Science1 publisher3 min readPublished
Students map about 300 mysterious holes ringing a dive wreck off Bundaberg, possibly dug by fish
The depressions are 8 meters wide and 2 meters deep, and they cover more seafloor than the wreck itself. CSIRO's Ben Arthur said the same pock marks once led RV Investigator onto a wreck it had almost given up finding.
The Scientist · Science desk
What happened
- Twenty Australian university students left Brisbane for Fiji in September 2026 aboard the CSIRO research vessel Investigator on a CAPSTAN sea training voyage that included shipwreck surveys off Queensland.
- Mapping the dive wreck Althea II off Bundaberg, honors student Lara Picton described about 300 holes, each typically 8 meters wide and 2 meters deep, reaching roughly 100 meters out on an otherwise flat seafloor.
- The team suggested large predatory fish such as the goldspotted rockcod are the chief architects, using the holes for shelter and to ambush other fish drawn to the wreck.
- In 2017 a biologist's spotting of similar pock marks at the edge of a search area prompted a wide turn that carried RV Investigator directly over the wreck of SS Macumba.
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Why it matters
- capability The workings cover ground about 200 meters across, so a multibeam line plan spaced widely enough to step over a single hull can still cross the fish diggings that surround it.
- constraint Nobody has counted the pock-mark fields that sit over bare sediment, so a survey can use the texture to extend a search box and cannot log it as a contact.
- decision Staffing an operations room becomes part of search design: the Macumba turn happened because someone aboard read sediment texture on the bathymetry as habitat.
- precedent If the hole-free band next to the hull really is predator avoidance, then the pattern of the field, and not only its presence, becomes readable evidence about what lives on a wreck before anyone dives it.
A disc 100 meters in radius covers about 31,400 square meters. Divide it among 300 depressions and each has roughly 105 square meters to itself, a square a little over 10 meters on a side [20]. The holes are 8 meters across, so they take up close to half the ground inside that circle [6][21]. Lara Picton, the Queensland University of Technology geology honors student who described the field, said, "What initially looked like a few depressions in the surface turned out to be far more widespread" [4][5].
The biological reading came from a drop camera, lowered from RV Investigator after people aboard guessed the holes were the work of animals [7]. The footage showed a site full of marine life, including large fish such as rockcod, and the team attributed the holes to bioturbation [8]. Maddison Cross, a Ph.D. candidate in marine biology at the University of the Sunshine Coast, said, "The process of living organisms moving and mixing sediment is called 'bioturbation.'" The organisms responsible, Cross said, "act as ecosystem engineers and can dramatically alter the shape of the seafloor" [9].
What the camera documented is occupancy. Cross said, "We've seen goldspotted rockcod repeatedly using some of these holes, so the similar shape and size of the holes might be because they reach a natural, ideal size for the life within them" [10]. Repeated use by a fish is not excavation by that fish, and the team named the rockcod as a likely architect in the conditional [11].
The holes reach about 100 meters out in every direction [6]. Immediately around the hull there are none at all. The team put that down to predators on the wreck making that ground dangerous to sit on [12].
Ben Arthur, the CSIRO voyage manager, had seen pock marks like these before [13]. In 2017, on a transit from Sydney to Broome, RV Investigator had half a day to find SS Macumba. The ship was a 2,500-ton merchant navy vessel, sunk by Japanese bombers off the Northern Territory coast during the Second World War [14][15]. Arthur said it was after midnight and the search was preparing to wind up. An experienced biologist in the room then noted "a series of mysterious 'pock marks' on the seafloor at the very edge of the search area," Arthur said [16]. Arthur said the biologist suggested those circular holes, likely caused by bioturbation, could point to a feature nearby [17].
On the next pass the acoustic technician running the survey asked the crew to swing the ship wide on the turn, outside the search area and near the pock marks, and the ship passed directly over the wreck [18]. Arthur described the operations room as feeling "a mix of excitement, exhaustion and incredible relief at finally solving this 74-year mystery" [19].
The account does not report how many pock-mark fields the ship has crossed with nothing beneath them. Treated as cylinders, meanwhile, the 300 holes at Althea II hold about 30,000 cubic meters of sediment that animals have moved off an otherwise flat bottom [23][6].
What to watch
- A count of pock-mark fields surveyed with no wreck beneath them, which would give the cue a false-positive rate.
- Repeat mapping of Althea II to test whether individual holes persist between visits or migrate with their occupants.
- Whether CSIRO writes pock-mark recognition into standard multibeam search procedure on later voyages.