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Volume 43 Issue 11
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Relationship between lunar phase, water depth and operation time and CPUE of purpleback flying squid (Sthenoteuthis oualaniensis) in South China Sea in spring

  • Corresponding author: Bin KANG, bkangfish@163.com
  • Received Date: 2018-11-28
    Accepted Date: 2018-12-17
  • According to the yield data of the Sthenoteuthis oualaniensis in the southern and northern sea areas of the South China Sea in spring in 2015 and 2016, the present research was carried out to analyze the relationship between depth, working time and moon phases and CPUE under the condition of operation. From the GAM model analysis, we knew that the effect of operation time and lunar day on CPUE was significant. The results showed that CPUE is relatively low at the depth of 0-999 m under the water in the bright moonlight. When there was nomoonlight, the CPUE in each water layer changed little, and the CPUE at the depth of 2 500-2 999 m was relatively higher. When the working time in the first half of the night (21:00—24:00), the CPUE was higher, which wan up to 399.4 kg/net at most, and the CPUE gradually decreased in the second half of the night (0:00—5:00). There was a great difference in the yield between the bright moonlight and moonless night, which were respectively 267.0 kg/net and 321.6 kg/net. El Niño has impact on the changes of the S. oualaniensis resources in various water layers to a certain extent. The research on the effect of operational conditions on CPUE of the S. oualaniensis can provide reliable suggestions for fishing ground.
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Proportional views

Relationship between lunar phase, water depth and operation time and CPUE of purpleback flying squid (Sthenoteuthis oualaniensis) in South China Sea in spring

    Corresponding author: Bin KANG, bkangfish@163.com
  • 1. Fisheries College, Jimei University, Xiamen    361021, China
  • 2. Fisheries College, Guangdong Ocean University, Zhanjiang    524088, China
  • 3. Center of South China Sea Fisheries Resources Monitoring and Assessment, Guangdong Ocean University, Zhanjiang    524088, China
  • 4. Guangdong Provincial Engineering and Technology Research Center of Far Sea Fisheries management and Fishing of South China Sea, Zhanjiang    524088, China
  • 5. College of Fisheries, Ocean University of China, Qingdao 266100, China

Abstract: According to the yield data of the Sthenoteuthis oualaniensis in the southern and northern sea areas of the South China Sea in spring in 2015 and 2016, the present research was carried out to analyze the relationship between depth, working time and moon phases and CPUE under the condition of operation. From the GAM model analysis, we knew that the effect of operation time and lunar day on CPUE was significant. The results showed that CPUE is relatively low at the depth of 0-999 m under the water in the bright moonlight. When there was nomoonlight, the CPUE in each water layer changed little, and the CPUE at the depth of 2 500-2 999 m was relatively higher. When the working time in the first half of the night (21:00—24:00), the CPUE was higher, which wan up to 399.4 kg/net at most, and the CPUE gradually decreased in the second half of the night (0:00—5:00). There was a great difference in the yield between the bright moonlight and moonless night, which were respectively 267.0 kg/net and 321.6 kg/net. El Niño has impact on the changes of the S. oualaniensis resources in various water layers to a certain extent. The research on the effect of operational conditions on CPUE of the S. oualaniensis can provide reliable suggestions for fishing ground.

  • 鸢乌贼(Sthenoteuthis oualaniensis)属于大洋性重要的头足类,分布在印度洋和太平洋的热带以及亚热带海域[1]。鸢乌贼种群可分为大型群、中型群、小型群和微型群[2],但南海无大型群个体[3]。迫于南海近海捕捞压力的增大,渔业资源的破坏,发展中远海鸢乌贼渔业资源有利于缓解这一难题。

    国内外学者对环境因子与鸢乌贼单位捕捞努力量渔获量(CPUE)的关系进行了研究[4-9]。Chesalin等[10]研究了阿拉伯海鸢乌贼生物量的变化规律。Paighambari等[11]分析了鱿鱼钓钩颜色和水深对捕获率的影响,认为钓钩颜色与捕获影响不大,浅水区的捕获率较高;Siriraksophon等[12]利用鱿鱼钓的作业方式结合探鱼仪分析了鸢乌贼夜晚在150 m水深栖息的海水温度范围为14~31 °C;晏磊等[13]分析了月相与鸢乌贼捕获率的关系,月黑天产量明显高于月光天。灯光罩网渔船作业对月光、作业时间和作业水深的把握能够较大地提高渔获产量,南海作业条件与CPUE关系的研究对鸢乌贼渔业资源的开发有着重要的作用。

