• ISSN 1000-0615
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Volume 43 Issue 9
Sep.  2019
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Growth, mortality and reasonable utilization of Sebastes schlegelii in the artificial reef area of Weihai, Shandong Province

  • Corresponding author: Yanli TANG, tangyanli@ouc.edu.cn
  • Received Date: 2019-04-16
    Accepted Date: 2019-07-09
  • The artificial reefs are an important part of the marine ranching. Sebastes schlegelii which occurs in the coastal waters of China, including Yellow Sea and East China Sea, is a delicious seafood and has great economic value. We studied the resource status of S. schlegelii in different reef areas, such as growth, mortality and utilization of resources assessment, based on the cage questionnaire data in Weihai artificial reef area, Shandong province, from 2016 to 2018, by the means of ELEFAN Ⅰ, length-converted catch curve, Yw/R curve and the biologic reference points. And uncertainty was incorporated into the estimation of the biological reference points F0.1 and Fmax by Monte Carlo simulation. The results of the first study on the resources of reef areas at different depths showed that the average body length, average weight, asymptotic body length and asymptotic weight of the S. schlegelii in shallow water areas were greater than those in the middle waters, and the deep water areas were the smallest, indicating that the artificial reefs in shallow water areas were more conducive to the protection of fishery resources. The fishing mortality coefficient and the natural mortality coefficient in the middle water area were greater than the deep water area, the shallow water area was the smallest. It is the first time to apply biological reference points F0.1, Fmax and uncertainty analysis to the resource assessment of different depths of reef area. The result showed that the judgment results of FBRP at the three uncertainty levels were consistent with the none uncertainty, but the value of Fmax was far greater than F0.1, making it more difficult to judge the amount of reef resources as overexploitation. Therefore F0.1 is more suitable for the evaluation of S. schlegelii. In combination with Gulland’s theory, biological reference points and yield per recruitment, reef resources were under the mild exploitation, and fishing intensity can be appropriately enhanced to increase catch yield. Shallow waters can be increased to F=0.39, and Yw/R=25.60, corresponding fishing age is 1.83 a. The middle water area can be increased to F=0.46,Yw/R=23.89 and fishing age 0.93 a, respectively. Deep water area can be increased to F=0.42, and Yw/R=16.74 corresponding to a fishing age of 1.12 a.
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    [10] 庄龙传, 叶振江, 李军. 青岛近海许氏平鲉年龄与生长特性的研究[J]. 中国海洋大学学报, 2015, 45(8): 32-37.Zhuang L C, Ye Z J, Li J. Age and growth studies of Sebastes schlegelii in Qingdao coastal waters[J]. Periodical of Ocean University of China, 2015, 45(8): 32-37(in Chinese).
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Growth, mortality and reasonable utilization of Sebastes schlegelii in the artificial reef area of Weihai, Shandong Province

    Corresponding author: Yanli TANG, tangyanli@ouc.edu.cn
  • College of Fisheries, Ocean University of China, Qingdao 266003, China

Abstract: The artificial reefs are an important part of the marine ranching. Sebastes schlegelii which occurs in the coastal waters of China, including Yellow Sea and East China Sea, is a delicious seafood and has great economic value. We studied the resource status of S. schlegelii in different reef areas, such as growth, mortality and utilization of resources assessment, based on the cage questionnaire data in Weihai artificial reef area, Shandong province, from 2016 to 2018, by the means of ELEFAN Ⅰ, length-converted catch curve, Yw/R curve and the biologic reference points. And uncertainty was incorporated into the estimation of the biological reference points F0.1 and Fmax by Monte Carlo simulation. The results of the first study on the resources of reef areas at different depths showed that the average body length, average weight, asymptotic body length and asymptotic weight of the S. schlegelii in shallow water areas were greater than those in the middle waters, and the deep water areas were the smallest, indicating that the artificial reefs in shallow water areas were more conducive to the protection of fishery resources. The fishing mortality coefficient and the natural mortality coefficient in the middle water area were greater than the deep water area, the shallow water area was the smallest. It is the first time to apply biological reference points F0.1, Fmax and uncertainty analysis to the resource assessment of different depths of reef area. The result showed that the judgment results of FBRP at the three uncertainty levels were consistent with the none uncertainty, but the value of Fmax was far greater than F0.1, making it more difficult to judge the amount of reef resources as overexploitation. Therefore F0.1 is more suitable for the evaluation of S. schlegelii. In combination with Gulland’s theory, biological reference points and yield per recruitment, reef resources were under the mild exploitation, and fishing intensity can be appropriately enhanced to increase catch yield. Shallow waters can be increased to F=0.39, and Yw/R=25.60, corresponding fishing age is 1.83 a. The middle water area can be increased to F=0.46,Yw/R=23.89 and fishing age 0.93 a, respectively. Deep water area can be increased to F=0.42, and Yw/R=16.74 corresponding to a fishing age of 1.12 a.

