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

克莱德湾因过度捕捞而被称为“生态沙漠”（Thurstan and Roberts, 2010）。从环境上看，密集捕捞可能促使社区经历了这种变化（Heath和Speirs， 2012）。然而，鉴于该地区对白鱼的定向捕捞几乎已经停止，为什么该社区在近20年的时间里没有恢复？克莱德底栖鱼类群落缺乏恢复的一种假设是，尽管该行业尽了最大努力减少副渔获，但在捕捞对虾的拖网渔业中，副渔获量足以维持种群的高但隐蔽的死亡率。该项目的目的是对克莱德湾底栖鱼类的所有相关数据进行全面的提取和综合。然后，结合科学拖网调查档案的数据，开发主要鱼类的种群评估模型，使我们能够确定捕捞在鱼类群落动态中的作用，并更好地确定需要哪些补救策略来恢复克莱德河健康的种群状态。至少从1982年起，苏格兰海洋科学就在克莱德湾开展了一项观察员计划，对水獭拖网渔船和对虾拖网渔船打捞上岸和丢弃的底潜鱼类进行取样。该学生需要在阿伯丁的MSS花一些时间，从观察员和市场抽样数据库中收集数据。此后，这些时间将在斯特拉斯克莱德度过，并定期前往阿伯丁，处理数据并进行种群评估。种群评估方法将以最近的出版物为基础，这些出版物描述了数据稀疏种群的新方法和基于长度的方法（Cook and Heath, 2018）。这些方法设置在贝叶斯参数估计框架中，以便在结果周围提供鲁棒可信区间。在项目中学习的数据处理和统计建模技能将为学生在商业、工业、政府以及科学领域的广泛职业生涯做好准备。

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.