    本次调查数据采集于2015和2016年春季灯光罩网渔船分别在南海两个不同海水深度海域进行捕捞生产的数据。利用GAM模型分析作业时间和农历日对CPUE的影响程度,探究水深与CPUE的关系,解释异常气候现象对鸢乌贼栖息水层的关系,以期为南海鸢乌贼渔场的寻找以及渔业资源分布规律提供参考依据。

1.   材料与方法
  • 数据来源于2015年(3—4月)和2016年(3—5月)春季灯光罩网渔船“琼儋州15029”分别在南海南部的南沙群岛附近海域(111°19′~114°15′E,9°10′~12°19′N)和北部的海南岛东部海域(110°19′~112°26′E,17°10′~18°29′)作业所提供的产量数据(表1),记录每网次的作业时间及产量。船体长度44 m,主机功率352 kW,渔船装配460盏1 kW的金属卤素灯。

    年份
    year
    海域
    sea area
    经度
    longitude range
    纬度
    latitude range
    水深/m
    depth range
    天数 day
    月光天
    bright moonlight
    月黑天
    no moonlight
    2015 南海南部 111.33°~114.25°E 9.18°~12.31°N 1 500~4 300 12 28
    2016 南海北部 110.33°~112.42°E 17.17°~18.47°N 400~1 500 11 29

    Table 1.  Information of survey in South China Sea in spring

    根据农历日区分月光天(初八至廿二)和月黑天(初一至初七、廿三至三十)[14],月光天和月黑天的月亮亮度对灯光诱捕渔业有一定的影响。南海南部和北部的调查海域水深范围为400~4 300 m,作为趋光性鱼类,鸢乌贼白天在水深400~1 100 m栖息,夜晚上浮至0~100 m水层捕食[15],调查海域覆盖了鸢乌贼栖息的各水层。

    2014—2017年每3个连续月的海洋尼诺指数(Oceanic Niño Index,ONI)来自NOAA公开数据(http://origin.cpc.ncep.noaa.gov/)。

  • 采用Excel 2013、SPSS 19.0、Primer 5、R语言软件进行数据处理及作图,利用Arcgis 10软件绘制调查海域分布图。

  • 记录每天各个网次的鸢乌贼产量数据,每天的网次数有差别(6.9网/天),对研究有一定影响,故采用每个网次的产量作为CPUE:

    式中,Y为鸢乌贼产量(kg或t),N为网次数(net)。

  • 利用Primer 5软件对鸢乌贼产量状况(产量、网次、CPUE、平均CPUE、最小CPUE和最大CPUE)进行对数转化,构建相似性矩阵,Bray-Curtis相似性系数进行聚类分析对各个水深范围进行区分。

  • GAM模型是非线性回归,多元线性回归的扩展,渔业资源的研究已经广泛地应用了GAM模型[16-17]。运用R语言建立GAM模型[18-19],对CPUE进行对数转化,进行标准化处理,分析响应变量(农历日和作业时间)对解释变量(CPUE)的非线性关系。本研究GAM模型表达式:

    g为连接函数(link function);c为常数截距项(intercept);s为平滑函数(smooth function);ε为误差项(error)。

  • 利用Microsoft excel对数据进行整理,SPSS 19.0对农历日、作业时间和水深等作业条件进行单因素方差分析(One-Way ANOVA),检验是否存在显著性差异。其中作业时间(F=2.858,P=0.002)与CPUE存在显著性差异,农历日(F=0.934,P=0.561)和水深(F=0.659,P=0.882)与CPUE无显著性差异。

2.   结果
  • 调查中月光天和月黑天各水层的CPUE变化情况有所不同(mean CPUE为各水层内每天CPUE的算术平均值)。

    春季南海整月时鸢乌贼CPUE范围为216.8~405.2 kg/网,月光天和月黑天分别为81.0~415.7和212.5~430.8 kg/网。月光天时CPUE在1 500~1 999 m水深时出现一个高峰,2 000~2 499 m水深时出现一个低峰,在大于2 500 m后趋于稳定;月黑天时CPUE在2 500~2 999出现一个高峰,其他水深范围在300 kg/网上下略微变化;结合月光天和月黑天的整月时,CPUE较为平稳,仅在2 000~2 499 m和2 500~2 999 m水深分别出现一个小低峰和一个小高峰(图1)。