  • 随着海洋资源的逐步开发,鱼类栖息地遭到一定程度的破坏,渔业资源急剧衰退,因此,海洋牧场的建设势在必行。人工鱼礁作为海洋牧场建设的重要组成部分,能为鱼类创造良好的生长、繁殖场所[1],其投放后的效果也受到广泛关注。

    西霞口海洋牧场位于山东省威海市西霞口近岸海域,是多种海洋生物洄游、索饵和产卵的场所。许氏平鲉(Sebastes schlegelii)营半定居性生活,是中国近海常见冷温性底层鱼类[2]。作为西霞口海洋牧场鱼礁区的优势品种,许氏平鲉一般是用地笼和刺网等渔具进行采捕。

    目前,不少学者研究了许氏平鲉体质量与形态性状的表型特征[3]、形态特征与主要环境因子的关系[4]、人工鱼礁模型和大型海藻对许氏平鲉与大泷六线鱼(Hexagrammos otakii)的诱集作用[5]、环境丰容对许氏平鲉早期发育阶段趋礁行为的影响[6]、环境对许氏平鲉丰度的影响[7-8]、许氏平鲉分布与近礁距离的关系[9]、许氏平鲉的年龄与生长特性的研究[10]和许氏平鲉资源评价[11-12]等,但主要侧重于资源生物学方面。本实验利用2016—2018年西霞口不同水深礁区进行的9次调查数据,比较研究许氏平鲉群体的生长、死亡等参数,并利用Beverton-Holt模型、生物学参考点讨论其资源利用状况,结合其生长特征、单位补充量渔获量,为西霞口渔业资源的可持续利用提供科学依据,从而在一定程度上指导渔业资源的合理开发利用。

    • 鱼礁区位于威海市西霞口近岸海域,本研究按水域深浅依次划分为浅水域(小于5 m)、中水域(5~10 m)和深水域(大于10 m),按照分层随机取样法每次调查分别在不同水深礁区随机取样3个站位。

      2016年8月至2018年8月对鱼礁区进行了9次渔业资源调查,其中春季2次、夏季3次、秋季2次、冬季2次,一年四季均有覆盖。调查渔具为地笼,其网目尺寸为2 cm,矩形尺寸为37 cm×22 cm,每只包含24节,1组由5只构成。每个站位放置一组地笼,置于底层,网具在海域内迎流放置48 h。鱼礁区的位置和调查站位如图1所示。

      Figure 1.  Location and station distribution map of Xixiakou artificial reef area

      样品采集后带回实验室,按照《海洋调查规范》(GB/T12763.6-2007)进行种类鉴别和生物学参数测量[13],包括体长、全长、体质量、纯重、性别、摄食等级等,其中各个站位不足50尾的全部测定,否则随机取样测定50尾。根据实验调查的许氏平鲉数据量依次为浅水域151尾、中水域176尾、深水域99尾。

    • 鱼类的生长使资源总量增加,它是影响资源群体数量变动的主要因素之一。

      体长-全长关系用线性回归来拟合,体长-体质量关系一般公认用幂函数[14]拟合,其表达式:

      式中W为个体体质量(g),L为个体体长(mm),a为生长的条件因子,b为幂指数系数。

    • 在建立渔业资源评估模型时,一般用Von Bertalanffy生长方程[15]来拟合并描述鱼类的生长:

