通过2006年10月-2007年6月在马绍尔群岛海域利用金枪鱼延绳钓调查所取得的43个站点的大青鲨兼捕数据,以及测得的温度、盐度、溶解氧浓度等环境数据,应用分位数回归的方法分析各水层(40～280 m,每40 m为一层)中各环境因子与大青鲨渔获率的关系,建立“栖息地综合指数(integrated habitat index,IHI)模型”,用来预测其空间分布,并利用另外的18个站点的数据对模型进行验证.结果表明,(1)模型的预测能力良好;(2)不同的水层影响大青鲨分布的环境因子不同;(3)大青鲨较适宜的栖息水层为80 ～ 120 m;(4)大青鲨IHI较高的海域有两个,分别为9°N～12°N,172.E～176°E与3°N～6°N,166°E～169°E.建议对大青鲨IHI较高的两海域采取规定延绳钓的作业深度为120m以深等管理措施.%This study is based on a survey carried out by the longliner "Shengliancheng 719" in waters near Marshall Islands from Oct,2006 to May,2007. Based on the survey data collected by "Shengliancheng 719" at 43 sampling stations, the vertical profile data of temperature, salinity, dissolved oxygen concentration and the catch rate data of blue shark were applied to develop the "Integrated Habitat Index (IHI)" models by the quantile regression method. Models were developed for six water strata from 40 m to 280 m(40 m each) and the entire water column to understand the blue shark' s spatial distribution. Models were developed with the consideration of interactions among environmental variables. IHI model of the entire water column was developed using the weighted average temperature, salinity, dissolved oxygen concentration and the thermocline parameters, such as, upper-limit depth, lower-limit depth, upper-limit temperature, lower-limit temperature, intensity, thickness, temperature difference. Models of five water strata from 40 m to 240 m and the entire water column were reasonably developed. The measured environmental variables at 43 sampling stations were input into the IHI models to predict the IHI of five strata and the entire water column. The paired two sample Mest was used to calculate the Poisson correlation coefficients between predicted IHI and observed catch per unit effort (CPUE) of five strata and the entire water column. The Poisson correlation coefficients were assumed to indicate the predictive power of the IHI model. The trend line of the arithmetic average about the predicted IHI of five strata was compared with those of the catch rates in the specific depth stratum. The measured environmental variables at the other 18 sampling stations were used to validate the models' predictive power. These data were input into the CPUE models to predict the CPUE of five strata and the entire water column. A comparison between the predicted and observed catch rates at five strata and the entire water column was conducted by a paired two sample f-test to validate the IHI models. The results showed; (1) the predicted CPUE had greater relevance to the observed CPUE,the models' predictive power was good; (2) the key environmental parameters in the IHI models differed among the depth strata. This might be resulted from the blue shark' s specific biology characteristic, the different ecological factors, and the different life stages of blue shark; (3) the blue sharks' Ihh in the areas of 9°N -12°N,172°E -176°E and 3°N-5°N,166°E -169°E were relatively higher; (4) the optimal depth that blue shark inhabit was from 80 m to 120 m in the survey area. The high IHI area in 80 -120 m stratum was similar to the high IHI area of the entire water column. It means we could use the IHI distribution in 80 -120 m stratum to express the IHI distribution of the entire water column.
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