    Figure 1.  Relationship between each water layer and CPUE

    观察整月、月光天和月黑天的整体情况发现,作业次数和产量较高的水深范围主要集中在1 000~1 999 m,但月光天在4 000~4 499 m和月黑天在2 500~2 999 m水深也有出现较高的作业次数和产量(图2)。

    Figure 2.  Relationship between each water layer and yield

    通过聚类分析发现,整月时水深分为3类:0~999 m和4 000~4 499 m为1类;2 000~2 499 m和3 000~3 999 m为2类;1 000~1 999 m和2 500~2 999 m为3类。

    月光天时0~499 m和3 500~3 999 m无调查数据,水深分为3类:500~1 499 m、2 500~3 499 m和4 000~4 499 m为1类;1 500~1 999 m为2类;2 000~2 499 m为3类。

    月黑天时水深分为3类:0~999 m、2 000~2 499 m和3 500~4 499 m为1类;1 000~1 999 m和2 500~2 999 m为2类;3 000~3 499 m为3类(图3)。

    Figure 3.  Cluster of each water layer

  • 灯光罩网渔船普遍从19:00开始开灯进行引诱,光照1~2 h后开始下网,6:00—7:00天亮前结束一个昼夜的工作。各作业时间CPUE的范围为213.2~399.4 kg/网,CPUE在21:00—23:00呈下降趋势,1:00—2:00出现小高峰后缓慢下降,在5:00时最低,6:00—7:00作业较少,但CPUE较高,为特殊情况(图4)。

    Figure 4.  Relationship between time and CPUE

    总作业次数和总产量月光天(121网,32.3 t)明显少于月黑天(431网,138.59 t)。月光天CPUE为267.0 kg/网,范围为100.5~420.0 kg/网;月黑天CPUE为321.6 kg/网,范围为230.5~391.1 kg/网(图5)。

    Figure 5.  Relationship between lunar and CPUE

  • 作业时间对ln(CPUE)偏差解释率贡献占10.3%,作业时间对ln(CPUE)有显著性差异(F=5.556,P=0.001<0.01)。ln(CPUE)呈缓慢下降的趋势,在21:00最高,1:00—2:00出现小高峰,大部分作业时间ln(CPUE)的偏差不大,6:00—7:00偏差较大(图6)。

    Figure 6.  Influence of time on ln(CPUE)

    农历日对ln(CPUE)偏差解释率贡献占30.2%,农历日对ln(CPUE)有显著性差异(F=3.555,P=0.009<0.01)。月光天ln(CPUE)呈下降后上升趋势,最低峰偏差较大,月黑天均较高且偏差较小(图7)。

    Figure 8.  Changes in the ocean Niño index from 2014 to 2017

    Figure 7.  Influence of lunar day on ln(CPUE)

3.   讨论
  • 南海水深环境适于大洋性头足类的栖息,盆地水深达4 000 m,最深处为5 550 m,平均水深为1 212 m[20],而鸢乌贼垂直移动达1 000 m,白天在水深400~1 100 m栖息,夜晚上浮至0~100 m水面进行摄食[15-21]。仔稚鱼多生活在海水表层至20 m左右的水深,鸢乌贼索饵行为也常发生在该水层[20]。鸢乌贼主要生活在水层300 m以浅[7],该水层鸢乌贼生物量是作为衡量渔场好坏的重要指标[22]

    在正常的销售情况下鸢乌贼出售价格为4~5元/kg[23],灯光罩网渔船一个作业天所需的成本约为5 000~6 000元,本研究中渔船平均每作业天下网6.9次,CPUE达200 kg/网渔船可获得利益。渔船作业是以经济利益为前提,本研究中发现,整月和月黑天时,各水层CPUE均大于200 kg/网;月光天时,部分水层CPUE较小。

    鸢乌贼的栖息水层为0~1 000 m[24],本研究结果中发现,在月光天时,0~999 m水深范围的CPUE明显的低于其他水深范围,相反,在月黑天时CPUE较为平稳,仅在2 500~2 999 m水深范围CPUE较高。水深大于3 000 m的海域,月光天和月黑天时CPUE变化都不大。鸢乌贼主要栖息1 000 m以上水深,月黑天由于近海作业渔船较多,夜晚作业时灯光驱使鸢乌贼往300~1 000 m水深海域移动。月光天整个海面都是光亮的,渔船作业并没对鸢乌贼垂直洄游造成影响,这是月光天0~999 m水深CPUE较低而月黑天该水层与其他水层CPUE差别不大的原因之一。月光天时渔船可以开往较深海域进行探捕,并增加网具的沉降深度到90 m以上[25],以获取更高的经济利益。

