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Chapter 3: Healthy and Biologically Diverse Seas

We are making some progress towards our vision of healthy and biologically diverse seas. There have been recent improvements in some fish communities in most regions: probably linked to a reduced amount of fishing. There have also been long-term improvements in waterbird populations since the 1970s, but climate change is now causing waders to over-winter on the coasts of mainland Europe rather than in the UK. Marine industries are generally well regulated and the pressures they impose on habitats and species tend to be small and localised, but the impacts of climate change and fishing have a much larger footprint. For example, although fishing has a significant economic value and is of benefit as a food source, mobile fishing gear has adversely affected large areas of the seabed. There have been declines in seabird and harbour seal populations in some regions but the reasons for this are not fully understood.

Key findings
  • The habitats assessment suggests that intertidal rocky and nearshore subtidal rocky habitats (see Habitats map), which cover a small area of the UK seas and coasts, are in reasonable condition. However, rising seawater temperatures are already affecting species composition in the English Channel and Celtic Seas. Many seabed sedimentary habitats in large areas of the North Sea, the Western Channel and Celtic Sea, and the Irish Sea have been adversely affected, particularly by mobile fishing gears.
  • Although there is some way to go before the exploitation of the majority of commercial fish stocks is at safe levels, there have been some improvements, probably because of a reduction in fishing effort. There are also signs of improvement since Charting Progress in the marine fish community. However, a number of species are suffering sharp declines, particularly sharks and rays, which are especially vulnerable to fishing pressure. Overall, the situation is still considerably worse than historical conditions. For estuaries, there have been improvements in certain species, probably as a result of better management and pollution control in recent years, but eel recruitment has declined in some regions, reflecting an Atlantic-wide downturn in the numbers of elvers returning to rivers.
  • Harbour seal numbers in some areas have declined dramatically since 2001. The causes are not clear, but contributory factors could be either natural or anthropogenic or both and include competition with grey seals, predation by killer whales around the northern islands of Scotland, declines in important prey species (such as sandeels) and unregulated shooting in some local areas.
  • There have been improvements in waterbird communities, but the numbers of some seabird species have been falling since the mid-1990s. Certain seabird species (e.g. kittiwakes) have suffered poor breeding success in recent years because of shortages in the availability of their prey species – sandeel. This is probably due to the combined effects of climate change and fishing. There is strong evidence of a rapid change in the wintering distribution of estuarine birds in response to global warming during recent years, which may explain recent declines in the numbers of some wader species in some regions.

Improvements in assessment methodology and future requirements

The wider scope of this assessment compared to Charting Progress and the link to pressures that are causing problems, are major contributions that should help determine exactly what we mean by healthy and biologically diverse seas and where actions need to be taken. This has also enabled us to identify the areas requiring more detailed assessments in the future.

Most of the assessments are based on expert judgement or a combination of expert judgement and a range of state and pressure indicators. Some of the assessments carry low confidence because of a lack of knowledge, data and assessment tools and this will need to be addressed.

Gaps in knowledge

We need to develop a better understanding of the causes of the decline of harbour seal populations in the north and east of Scotland in order to develop effective management measures to protect them.

We have gaps in our basic understanding of certain fish species, such as lampreys, sturgeon and shad, and need to know more about the causes of decline in salmon and eel recruitment in some catchments.

We need to know more about the links between human activities and the marine environment, particularly the cumulative impact of several activities in one area and the ability of a species or habitat to recover once a pressure has been removed. This will enable us to develop better measurement tools and to influence what the state of the marine environment should be in the future. We also need better models that integrate more fully the biological and physical components with the pressures at different scales.

In addition, we need better data on those habitats where there is a lack of knowledge. To get a better assessment of the status of microbes, turtles and cetaceans, we would need new, targeted and long-term monitoring programmes.

Current habitat maps cover only 10% of the UK continental shelf and we are forced to rely on modelling for the rest. For future assessments we will need to improve the accuracy, resolution and scope of these habitat maps by undertaking more surveys and making the existing data more widely available.

Summary maps

The summary maps display the status and trends of the healthy and biologically diverse components of the eight regions. For further details see the Chapter 3 summary table and for further information on how ‘traffic light status’ and trend arrows have been assigned see Communicating the findings.

Note: In some cases an assessment has not been possible. This is also the case in the clean and safe seas assessment. Further details are found in the Chapter 3 and Chapter 4 summary tables respectively.