Drift simulations trace most of Aldabra's 500 tons of plastic to boats in Seychelles waters

The study begins with where the boats were. Satellite tracking positions for fishing and shipping vessels from 2018 to 2022 gave the authors a five-year map of activity across the region ^[5]. They then released billions of virtual fragments into simulated currents, seeded by that activity, and recorded where each one beached ^[6]. The output is a risk map: for any given vessel location, how likely debris leaving it is to reach a Seychelles island, computed separately for fishing and for shipping ^[7].

Scored that way, most of the risk sits close to home. The authors report that most of the pollution probably comes from vessels in or near the Seychelles' own waters, which cuts against previous work assuming island plastic mainly drifts in from distant shores ^[8]. For gear specifically, most of what washes up came from fishing inside the country's own exclusive economic zone, the 200 nautical miles over which it controls marine resources ^[9].

A risk map ranks stretches of water. It says fragments released in one place tend to end up in another, and it gives that in probabilities ^[7][8]. The one ownership count in the record comes from elsewhere: a report presented to the Indian Ocean Tuna Commission found that 76% of 214 drifting fish-aggregating devices in the Seychelles' exclusive economic zone were from Spanish-owned vessels ^[11]. Those are 214 devices that were located. That is not the same as a count of all the gear lost.

The cleanup estimate covers one atoll. US$4.68 million and 18,000 hours of labour against more than 500 tons works out to roughly $9,360 and 36 hours per ton, and both figures are ceilings, because the tonnage is a floor ^[19][20]. Most of the debris is still on the beaches ^[3].

The source gives sterling equivalents, which makes one comparison possible. Clearing Aldabra once was costed at £3.46 million; the renewed 2026-30 agreement pays £4.89 million a year for access by 38 EU vessels ^[24][25][12]. One atoll's removal bill is therefore about 71% of a single year's fee ^[26]. Reports cited by the authors say the Seychelles government pushed for a 30% rise in that payment and settled on 7% ^[13]. If EUR5,750,000 is the post-increase rate, the prior rate was about EUR5.37 million, a 30% rise would have reached about EUR6.99 million, and the gap between the two outcomes is roughly EUR1.24 million a year ^[21].

Shipping debris concentrates far more tightly. More than 90% of the plastic reaching Seychelles coasts from shipping comes from just five lanes crossing the western Indian Ocean, on the study's account ^[14]. The ports at either end of those lanes line up with the countries named on labels of plastic bottles washed ashore on Aldabra ^[15]. A label records where a bottle was filled, so the match narrows the source region while leaving the vessel unidentified.

For the fishing stream, the parties are already under contract. Seychelles waters are heavily fished by European purse seiners and longliners under a longstanding agreement, and the authors write that it is likely some of the gear and plastic waste is coming from EU vessels ^[10]. The same authors argue that the Seychelles-EU deal is small compared with the indirect damage imposed on the nation ^[23].