Global warming could cut commercial fish catches around Scotland by 20% while they increase by 10% around the south of England, according to a new study by more than 150 Government and university scientists.
Gradually rising temperatures caused by climate pollution could drive porpoises, whales and dolphins away from Scotland's shores. The sea will also become increasingly acidic, which could harm some marine wildlife, the study says.
The Marine Climate Change Impacts Partnership has released its report card for 2013. It summarises the latest research from 55 UK science organisations including Scottish Natural Heritage, Marine Scotland and the Scottish Environment Protection Agency.
The report points out that over the last 30 years landings of cold-water fish like cod, haddock and whiting from the north-east Atlantic have halved. This trend is predicted to continue in the coming decades.
Northern UK seas like the central and northern North Sea will become "up to 20% less productive, with clear implications for fisheries", it says. But at the same time southern seas like the English Channel and the Celtic Sea will become up to 10% more productive.
Although fish that prefer warmer water like hake and anchovy might increase, the cold-water species that have traditionally been a mainstay of the Scottish fishing industry will decline. Climate projections suggest fish will move northwards faster than in the past.
While the number of white-beaked dolphins, harbour porpoises and minke whales looks likely to decline around the east and north of Scotland, the report says other species of striped and short-beaked dolphins may increase, as they move from southern waters.
"The current rate of increase in acidity is probably more rapid now than any time in the last 300 million years," the report says. This has a complex effect on wildlife.
The extent of sea ice in the Arctic has reached record lows in each of the last seven years, with the lowest in September 2012. The report says the rate at which the ice is thinning has increased from 60cm a decade before 2008 to 75cm a decade now.
"This is a worrying report and confirms that major changes are coming for Scotland's marine environment, with water temperatures and acidity both rising, and important fish stocks and wildlife on the move," said WWF Scotland director Lang Banks. "It would be a great pity if all the good work being done to increase fish stocks was to be undone by climate change."
The fishing industry commended the new study, but sounded a note of caution. Paul Williams, chief executive of industry body Seafish, noted the report showed low confidence in its conclusions, but added: "Nonetheless it is important to understand any potential scenarios as clearly as possible, and having worked with many of the contributors to this report on a range of environmental issues over the years, we'd be keen to engage on behalf of the seafood industry."
The report highlights how little is known about climate change impacts on the marine economy, despite its importance for food, energy and transport.
"The marine environment is subject to a wide range of man-made pressures but can also change in response to natural processes," said Dr Matthew Frost, a scientist from the Marine Biological Association who chaired the report's working group. "Disentangling these factors to enable identification of current and potential future impacts of climate change continues to be one of the greatest challenges facing marine scientists today."