61% of dark events logged in the last 45 days originated in five Gulf anchorage clusters. Those clusters account for 28% of total tracked vessel-hours in the same window.
The Setup
Dark events — AIS transmission gaps exceeding the minimum threshold — are distributed unevenly across port regions. The aggregate count now sits above 124,000 entries, but the distribution tells a more specific story than the total.
Five clusters dominate: Houston Ship Channel outer anchorage, Corpus Christi outer roads, Port Sulfur anchorage, Mobile Bay outer anchorage, and Galveston Island anchorage. Combined, they produced 9,841 dark events between May 12 and June 26, 2026. That is 61% of the period's total, from clusters that represent 28% of the total vessel-hours in the dataset.
Pacific port clusters — Los Angeles–Long Beach, Seattle–Tacoma, Oakland — produced 14% of dark events despite representing 33% of vessel-hours. Atlantic clusters (Baltimore, Norfolk, Savannah, Charleston) split the remainder.
The Chain
The Gulf ratio is not explained by traffic volume alone. Vessel-hours in the Gulf are lower than the Pacific. The implication is that Gulf anchorage vessels go dark at a higher per-vessel-hour rate — 3.2× higher than Pacific counterparts when normalized by vessel-hours.
Nav status at gap-start explains part of it: 58% of Gulf dark events began while the vessel was reporting "at anchor." Pacific dark events start at anchor 43% of the time. The anchor-status concentration suggests crew rotation logistics — Gulf vessels cycling crew in outer anchorage, disabling AIS during the transition period — rather than deliberate evasion.
Duration compounds the geographic skew. Gulf dark events run a median of 8.4 hours. Pacific: 3.1 hours. Atlantic: 4.7 hours. The 8.4-hour Gulf median is consistent with a crew rotation window, not a brief transponder fault.
The Implication
If the Gulf concentration reflects crew rotation masking AIS gaps rather than deliberate evasion, the compliance burden is different. Crew-rotation dark events still produce a gap in the chain of custody, but the risk model for sanctioned cargo differs from an identity-manipulation event.
The problem is that the dataset contains no flag that distinguishes intent. A 9-hour gap starting at anchor in Corpus Christi outer roads looks identical to a 9-hour gap that precedes a ship-to-ship transfer. Both land in the same unsubtyped queue.
With 97% of dark events still lacking a subtype classification, the geographic asymmetry is analytical signal — it suggests where classifier work would have the highest marginal return. Gulf anchorage rings are the most concentrated source of raw, unclassified gaps in the dataset.
What to Watch
Gulf dark event volume relative to vessel-hours. If the ratio narrows — more vessel-hours without a proportional increase in dark events — that suggests classifier suppression activity is declining or crew-rotation AIS discipline is improving. If it widens, the gap in the unsubtyped queue is growing faster in the highest-concentration region.
The 2,066 critical-tier events flagged in the current subtype-freeze period should be cross-referenced against Gulf origin. If critical events are disproportionately Gulf-originating, the triage priority shifts.
Limitations
Port region assignment uses the last known AIS position before gap-start, which may not reflect the vessel's actual anchorage location if there was positional drift before the gap. Vessel-hours are derived from AIS report frequency and are under-counted for vessels with low reporting rates — Gulf vessels, which tend to operate in areas with higher reporting discipline gaps, may be slightly under-represented in the denominator, which would narrow the 3.2× ratio somewhat.
Overwatch | Analysis | Axiom Intelligence — June 26, 2026