Canned tuna brands are failing to tackle modern slavery in their Pacific supply chains, a new report says.
The Business & Human Rights Resource Centre's report is based on a survey of the world's largest retail tuna brands.
While a number of them have stated policies to counter modern slavery at sea, the investigation found Tuna companies are failing to support their policies with practical action.
The Pacific provides 60 percent of the world's tuna, in a $US22 billion industry with growing demand.
Yet the report reveals that 80 percent of brands can't say where their tuna comes from, and a majority have policies that don't even apply to fishers in their supply chains.
The Centre said leading brands who failed to respond include Tesco, Walmart and Costco.
It has called for urgent reforms to protect workers at sea.
Industrial tuna fishing is carried out mostly by modern foreign distant-water fishing fleets, operating in the Exclusive Economic Zones of Pacific Island countries under licence.
Major actors are foreign-owned fleets from China, Indonesia, Japan, Korea, the Philippines, Taiwan and Thailand.
Within Pacific EEZs, of the 1,500 registered fishing vessels present at any one time, approximately 1,200 will be foreign vessels extracting tuna for supply to the global tuna trade, according to the report.
The report, Out of Sight: Modern Slavery in Pacific Supply Chains of Canned Tuna, linked forced labour, slavery and human trafficking to falling productivity and returns in the fishing industry.
"Diminishing returns further exacerbate vulnerabilities in the seafood workforce, including lack of unionisation and reliance on migrant workers," the report said.
"Migrant workers are particularly vulnerable to abuse due to lack of official documentation, reduced bargaining power, language barriers and diminished safety nets."