Threats and hopes for the Scottish seas
Planet Earth is famously referred to as the blue marble, with the blue colour coming from the fact that most of it is covered in salt water. It is not surprising, then, that the oceans are a critical component of the environment. For example, the oceans are responsible for roughly half of carbon cycling on the planet, and host almost 3/4s of its animal biomass. The importance of the marine realm is particularly relevant for countries like Scotland, where around 90% of the territory is sea. The Scottish marine area equates to approximately six times more than her landmass and comprises over 60% of UK waters. With over 900 islands and complex firths, Scotland has over 18,000 kms of coastline. The overwhelming majority of people living in Scotland are within a 10 km distance from the sea. The Scottish seas are therefore central to the country’s resources, economy and culture. Like the terrestrial realm, the seas are impacted by varied combinations of threats, including climate change, over exploitation, pollution and invasive species. Here, we discuss these threats in the context of the Scottish seas, as well as the implications they have for marine biodiversity.
By Faye Moyes, Anne E Magurran and Maria Dornelas
Scotland as a marine nation
Scotland is a proud maritime nation with a long history of marine based industry, from early settlers gathering shellfish in Mesolithic times, through heavy industrial fisheries and fishing related industries, shipbuilding and whaling, oil and gas to renewable energies and marine tourism. The East Neuk of Fife was a particularly rich source of fish and in fact, King James VI coined the phrase ‘a beggar’s mantle fringed with gold’ to describe the Fife area because of the rich seam of fish around the coast. In the 19th century, Anstruther was an important port and trading centre for fisheries, particularly the herring industry which was significant at the time. Indeed, it was the richest town in Scotland at the height of the herring boom and the Dutch, who were prominent in the herring industry of the time, influence is evident in some of the architecture even today.
Currently around 60% of the value and tonnage of UK vessels are Scottish. Despite the huge decline in the fishing industry over the last 100 or so years, it remains an important part of the economy, generating millions in revenue. Human induced pressures, such as overfishing and climate change have somewhat depleted the variety and abundance of many species in Scotland’s seas. In her book of recollections (Queen of Science) Mary Somerville recalls how, in the late 1700s, the Firth of Forth was ‘rippled by herring’, while whales were often frequently spotted. Although the herring stocks subsequently collapsed, there remains a diverse range of marine life, including charismatic species such as Atlantic puffins, Fratercula arctica, bottlenose dolphins, Tursiops truncatus and grey seals, Halichoerus grypus. Scotland is home to many such iconic species, and marine tourism and nature breaks are increasingly popular. For example, trips to the Isle of May to see puffins and other seabirds, trips to the Bass Rock to view the largest colony of Northern gannets, Morus bassanus (a species whose scientific name honours this provenance) in the world, and dolphin and whale watching in the Moray Firth are available. Scottish waters are home to a large number and wide variety of marine life and biodiversity. The marine environment is important for Scotland’s economy, generating ~£5 billion annually and accounting for almost 3% of the overall economy. Additionally, the Scottish marine realm stores more carbon than her terrestrial forests and is of critical importance, not only as a source of income, but as a resource for human health.
Environmental change
In common with oceans around the world, the biodiversity in Scotland’s seas is subject to a range of anthropogenic pressures. These include direct pressures, such as fishing and wind farms, where human activities directly impinge on specific marine ecosystems, and indirect pressures, including climate change and acidification, where the oceans integrate anthropogenic impacts occurring at the global scale. Scotland’s Marine Assessment 2020 documents the direct pressures in each of 21 Scottish Marine Regions. The Forth and Tay Region report, for example, mentions disturbance to the sea floor due to bottom trawling, scallop-dredging, the removal of non-target species, including seals and cetaceans, and underwater noise associated with fishing, construction, military activities and commercial shipping. These impacts are widespread in Scottish waters. Other direct pressures, such as aquaculture, tend to be more geographically focussed. In the West Highland Region, for instance, salmon farming is mentioned as a concern because of contamination linked to the use of pharmaceuticals, deoxygenation, escapes of non-indigenous species, the spread of disease such as sea-lice as well as noise pollution associated with the deployment of acoustic deterrent devices. Aquaculture raises further concerns due to the practice of fishing smaller, less commercially important fish or juveniles to be used in fishmeal or oil, leading to depletions in natural fish stocks. Physical disturbance to the sea floor due to oil and gas sector infrastructure is another example of a pressure affecting certain sectors of Scottish waters, such as the Fladen and Moray Firth Offshore Region. Added to this catalogue are more recent sources of anxiety, for instance microplastics and ‘forever chemicals’ such as PFAs, that in the past have not been systematically monitored but have the potential to damage Scotland’s marine biodiversity.
