More fish, cleaner and greater biodiversity

Thousands of holidaymakers heading to British beaches this summer will be cheered by a major government report into the state of the UK’s seas.

Coastal waters are getting cleaner, fish stocks are improving and species diversity in estuaries is increasing, according to the most authoritative examination ever carried out of UK seas.

But while the Department for Environment Food and Rural Affairs study boasts of “significant improvements” since the last such report in 2005, it also paints a picture of an environment being rapidly affected by a warming world. Seas around the British Isles are higher, warmer and more acid, it says, and coastal litter levels are at a record high.

The sea surface temperature of UK waters has risen on average by between 0.5 and 1C since the 1870s, which could affect the fish that appear on our plates in future. Of the 330 species found around the UK, cold-water species such as cod are in retreat, while warm-water fish including red-mullet, seabass and John Dory are spreading rapidly.

Fish stocks are improving overall, partly due to fishing reductions brought about by European Union quotas, despite criticism from marine conservation groups that the quotas are set too high to maintain fish stocks. The proportion of fin-fish stocks in UK waters being harvested sustainably has risen from 10% in the early 1990s to 25% in 2007.

However, the report notes that a large majority of stocks are still being fished at unsustainable levels. Fish are simultaneously being hit by warming waters, which are causing the cold and warm water zooplankton that fish feed on to move north. The warm water zooplankton tend to be smaller and less nutritious, affecting fish larvae and stocks.

Climate change is also causing sea levels to rise, with the mean sea level rising by 1.4mm per year in the 20th century. While slower than global growth of 1.7mm per year in the same period, the rise has not always been steady – in the 1990s, it was going up by 3-4mm each year. More coastal erosion and more flooding are likely to occur as a result, says the report, with the Humber estuary and Norfolk coast particularly at risk.

UK waters are also not exempt from the global trend of ocean acidifiation due to higher levels of dissolved CO2. This leads to harmful effects for marine life that rely on calcification, such as crustacea and molluscs. But the authors of the report admit the lack of a baseline for pH levels makes it hard to measure the rate of our acidifying seas.

Levels of pollution continue to drop since Defra’s research in 2005, including heavy metals such as lead and mercury. However, there are still some localised problems such as polychlorinated biphenyls (PCBs) which, while stabilising nationally, are still found in places at levels that affect wildlife, including harbour porpoises. Litter levels doubled, though, between 1994 and 2007, with 2,000 items per kilometre of coastline. Litter was even found at a depth of 1,000 metres.

The picture for waterbirds and seabirds is mixed. Waterbird numbers are largely healthy, with the 2006/2007 population numbers 85% above levels in the 1970s. But seabirds have seen a 9% decrease in numbers since 2005, with herring gull numbers down over 50% since 1969.

Seabirds are suffering particularly badly in north and north-west Scotland, due to the arrival of invasive species such as rat and mink, which affect nesting sites.

The evidence in the report was gathered from peer-reviewed science provided by universities, government agencies, NGOs and industry.