Organisers estimated as many as 200 vessels could participate in the day-long nationwide action, forming flotillas bearing flags and sounding horns as people also demonstrate on docksides.
"Fishermen and fishing communities are enraged that the government has capitulated to Britain having to obey all EU law after Brexit," said the pro-Brexit organising group Fishing for Leave, in a statement.
"Fishermen fear the EU will be able to enforce ill-founded rules to cull the British fleet and use international law to claim the resources the UK would no longer be able to catch."
Protests began in Newcastle, where a 15-boat flotilla assembled Sunday morning, before others mustered in Milford Haven, Wales, and Plymouth, southwest England, later in the day.
Further demonstrations were set for other sites, including Whitstable, Kent, where up to 40 vessels are expected and organisers plan to burn a disused boat in a shore-side bonfire during the evening.
"I think this is going to draw attention -- we want our voice heard," said Brendon Hall, 21, of Teignmouth, Devon, who followed his father into the industry four years ago and had sailed to Plymouth to protest.
"The main part of the leave campaign was leaving the CFP (Common Fisheries Policy) but we're staying in with no veto and no say," he added, referring to the 2016 referendum that saw Britons vote for Brexit.
A draft deal struck with the EU last month will effectively keep Britain bound by the CFP -- which ensures equal access to member states' waters and sets quotas on catch -- during a 20-month transition period following its formal departure from the bloc on March 29 next year.
Fishing for Leave spokesman Alan Hastings said the agreement was a "death sentence" for the industry, "as the EU will be free to enforce and impose detrimental rules on us to cull what's left of the UK fleet."
A petition posted on the British parliament's website calling on the Government to abandon adopting the CFP post-Brexit has garnered more than 61,000 petitions.
After 100,000 signatures, a petition is considered for debate in the House of Commons.
The government has insisted Britain will be leaving the CFP when it departs the EU, and will negotiate a new fisheries policy independently from December 2020.
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![33 passengers and one crew member died on the dive boat, Conception [Brian van der Brug/Los Angeles Times/AP]](data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'300'%20height%3D'172'%20data-ring-placeholder%3D'1'%3E%3C%2Fsvg%3E "33 passengers and one crew member died on the dive boat, Conception [Brian van der Brug/Los Angeles Times/AP]")