These direct pressures occur alongside, and interact with, indirect pressures, of which climate change is a major concern. Scotland’s seas have warmed over the past three decades, when judged against records since the 1890s, but this rise in temperature has occurred unevenly with the Faroe-Shetland Channel seeing the greatest increase. Sea level is rising, also at different rates along different parts of the Scottish coastline. Increased rainfall in Scotland in recent years, in conjunction with more extreme weather events, amplifies the effects of sea level rise on coastal ecosystems.
There are many reasons to be concerned about anthropogenic impacts on Scotland’s seas, but the way in which these impacts lead to biodiversity change can be complex, with our understanding constrained by substantial knowledge gaps. Wind farms, for example, have a largely negative effect on marine biodiversity, particularly on some fish and birds, during the construction phase, but with a more mixed set of influences during the operation phase. Once established, the bases of wind turbines in the North Sea can support distinctive benthic communities by providing a type of habitat – hard substrate – that was present in the past but largely removed by bottom trawling. Fish may also gain advantages. There is evidence that cod (Gadus morhua) populations can exploit wind farms for both feeding and reproduction while fish species associated with rocky habitats also appear to benefit.
In contrast, it is increasingly clear that wind farms are a hazard for migrating birds, particularly when migratory behaviour is also being affected by climate change and shifts in food supply. Questions also remain about the legacy benefits, and costs, of the artificial reefs remaining when oil and gas installations are decommissioned.
Biodiversity trends
Biodiversity change in the face of climate change is equally multifaceted. All ecosystems experience natural changes, over time, in species composition. Fish ranges, and therefore the species present in a given locality, track underlying climatic drivers, such as the North Atlantic Oscillation. These natural trends have been intensified in recent years by ocean warming with the North East Atlantic, including the seas around Scotland, experiencing increases in species richness and a speeding up of compositional turnover and biotic homogenisation.
Invasive and non-native species, such as wireweed (Sargassum muticum), now well established in Scottish waters, make further, and often difficult to predict, contributions to the reorganisation of marine assemblages.
These complexities speak to the challenge of unravelling the causes, and understanding the consequences, of biodiversity change in Scotland’s marine ecosystems. There are many different drivers, some of which are local issues, others widespread ones. Direct pressures interact with indirect ones. Some taxa may gain from a particular set of circumstances while others are harmed. A rise in species richness could imply that there is no need to worry about the impact of human activities on biodiversity, but may mask a restructuring of the system that threatens adaptive responses. We know very little about how these changes affect the functioning of the ecological communities concerned.
Biodiversity globally is undergoing substantial changes due to anthropogenic pressures; the marine realm is no different. Pressures such as warming waters and overfishing lead to changes in the distribution of fish populations, which can in turn affect the ecosystem integrity of these systems. There are shifts in the dominant species in Scottish marine systems even over relatively short time scales, along with concomitant change in species rarity. Despite this there is less change in functional diversity suggesting that fundamental aspects of the systems remain intact. Recent work suggests that trait structure and functional importance are crucial in the maintenance and resilience of marine systems and that this holds true, even whilst species composition is changing. Distinctions between the biodiversity of the North Sea and Celtic Biscay Shelf systems, suggest that habitat, connectivity and fishing pressure may be important contributory factors. These differences are also reflected in the slight disparity in sea surface temperatures in these systems.
