How does transshipment at sea increase forced labor risk in tuna supply chains?

At-sea transshipment increases forced labor risk in tuna supply chains because it allows fishing vessels to stay at sea for months or even years without returning to port, removing them from the oversight systems that normally catch labor abuses. Workers on these vessels can be held against their will with no realistic means of escape or contact with authorities. This article breaks down how transshipment works, which regions carry the highest risk, and what buyers and brands can do about it.

What actually happens during at-sea transshipment?

At-sea transshipment is the process of transferring fish directly from a fishing vessel to a refrigerated cargo ship, called a reefer, while both vessels are out at sea. This allows the fishing vessel to keep operating without returning to port to offload its catch. The reefer then carries the fish to a processing facility or port, often in a different country from where the fish was caught.

From a purely logistical standpoint, transshipment makes sense. Fishing vessels can stay on productive fishing grounds longer, and operators reduce fuel and time costs. But this efficiency creates a serious blind spot. Once a vessel is at sea for extended periods, it operates largely outside the monitoring systems that ports, labor inspectors, and customs authorities depend on.

The crew on a fishing vessel engaged in transshipment may not set foot on land for months. They cannot leave the vessel voluntarily, cannot access medical care easily, and often have no reliable way to communicate with family or report problems. That isolation is exactly the condition that makes forced labor in the fishing industry possible.

Why does transshipment at sea make forced labor harder to detect?

Transshipment at sea makes forced labor harder to detect because it eliminates the port visit, which is the primary moment when inspectors, port state authorities, and labor monitors have physical access to a vessel and its crew. Without that touchpoint, there is no routine opportunity to interview workers, review conditions, or verify that crew members are there voluntarily.

Several factors compound this problem. Fishing vessels operating in international waters may fall under the jurisdiction of a flag state that has limited enforcement capacity or motivation to investigate. Crew members are often recruited through labor brokers across multiple countries, making it difficult to trace employment contracts or verify that workers were hired under legitimate terms.

Satellite tracking systems like AIS can show where a vessel is, but they cannot tell you whether the people on board are being paid, whether they can leave, or whether they have been subjected to violence or debt bondage. The data gap between vessel position and crew welfare is where forced labor in the fishing industry hides most effectively.

Which tuna fisheries and regions carry the highest transshipment risk?

The highest transshipment risk is concentrated in distant-water fisheries operating in the Western and Central Pacific Ocean, the Indian Ocean, and parts of the South Atlantic. These are large, remote FAO fishing zones where monitoring and surveillance infrastructure is thinner, flag state oversight is often weaker, and vessels can operate for extended periods without meaningful inspection.

Longline tuna fisheries carry particularly elevated risk. Longline vessels tend to be smaller, operate individually rather than in fleets, and spend more time at sea than purse seine vessels. They are also more likely to use transshipment to extend their time on the water. Some flag states with large distant-water longline fleets have faced repeated scrutiny from regional fisheries management organizations and labor rights investigators for inadequate crew welfare protections.

High-seas pockets, areas of international waters surrounded by exclusive economic zones, are also a concern. These areas sit outside the direct jurisdiction of any coastal state and are harder for regional fisheries management organizations to monitor effectively. Vessels operating in these zones and using transshipment can move fish through multiple jurisdictions before any documentation is created.

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How does transshipment enable IUU catch to enter the supply chain?

Transshipment enables IUU (illegal, unreported, and unregulated) catch to enter the supply chain by creating a point where fish from different sources can be mixed, relabeled, or misrepresented before documentation is created. When a reefer vessel receives fish from multiple fishing vessels at sea, the chain of custody becomes difficult to verify, and IUU catch may be blended with legally caught fish.

This commingling problem is compounded by the fact that transshipment often occurs in areas where observer coverage is low or absent. Without an independent observer on board, there is no third-party record of what was transferred, in what quantities, or from which vessel. Paper-based logbooks and self-reported catch data can be manipulated, and by the time the fish reaches a processing facility, the original catch records may be impossible to verify.

