Once a year, the Seattle Aquarium enlists local divers to search for giant Pacific octopuses in the Puget Sound.
Hallie Golden – Citylab -8 November 2018
On a recent Sunday, two divers at a small cove in West Seattle pulled on their suits, air tanks, and masks. With their fins in their hands, they walked slowly towards the edge of Puget Sound, ready to descend dozens of feet into the water’s foggy depths in search of the largest octopus in the world—the giant Pacific octopus.
Jerry Dollar, a seasoned amateur diver who organized the expedition through the Emerald Sea Dive Club, offered Andrew Creighton and Mark Newland some last-minute advice. Keep an eye out for piles of clam and crab shells, because that may indicate you’re next to their den, he told them. Look carefully through piles of rocks and in the Honey Bear, a shipwrecked boat about 35 feet under water. And don’t skip the shallow areas.
“I’ve seen [octopuses] in 10 feet of water,” Dollar told Creighton and Newland. “They’re opportunistic. They go where the food is.”
This West Seattle expedition was one of dozens of local dives carried out as part of the 18th Annual Seattle Aquarium Octopus Survey. For about one week during the month of October, 60 volunteers searched Puget Sound at 26 dive sites and reported their findings back to the aquarium. After each underwater trip, the citizen scientists submitted an online form detailing the location and depth of their dive, the number of giant Pacific octopuses they saw, and their general size.
The decrease isn’t a cause for alarm, she said. “Over the last 18 years, we have seen the numbers cycle up and down. So even though we saw less octopuses this year, it doesn’t mean the population is in decline. It seems to be part of their natural population cycle.”
The divers at the West Seattle cove didn’t find any giant Pacific octopuses during their first one-hour dive. “If you’re lucky, you’ll find some. If you aren’t, you won’t,” as Dollar put it. “That’s the way it is out there.” During their evening dive, they found five octopuses, but these were likely all East Pacific red octopuses, which are smaller and overall more common than the giant Pacific on the West Coast.
Initially, the octopus survey was launched to try to answer a question that staff members got regularly at the Seattle Aquarium: How many giant Pacific octopuses live in the Puget Sound? It turns out it’s not an easy question to answer, since there isn’t a firm population number for giant Pacifics.
These octopuses normally live about three years. They eat a lot of crustaceans, mollusks, squid, fish and sometimes other species of octopus. They are so big that they only really have to watch out for extremely large fish, such as halibut and lingcod, and some marine mammals. But they hatch from an egg the size of a rice grain, so for more than a year after they’re born, they are at the mercy of a wide array of predators.
But perhaps the biggest challenge with keeping tabs on these creatures is the fact that standard counting methods are virtually impossible to use. They’re soft-bodied animals, so scientists avoid rigid tags to mark them. They also can’t reliably use dyes to tag them because it’s so difficult to see the color when they’re in their dens. “It’s really difficult,” said Hollander. “We haven’t really found any tried and true method on how to tag them.”
Almost two decades ago, staff members at the aquarium decided they’d try something a little different. They enlisted members of the very active local dive community to try to help them collect information on the giant Pacific population. “While we may never be able to tell you exactly how many GPOs are in the [sound], we can see general trends and changes that [are] maybe happening in their population or where they are being found,” said Kegel.
Three years ago, the survey’s organizers refined it to get more consistent findings. Rather than having divers explore any site they wanted, they enlisted some of them to check the same key six sites, which are now visited every year. They also moved the event from January to October, in the hopes that better weather would increase participation.
That seems to be paying off. The census has become an annual, up-close look at the giant Pacific octopus, so if the population is impacted by environmental changes or pollution, the aquarium staff will know. “If our [scheduled] sightings and reports stay the same, yet we’re getting very, very, very low numbers for probably two to four years, then we probably would raise the flag to the Department of Fish & Wildlife and say, ‘You guys might want to take a look at this,’” said Hollander.