Lobster fishermen are on alert after animal rights activists threatened to wage a "war" against them.
Some 30 live lobsters were set loose and paint thrown over pots
An anonymous email from the Lobster Liberation Front claims responsibility for a recent campaign of vandalism against a Dorset lobster fisherman.
Jonathan Lander, 41, has twice had his boat wrecked and lobsters set free.
The warning, posted on an animal rights website, says: "The war against the lobster industry has begun. We will attack anywhere, at any time."
Dorset Police are investigating the claim, while Welsh police are looking into a spate of similar attacks on lobster pots in Cardigan and nearby Crymych.
It comes as the government launches a crackdown on animal rights campaigners who use direct action, with greater police powers to combat protests.
Mr Lander, a single parent whose family has fished the waters off Purbeck in Dorset for five generations, has been singled out by a group of activists.
In June, his boat was broken into and seriously damaged at Chapman's Pool and 30 lobsters were set loose from their pots.
The same night, vandals splashed red paint over the house in the nearby village of Worth Matravers where he lives with his sons, aged nine and 11.
Just weeks earlier, the same boat, boathouse and some 50 lobster pots were vandalised.
The Lobster Liberation Front has said it carried out both attacks and warned of more serious damage if Mr Lander carries on fishing.
Its email on the Southern Animal Rights Coalition website says: "On 23 May buccaneers from the Lobster Liberation Front attacked a boathouse belonging to Jonathan Lander.
Pots are filled with bait and lowered onto the sea bed
Lobsters crawl in but cannot get out again
Those measuring less than 87mm must be put back
Prices reach £18 a kilo in the run up to Christmas
In summer they can fall to £5
The shellfish industry is worth £20m in Hampshire and Dorset
Some 2,500 fishermen make their living there
There are 450 Defra-licensed boats in the region
"Jonathan foolishly ignored the first warning, so a second, and final warning has been given.
"If this is ignored then the real damage must begin.
"No animal should be sacrificed for human greed, let alone boiled alive."
It adds: "This attack against Jonathan Lander was merely a skirmish.
"The war against the lobster industry has begun. We will attack anywhere, at any time, and pots will be smashed, boats sunk, and sea life liberated.
"We are ready, are you?"
Mr Lander told BBC News Online: "I'm shocked that they can do that to anyone making a living - we're only catching food.
"I've got nothing else I can do apart from go on the dole. We've all got bills and loans - what do you do?
"I'm a single parent and probably the easiest target in the whole wide world to hit as I'm not at the boat that often because I'm always looking after the kids.
"I have got nothing to say to the Lobster Liberation Front."
Pc Jonathan Maunder, from Swanage police, said: "We are aware of the claims of the Lobster Liberation Front and further investigations are currently taking place.
"If anyone - particularly fishermen - sees anything suspicious or anyone acting suspiciously, I ask them to contact us as soon as possible in confidence."
Some 80% of catch landed off Hampshire, Dorset and the Isle of Wight is shellfish.
As well as lobsters, there is a mussel and clam fishery in Poole Harbour and the UK's largest native wild oyster fishery in the Solent.
Dorset fishermen also harvest thousands of brown and spider crabs, the latter sold as a delicacy on the Continent.