      式中Lt (mm)、Wt (g)分别表示个体在t龄时的体长和体质量;L(mm)、W(g)分别表示个体的渐近体长和渐近体质量;t0表示理论上体长(Lt)和体质量(Wt)等于0的年龄,是一个假定的理论常数。K为生长曲线的平均曲率,表示趋近渐近值的相对速度。

      将许氏平鲉的体长分布频率数据按时间序列输入由FAO(联合国粮食及农业组织)开发的FISATⅡ软件中,利用其中的ELEFANⅠ(electronic length frequency analysis)[16]对生长参数LK进行估算。

      理论初始年龄t0的估算参照一下Pauly经验公式[17]

      其中TL(cm)为渐近全长,通过体长-全长关系拟合获得。

    • 鱼类的死亡也是影响群体数量变动的主要因素。死亡系数可分为总死亡系数(Z)、捕捞死亡系数(F)和自然死亡系数(M),三者之间的关系:

      运用FISATⅡ软件中的变换体长渔获曲线法[18],基于许氏平鲉时间序列的体长频率分布数据来估算总死亡系数Z

      N为各体长组的尾数占总渔获尾数的百分比;Δt 为相应体长组的下限生长到上限所需的时间;t为各体长组中值所对应的年龄,总死亡系数即为下降部分的点做回归所得斜率的负值,即Z=−b

      通过Pauly经验公式[19]获得自然死亡系数M

      其中,TL为渐近全长(cm),通过体长-全长关系拟合;K为生长曲线的平均曲率;T为年平均表层水温(°C),为各个站位实测水温的平均值。

      此外,开发率E指捕捞死亡系数与总死亡系数的比值,即E = F/Z

    • 资源利用状况评价是渔业资源评估的核心,是生长死亡参数运用的最终环节。

      本实验对资源利用状况的评价基于Beverton-Holt模型得出的单位补充量渔获量(yield per recruitment, YPR)[20]

      式中YW/R为单位补充量渔获量;W为渐近体质量,由体长-体质量关系求得;tc为开捕年龄,根据变换渔获量曲线50%选择体长L50计算获得[21]tr为补充年龄,以渔获物中第一次大量捕获的体长为基础求得[22]tλ为渐近年龄,本实验取值为8龄。

      根据Pauly经验公式得出的参数,带入公式(8)便可求得不同Ftc对应下的单位补充量渔获量YW/R,使用VBA编程完成运算,用Surfer10.0软件绘制单位补充量等渔获量曲线。

      渔业管理将生物学参考点F0.1Fmax作为管理的参考基准[23-25]Fmax是指在当前开捕年龄下,单位补充量渔获量达到最大值时的捕捞死亡系数。F0.1为单位补充量产量曲线的斜率为原来资源斜率的10%时对应的捕捞死亡系数。F0.1Fmax可分别根据下式求得[26]

    • 不确定性受诸多因素的影响,如种群的自然变化和动态信息的缺乏、参数估计统计方法的不恰当选择及模型假设误差等,影响当前捕捞死亡系数Fcur和生物参考点BRP的估计,使得FcurFBRP中含有大量的不确定性,有可能得出错误的评估结论和管理措施。

      以生长、死亡、资源评价为基础,将3个水平的不确定性引入到单位补充量渔获量模型,采用蒙特卡罗模拟法估算出FmaxF0.1在不同水平下的概率分布,绘制FmaxF0.1Fcur的概率分布图,通过比较来分析不确定性的影响。

      把不确定性引入FmaxF0.1的步骤:(1) 将生长死亡参数代入Beverton-Holt模型,计算出体长-体质量数据的“预测值”;(2) 在预测值中加入不同水平的随机误差来引入不确定性,产生“观测值”;(3) 采用一元线性参数估计法和非线性最小二乘法来估算生长参数和体长-体质量参数的“观测值”;(4) 将生长、死亡参数的“观测值”重新代入到Beverton-Holt模型,重新估算F0.1Fmax的值;(5) 重复上述步骤800次,便可获得F0.1Fmax的数据,进而绘制F0.1FmaxFcur的概率分布图,通过比较三者之间的相对位置关系,进而得出礁区资源的利用现状[27]

      本实验设置3个水平不确定性,变异系数分别为0.1、0.2和0.3。用标准差乘服从正态分布的随机变量的方法产生随机误差[27]。体长年龄数据模拟中,共模拟800次;体长-体质量数据模拟中,对每个体长组模拟50次,共计1 000次。

