南海鸢乌贼栖息地模型优化及季节性差异分析

Habitat model optimization of purpleback flying squidinhabiting South China Sea and its seasional change

鸢乌贼(Sthenoteuthis oualaniensis)是南海经济价值较高的头足类种类,栖息地分布及其季节性变化规律研究对其资源科学利用和养护具有重要的意义。本文根据2014—2017年3—11月份南海鸢乌贼春、夏、秋3个季节的渔业数据,结合春、夏、秋三个季节关键环境因子构建基于不同权重的栖息地模型(HSI),筛选出最优栖息地模型预测HSI值,以春、秋季为案例对比了2个季节鸢乌贼栖息地分布格局的差异性,并进一步评估了2015年超强厄尔尼诺事件对鸢乌贼栖息地的影响。结果发现,各月筛选的最优栖息地模型可精准预测南海渔场,春、夏、秋对应的模型精度达到86%、75%和76%。春季鸢乌贼适宜栖息地面积(HSI≥0.6)和最适宜栖息地(HSI≥0.8)显著高于秋季,且广泛分布在南海北部海域,而秋季栖息地适宜性降低,中沙和南沙最适宜栖息地基本消失,极少部分分布在南海东北部水域。从空间上看,2014—2016各年春季最适宜栖息地经纬度重心相对秋季显著向西南部迁移,而不适宜栖息地(HSI≤0.2)向东北方向迁移。研究表明,基于关键环境因子和加权重算法的栖息地模型可以精准预测南海鸢乌贼栖息地,其分布模态呈现显著的季节性差异。

Purpleback flying squid(Sthenoteuthis oualaniensis)is a cephalopod species with high economic values.It is largely exploited by Chinese fishing vessels in the South China Sea.The location of fishing ground showed seasonal differences,which may be related to habitat distribution of this squid species.Based on the fisheries data of S.oualaniensis in the South China Sea from Spring to Autumn,2014-2017,and by combining with key environmental factors each season including water temperature at 50 m(Temp_50 m),chlorophyll-a concentration(Chla)and mixed layer depth(MLD)in spring,sea surface temperature(SST),Chla and water temperature at 100 m(Temp_100 m)in summer,and SST,Chla and MLD in autumn:,a weighted-based habitat suitability index(HSI)model was developed in this study.The optimal HSI model was selected each season to predict the HSI value.The seasons,spring and autumn,were taken,for example,to compare the habitat patterns and further examine the impacts of the strong El Niño events on S.oualaniensis habitat.The results suggested that the selected optimal HSI model can accurately predict the fishing ground of S.oualaniensis,with the model precision of 86%in spring,75%in summer and 76%in autumn.The area of the suitable habitat with HSI>0.6 and the optimal suitable habitat with HSI>0.8 enlarged in spring comparing to the autumn,and the optimal habitats were widely distributed in the northern waters of the South China Sea.While the habitat suitability in autumn clearly decreased,the optimal habitats in Zhongsha and Nansha Island mainly disappeared,with a few occurred in the northeastern waters.From a spatial perspective,the latitudinal gravity centers of the optimal habitats in spring during 2014-2016 moved northeastward relative to the habitat in autumn,whereas the poor habitat with HSI<0.2 shifted southwestward.Comparing the year of 2014 with normal climate condition with the year of 2015 with strong El Niño event,it was found that the area of the optimal habitats significantly decreased and the poor habitats dramatically increased.Our findings suggested that the HSI model based on the weighted-based algorithm and key environmental factor could be applied to predict habitat hotspots of S.oualaniensis in the South China Sea.The habitat pattern showed seasonal difference,and the strong El Niño event yielded profound negative effects on habitat suitability of S.oualaniensis.