A rare bluefin tuna run, orcas in Strangford Lough and bottlenose dolphins “partying” off Teesside were among the sights from the seas this year.

In their annual review of the UK’s coasts, Wildlife Trusts across the country reported a surge of public interest in marine life and coastal species in a year of seaside staycations due to the pandemic.

Volunteers and conservation experts spotted minke whales, a rare sea slug, a baby Risso’s dolphin, discovered a new seagrass bed and recorded breeding successes for grey seals, guillemots and terns.

But wildlife is still under threat from plastic, including pellets known as nurdles, litter, discarded fishing gear and disposable personal protective equipment such as masks, the wildlife groups warn.

Naturalist Sir David Attenborough warned of the need to protect the UK’s seas and their “extraordinary wildlife” from damaging activities such as trawl fishing, cable-laying and plastic pollution.

“We’re fortunate that our seas are protected by a blue belt of marine protected areas but sadly this does not prevent damaging activities still occurring in these special places.

“For too long we have taken from the sea with little regard of the consequences.

“We are all aware of the problems presenting by plastic litter, but some pollutants and impacts are hidden from view, beneath the surface of the waves.

“Our Government needs to tackle these problems but we can all do our bit too,” Sir David urged.

Among the highlights of 2020 was rare evidence of a baby Risso’s dolphin captured on camera by a wildlife enthusiast, clearly showing foetal folds that indicated it had just been born off the coast of Anglesey, Wales.

The evidence indicates the Welsh coast could be an even more important place for the species than previously thought, North Wales Wildlife Trust said.

A Cornwall Wildlife Trust Sea search volunteer spotted an extremely rare species of sea slug, Placida cremoniana, a tiny millimetres-long orange and black creature that resembles a spiky, glowing lump of coal.

Local people along the English Channel from Cornwall to Kent were treated to the sight of an Atlantic bluefin tuna run, with hundreds of the fish hunting along the coast, joined at times by porpoise, minke whales and dolphins.

Two orcas were seen in Strangford Lough for the first time since 1962 in May, part of the UK’s only resident population of the marine mammals, who rarely come close to the coast, according to Ulster Wildlife.

And more than 30 bottlenose dolphins were seen in playful displays off the coast of Teesside in August.

Jacky Watson, wilder coast officer, Tees Valley Wildlife Trust, said the sighting was a revelation for many local people who had no idea the animals could be seen in UK waters.

“This partying pod of dolphins were highly visible, playing, breaching vertically, racing along at top speed with fin after fin arcing through the waves.”

There was an increase in minke whale and porpoise surveys carried out by members of the public in Yorkshire, and a humpback whale was captured on film four miles off Flamborough Head.

Elsewhere, there was good news for grey seals with increases in numbers at colonies and pups in various parts of the UK, while guillemot numbers were at their highest seen since 2004 on Scottish Wildlife Trust’s Handa Island.

And there was a huge increase in Arctic terns, and sightings of rare roseate terns, at North Wales Wildlife Trust’s Cemlyn nature reserve.

Conservation action has established a new home for sand lizards, at Fylde sand dunes, Lancashire, where they are breeding for the first time since the 1960s following work to restore the dunes and a reintroduction of lizards.

Ulster Wildlife discovered a previously unrecorded seagrass bed of around five acres off the Ards Peninsula on the Irish Sea coast, providing habitat for wildlife and storing carbon.

Organised beach cleans had to be cancelled due to Covid-19 restrictions but many people were still out picking up litter during the lockdown.

Ruth Williams, from Cornwall Wildlife Trust, said: “Disposable PPE gloves and face masks were everywhere this summer and our beach cleans find it every time.”

She urged people to take their PPE home and dispose of it properly, as it was not only unsightly but could also pose a risk to wildlife.

Chances for people to take part in citizen science surveys of the coastline were also cancelled, but the Wildlife Trusts said they had run online events and talks to engage people during the pandemic.

Joan Edwards, The Wildlife Trusts’ director of living seas, said: “In 2020 people flocked to the sea as soon as lockdown restrictions were lifted – they needed the coast as never before.

“Wildlife Trusts around the country were reporting a surge of public interest in marine life and coastal species.”

People were “delighted in seeing marine life and it lifted the hearts of millions in this difficult year”, she said, but warned the oceans were in trouble and the UK would not achieve its climate and environmental targets without restoring marine habitats.