    • 拐点年龄指体质量增长速度达到最大值时的年龄,根据公式(11)估算:

      临界年龄Tc指一个世代在没有捕捞的情况下资源生物量达到最大值时的年龄,计算公式:

    2.   结果
    • 对各水域内许氏平鲉的体长和体质量进行统计分析,浅水域的平均体长、平均体质量频数分布较均匀(图2)。

      Figure 2.  Standard length and body weight frequency distributions of S. schlegelii in shallow, medium, deep waters

      各水域内许氏平鲉的体长和体质量分布特征分析发现,浅水域的平均体长、平均体质量均大于中水域,深水域最小(表1)。

      浅水域 shallow waters中水域 middle waters深水域 deep waters
      体长组成
      standard length composition
      范围/mm range 46~252 27~240 35~215
      平均值/mm mean 142.36 136.49 122.12
      优势组/mm dominant class 60~70、110~120、150~160 150~160 90~110
      占比/% percentage 23.84 11.36 24.44
      体质量组成
      body weight composition
      范围/g range 2.22~419.10 3.47~458.56 1.02~321.93
      平均体质量/g mean 111.66 91.70 71.64
      优势组/g dominant class 0~10 0~10 20~30
      占比/% percentage 12.58 10.80 16.16

      Table 1.  Statistical table of standard length and body weight composition of S. schlegelii in shallow, medium, deep waters

    • 根据公式(1)对许氏平鲉体长、体质量数据进行拟合(图3)。根据b值可知,在各水域内许氏平鲉的生长均为正异速生长。

      Figure 3.  Relationship between standard length and body weight of S. schlegelii in shallow, medium, deep waters

      根据体长频率时间序列,运用ELEFANⅠ求得von Bertalanffy各生长参数(表2)。

      浅水域
      shallow waters
      中水域
      middle waters
      深水域
      deep waters
      条件因子/×10−5 (a)
      conditional factor
      2.10 2.60 1.54
      生长指数 (b)
      growth index
      3.06 3.01 3.12
      样本数/尾 (n)
      no. of samples
      151 176 99
      渐近体长 mm/(L)
      asymptotic length
      267.75 246.75 225.75
      生长曲线平均曲率 (K)
      average curvature of growth curve
      0.17 0.33 0.27
      渐近体质量 g(W)
      asymptotic weight
      566.89 413.87 337.38
      初始年龄 (t0)
      initial age
      −0.98 −0.50 −0.63

      Table 2.  Statistical table of growth parameters of S. schlegelii in shallow, medium, deep artificial reef

      由上表知,浅水域许氏平鲉的生长方程为Lt=267.75[1−e−0.17(t+0.98)]、Wt=566.89[1−e−0.17(t+0.98)]3.06;中水域为Lt=246.75[1−e−0.33(t+0.5)]、Wt=413.87[1−e−0.33(t+0.5)]3.01;深水域为Lt=225.75[1−e−0.27(t+0.63)]、Wt=337.38[1−e−0.27(t+0.63)]3.12。浅水域的渐近体长、渐近体质量均大于中水域,深水域最小。

      ELEFANⅠ基于体长频率时间序列估计的生长曲线得知,浅水域许氏平鲉的时间分布较均匀且体长分布范围最广(图4)。

      Figure 4.  Standard length frequency distribution of S. schlegelii and growth curves estimated by ELEFAN Ⅰ in shallow, medium, deep waters

    • 基于许氏平鲉体长频率分布,根据FISAT模型中的体长转换渔获量曲线(length-converted catch curve)可得出回归数据点,其回归直线的斜率即为瞬时总死亡系数。

      因此,浅水域Z=0.49,M=0.39,F=0.1;中水域Z=0.97,M=0.61,F=0.36;深水域Z=0.73,M=0.53,F=0.2。由此可知,中水域的自然死亡系数和捕捞死亡系数最高,且总死亡系数也最高(图5)。

      Figure 5.  The estimation of total mortality from length-converterd catch curve of S. schlegelii in shallow, medium, deep waters

