As a complement to our Wild Sharks activities, biologists at the Seattle Aquarium recently conducted the latest installment of sixgill shark research in the waters just off the end of the Aquarium’s pier. The Aquarium has been conducting research on sixgill sharks since 2003. Three times a year, for three consecutive days/nights, divers place bait approximately 60 feet below the surface at 2pm, then record video of what happens over the next 18 hours. This time, research took place on July 29, 30 and 31.
Before we share the results of the research, though, a bit of background on sixgill sharks: they’re the world’s third-largest predatory shark, comparable in size to great white sharks. They’re found in tropical and temperate waters worldwide. And they’ve been around for literally millions of years—in fact, sixgills were on earth before dinosaurs.
But little is known about this species. Sixgills tend to live deep in the ocean and stay away from light. They’re so elusive that their population status is currently unknown. But they’ve been sighted at depths as shallow as 20 feet in Puget Sound, which presents a rare opportunity for us to study them.
“We know sixgills are in the Sound pretty much all the time,” says Project Coordinator Denise Griffing. “But the numbers we see during our active research differ dramatically.” Sixgills were relatively abundant during 2000-2007, but since then, they’ve been scarce—both at our research site and throughout the rest of Puget Sound. In fact, no sixgills were sighted during our most recent research dates, although we did receive a report of a diver sighting a sixgill off Redondo Beach on July 27.
If we’re not seeing sixgills, why do we continue the research? There are several answers to that question. First, just because we’re not seeing them, it doesn’t mean they’re not there. “This time we just couldn’t attract them to a 60-foot depth with our bait,” explains Denise.
It’s also important to know whether the sixgill population is ebbing and flowing, or declining. Continued research will help us answer that question. For example, we saw good numbers of sixgills in 2004 and 2005. Is this part of a regular cycle? And if so, how regular? For now, we don’t know. But we may find out soon.
“Local researchers have a theory that the Sound may be a nursery area for sixgills,” comments Denise. “Almost all the sixgills sighted here are sub-adult.” Once the sixgills reach a certain age/size, they may then move out to other parts of the world. If this theory is correct, we can expect to begin receiving reports of small sixgills as the new group grows large enough to be seen by our research and/or local divers.
Continued research may also help answer the sixgill population question. Research conducted by the Aquarium’s Curator of Conservation Research Shawn Larson suggests a sixgill population of 566,000—but is that in Puget Sound? (Not likely.) The Pacific Ocean? The entire world? Right now, we can’t say. But it’s important to get a sense of the overall species population.
Lastly, it’s easier to study sixgills in Puget Sound than in virtually any other location in the world, because of the shallow depths at which we’re able to see them. In Puget Sound, we can study sixgills with SCUBA divers and underwater video cameras. Elsewhere, a submarine and much more sophisticated equipment would be required. “And,” says Denise, “Anything we learn here, we’re adding to the overall body of knowledge about this species.”