IR-SPECIES-015 · DECLASSIFIED FIELD DOSSIER · B GRADE · DEEP-SEA SPECIALIST · SALTWATER · UPDATED 2026-08-27
Angler’s one-line briefing: This is not a “fish deep” species. It is a shelf-and-slope shark whose usable zone is set by contour, darkness, oxygen, local law and a presentation you can still control.
01. Ultimate File — Identity, Scale & Official Record
The bluntnose sixgill shark, Hexanchus griseus, is the largest living sixgill shark: a heavy-bodied animal of the outer shelf and continental slope, not a reef shark with a deep-water nickname. It is a B-grade “deep-sea specialist” here because the encounter is rare, the animal is large and slow-lived, and a poor release plan is reason enough not to fish.
Field — Verified archive value
Scientific name — Hexanchus griseus (Bonnaterre, 1788)
Core range — Patchy, near-circumglobal shelf, slope, seamount and ridge waters [1]
Biological ceiling — 600 cm TL; 590 kg maximum published mass [1]
Reproduction — Reported birth size 60–75 cm; 47–108 pups [1]
Global conservation display — Near Threatened (assessment dated 2019-11-21) [1]
Those biological figures are deliberately separate from sport records. Two historical record sources identify a 588.76 kg / 1,298 lb Ascension Island sixgill, landed by Clemens Rump in 2002 [8]. The live IGFA card must be rechecked before any public page calls that the current official All-Tackle record. A historical record is not a reason to design a casual trophy trip.
Date of capture: November 21, 2002.Angler: Clemens Rump.
Location: Ascension Island, a British Overseas Territory in the central Atlantic Ocean.
02. Field Identification — What Matters at First Sight
Do not begin with size. Begin with three checks: a broad, rounded head, six long gill slits, and one small dorsal fin far back toward the tail. The mouth is low and strongly arched; the body is thick, grey-brown, and the tail is asymmetrical rather than a tuna-like crescent. [1][7]
The nearest dangerous label error is “bigeye sixgill.” A six-gilled shark is not automatically H. griseus. The bluntnose sixgill is the heavy, broad-headed form with relatively small eyes; bigeye sixgills are much smaller and have conspicuously larger eyes. Count gills, photograph the head and dorsal-fin position, and do not build an identification on a single murky silhouette.
03. Habitat Topology — Where the Fish Actually Lives
The right map is vertical, not merely geographic. Sixgills use outer shelf breaks, continental slopes, seamounts and ridges. Reported occurrences span shallow records to 2,500 m, but adults generally use deeper water while juveniles appear more often inshore or at colder poleward sites. [1]
Hawai‘i tag work showed a clear local pattern: tagged sharks were often below 500 m during the day and rose to about 200–350 m at night, crossing strong temperature and oxygen gradients. [3] Puget Sound sharks were also shallower and more active at night, while a Cantabrian study did not produce the same simple day/night rule. [4] The instruction is therefore: use depth as a hypothesis tied to your coast, not as a universal number.
For an angler, three zones matter:
- Night slope edge / thermocline: If local evidence supports a rise, use an open shelf-edge lane where bait can be held and its line angle read. If current makes the line bow beyond recognition, reset; heavier lead is not a cure for an uncontrolled rig.
- Crepuscular transition: A shark changing depth is moving, not necessarily holding on a mark. Stay on the usable contour and do not chase an imagined fixed number.
- Day slope/bottom zone: On a deep mark, keep the bait just off bottom. A rig dragged on rock, cable or wreck steel loses bite signal and creates the failure that ends the fight before it begins.
04. Odd Logic, Read Water & Bite Mechanics
This shark’s unusual logic is its ability to work a very different water column over one daily cycle. The proven visual cue is not birds or surface bait: it is a clean working relationship between contour, depth, current and darkness. The line must remain controllable enough to tell a bite from bottom contact.
Stage 1 — preparatory contact
At the bait station, sixgills did not always simply rush in and swallow. Researchers documented preparatory bites and prey manipulation before a capture bite. [6] Expect a slow load, a direction change, a brief drop, or an intermittent draw.
Do not: snap the rod vertically at the first touch. That can remove bait during handling and leave slack around an already complex deep rig.
Do: hold the rod low in the line path, wind only enough to recover slack, and wait for load that continues away from the bait position.
Stage 2 — continuous load
When the load persists, let the hook system do the work it was designed for. A non-offset circle hook needs steady forward pressure to rotate toward the mouth corner; a legal J-style bait hook needs a controlled side sweep only after the bait has been taken. Keep the line exit low and lateral, then steer away from rock, hull, cable or anchor line. [6][9]
05. Tactical Engineering — Routes, Hardware & Field Cases
Two real routes, and one route we refuse to invent
Route A — deep drift or slope bait. Irish deep-wreck practice uses a large whole fish bait and a wire trace; that is useful local evidence for tooth and abrasion risk, not a global bait law. Set the presentation on the open side of a contour, then hold it clear of substrate. [9]
Route B — observation-station logic. Puget Sound bait-station work gives the more transferable lesson: a bait must be presented where its handling phase can be detected. A bait that is simply dragged unseen along the bottom makes both ethical release and tactical reading worse. [6]
Route C — no universal jig recipe. This dossier found no high-grade species-specific evidence for a global sixgill jig weight, colour or cadence. We do not invent a technical “deep jig” routine merely to make the page sound complete.