  • 自然条件下,鸢乌贼没有集群的生活习性[26],夜间由于光诱作用,鸢乌贼开始聚集于光源附近。白天,太阳光照均匀使得鸢乌贼分布于整片栖息海域,受海水温度以及其他要素的影响,鸢乌贼在400~1 100 m水层栖息。傍晚,太阳光逐渐消失,鸢乌贼也从较深水层上浮到0~100 m水层索饵,19:00开始开启集鱼灯对鸢乌贼进行诱集,通过1~2 h的诱集,较为分散的鸢乌贼资源会聚集于渔船附近,从而开始一个夜晚的作业。

    本研究中,21:00为试捕阶段,相对其他时间段的产量会偏低,但CPUE在各个时间段中是最高的,为399.4 kg/网。产量较高的时间段是22:00和23:00,但CPUE略有下降,此时为鸢乌贼聚集的高峰期,作业次数以及产量都相对较高。凌晨1:00开始,CPUE逐渐下降,6:00和7:00接近于天亮,该时段仅在资源量较高的情况下才会作业,产量和作业次数均较低,但CPUE较高。3:00除鸢乌贼外的其他种类产量在各个时间段是最高的,鸢乌贼作为中远海生态系统食物链重要的“桥梁”,大洋性鱼类以鸢乌贼作为饵料[8, 27-29],鸢乌贼资源的集群,诱导更多的鱼类汇集进行捕食鸢乌贼,造成该时段其他种类产量较高。

  • 月光天时的满月前后的一段时间产量会逐渐下降[30],作业次数也会相应减少,CPUE也有所下降。本研究中,月光天(121网,32.3 t,267.0 kg/网)的作业次数和产量相对月黑天(431网,138.59 t,321.6 kg/网)要少,CPUE也有明显的差异。月光天开始的5 d,产量开始下降,相应减少作业次数,CPUE仅为157.9 kg/网,低于200 kg/网,逐渐停止作业;根据月光休产4~5 d后,逐渐开始尝试性捕捞,月光天结束前的6 d,CPUE可达311.4 kg/网,待产量恢复后增加作业次数,以增加产量。月光天结束前的6 d,由于只是尝试性捕捞,平均作业次数和产量都比月黑天时低。

    影响渔获率的主要原因是月光[31],但月相不止对捕捞对象的诱集效果造成影响,同时对水温、潮流等外部环境条件造成影响[32-33]。由于月光天和月黑天的作业条件的差异,合理地安排作业时间,减少月光天的工作天数和投网次数,能够降低作业成本,从而增加渔船的经济效益。投网次数是影响产量的主要因素之一[34],但在月光天时合理地控制投网次数能够有效的对渔场进行判断,从而减少能源的耗费。水下集鱼灯能够克服月光对诱集效果的影响[31],但多大的集鱼灯才能够较好的配合灯光罩网渔船作业,有待进一步的研究。40 m水层以下的光照度差异较小,适当的光照强度,能够增加鱿鱼类的聚集密度,提高渔获率[35]

  • 异常的气候变化与渔业资源变动密切相关,是目前相关研究的热点之一[36]。厄尔尼诺现象对鸢乌贼资源量[9]以及生长[37]造成影响。5~50 m水温垂直梯度的变化对鸢乌贼产量的影响较大[38],而厄尔尼诺现象的基本特征是海水温度异常的增高,这种增温现象不仅表现在表层,甚至会在200 m水深出现异常的增温[39]

    根据ONI指数,2014和2017年属于正常年,研究年间2015—2016年正好发生了强厄尔尼诺现象(图8)。异常气候变化时,海水表层温度升高,温跃层结构变化,透光层营养物质减少,鱼类往较深的海域移动[40]。2015年春季厄尔尼诺现象还没开始,CPUE为316.8 kg/网,2016年强厄尔尼诺现象的发生,在一定程度上影响了鸢乌贼资源量的变动,CPUE为301.5 kg/网。厄尔尼诺现象是直接或间接地对鸢乌贼资源量造成影响,需要进一步的研究。异常的气候对饵料生物、海水温度和其他环境因素的影响都有可能是造成鸢乌贼栖息水层的变化以致资源量变动的原因。

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