Historically sea fish were thought to be an inexhaustible resource, in 1882 Thomas Huxley recognised that it was possible to extirpate some fisheries such as the UK oyster and salmon fishery, but he thought "in relation to our present modes of fishing" sea fish were so abundant that they were inexhaustible. Fishing causes impacts other than overfishing, such as bycatch of non-target and vulnerable species discarding and damage to habitats and ecological communities. Fishing intensity has been increasing since the industrial revolution through which technological advances have given fishing vessels the ability to go further and for longer. This has resulted in the need for an ecosystem focused method of management for fisheries, known as ecosystem based fisheries management (EBFM). EBFM requires the development of indicators which represent the ecosystem with which thresholds can be set against fishing pressure. This was investigated for "Sea-pen and burrowing mud megafaunal communities", which have been identified by OSPAR as a threatened or declining habitat in the North Sea and Celtic Seas. Baited cameras were used to monitor mobile megafauna communities across a gradient of fishing intensity to determine which species are sensitive to fishing pressure and could be used in metrics to monitor recovery in areas proposed for protection. Trawling had a negative effect on species richness of mobile megafauna, Munida rugosa, Cancer pagurus and Liocarcinus depurator, but no effect was found on deep burrowing species (Nephrops norvegicus and Goneplax rhomboides). This study identified species that demonstrated different trends with trawl intensity, the trends are related to the ability to burrow and the species mobility. This gives support to the use of biological traits as indicators to detect changes of communities to fishing pressure. In addition to the development of indicators EBFM supports the use of spatial closures as a tool for fisheries management. This method of management is widely used yet remains controversial, often due to the lack of clear objectives and monitoring. Evidence is growing in support of their use but results are often seen after an extended period of long-term monitoring. Clear objectives for each spatial area closure are essential to be able to set relevant targets and reference points, this allows for robust monitoring and improves the ability to effectively manage the area. Although the use of experimental design and statistical analysis to monitor the effects of area closures throughout the world is increasing, there is still a lack of standardisation and the use of theoretically robust survey designs The use of the Before-After, Control-Impact (BACI) design has been identified as the most robust method to monitor areas closed to fishing Few studies have been conducted using this method due to the difficulty in obtaining sufficient temporal and spatial data prior to the implementation of the area closure. There can also be difficulty in identifying suitable reference sites; monitoring begins after closures have already been established or there are limited funds to allow intense temporal and spatial replication. Area closures are particularly beneficial for species which have key life history stages that congregate, such as for spawning. Although the use of area closures are now common place in the UK, this management approach remains controversial due to the frequent lack of clear objectives, monitoring and impact studies. Providing evidence is therefore vitally important to support decision-making for future area closures and to evaluate whether existing closures are achieving their objectives. This was addressed by evaluating an existing seasonal area closure for Atlantic cod (Gadus morhua) in the Firth of Clyde off the Scottish West Coast. The study uses standardised scientific trawl data and a beyond-BACI approach to compare population trends of the Clyde spawning aggregations with two other sub-populations of the same stock. There was no evidence of local recovery in terms of abundance, biomass or reduced mortality in the Clyde more than a decade after the closure was established. Considering the severely depleted state the Clyde sub-population was in when the closure was implemented it appears that the measure was too little and too late. The advantage of EBFM and using an area closure is when there is uncertainty with regard to the effects of fishing on environment and fish stocks, for example if the sensitivity of a habitat to fishing disturbance is unknown or there is not enough data to accurately assess a stocks biomass. This is applicable for deep-sea in the north east Atlantic where since the onset of deep-sea fishing in the 1970s there has been a decline in the abundance of commercial fish species. Management measures were introduced in 2003 which set Total Allowable Catch (TAC) and restricted days at sea, but this still did not allow for the recovery in biomass of commercial species. Also the fishery has high levels of bycatch, including vulnerable deep-sea sharks, which are estimated to have declined by up to 90%. There has been a recent global debate as to whether there is a depth beyond which fisheries cannot be expected to operate in an economically and ecologically sustainable way. The European Union is currently considering new legislation to manage deep-sea fisheries, including the introduction of a depth limit to bottom trawling. However, there is little evidence to suggest an appropriate depth limit. This was addressed using long-term scientific deep-sea trawl data and calculating important ecological and economical indices. The non-linear trend and first derivatives of these indices were calculated with depth. The results suggest that between 600 and 800 m the commercial benefits derived from fishing start to be outweighed by potentially negative ecological consequences. In the marine environment uncertainty is a great impediment for the sustainable management of resources, this thesis demonstrates that with long-term commitments to monitoring, clear objectives and the development of novel techniques to interrogate data, strong evidence can be established to support policy and decision-making.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:705619 |
| Date | January 2017 |
| Creators | Clarke, Jo |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/8009/ |
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