Forced labor and IUU fishing are also closely connected practices. Vessels that operate outside legal frameworks to avoid fishing regulations are often the same vessels most likely to cut corners on crew welfare. Transshipment serves both problems by keeping vessels away from the oversight systems designed to catch either violation.

What are the legal and reputational consequences for brands?

Brands that source tuna from supply chains involving unmonitored transshipment could face significant legal and reputational consequences if forced labor or IUU catch is later identified in their supply chain. In jurisdictions such as the EU and the USA, import regulations increasingly require documented proof of legal and ethical sourcing, and failure to provide that proof could result in shipment seizures, import bans, or fines.

In the USA, the Tariff Act of 1930 prohibits the import of goods made with forced labor, and US Customs and Border Protection has the authority to issue Withhold Release Orders against specific vessels or companies. The EU’s Corporate Sustainability Due Diligence Directive, which is being phased in from 2026, places a legal obligation on companies to identify and address human rights risks in their supply chains, including at the first mile of fishing.

Beyond regulatory penalties, the reputational damage from a forced labor association can be severe. Consumer-facing tuna brands that have built their identity around sustainability and ethical sourcing are particularly exposed. A single investigative report linking a brand’s supply chain to a vessel with documented labor abuses could undermine years of brand investment. Some major retailers have already faced costly lawsuits and public campaigns tied to sourcing practices they were unable to document or defend.

How can traceability technology reduce transshipment-related forced labor risk?

Traceability technology reduces transshipment-related forced labor risk by capturing vessel activity data in real time, creating a verifiable record of where a vessel operated, who it transshipped with, and what documentation exists for that catch. When this data is collected from the first mile and linked to a unique batch identifier, it becomes much harder for problematic catch to move through the supply chain undetected.

Satellite-based vessel monitoring systems and AIS tracking can flag unusual behavioral patterns associated with forced labor risk, including vessels that stay at sea for unusually long periods, vessels that disable their tracking signals, or vessels that conduct transshipment in areas with low observer coverage. When these signals are combined with social compliance records, crew welfare certifications, and observer or electronic monitoring reports, buyers get a much clearer picture of what is actually happening at sea.

The most effective systems integrate these data streams into a single verifiable record per batch. Rather than relying on paper documentation that can be altered, digital traceability platforms assign a unique identifier to each batch at the point of discharge, linking it to the vessel records, transshipment logs, and compliance documentation that were generated before processing began. This approach makes it significantly harder for IUU catch or catch associated with forced labor to be laundered into a legitimate supply chain.

Should tuna buyers require transshipment monitoring as a sourcing condition?

Yes, tuna buyers should consider requiring transshipment monitoring as a sourcing condition, particularly for supply chains that involve distant-water fisheries or longline vessels. Without documented evidence of what happened during transshipment, buyers may have no reliable way to verify the origin or legality of the fish they are purchasing, or to confirm that crew welfare standards were met.

Practically, this means asking suppliers to provide transshipment authorization records, observer coverage reports, and satellite tracking data for the vessels involved in their supply chain. Buyers may also want to verify that transshipment events were conducted in authorized ports or under conditions approved by the relevant regional fisheries management organization, and that the reefer vessels used are registered and not flagged on IUU blacklists.

As regulatory requirements tighten in 2026 and beyond, the burden of proof for ethical sourcing is shifting toward buyers and brands. Waiting until a regulatory deadline to build traceability into sourcing contracts is likely to be more costly and disruptive than establishing those requirements now. Suppliers who already have robust transshipment monitoring in place are generally better positioned to meet emerging due diligence requirements, which makes monitoring capability a useful proxy for overall supply chain quality.

SmarTuna’s digital traceability platform captures first-mile vessel data via satellite VMS and AIS, assigns a unique Raw Material ID at discharge, and integrates social compliance records directly into each batch’s traceability record, giving buyers verifiable evidence of what happened at sea before the fish ever reaches a processor.

