What is the role of discarding in the dynamics of the demersal fish community of the Firth of Clyde?

众所周知，克莱德湾被称为过度捕捞的“生态沙漠”(瑟斯坦和罗伯茨，2010)。从具体情况来看，密集捕捞似乎促使该社区经历了这种变化(Heath and Speir，2012)。然而，鉴于该地区几乎停止了对白鱼的定点捕捞，为什么该社区在近20年的时间里仍未恢复？Clyde底层鱼类群落缺乏恢复的一个假设是，尽管该行业尽了最大努力减少副渔获物，但在用于对虾的拖网渔业中，底层鱼副渔获物足以维持较高的但隐藏的种群死亡率。本项目的目的是对克莱德湾底层鱼类的所有相关数据进行全面提取和综合。然后，结合科学拖网调查档案中的数据，开发主要鱼种的种群评估模型，使我们能够确定捕捞在鱼类群落动态中的作用，并更好地确定恢复克莱德湾健康种群状况所需的补救策略。至少自1982年以来，海洋苏格兰科学公司一直在克莱德湾维持一个观察员方案，对底层拖网渔船和对虾拖网渔船的上岸和丢弃的底层鱼类进行采样。这名学生将需要在阿伯丁的MSS花一些时间来汇编来自观察者和市场抽样数据库的数据。此后，这些时间将在Strathclyde度过，并定期前往阿伯丁，处理数据并制定库存评估。库存评估方法将建立在最近描述数据稀疏股票方法和基于长度的方法的最新出版物的基础上(Cook和Heath，2018)。这些方法建立在贝叶斯参数估计框架中，以便在结果周围提供可靠的可信区间。在项目过程中学到的数据处理和统计建模技能将为学生在商业、工业和政府以及科学领域的广泛职业做好准备。

The Firth of Clyde has notoriously been referred to as an 'ecological desert' having been intensively overfished (Thurstan and Roberts, 2010). Circumstantially, it appears that intensive fishing may have driven the community to undergo the change (Heath and Speirs, 2012). However, given that targeted fishing for white-fish has all but ceased in the area, why has the community not recovered over an almost 20 year period? One hypothesis for the lack of recovery of the Clyde demersal fish community is that by-catch of demersal fish in the trawl fishery for prawns is sufficient to maintain a high, but hidden, mortality rate on the stocks despite best efforts to reduce by-catch by the industry.The purpose of this project is to conduct a comprehensive extraction and synthesis of all the relevant data for demersal fish species in the Firth of Clyde. Then, combined with data from the archive of scientific trawl surveys, develop stock assessment models for the main fish species that will enable us to determine the role fishing in the dynamics of the fish community, and better define what remediation strategies are necessary to restore a healthy stock status in the Clyde.Marine Scotland Science has maintained an observer programme in the Firth of Clyde since at least 1982, sampling landings and discards of demersal fish from both demersal otter trawlers and prawn trawlers. The student would need to spend some time at MSS in Aberdeen to compile data from the observer and market sampling databases. Thereafter, the time would be spent at Strathclyde, with regular trips to Aberdeen, working on the data and developing the stock assessments.The stock assessment methodology will build on recent publications describing new methods for data-sparse stocks, and length-based methods (Cook and Heath, 2018). These methodologies are set in a Bayesian parameter estimation framework so as to provide robust credible intervals around the results.The data handling and statistical modelling skills learned during the project will prepare the student for a wide range of careers in business, industry and government, as well as in science.