基于Schaefer模型的东南太平洋茎柔鱼资源评估和管理

东南太平洋茎柔鱼(Dosidicus gigas)是世界范围内最重要的经济头足类之一,也是我国鱿钓渔船的重要捕捞对象。本文根据2003—2012年中国大陆的渔业数据和FAO统计的东南太平洋茎柔鱼产量数据,利用Schaefer模型,基于贝叶斯统计方法,分基准方案和敏感性分析方案对东南太平洋茎柔鱼资源进行评估,并对其管理策略做了风险分析。结果表明,年渔获量和CPUE数据为贝叶斯资源评估模型提供了足够多的信息。2003—2012年捕捞死亡率低于目标参考点F0.1,渔获量小于最大可持续产量,资源量大于目标参考点Bmsy,资源状况良好,未遭受过度捕捞。在基准方案下,最大可持续产量为142.9万吨,维持最大可持续产量的资源量为214.7万吨,此时的捕捞死亡率为0.682;在敏感性分析方案下,最大的可持续产量为152.5万吨,维持最大可持续产量的资源量为229.6万吨,此时的捕捞死亡率为0.691。决策分析和风险分析表明,当捕获率设定为0.3以下时,资源能够得到较好的养护,资源崩溃的可能性很低。将捕获率设定在0.3左右是最适的管理策略,此时的持续产量为99万吨左右。

Stock assessment and management of Dosidicus gigas in the Southeast Pacific Ocean with Schaefer model

Dosidicus gigas is one of the important economic cephalopod in the world. It is widely distributed in the east of Pacific Ocean. Nowadays the yield of Dosidicus gigas occupies more than 50% of the total yield of squid in China mainland. In 2012 ,the yearly catch in China mainland reached 221.1 thousand tons,the number of fishing vessels are more than 250. It is necessary to assess the stock for making the fishery sustainable. Unfortunately little work is done in this field.The stock assessment and risk analysis of alternative management strategies for Dosidicus gigas in the Southeast Pacific Ocean were carried out by using a Bayesian Schaefer model,in which two scenarios,standard scenario and sensitivity analysis scenario,are considered.The Schaefer model was chosen because of the lack of age-data of Dosidicus gigas and also because the migration mechanism and stock structure of the squid was very complex which was not completely understood by us. In many cases,Schaefer model performed better than many other more complex models such as age-data based models or metapopulation model. For parameters K and q in standard scenario,the posterior distribution are approximately normal distributed. It is totally different with the prior distribution which is set to be uniform distribution. Compared with the two scenarios,the results of posterior distribution of the three parameters are similar .The study indicated that the data of yearly yield and CPUE provided sufficient information for the valuation of model parameters. Under standard scenario,the MSY (maximum sustainable yield)is 1.429 million tons. To maintain MSY,the biomass and fishing mortality should be 2.147 million tons and 0.682,respectively. Under sensitivity analysis scenario,the MSY is 1.525 million tons. To maintain MSY,the biomass and fishing mortality should be 2.296 million tons and 0.691,respectively. Under both scenarios,the fishing mortalities and yearly catches from 2003 to 2012 were lower than reference points F_0.1 and MSY,and the biomass was greater than target reference point B_msy. Status of resource was good and it was not suffering overexploiting or exploited. We set 7 indexes to evaluate alternative strategies and simulated 1 000 times for every single harvest rates from 0.1 to 0.8. Strategy and risk analysis indicated that when the harvest rate was up to 0.7,the average yearly catches would be decreasing. And when the harvest rate was set below 0.3,the resource could be well protected and the probability of resource collapse would be very low. It is concluded that the harvest rate of 0.3 appears to be the best management regulation and the MSY will attain at 990 thousand tons. The harvest rate from 2003 to 2012 were all below 0.3,it was a reason for us to be optimistic for this potential resource. However there were many uncertainty factors in the simulation which should be considered in future studies.