John Ovenden, the amateur photographer behind the pictures, says he has seen the creatures on each of his trips to sea.
Speaking about his sightings this year, he said: ‘Once you know where they are, you do see them. I have been spending more time looking for them this year. A lot of people know roughly where they are. You can even sometimes see them from the coast but a lot of people are not looking for the signs that they are there. I see them every time I go out.
‘There have been a few times where I have seen them on the north coast just out of the car window. If they are really on it, and chasing fish, the water will just boil and they will jump out of the water.’
He added: ‘I am also seeing a lot of seabirds that I never normally see. They only seem to feed when the tuna are also feeding, otherwise they just sit in big rafts for a few hours, then go off in a big frenzy when the tuna come back and then calm down again.’
Despite the average Atlantic bluefin tuna weighing up to 250kg and growing up to 6.5 feet in length, Mr Ovenden said he had only seen the species hunting for smelt – a small silver-coloured fish which usually grows up to eight inches long.
‘If the tuna come across a little shoal of fish, then it is one or two moments of madness of them piling into it,’ he said.
‘They move at about 40mph and are really explosive when they hunt. It is amazing to watch.’
Mr Ovenden added that he has also seen unusually large numbers of rare balearic shearwaters, manx shearwaters, sooty shearwaters, arctic skuas and great skuas this summer.
‘I travelled for 25 years and I have not seen the amount of shearwaters anywhere that we have got offshore now,’ he said.
Last month, the government’s marine resources department, together with a scientist from the University of Exeter, worked on a project to safely capture and electronically tag seven bluefin tuna as part of a project to study the species’ numbers.
Tags on five of the fish have been set to collect data for up to a year when they will detach automatically. The remaining two are due to collect data for two years.
Data from the tags are transmitted via satellite following detachment.