Since the 1950s, when spearfishing was a central focus of the sport dive, there has been a shift in popular emphasis to hunting with an underwater camera. Most recently, Pacific Northwest divers have enjoyed a bold trend toward unarmed encounters with giants of the North Pacific deep–divers peacefully observing dens of wolf eels and giant Pacific octopus, swimming with killer whales, and now, diving down to see deep-water sixgill sharks.
The alluring aspect of such a dive is that the sixgill is a real shark’s shark, not just a puny dogfish and definitely not a common item. Sixgills are big and they have only been sighted with predictability at two localities: one on the protected east coast of Vancouver Island, Canada and one on Vancouver Island’s west coast, near the open Pacific Ocean. In addition, sightings have been in relatively deep water for most sport divers, at depths over 25 meters (82 feet); the sixgills go much deeper as a rule. No other large sharks are ever seen by divers in this part of the world, so perhaps the latest and most exclusive achievement for the accomplished diver in Washington or British Columbia is to become one of the few to sight a sixgill.
The sixgill shark is one of the most primitive living members of an altogether ancient group of cartilaginous fishes, the sharks. All sharks inspire awe, sharing a heritage of unsurpassed perfection in their evolutionary design as predators. All sharks swim with the sinister, broad grace which is forced upon them by the fixed attachment of their fins, in contrast to the “modern,” agile-jointed, bony fishes. The sharks also have an abrasive, denticle-covered or “toothed” skin, and the majority of living species have five pairs of gill slits in the throat region; whereas the sixgill has six.
The sixgill shark is further distinguished from most other living shark species by having only one dorsal fin along the back, instead of the usual two. This single dorsal fin is far back toward the tail and the upper lobe of the tail fin is elongate.
Sixgill sharks in captivity swim constantly, albeit sluggishly. Aquarium specimens have usually included small, immature individuals which appeared docile. In the summer of 1975, however, the Vancouver Public Aquarium briefly exhibited three sixgills, each about three meters long. The largest of these three sharks was fatally attacked by one of the others.
Maturity in sixgills occurs at around two meters in length. They are known from biologist’s examinations to bear nearly 100 live young, a prolific number of offspring compared to other sharks, but very few in comparison with egg laying bony fishes. Sixgills have been recorded at eight meters, probably over a half ton in weight. The size record sixgill for San Francisco Bay was 3.35 meters and 210 kilograms (11 feet, 462 pounds).
Sixgill sharks are captured in the nets of commercial fishermen, so are presumed to prey upon commercially important fish species. Sixgills occur outside the northeast Pacific Ocean region, in temperate marine waters of the entire world, including the southern Indian Ocean, the Caribbean and the Mediterranean. Wherever they occur, sixgills are noted for the great depths they inhabit. California specimens are taken in submarine canyons at 1000 meters and deeper. In British Columbia waters, however, sixgills rise within the depth range of sport divers during the summer months of June to August. It has been during these summer months that a select few have had the good fortune to witness the ascent of these creatures from the ocean depths.
Guided dive trips have regularly succeeded in encountering sixgill sharks at 25 to 70 meters deep off Hornby Island in the northern Strait of Georgia, east of Vancouver Island, and at the mouth of Alberni Inlet in Barkley Sound, on the west coast of Vancouver Island. Both sites are removed from the surge of open ocean waters. Both sites have deep tidal currents and lie in the path of major salmon migrations. They may have regular upwelling of colder, deep water. Many other areas share these characteristics, though, so very likely there are other potential areas to see sixgill sharks.
Nothing is understood of the biological reasons for these sharks venturing into relatively shallow water in summertime. Specimens have been caught on longlines at the shallowest depths of under 30 meters on dark, moonless nights in the Strait of Georgia, illustrating a tendency of various sharks, including the common dogfish, to migrate up shallower on dark nights.
Rick Brock, an Everett, WA photographer, saw sixgills on a reconnaissance trip to Barkley Sound, then he returned for the explicit purpose of photographing one. The big, 100 kilogram beast that allowed itself to be photographed at close range was slowly cruising around the 30 meter depth range. It appeared so placid that Rick felt the urge to reach out and give it a gentle pat on the side. The brute immediately arched its back and wheeled around to face Rick, a bit more reaction than had been hoped for.
Other close encounters indicate a need for caution in dealing with sixgills. In the early 1970s, prominent Vancouver businessman Bruce Howe discovered the sixgills off Hornby Island and had a closer encounter than he had even intended. He accidentally bumped into the side of a large sixgill’s head and only realized what it was when he saw its eye in front of his facemask. The four meter shark compounded Howe’s surprise by swimming in a tight arc and returning toward him with its enormous mouth agape. Bruce Howe pressed his back against the side of the reef and shot for the surface as fast as he could swim, but saw no evidence that the sixgill followed. This escapade occurred at under 25 meters, so maybe that sixgill was pushing its upper depth limit, or maybe it was just returning a threat signal to the intrusive diver.
Another incident suggests the sixgill will not attack without real provocation, but it will not ignore taunts. This incident also took place at Hornby Island, just recently. Two Alberta divers were on a guided sixgill dive and they tried to grab hold of a shark to hitch a ride. The shark thrashed free of the first diver’s grip and went around in a broad circle before returning to the area of the divers. Rather than respect the first reaction of the sixgill, these divers foolishly risked a second try. The response from the shark was again to wrest itself free, but then to swim down out of the depth range of the divers. In two successive days of searching after that, no more sixgills were sighted.
Whether as the result of newly emerged understanding of marine wildlife, or because of jaded disregard born of familiarity with dive technology and the need for fad, divers are now accepting new risks for the thrill of encountering creatures from atop the pyramid of marine life. With real understanding and respect, these exciting forays, ventures into the realm of man’s rivals in power and nerve, can add new dimensions to the scuba diver’s special appreciation of the marine world.