    • 根据变换体长渔获曲线知浅水域许氏平鲉L50为102 mm,即当前开捕年龄tc为1.84 a;第一次被大量捕获的体长为75 mm,即补充年龄tr为0.95 a。同理,中水域的L50为93 mm,tc为0.93 a;第一次大量捕获的体长为75 mm,tr为0.59 a。深水域的L50为85 mm,tc为1.12 a;第一次大量捕获的体长为60 mm,tr为0.51 a。

      各水域根据B-H模型绘制的等渔获曲线中(图6),AA’均为F一定,tc变化的最大产量点连线,即最佳tc点连线;BB’均为tc一定,最大产量点连成的最佳F点连线,两者之间区域为最适产量区。浅水域的渔业现行点P(Fcur=0.1,tc=1.84)位于最适产量区内,其对应的Yw/R为12.64 g,表明处于合理开发状态。若保持tc不变,提高Fmax=0.77时,Yw/R为27.67 g;当F0.1=0.39时,Yw/R为25.60 g。

      Figure 6.  The Yw/R curve of S. schlegelii in shallow, medium, deep artificial reefs

      同理,中水域P(Fcur=0.36,tc=0.93)位于最适产量区内,其Yw/R为22.13 g,表明处于合理开发状态。若保持tc不变,提高Fmax=0.93时,Yw/R为26.05 g;当F0.1=0.46时,Yw/R为23.89 g。

      深水域P(Fcur=0.2,tc=1.12)位于最适产量区内,其Yw/R为12.36 g,表明处于合理开发状态。若保持tc不变,提高Fmax=0.84时,Yw/R为18.21 g;当F0.1=0.42时,Yw/R为16.74 g。

    • 对许氏平鲉进行资源评估时,需要进行不确定性分析,其中浅水域各YPR参数的模拟结果见表3

      平均值
      mean
      标准差
      standard deviation
      置信上限
      upper limit
      置信下限
      lower limit
      L 高不确定性 269.77 78.53 275.22 264.32
      中不确定性 269.10 52.35 272.73 265.46
      低不确定性 268.42 26.18 270.24 266.61
      K 高不确定性 0.171 0.050 0.175 0.168
      中不确定性 0.171 0.033 0.173 0.169
      低不确定性 0.170 0.017 0.172 0.169
      t0 高不确定性 −0.987 0.287 −0.967 -1.007
      中不确定性 −0.985 0.192 −0.972 −0.998
      低不确定性 −0.983 0.096 −0.976 −0.989
      a 高不确定性 6.98×10−4 1.99×10−4 7.12×10−4 6.84×10−4
      中不确定性 1.03×10−4 1.16×10−5 1.04×10−4 1.02×10−4
      低不确定性 3.17×10−5 1.98×10−6 3.18×10−5 3.15×10−5
      b 高不确定性 2.368 0.049 2.371 2.364
      中不确定性 2.745 0.022 2.747 2.744
      低不确定性 2.980 0.013 2.981 2.979
      M 高不确定性 0.393 0.114 0.401 0.385
      中不确定性 0.392 0.076 0.397 0.387
      低不确定性 0.391 0.038 0.394 0.388
      Fmax 高不确定性 0.776 0.226 0.792 0.760
      中不确定性 0.774 0.151 0.784 0.763
      低不确定性 0.772 0.075 0.777 0.767
      F0.1 高不确定性 0.393 0.114 0.401 0.385
      中不确定性 0.392 0.076 0.397 0.387
      低不确定性 0.391 0.038 0.394 0.388
      Fcur 高不确定性 0.101 0.029 0.103 0.099

      Table 3.  Summary statistics of related parameters at three levels of uncertainty

      各水域鱼礁区F0.1Fmax基于不同水平不确定性的概率分布可以获得,随着不确定性水平提高,F0.1Fcur概率分布重叠的面积越来越大(图7)。在低水平时,F0.1Fcur的概率无重叠且位于右侧,表明P(Fcur<F0.1)=100%,即资源处于合理开发状态。在中水平时,F0.1的分布变缓变宽,与Fcur有了交集,出现了Fcur>F0.1的可能;在高水平时,F0.1的分布继续变缓变宽,重叠面积增大,但P(F0.1>Fcur)仍十分接近100%,表明高水平不确定性对资源评估结果影响较小。Fmax的概率分布趋势相似,不确定性对资源评估的影响也较小。

