| dc.description.abstract | Climate change, caused predominantly by rising levels of atmospheric carbon dioxide, is changing the function and composition of marine communities. This thesis considers the past and potential future effects of warming seas, on the fish assemblage of the south-west UK. Using fishery-independent data, this research aims to identify trends in the abundance and diversity of key fish species over the past three decades, and predict how these trends may continue over the 21st century, according to forecasted climate scenarios.
The oceans have absorbed over a quarter of anthropogenic carbon dioxide since the Industrial Revolution, as well as over ninety percent of the Earths excess heat which has helped to mitigate the impacts of climate change. However, carbon dioxide emissions, and the subsequent rise in air and sea temperatures, have reached unprecedented levels in recent decades. Consequently, oceans are becoming more acidic, sea levels are rising, and weather events such as storms are increasing in both frequency and severity. Due to the complex and integrated nature of marine ecosystems, climate-induced changes are likely to affect organisms and communities at all levels, both directly and indirectly. This could mean changes to the composition of fish assemblages, which consequently will affect human populations reliant on them for food and income. Whilst fish stocks are prone to natural fluctuations and variability, there is a growing body of literature demonstrating that anthropogenic activity is having a significant, and perhaps irreversible effect on some fish populations.
The first part of the research conducted here demonstrates that since the mid-1980s there has been a significant increase in the species richness and diversity of the south-west UK fish assemblage, likely driven by an increase in the abundance of warm-water adapted species. In addition, some commercially important fish species typically associated with colder waters have decreased in abundance. The second part of the research in this thesis uses a data-driven predictive modelling approach to forecast how key species of the UK fish assemblage may respond (in terms of abundance and spatial distribution) to the latest predicted climate scenario. The results demonstrate that, according to a “best case scenario” of carbon emissions, many of the warm water species shown to have increased in abundance over the last three decades will continue to do so. Similarly, many cold water species will continue to decline, such that some economically valuable species may be absent from south-west UK waters by the end of the century. The results also suggest that by the end of the century, the fish assemblage is likely to be characterised by species that currently have a lower latitudinal preference, smaller mean body size and lower trophic level.
The ability to predict and anticipate how fish populations may respond to a changing climate will be essential for the successful continuity of the fishing industry. As such, management plans and fishing practices will need to be adaptive and flexible in order to exploit new opportunities, as well as protecting and preserving the stocks most threatened by climate change. | en_GB |
