The Niue Treaty Subsidiary Agreement (NTSA) is an agreement on cooperation between Forum Fishery Agency (FFA) members about monitoring, control and surveillance of fishing it includes provisions on exchange of fisheries data and information, as well as procedures for cooperation in monitoring, prosecuting and penalising operators of IUU fishing vessels.

The NTSAs objective is to enhance the active participation in cooperative surveillance and enforcement activities by providing a framework for Parties to share resources and exchange information, including fisheries data and intelligence, in order to:
Maximise the operational reach and effectiveness of fisheries monitoring, control and surveillance tools;
Prevent, deter and eliminate illegal, unreported and unregulated (IUU) fishing; and
Contribute to the broader regional law enforcement efforts;
with the purpose of supporting the continuous improvement of the management and development of the fishery resources in the region, ensuring their sustainability, and maximising the social and economic benefits.

Core to operationalising the NTSA is the Niue Treaty Information System (NTIS) which provides a means for achieving the objectives of the NTSA by facilitating fisheries surveillance and wider law enforcement activities. The NTIS expedites cooperation between Parties and provides flexibility for Parties.

Tonga is a party to the NTSA and is now implementing this Agreement