      Figure 7.  The probability distribution of F0.1and Fmax at three levels of uncertainty in shallow, medium, deep artificial reefs

      通过对F0.1FmaxFcur的分析,在浅、深水域中,不确定性对F0.1Fmax的影响较小。但在中水域中,低水平不确定时F0.1Fcur有了较大的交集,当高水平不确定性时,P(Fcur>F0.1)>70%,表明当前捕捞死亡系数较高,不确定性对资源评估的影响较大,但是都不足以与Fcur重叠,表明资源仍处于合理开发状态。

      由上述分析可知,在低、中、高不确定性水平下,F0.1Fmax进行资源评估时与无不确定条件下得出的结论一致,但是,Fmax使资源量更不容易判定为过度开发,不利于许氏平鲉渔业资源的可持续利用和正确评价。由此可知,在不确定性的影响下,生物学参数F0.1Fmax更适合作为评价指标。

    • 根据公式求得,浅水域ttp为5.60 a,拐点体长为180.27 mm;Tc为4.01 a,临界体长为152.92 mm。同理,中水域ttp和拐点体长为2.84 a和163.71 mm;Tc和临界体长为2.43 a和151.99 mm。深水域ttp和拐点体长为3.58 a和153.70 mm;Tc和临界体长为2.89 a和138.71 mm。

    3.   讨论
    • 在西霞口各水深礁区中,浅水域许氏平鲉的平均体长、平均体质量、渐近体长和渐近体质量均大于中水域,深水域最小,表明浅水域许氏平鲉资源的生长状况最好。鱼礁表面附着物及周边浮游生物为许氏平鲉提供饵料,鱼礁间的空隙为鱼类提供避敌和栖息场所。

      中水域的总死亡系数、自然死亡系数和捕捞死亡系数均大于深水域,浅水域最小,表明西霞口礁区中水域的许氏平鲉死亡率最高。

    • Gulland[28]认为,E介于0~0.5的资源群体属于轻度开发,介于0.5~1的属于过度开发。若以此标准来判断,其开发率(0.2、0.27、0.37)均处于轻度开发状态。从生物学角度看,F0.1Fmax是渔业资源评估中常用的参考点。各水域中Fcur<F0.1<Fmax,表明不论以F0.1还是Fmax为参考点,均处于合理开发状态。

      通过单位补充量渔获量曲线可知,浅、中和深水域均位于最适产量区,但仍可通过提高捕捞强度,使Yw/R达到更大值。从以上分析中,生物参考点和Gulland分析得出一致结论,各水域资源均处于合理开发状态。

      临界年龄前资源生物量逐渐增加,其后则逐渐下降,因此西霞口开发许氏平鲉应在生物量下降之前,即临界年龄分别为浅水域4.01 a,中水域2.43 a和深水域2.89 a之前,对应体长分别为152.92、151.99和138.71 mm。

    • 有学者在评估东海白带鱼 (Strongylocentrotus droebachiensis)[27]、北部湾二长棘鲷 (Parargyrops edita)[29]时提出,在不确定性影响下,F0.1Fmax更稳定。在本研究中,Fcur<F0.1<Fmax, F0.1明显小于Fmax,若以Fmax为评价指标,则资源更难以判定为过度开发,导致资源的衰退,故采用F0.1作为评价指标更合适,与之前学者研究结论相一致。

      本研究取样时间四季均有覆盖,借助SPSS分析软件对季节间许氏平鲉的个体大小进行分析,结果无显著性差异。本研究在一定程度上也存在样本量不足的情况,调查范围和研究对象可以进一步扩大,能更好的指导渔业的可持续发展。

    4.   结语
    • 本研究表明,礁区的许氏平鲉资源处于合理开发状态,鱼礁的投放对渔业资源起到一定的保护作用。通过单位补充量渔获量和Gulland分析结果一致,表明渔业资源处于合理的开发状态,且F0.1更适合作为评价指标,对西霞口鱼礁区内的许氏平鲉资源而言,可适当提高捕捞强度,来增加渔获物产量,更利于渔业资源和经济的发展。

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