基于支持向量机的库克群岛海域长鳍金枪鱼栖息环境综合指数

An integrated habitat index for albacore tuna(Thunnus alalunga) in waters near Cook Islands based on the support vector machine method

掌握海洋环境因子对长鳍金枪鱼(Thunnus alalunga)资源密度分布的影响有利于该资源的可持续利用。根据2013年9-12月在库克群岛海域利用延绳钓调查所获得的共计56个站点的长鳍金枪鱼渔获率数据,以及测得的温度、叶绿素a浓度、水平海流及垂直海流等环境因子数据,采用支持向量机方法分析了各水层(40.0~239.9 m,每40 m为一层)及整个水体中各个环境因子与长鳍金枪鱼渔获率的关系并建立了长鳍金枪鱼栖息环境综合指数(IHI)模型,并利用验证站点对模型进行了验证。结果表明:(1)预测渔获率与其对应的名义渔获率无显著性差异;(2)IHI模型的预测能力较好,能有效预测长鳍金枪鱼的分布;(3)不同水层影响长鳍金枪鱼分布的主要因素不同,在40.0~79.9 m、80.0~119.9 m、120.0~159.9 m、160.0~199.9 m和200.0~239.9m水层其分布分别主要受叶绿素a浓度、水温、垂直海流、叶绿素a浓度和温度的影响。整个水体影响长鳍金枪鱼分布的主要因素为温度;(4)长鳍金枪鱼分布密度较高的水层为120.0~199.9 m;(5)长鳍金枪鱼IHI指数分布较高的3个区域分别为9°00′S-12°20′S,159°00′W-164°00′W、13°30′S-14°30′S,159°00′W-161°00′W和10°30′S-12°30′S,167°00′W-168°00′W,建议在上述海域作业时,应使钓具沉降到120~199.9 m水层,以减少其它物种的兼捕率并提高长鳍金枪鱼的渔获率。

It will be beneficial to the sustainable utilization of albacore tuna （Thunnus a!alunga） resources to better understand the integrated influence of the environmental variables on its distribution. The catch rates and environmental variables （temperature, chlorophyll-a, horizontal current, vertical current） were collected from 56 sampling stations in waters near Cook Islands from Sep, 2013 to Dec, 2013. The relationships between the catch rate of albacore tuna and the environmental variables were analyzed and the models were developed to estimate integrated habitat indices （IHI） for albacore tuna at five depth strata （40 m each） and the entire water column between 40m and 240 m, and to predict the spatial distributions of albacore tuna in these depths. The support vector machine （SVM） method was used to develop the IHI models. These IHI models were verified by using the data collected at 14 verification stations. Results showed that：（1） there was no significant difference between the nominal catch rates and the predicted catch rates; （2） The IHI models developed in this study performed well in predicting catch rate distribution of albacore tuna with selected environmental variables; （3） The key environmental parameters in the IHI models differed among the depth strata. The chlorophyll-a concentration, water temperature, vertical current, chlorophyll-a concentration and water temperature were the key variables that influenced the albacore tuna distribution at the depth strata of 40.0-79.9m, 80.0-119.9m, 120.0~159.9m, 160.0~199.9m and 200.0~239.9m, respectively. The temperature was the key variable that influenced the albacore tuna distribution at the entire water column; （4） The preferred swimming depth stratum of albacore tuna was 120.0 ~ 199.9m; （5） The IHIs for albacore tuna in the areas at 9°00′S-12°20′S,159°00′W-164°00′W、13°30′S-14°30′S,159°00′W-161°00′W and 10°30′S-12°30′S,167°00′W-168°00′W were relatively high. Results suggested to deploy the longlines at the water depth of 120-199.9 m to improve the catch rate of albacore tuna and reduce the by catch rate when fishing in these areas.