Research Log · Anti-Poaching Forensics · RL-2091-041

Acoustic Telemetry Exposes an Illegal Fleet's Bycatch Corridor

Acoustic-tag tracks of pelagic sharks, overlaid on AIS-gap vessel detections, resolve a recurring spatiotemporal overlap that identifies an unflagged fleet's longline bycatch corridor across a migratory bottleneck.

Anti-Poaching Forensics Restricted Method: acoustic telemetry × AIS-gap fusion

Abstract

A migratory bottleneck was returning unexplained tag losses — animals going silent mid-track in the same place, at the same season. We instrumented 54 pelagic sharks across three species with acoustic and satellite tags and built their movement model, then fused it with a year of vessel data — including AIS-gap detections, the dark periods when a vessel switches off its transponder. The shark corridor and the AIS-gap clusters overlapped in space and time at a level far beyond chance (overlap index 0.74; permutation p<0.001). Tag-loss mortality inside the overlap zone ran 6.3× the background rate, and the temporal signature — abrupt depth-then-surface excursions ending in silence — is the acoustic signature of a longline haul. The analysis converts a conservation telemetry study into evidence of an illegal fleet's bycatch corridor, now an open dossier with the dispatch desk.

Background & Question

Three of the tagged species are protected (AE-SPX-0051 · Scalloped Hammerhead, AE-SPX-0009 · Oceanic Whitetip Shark, AE-SPX-0053 · Pelagic Thresher Shark) and legally must be released alive if caught. Yet tags were vanishing in a pattern that looked nothing like natural mortality. The question was forensic, not ecological: is the tag-loss pattern explained by fishing, and if so, can it be tied to a specific fleet operating dark? A clean answer requires showing both that the losses cluster where vessels go dark, and that the loss signature is consistent with capture rather than predation or tag failure.

Methods

Tagging: 54 sharks (3 species) fitted with combined acoustic transmitters and pop-up satellite archival tags logging depth, temperature, and light; deployed at the bottleneck approaches.
Receiver mesh: AquaLink acoustic-receiver curtain across the bottleneck (AE-MET-036 · Sensor Mesh Coverage); detections time-synced fleet-wide.
Vessel data: one year of AIS tracks plus AIS-gap events (AE-MET-019 · AIS-Gap Detections) — intervals where a vessel's transponder goes dark in open water — cross-checked against night-light and SAR vessel detections.
Overlap analysis: utilization-distribution overlap (Bhattacharyya) between shark corridor and AIS-gap clusters; significance by spatiotemporal permutation (10,000 iterations).
Loss-signature classification: archival depth/light traces at tag-silence classified as capture (rapid ascent, surface-then-flat, sensor signature of deck) vs. predation vs. tag failure.
Chain of custody: dossier assembled under AE-SOP-0301 · Target Dossier Opening & Tiering; interdiction readiness referenced to AE-SOP-0320 · Driftnet Interdiction & Gear Recovery.

Findings

The shark corridor and the AIS-gap clusters overlapped at index 0.74 — far above the permutation null (95th percentile 0.18; p<0.001). Of 17 tag losses, 13 occurred inside the overlap zone, a mortality rate 6.3× the corridor background. Loss-signature classification assigned 11 of those 13 to capture (the characteristic rapid ascent and deck-flat depth trace), two to predation; outside the overlap zone, losses were predation or failure only. The temporal overlap concentrated in two seasonal windows matching the protected species' migration peaks — precisely when an operator would target the bottleneck.

Corridor Overlap0.74null 0.18 · p<0.001

Mortality in Zone6.3×vs. background

Losses = Capture11 / 13depth-trace classified

Zone	Tag losses	Capture signature	Predation	Tag failure
Inside overlap	13	11	2	0
Outside overlap	4	0	3	1

Implications

This is the League's enforcement doctrine made literal: evidence over force. A conservation telemetry program, run to peer-review standard, has produced a defensible map of where and when an unflagged fleet is illegally taking protected sharks while running dark. The corridor model and loss-signature evidence have been sealed into an open target dossier and handed to the dispatch desk for tiering; the seasonal windows give Operations a predictive interdiction calendar rather than a reactive one. Where the law is asleep, the proof is built first — and where proof cannot stop the haul, the corridor is now charted for those who can. Bycatch averted is tracked under AE-MET-038.

References & Linked Records

Imaging note. Visual record pending generation. Art-direction prompt on file: “A dark ocean map glowing with overlaid shark-track lines and red AIS-gap clusters converging on a narrow migratory bottleneck, a scalloped hammerhead silhouette over the chart, tactical intelligence-console aesthetic, deep blue and warning-red palette.”

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