Sharks in the abyssal zone

FNRS 3

Painting of the F.N.R.S. 3 and gulper sharks by Michael Ramus, from Houot (1958).

It is currently thought that sharks do not inhabit the abyssal zone (depths >4,000 m) due to physiological constraints (Priede et al., 2006; Laxson et al., 2011; Treberg & Speers-Roesch, 2016). However, there is at least one abyssal occurrence that has been overlooked in the scientific literature. The deepest ever sighting of a shark was reported by Georges Houot in the July 1954 issue of National Geographic (Houot, 1954). It happened in the Atlantic Ocean 258 km (160 mi) southwest of Dakar, Senegal on February 15, 1954. Houot and his companion Pierre Henri Willm were diving in the bathyscaphe F.N.R.S. 3. They touched down on the seafloor at 4,050 m (13,287 ft), which at that time was the deepest manned dive ever. It was there that they saw the shark; Houot described it as being 2 meters (6.5 ft) long and having large eyes.

“Willm took over the porthole. In a moment he shouted, ‘A shark!’ It is a cry that should become frequent among men who go to these depths. It would be odd to parachute aimlessly into mid-Sahara and land beside a lion; yet each time we have visited the bottom wastes in the bathyscaphe we have seen at least one shark. Unless our luck has been phenomenal, this must mean there are thousands of them living in the world’s dark basement. Willm’s fish was about 6½ feet long. Though it must have known nothing but everlasting darkness, it swam without hesitation into the glare of our lights and looked at the porthole with its great protruding eyes. The long body undulated lazily in the droplight.”

gulper shark

Photograph of a gulper shark (Centrophorus sp. uyato [see addendum]), from Houot (1958).

In a subsequent article, Houot clarified that the shark was a ‘dogfish’, or squaliform (Houot, 1958). He had seen the same kind of ‘dogfish’1 in Toulon Canyon off the coast of France in the Mediterranean Sea. He included a photograph of one taken in Toulon Canyon at a depth of 2,286 m (7,500 ft) [see addendum]. This shark appears to be a species of gulper shark, Centrophorus

“There are, first of all, the dogfish of the great depths, the largest of the animals seen thus far through the porthole. It would be an exaggeration to assert that dogfish come to pay us a visit at each dive, but I have seen them off Toulon as well as 13,287 feet deep in the Atlantic. It is easy to see from photographs that these small sharks resemble rather closely their relatives at the surface, but their eyes are very big and globular, like two hemispheres bulging from their head.”

Assuming that the shark sighted off Dakar at 4,050 m was also a gulper shark, it was either C. granulosus or C. squamosus. These are the only species comparable in size to the reported length of 2 m. C. granulosus attains a max length of 1.76 m (5.77 ft), while C. squamosus attains a max length of 1.66 m (5.45 ft) (Ebert et al., 2021). Houot probably overestimated the size of the shark. The next deepest record of a gulper shark is a C. squamosus caught from a depth of 3,280 m (10,761 ft) on the Mid-Atlantic Ridge (Priede et al., 2006). The next deepest record of any shark is a Portuguese dogfish (Centroscymnus coelolepis) caught from a depth of 3,658 m (12,001 ft) in the Bay of Biscay (Forster, 1973). 

Centrophorus granulosus

Illustration of Centrophorus granulosus by Marc Dando, from Ebert et al. (2021).

It is plausible that Houot and Willm saw a gulper shark, or a similar squaliform, in the abyssal zone. It seems unlikely that they misidentified another fish, especially since they already correctly identified other deep sea sharks. Considering previous depth records, an occurrence in the upper 50 m of the abyssal zone is not outlandish. While not nonexistent, abyssal sharks are probably still rare because of physiological constraints. None have been sighted or caught after the 1950’s and they might have become even rarer as a result of anthropogenic effects.

Notes

1An interesting aside is that Houot mistakenly believed these sharks were blind and used echolocation to navigate!

Addendum (6/7/2022)

Pérès (1958) identified the gulper shark in the photo published by Houot (1958) as Centrophorus uyato (misspelled “uyatus“). Contrary to Houot, Pérès stated that this photo was taken at a depth of 1,390 m (4,560 ft) in Sicié Canyon.

References

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