Frequently Asked Questions

How do I know if my tuna supplier is using at-sea transshipment?

Start by requesting transshipment declarations and catch documentation directly from your supplier, and ask specifically whether any vessels in their supply chain conducted at-sea transfers rather than port offloading. You can cross-reference vessel identifiers against regional fisheries management organization (RFMO) transshipment authorization records and check reefer vessels against IUU blacklists maintained by bodies like the WCPFC or IOTC. If your supplier cannot provide transshipment logs or observer coverage reports, that absence of documentation is itself a meaningful risk signal.

What is the difference between authorized and unauthorized transshipment, and why does it matter?

Authorized transshipment is conducted in compliance with rules set by the relevant RFMO, which may require pre-notification, observer coverage, and reporting of the quantities and species transferred. Unauthorized transshipment happens outside these rules, often in high-seas areas with no observer present, and creates no verifiable chain of custody for the fish. For buyers, the distinction matters because unauthorized transshipment is a strong indicator of IUU activity and removes any credible basis for claiming the catch was legally and ethically sourced.

What are the most common mistakes buyers make when trying to address transshipment risk?

The most common mistake is relying solely on certifications or supplier self-declarations without verifying the underlying vessel-level data. Certifications can cover a processing facility or a company without capturing what actually happened at sea during transshipment. A second common mistake is treating AIS tracking as sufficient evidence of compliance — vessel position data confirms where a ship was, but says nothing about crew welfare, catch legality, or whether a transshipment event was authorized. Effective due diligence requires layering vessel behavior data, observer reports, and social compliance records together.

Are there specific red flags in vessel behavior that suggest forced labor risk during transshipment?

Yes. Key behavioral red flags include vessels that remain at sea for unusually long periods (often exceeding six months without a port call), vessels that disable or spoof their AIS transponders around the time of a transshipment event, and vessels that repeatedly transship in areas known for low observer coverage such as high-seas pockets. Other warning signs include vessels flagged to states with weak labor enforcement records, vessels that appear on RFMO IUU vessel lists, and supply chains where the reefer vessel used for transshipment has no verifiable registration or compliance history.

How does the EU Corporate Sustainability Due Diligence Directive (CS3D) specifically apply to tuna supply chains involving transshipment?

CS3D requires in-scope companies to conduct ongoing human rights and environmental due diligence across their full value chain, including at the first mile of fishing — which means the vessel level, not just the processor or trader. For tuna supply chains involving transshipment, this translates to a practical obligation to identify which vessels contributed catch, whether transshipment was conducted under monitored conditions, and whether there are credible indicators of forced labor in those vessel’s operating history. Companies that cannot document these facts for their supply chains will struggle to demonstrate compliance when the directive’s requirements are phased in from 2026.

Can small or mid-sized tuna brands realistically implement transshipment monitoring, or is it only feasible for large buyers?

Transshipment monitoring is increasingly accessible to buyers of all sizes, largely because digital traceability platforms now aggregate vessel monitoring data, RFMO records, and compliance documentation in a single interface rather than requiring buyers to build their own data infrastructure. Smaller brands can start by prioritizing their highest-risk supply chains — typically those involving distant-water longline vessels — and requiring suppliers to provide structured transshipment documentation as a sourcing condition. Working with suppliers who already have traceability systems in place is often the most practical entry point for smaller buyers operating with limited compliance resources.

What should I do if I discover that a vessel in my supply chain has a history of transshipment violations or labor abuse allegations?

First, suspend purchasing from that vessel’s catch pending a formal review, and document the discovery and your response steps — this record will matter for regulatory and reputational purposes. Next, engage your supplier directly to understand whether the vessel is still active in their supply chain and what corrective measures, if any, have been taken. Depending on the severity of the findings, you may need to conduct a broader audit of your supplier’s vessel fleet, revise your sourcing contracts to include explicit transshipment monitoring requirements, and in some cases report the findings to the relevant RFMO or national authority if the violations are ongoing.

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