差异。鲨鱼群落更倾向于栖息在具有较高生产力水平(叶绿素浓度>0.10 mg·m^(-3))和海平面距平偏低(海平面距平值<0 m)的温水(海表面温度>25℃)海域。研究利用α多样性指数识别了以中东太平洋赤道水域(10°N~5°S、110°W~130°W)为主的鲨鱼物种多样性热点区域,有助于了解大洋生态系统鲨鱼物种多样性的时空分布特征,为制定针对鲨鱼的养护管理措施提供科学参考。

Sharks are one of the most threatened groups of marine animals,as high exploitation rates combined with low resilience to fishing pressure have led to population declines worldwidely.Designing conservation strategies for sharks depends on basic knowledge of the geographic distribution and diversity of known species.So far,this information has been fragmented and incomplete.In this study,observer data from 1874 sets of Chinese tuna longline fisheries in the Eastern and Central Pacific were used to estimate the biodiversity of sharks by applying alpha diversity measures,such as species richness,Chao2 index,Shannon index,species evenness,species density and rank-abundance curves,and the relationships of species richness and Shannon index with spatiotemporal and environmental factors,such as year,season,latitude,longitude,sea surface temperature,chlorophyll-a,and sea level anomaly were analyzed using the generalized additive models.Results showed that a total number of 20 sharks were observed,mainly consisting of Prionace glauca and Carcharhinus falciformis in the Eastern and Central Pacific.We found that there was a similar species composition in the Eastern and Central Tropical Pacific(Chao2=23.98)and Southeastern Pacific(Chao2=22.50),but the species evenness in the Tropical Pacific was higher than that in the Southeastern Pacific.The shark community in the Eastern and Central Tropical Pacific was dominated by Prionace glauca(28.97%)and Carcharhinus falciformis(23.85%),while in the Southeastern Pacific it was overwhelmingly dominated by Prionace glauca(76.64%).In the Eastern and Central Pacific,the biodiversity of sharks,such as species richness(S),Shannon Index(H’),and species density in the tropical area was higher than that in the temperate area.The species richness and diversity of sharks showed large spatiotemporal differences and were significantly influenced by habitat environmental characteristics.In terms of inter-annual variation,shark community diversity showed an increasing trend from 2012 to 2017 and a slight decrease from 2017 to 2019.The season with the highest diversity was the third season and the lowest diversity was found in the first season.Sharks preferred to inhabit the areas characterized by warm waters(sea surface temperature≈25℃),intermediate productivity concentrations(chlorophyll-a>0.10 mg·m^(-3))and abnormally low sea level(sea level anomaly<0 m).The alpha diversity performed well in identifying hotspots of biodiversity.The study helps to understand the shark biodiversity in pelagic ecosystems and identify,for conservation purposes,the critical habitats of the shark’s community in tuna longline fisheries in the Eastern and Central Pacific Ocean,and contributes to the future implementation of the protected marine areas,fishing moratorium or restricted fishing zone to manage the pelagic ecosystem in a holistic and more integrated way.