Biodiversity is multidimensional and changes in one dimension are not necessarily reflected in changes in another. For example, increases in taxonomic diversity do not always mean corresponding increases in functional/trait diversity. This means that it is important to examine change in the different components of a system, alongside relevant environmental factors. The health of an ecosystem can depend on multiple factors, including how resilient species or functional groups are, interactions between taxa (e.g., predator-prey) and the effects of environmental influences. Measuring ecosystem integrity means evaluating the whole system and how it differs from a baseline, or is changing over time. This can be done by quantifying change in the dimensions of biodiversity alongside change in biomass, productivity and the environment.
Protection of marine life
Scotland boasts many marine protected areas (247, see Figure 1 for map illustration), both inshore and offshore. The level of protection within these areas is variable, with approximately 1/10th of these including no fishing policies, particularly in relation to the protection of endangered and vulnerable species such as the flapper skate, Dipturus intermedius which appears as Critically Endangered on the IUCN red list. The Scottish Biodiversity plan is an ambitious one and includes new conservation and protection strategies for marine species, particularly those already known to be vulnerable, i.e., many Elasmobranchii species (skates, rays and sharks), seabirds, marine mammals and bottom dwelling shellfish. Scotland’s MPAs are now more comprehensive and cover a more diverse range of marine species. However, the protection of Scottish seas has had its share of controversies, most notably surrounding the now discontinued HPMAs (Highly Protected Marine Areas). Plans are now in place to add to the 27 MPAs that include measures to restrict fisheries either completely or in part, but these will be undertaken with early involvement with industry in order to ensure cooperative participation. The vast majority of fishers readily comply with any bans or restrictions on fishing activity and any infringements of these measures are subject to extensive legislation.
Long term monitoring projects such as the scientific surveys undertaken by ICES are of huge importance not only for scientific analyses and reporting but to inform and recommend fisheries management and marine planning. ICES also have many other monitoring programmes in place and record landings by statistical rectangle allowing for analyses alongside survey data. Fishing pressure by depletion of fish stocks is not the only threat the industry poses to marine life – accidental bycatch can have a serious impact on the populations of vulnerable marine mammals, seabirds and fish. Marine monitoring programmes such as the Bycatch Monitoring Programme (BMP) set up by senior academics at the University of St Andrews help with the quantification of numbers and information on these bycaught animals: marine mammals, birds and endangered sharks, skates and rays. This programme makes use of scientific observers on board vessels and is an important tool in aiding successful collaboration between science and industry.
There are also measures in Scotland to regulate the harmful dredging methods of fishing for certain molluscs and crustaceans such as the Queen scallop, Aequipecten opercularis and Norway lobster, Nephrops norvegicus This is due to the detrimental effect of dredging on many invertebrate species, such as soft corals and crustaceans as well as bottom dwelling fish. Recently, as a result of RSPB campaigning a full ban came into place on sandeel fisheries in Scottish waters, in recognition of the crucial importance of sandeels to seabirds like puffins, Fratercula arctica and kittiwakes, Rissa tridactyla, both with an IUCN status of Vulnerable.
The presence of non-native species, which can often have an adverse effect on native marine life, is becoming more prevalent in Scottish waters. However, once a species is established it can be extremely difficult to eradicate. It is, therefore, imperative that care is taken to prevent the introduction of non-native marine species wherever possible, for example, by ensuring there is no release, accidental or otherwise of aquarium species or research animals.
Generally speaking, Scotland does well in protecting the marine environment, whether this be through integrated fisheries and conservation planning or the creation of protected areas and species. Nevertheless, there is an opportunity to push towards adopting an ecosystem approach to marine planning, fisheries management and conservation, which would be a significant step towards creating sustainable, healthy and profitable marine systems for all.
Conclusion
In conclusion, Scotland’s seas are invaluable culturally, economically and for intrinsic reasons. We have a long history of human exploitation of these waters, and varied threats that affect them, including warming, pollution and overexploitation. However, there is also much that is positive about how the Scottish seas are monitored and managed. Fish monitoring is exceptionally good, and done in cooperation with European based regional centres. Effective monitoring allows us to see that despite all threats, there are mixed trends among Scottish marine biodiversity. There are also bright spots on the side of protection, with a significant proportion of the Scottish seas covered by protected areas. While much remains to be done to future proof the marine environment in Scotland, there is hope for preventing further damage, and reversing previous threats.
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