厄尔尼诺/拉尼娜现象对中西太平洋鲣资源丰度的影响

Influence of El Nino / La Nina on the abundance index of skipjack in the Western and Central Pacific Ocean

鲣鱼是中西太平洋重要经济种类,其资源丰度与渔场易受海洋环境的影响。根据1995—2010年中西太平洋金枪鱼围网鲣鱼的资源丰度(单位网次产量,CPUE),结合厄尔尼诺/拉尼娜事件(以Nino 3.4指数来表示),利用时间序列分析,研究厄尔尼诺和拉尼娜事件对中西太平洋鲣鱼资源丰度的影响。研究认为,16年间中西太平洋鲣鱼资源丰度年间和季节变化幅度较大,其中月CPUE最大值出现在1995年2月,为30.37t/网,最小值出现在1997年10月,为5.35 t/网;Nino 3.4区指数对CPUE的影响滞后0~2个月,但同步(滞后0月)时相关性最高,两者呈显著负相关关系。根据16年资源丰度变化趋势与Nino 3.4指数的高低,以每年8—12月CPUE值来表征厄尔尼诺/拉尼娜事件,以2000年为界分为2个时间段:第一个时间段为2000年以前,这段时间中有强厄尔尼诺(SSTA>1.0℃)、强拉尼娜(SSTA<-1.0℃)与正常年份(-0.5℃<SSTA<0.5℃);在发生强厄尔尼诺年份(1997年)时,鲣鱼的资源丰度处在较低的水平,为7.05 t/网;强拉尼娜(1998年)发生时,其资源丰度较高,为19.61 t/网。第二个时间段为2000年以后,包含了弱厄尔尼诺(0.5℃<SSTA<1.0℃)、弱拉尼娜(-1.0℃<SSTA<-0.5℃)与正常年份(-0.5℃<SSTA<0.5℃);发生弱厄尔尼诺时,鲣鱼资源丰度(如2002、2006年CPUE分别为15.27 t/网、16.81 t/网)在总平均CPUE值(15.73 t/网)左右浮动,但低于拉尼娜事件年份的月平均CPUE值(19.90 t/网),两者均高于正常年份的月平均CPUE(14.16 t/网)。整体比较来看在发生拉尼娜事件时,鲣鱼资源丰度增高,但是拉尼娜事件的强弱对增高的程度并没有直接影响关系。研究认为,由于厄尔尼诺/拉尼娜现象引起的海洋环境变化使得初级生产力发生变化,进而使得鲣鱼资源时空分布产生差异。

Skipjack tuna, Katsuwonus pelamis, is an important economic species in the central-west Pacific Ocean, and this species is vulnerable to the change of marine environment. In this paper, according to the abundance index （unit net yield, CPUE） of skipjack tuna collected from the tuna large purse seine fisheries in the central-west Pacific Ocean from 1995 to 2010, combined with the El Nino/La Nina events （expressed by NINO 3.4 index）, the influence of El Nino/La Nina on the abundance index of skipjack was studied with the time series analysis. The results showed that the yearly and seasonal abundance index of skipjack varied greatly in 16 years, in which the maximum monthly CPUE appeared in February 1995 with 30.37 t/net, and the minimum occurred in October 1997 with 5.35 t/net. The effect of Nino 3.4 index on monthly CPUE lagged 0 - 2 months in time, but the synchronization （ lag 0 month） had the highest correlation. The Nino 3.4 index and monthly CPUE had significant negative correlation. According to the level of 16 years abundance index of skipjack and Nino 3.4 index, we chose four months （August to February of the next year） of CPUE values as studying object, and divided 16 years into two periods： 1 ） First period was before 2000, this time period had a strong El Nino （ SSTA 〉 1.0 ℃ ）, strong La Nina （ SSTA 〈 1.0 ℃ ） and normal years （0.5 ℃ 〈 SSTA 〈 0.5 ℃ ）. When the strong El Nino year occurred （ 1997）, the abundance index of skipjack was at a lower level with monthly CPUE of 7. 05 t/net. When a strong La Nina （ 1998 ） occurs, the abundance index was high with monthly CPUE of 19.61 t/net. 2） The second period was after 2000, which contains weak ElNino （0.5 ℃ 〈SSTA〈1.0 ℃）, weak La Nina （ -1.0 ℃ 〈SSTA〈 -0.5 ℃） and normal years （ - 0.5 ℃ 〈 SSTA 〈 0.5 ℃ ）. In the years of weak El Nino, the abundance index of skipjack （such as, the average CPUEs in 2002 and 2006 are 15.27 t/net and 16.81 t/net respectively） fluctuated around the mean CPUE value （ 15.73 t/net）, but still lower than that in the La Nina year＇ s （ 19.90 t/net）. Both the CPUEs during weak El Nino and weak La Nina were higher than that in the normal year （ 14.16 t/ net）. In conclusion, the temporal and spatial abundance index of skipjack varied with both the changes of marine environment and the primary productivity caused by the El Nino/La Nina phenomenon.