Travel giant Thomas Cook has said it will stop selling tickets to attractions in Florida and Tenerife which keep killer whales in captivity.

The company said the decision affecting SeaWorld and Loro Parque was made due to animal welfare concerns. It will come into force next summer.

The ban means millions of Thomas Cook’s customers will have to go elsewhere to purchase tickets for the amusement parks.

With thousands of day-tickets sold each year, the firm could lose hundreds of thousands of pounds in sales.

SeaWorld and Loro Parque both feature in the Netflix documentary ‘Blackfish’, which chronicled the lives of captive killer whales, known as orcas, held there.

The backlash generated by the 2013 film saw SeaWorld’s visitor numbers plummet and the attraction confirm it would end its orca breeding programme.

But SeaWorld said ‘Blackfish’ was “manipulative”. The firm has said that staff at its parks are “leading research that will help scientists understand how to protect orcas in the wild.”

“The opportunity to see orcas up-close has inspired millions of people, especially children, to care more about marine animals, the oceans and the environment,” it added.

Thomas Cook’s decision could now prompt rivals to follow suit.

The firm’s Peter Fankhauser said on Sunday: “This was not a decision we took lightly. We always said that we would continue to review our policy, conscious that the more we got into this area, the more we would learn, and conscious also of changing customer sentiment.

“We have actively engaged with a range of animal welfare specialists in the last 18 months, and taken account of the scientific evidence they have provided. We have also taken feedback from our customers, more than 90% of whom told us that it was important that their holiday company takes animal welfare seriously.

“That has led us to the decision we have taken today.”

Fankhauser said both SeaWorld and Loro Parque “passed our audit process and made improvements to the way they treat animals” and that the firm will work with both “to prepare for our exit”.

Thomas Cook also announced that it will end relationships with 29 other attractions over animal welfare issues.

A representative for SeaWorld said: “Millions of UK guests have visited our parks for fun, education and to help contribute to the protection of marine animals and their habitats.  

“They have seen first-hand the incredible care we provide all of our animals and learned about how we are protecting and saving species in the wild. Although we have ended breeding for orcas, the current animals in our care will be with us and our visitors for many years to come.

“We will continue to welcome the public into our parks for the unmatched experiences we create every day. ”

Loro Parque, which was once recognised as the largest tourist attraction in Spain, has been contacted for comment.

This article was updated with a comment from SeaWorld’s British representative.