Sharks in the abyssal zone

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.”

Photograph of a gulper shark (Centrophorus sp. uyato [see first 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 first 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) [see second addendum]. 

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 [or possibly the 1970’s, see second addendum] 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.

Addendum (10/7/2023)

In their survey of manganese nodules in the central North Pacific Ocean, Kolbe & Siapno (1974) reported seeing a sleeper shark (Somniosus pacificus) at 4,000 m (13,123 ft) using a television camera.

“TV provides some observations of animal life in the abyssal depths. At a depth of 4000 m a blackish sleeper-shark confidentially approached the screen.”

However, given the lack of further information and confirmation (e.g., they did not say if the footage was recorded or where exactly it was taken), this sighting seems far less reliable than Houot and Willm’s. The shark may have been misidentified or the depth stated may have been an error. The next deepest instance of a Pacific sleeper is 2,205 m (7,234 ft) (Yeh & Drazen, 2009). The next deepest sleeper shark overall, the Greenland shark (Somniosus microcephalus), is 2,992 m (9,816 ft) (Porteiro et al., 2017).

Additionally, a Centrophorus squamosus caught at 3,366 m (11,043 ft) on the Mid-Atlantic Ridge extends the depth range for this species (Porteiro et al., 2017). The deepest confirmed shark is a cookiecutter (Isistius brasiliensis) trawled from 3,700 m (12,139 ft) in the Gulf of Mexico (Retzer, 1990).

References

• Ebert, D.A., Dando, M., & Fowler, S. (2021). Sharks of the World: A Complete Guide. Princeton University Press.
• Forster, G.R. (1973). Line fishing on the continental slope: the selective effect of different hook patterns. Journal of the Marine Biological Association of the United Kingdom, 53(4), 749-751.
• Houot, G.S. (1954, July). Two and a half miles down. National Geographic, 106(1), 80-86.
• Houot, G.S. (1958, May). Four years of diving to the bottom of the sea. National Geographic, 113(5), 715-731.
  
• Kolbe, H., & Siapno, B. (1974). Manganese nodules. Further resources of nickel and copper on the deep ocean floor. Geoforum, 5(4), 63–82.
• Laxson, C.J., Condon, N.E., Drazen, J.C., & Yancey, P.H. (2011). Decreasing urea:trimethylamine N-oxide ratios with depth in Chondrichthyes: a physiological depth limit? Physiological and Biochemical Zoology, 84(5), 494-505.
• Pérès, J.-M. (1958). Trois plongées dans le canyon du Cap Sicié, effectuées avec le bathyscaphe F.N.R.S. III de la Marine Nationale. Bulletin de l’Institut océanographique, 1115, 1-21.
• Porteiro, F., Sutton, T., Byrkjedal, I., Orlov, A., Heino, M., Menezes, G., & Bergstad, O.A. (2017). Fishes of the northern Mid-Atlantic Ridge collected during the MAR-ECO cruise in June-July 2004. An annotated checklist. Arquipelago: Life and Marine Sciences, Supplement 10, 1-125.
• Priede, I.G., Froese, R., Bailey, D.M., Bergstad, O.A., Collins, M.A., Dyb, J.E., Henriques, C., Jones, E.G., & King, N. (2006). The absence of sharks from abyssal regions of the world’s oceans. Proceedings of the Royal Society B, 273(1592), 1435-1441. https://doi.org/10.1098/rspb.2005.3461
• Retzer, M.E. (1990). New records and range extensions of twelve species of fishes in the Gulf of Mexico.  Northeast Gulf Science, 11(2), 137-142. 
• Treberg, J.R., & Speers-Roesch, B. (2016). Does the physiology of chondrichthyan fishes constrain their distribution in the deep sea? Journal of Experimental Biology, 219(5), 615-625. https://doi.org/10.1242/jeb.128108
• Yeh, J., & Drazen, J.C. (2009). Depth zonation and bathymetric trends of deep-sea megafaunal scavengers of the Hawaiian Islands. Deep-Sea Research Part I: Oceanographic Research Papers, 56(2), 251-266.
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