Nine of the world’s biggest fishing companies have signed up to protect the world’s oceans, pledging to help stamp out illegal activities, including the use of slave labour, and prevent overfishing.

The initiative will be announced on Friday, as part of the UN Ocean Conference this week in New York, the first conference of its kind at which member states are discussing how to meet the sustainable development goal on ocean health.

Goal 14 of the roster requires countries to “conserve and sustainably use the oceans, seas and marine resources”. However, little has yet been done to set out concrete commitments on meeting this target. The UN is hoping countries, companies and organisations will set out voluntary plans this week to work on issues such as pollution, overfishing, the destruction of coastal habitats, and acidification.

The Seafood Business for Ocean Stewardship (SeaBOS) initiative, supported by the Stockholm Resilience Centre, marks the first time that companies from Asia, Europe and the US have come together aiming to end unsustainable practices. Although the fishing industry is highly fragmented at the local level, with millions of small boats and subsistence fishermen, about 11 to 16% of the global catch goes to just 13 companies, who are thought to control about 40% of the most valuable and biggest species.

Henrik Osterblöm, deputy science director at the Stockholm Resilience Centre, which brought the initiative together, said: “Sustainable marine ecosystems will be essential to feed a growing population, but the oceans are at risk. Seafood makes up 20% of the global intake of animal protein.”

The nine fishing companies signed up to SeaBOS have a combined annual revenue of about $30bn (£23bn), making up more than one-third of that of the top 100 seafood companies. They pledged to eliminate from their supply chains any fish that could have come from piracy or other illegal sources. As much as half the world’s fish catch is thought to involve “black” or illegal fishing, where vessels trespass into other national waters, use illegal gear, catch more than their quota or target endangered species or fish for which they have no quota. These fish are often “laundered” to find their way into legal fish markets.

Slavery has also been a serious problem in fisheries, as spotlighted by the Guardian’s investigation into slavery in the Thai prawn fishing industry, which found worker exploitation and the deprivation of people’s rights was widespread in parts of Asia’s fishing grounds. The new declaration binds SeaBOS members to develop and enforce a code of conduct for their operations and those of their suppliers.

The companies said: “We will also work towards full traceability and transparency throughout our supply chains. We also pledge to work actively together with governments to improve existing regulations for fisheries, for aquaculture, and for the ocean.”

Fish farms have also been a cause of concern to ocean experts, with the heavy use of medicines and disinfectants causing marine pollution, and the use of millions of tonnes of fishmeal from ground-up wild fish to provide food for the farmed fish – as much as five tonnes of wild fish for every tonne of farmed.

These factors undermine the claims of the fish farming industry to provide a sustainable source of fish, protecting wild populations. The SeaBOS signatories pledged: “We [will] make efficient use of aquaculture and use fish feed resources from sustainably harvested stocks. We will actively use and apply existing certification standards and prevent harmful discharges and habitat destruction. We call on the whole industry to do the same.”

SeaBOS comprises: the two biggest seafood companies by revenue, Maruha Nichiro and Nippon Suisan Kaisha; two of the biggest tuna specialists, Thai Union Group and Dongwon Industries; the two biggest companies selling feed to fish farms, Nutreco (parent company of Skretting) and Cargill Aqua Nutrition; and the two biggest farmed salmon companies, Marine Harvest and the Cermaq subsidiary of Mitsubishi; and the Japanese tuna purse seine company Kyokuyo. Most of these are not household names to consumers, but their products are found all over the world. The group aims to sign up more companies, and to lobby governments to enforce better regulations, and to review its progress in a year.