Rig architecture: build for teeth, bottom and recovery
- Main line: an 80–130 lb tested main line is a conservative starting envelope, selected around legal tackle, reel capacity and depth—not an automatic species requirement.
- Connection: use a compact, tested wind-on or leader connection. Any guide strike or shock event triggers reinspection.
- Abrasion leader: roughly 2–4 m of heavy leader creates distance from rock, skin and deck-edge abrasion. Too short lets braid meet the problem; too much stiffness can make handling worse.
- Wire trace: where legal, use a short coated multi-strand or other certified bite-resistant trace. A kink is not cosmetic; it is a replacement trigger.
- Terminal / hook / weight: use rated hardware, a lawful heavy bait hook or non-offset circle where required, and only enough weight to hold the intended lane. If the rig starts towing bottom, retrieve and reset.
- Drag: begin near 20–25% of tested breaking strength, then check it at the rod. Do not use extra drag to compensate for a bad line angle or a lack of steering room.
Combat FMEA — failures before they become break-offs
- Bottom/wreck abrasion: Root cause is a bowed or slack line lying on hard slope structure. Early warning is loss of vertical reference or irregular pulsing. Prevention is simple: keep bait clear, retrieve after contact, and inspect before resetting.
- Bite-off or trace fatigue: Root cause is tooth contact with soft leader or a kinked wire trace. Inspect after every contact; a damaged trace is replaced, never straightened and reused.
- Early pull-out: Root cause is an aggressive high set during the manipulation phase. The prevention is a low rod, slack recovery, then pressure only after continuous load.
- Close-boat terminal shock: Root cause is high drag and short line as a large shark turns beside structure. Keep pressure lateral, reduce force before a hard edge, and have a water-level release plan.
What the cases actually teach
- Hawai‘i tag work placed five large animals on the day-deep/night-shallower pattern that informs the water-column map; it is a local telemetry case, not an offshore charter guarantee. [3]
- Puget Sound bait cameras establish the value of patience at first contact: preparation and capture can be separate acts. [6]
- The Ascension historical record lead establishes possible scale. Its discipline lesson is the opposite of “pull harder”: verify the record and do not confuse historic harvest practice with today’s release standard. [8]
06. Foodways, Folklore & Human Connection
06.1 Food and culinary history
This shark appears in commercial-fisheries references, but a globally responsible “table fish” verdict would be false. The value of meat or liver products, contaminants and legal retention all vary by location. This dossier therefore gives no universal keep recommendation and no raw-consumption advice. [1]
06.2 Folklore, place memory & angling mythology
It has accumulated names—cow shark, mud shark, gray shark, kagurazame and many local variants. [7] But this research pass did not find a source strong enough to assign a single indigenous myth, taboo, or ritual to H. griseus across its enormous range. “Prehistoric sea monster” is modern media shorthand, not an inherited cultural fact. The honest story is that an animal this large can still remain mostly invisible from the surface.
06.3 Popular culture and symbolic status
Its modern symbol is scientific access. Bait stations, deep cameras, tagging and submersibles have turned the sixgill into an emblem of deep-water ignorance becoming measurable: depth, oxygen, temperature and behavior can be recorded only when the observer follows the fish into its world. [3][6]
06.4 Minimal rules & release ethic
Check jurisdictional shark rules on the day of the trip. Where release is allowed, do not plan a dock lift, gaff or prolonged deck photo. Keep the shark in water where feasible, avoid vertical suspension, use appropriate dehooking tools, and do not fish an extreme depth or structure if a safe release cannot realistically be made. Gear and handling affect outcome; fishing deliberately without a workable release plan is not technical angling. [9]
Appendix A — Taxonomy & naming
Accepted name: Hexanchus griseus (Bonnaterre, 1788), family Hexanchidae, order Hexanchiformes. H. griseus australis is a synonym in WoRMS. The all-purpose label “sixgill shark” must not be used as an identification conclusion. [2]
Appendix B — Fact-check ledger & visual assets
[1] FishBase: identity, size, depth, reproduction and global IUCN display. [2] WoRMS: accepted taxonomy. [3] Coffey et al. / PLOS ONE: Hawai‘i telemetry. [4] Andrews et al.: regional diel movement evidence. [5] Ebert: diet study. [6] Bait-station feeding study. [7] Florida Museum: field profile. [8] Historical IGFA record corroboration; live card must be checked before public-record wording. [9] Regional deep-wreck practice and legal context, not a global method standard.
All artwork in this internal draft is original explanatory illustration. Sources and morphology/visual audit are recorded in 02_sources.md and 02_Images/visual_ledger.md.