The great predators of Britain's seas need protection from over-fishing, pollution, boat traffic and marine development, a report says.
The Wildlife Trusts are calling on the government to create 17 protected zones for whales, dolphins, porpoises and sharks round the coasts of England and Wales.
Their report says current policy fails to safeguard cetaceans.
The government says it is working to support the creatures.
But it adds that it is not convinced protected zones offer the best way forward.
The Trusts argue that survival rates will improve if ministers designate areas where nutrient-rich water wells up from the deep ocean, feeding plankton which in turn attract species of fish.
These areas should be free from intensive boat-use, scallop-dredging, bottom trawling and noisy development of offshore structures like wind farms, they say.
The UK Government is working towards what it calls an ecologically coherent network of Marine Protected Areas. But the Trusts' report said: "There's a glaring omission: the absence of protection for the nutrient-rich places on which marine megafauna most depend."
It says in England and Wales only one Special Area of Conservation - in Cardigan Bay - has been designated specifically to protect for bottlenose dolphins. The Scottish government has earmarked three potential zones for protecting whales, dolphins and basking sharks.
Joan Edwards, of the Wildlife Trusts, told BBC News: "These charismatic creatures are under threat. There's a significant gap in marine protection policy - we have to do more."
The report says the seas round the UK have 29 different species of whale, dolphin and porpoise and the second largest shark in the world - the basking shark. It says the reported numbers of many of the creatures have been falling.
"Hotspots" proposed for protection
- Farnes East, Coquet to St Marys - notable for white-beaked dolphin, harbour porpoise and minke whale
- Mid St George's Channel - notable for common dolphin
- Bideford North to Foreland Point - notable for harbour porpoise
- East of Celtic Deep - common dolphin and fin whale
- Celtic Deep - common dolphin and fin whale
- South of Celtic Deep - common dolphin and fin whale
- Western Channel - common dolphin, humpback whale and fin whale
- Manacles - basking shark, harbour porpoise and (seasonally) minke whale
- Lizard, Western channel - common dolphin, harbour porpoise, bottlenose dolphin and basking shark
- Lyme Bay - harbour porpoise
- North and west coasts of Anglesey - harbour porpoise
- Lleyn Peninsula and the Sarnau - harbour porpoise and Risso's dolphin
- Cardigan Bay - harbour porpoise
- Pembrokeshire Marine - harbour porpoise
- North of Celtic Deep - common dolphin.
- Eastern coastline including Silver Pit - harbour porpoise
- Dogger bank - notable for harbour porpoise and white-beaked dolphin
A Defra spokesperson told BBC News: "We recognise the importance of whales and dolphins - these are much loved, iconic animals which form a vital part of the marine ecosystem.
"But they can move across large areas of sea, so for this reason Marine Protected Areas may not be the most effective way to protect them. That's why we continue to focus our efforts on more effective measures, such as reducing by-catch in fisheries."
Joan Edwards replied: "We know dolphins, whales and sharks frequent areas of high productivity and use these areas not just for feeding but for important life stages such as mating and giving birth.
"Over 900 areas of high productivity have been designated as MPAs for cetaceans around the world - England and Wales are lagging behind.
"We accept that MPAs alone are unlikely to be the answer - yet they are a vital first step."
The UK government is facing the risk of infraction by the European commission because it has not identified more MPAs for porpoises.
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