The study named Yo! Sushi and Pret A Manger as the most sustainable restaurants with ‘highly responsible’ approaches to buying seafood.
But Wagamama, Ask, Harvester, Bella Italia, Café Rouge, Chiquito, and Frankie & Benny’s all failed to reach the minimum sustainability standards.
Restaurants were found to serve sea bass, whitebait, cod and king prawns from fisheries rated ‘avoid’ by the Marine Conservation Society (MCS) or for which the source is unclear.
The research, carried out by sustainable restaurant guide Fish2Fork and the MCS, surveyed 12 restaurant groups with more than 50 sites serving at least four species of seafood.
Two-thirds of operators served at least one species of seafood that could have come from an overfished area, while half were unwilling to provide full answers when questioned about the sources of their seafood.
“We believe the [restaurant] sector as a whole should be putting much more effort into sourcing practices and the information given to customers,” said Tim Glover, co-founder and managing director of Fish2fork.
“Diners want to eat with a clear conscience, to know that their menu choices are not further damaging our hard-pressed seas.
“Our assessments show that too many restaurants are either serving seafood we believe should be kept off the menu, or are giving so little information on menus and websites that customers can have little clue to the origins.”
But Casual Dining Group, which owns Bella Italia and Cafe Rouge, told BigHospitality that sustainability was an 'important issue' it took seriously.
"All our fish at Bella Italia and Café Rouge comes from sustainable sources and none are species designated as endangered," a spokesperson said.
"We take great care in choosing suppliers, who share our values and are as committed to this issue as we are. We will be engaging directly with the MCS to ensure they are aware of our current position, which isn’t reflected in these results.”
Fish2fork rated restaurants on a scale of 5 red fish (least sustainable) to 5 blue fish, (most sustainable).
The full ratings are as follows:
Pret a Manger - 4.5 blue
Yo! Sushi - 4 blue
Hungry Horse - 2.5 blue
Table Table - 2.5 blue
Zizzi - 1 Blue
Cafe Rouge - 0.5 red
Harvester - 0.5 red
Wagamama - 0.5 Red
Ask - 1 red
Chiquito - 1 red
Frankie & Benny's - 1 red
Bella Italia - 1.5 red