Results of The First Giant Octopus Survey in Puget Sound

<< Cephalopod Articles | By Dr. Roland C. Anderson, Puget Sound Biologist, The Seattle Aquarium

In my job as the octopus caretaker at the Seattle Aquarium I am frequently asked how many octopuses there are in Puget Sound and how the population has been doing over the years. To answer these questions, on February 19, 2000, the Saturday of President's Day weekend in the US, we organized a divers' survey of the giant Pacific octopuses in Puget Sound. We hoped to establish a baseline of how many octopuses are in the area and conduct this survey every year, so we can see if the population is healthy or if there are fluctuations from year to year.

In addition to the large cadre of volunteer divers at the Aquarium, we enlisted the help of sport divers in the area to look for octopuses. In support of this effort, I spoke to numerous scuba diving clubs, sent information out by mail and Email to dive shops and web addresses and made numerous phone calls alerting divers of the upcoming octopus census. In addition, our public information specialist, Galen Goff, arranged for media coverage of the event, resulting in publicity in newspapers, radio and television.

We chose a late winter date because it seems more octopuses are seen in winter. There is some evidence that octopuses migrate down to deeper, colder, darker waters in the summertime, and because of this, there seem to be more octopuses seen in the winter, although this may be due to less kelp covering the dens. President's Day weekend is a holiday weekend and while in the wintertime, usually has decent diving weather in the Pacific Northwest. The underwater visibility also tends to be better in the winter because of the lack of plankton. Reports from this survey indicated that the visibility averaged 20-25 feet on the day of the survey, quite reasonable for Puget Sound.

I asked all divers on that particular day to report any octopus sightings to me at the Aquarium. The information requested was the location of the dive site, where the octopus was in relation to shore landmarks, the depth of the water, time of day (so we could correlate the depth to the level of the tide), a description of the octopus's den, and an estimate of the size of the octopus, including the size of some feature of the octopus such as width of the largest sucker seen. This size estimate was used to distinguish between sighting of the giant Pacific octopus and another species present in Puget Sound, the little red octopus.

The day of the event dawned clear, calm and sunny. I received reports from sport divers and shore observers who questioned emerging divers. As far as I could determine, at least 114 divers participated in the survey, including four Aquarium divers diving in Elliott Bay at the Aquarium, a spot where octopuses are frequently seen. Some of the other dive sites I know were surveyed were Day Island, Titlow Beach, Les Davis Pier, Redondo, Three Tree Point, Lohmann Park, the Alki Pipeline, the Alki Lighthouse, the Alki "Junkyard," Seacrest, the Seattle Aquarium, the Elliott Bay Marina, the Mukilteo "T" dock, Keystone, Mike's Dive Resort, Sund Rock, Octopus Hole and Triton Head. In spite of all these divers looking for octopuses in these many places on a beautiful sunny day, only 18 octopuses were spotted and reported back to the Aquarium, of which 13 were seen in Hood Canal, mostly at Sund Rock, including four females guarding eggs. Two were seen at Titlow Beach, two at Les Davis Pier and one at Mukilteo. Surprisingly, none were seen at Three Tree Point or at Keystone, normally octopus-rich areas, and none were seen in the Seattle area. We usually have one or two octopuses under the Aquarium piers but none were spotted on that day.

This is a rather small number of octopuses, considering the large number of divers participating. This is only 0.16 octopuses per diver, or, assuming each diver dove with a buddy, 0.32 octopuses per dive. In other words, there was only one octopus seen per 3.125 dives. This is perhaps an over-simplification, especially considering that 10 octopuses (four of which were females guarding eggs) were seen at two close dive sites in Hood Canal - Sund Rockand Octopus Hole. The presence of so many octopuses at these sites that are heavily used by divers confirms that the octopuses are not being disturbed or scared by divers.

Nearly all the octopuses seen had made dens under large rocks. One was seen in a den excavated under a fallen concrete piling and one was out in the open, sitting unprotected on the bottom, a large octopus, probably senescent, that eventually crawled away from the observing divers down to deeper water. Some were in dens that had been used sporadically with wolf eels for many years. The average depth of octopus sightings was 59 feet, with a range of 44-88 feet.

I don't think we need to worry yet about the low numbers seen, especially in the Seattle area. Octopus populations may "fluctuate" with climate changes, with the seasons, with annual rainfall, with brood hatching success, and of course, with pollution. Giant Pacific octopuses are good barometers to the health of Puget Sound, since they spend the first two months of their lives living and floating among and eating the plankton before settling to the bottom to begin an adult life where they eat crabs, clams and snails, among other things.

The reported observation of many, live, red rock crabs at many of the observation sites indicated it is not a lack of proper food that is limiting the octopus populations at these sites. Additional indications that the health of the sites may not be in jeopardy is the large number of ling cod seen, especially males guarding eggs. In considering the total ecology of an area, of course the presence of large numbers of ling cod may have something to do with the low numbers of octopuses, since ling cod are known to eat small octopuses among many other food items, and male ling cod may be competing with octopuses for den sites as may wolf eels.

In addition to learning information about our octopuses, we learned a lot about on how to conduct such a survey and we will conduct it a bit differently next year. More and better advertising before the event will help. I think its' becoming an annual event will encourage more divers to participate, which is important and getting them to dive at more locations is important. We need to be sure that all divers in the area report back, whether they saw octopuses or not, so that we can get a better idea of the diver effort involved per octopus sighting. In addition to the general census, we should concentrate in a specific area each year. This year the Marker Buoy Dive Club concentrated on the Sund Rock/Octopus Hole areas of Hood Canal and produced encouraging results. Other dive clubs did the same in different areas, and while not seeing many octopuses for whatever reasons, covered the areas thoroughly. In future years we may use trained Aquarium divers to survey some of the popular dive sites to compare the results with those reported by sport divers.

There may be additional pressures on the octopus population other the environmental factors. There is the possibility that octopuses are being poached for either personal use or commercial sale. To date we have no confirming evidence of that happening. Furthermore, very few octopuses are being taken alive for public aquariums. There is only one commercial collector of octopuses in Washington for this trade, located on Sequim Bay, who uses tires to capture octopuses alive and ships them across the country. The Seattle Aquarium itself took only three octopuses from the wild in 1999, none taken from popular dive sites, two of which came from the Neah Bay area and the other from Hood Canal.

I had hoped to make an estimate of the total number of octopuses in Puget Sound based on these findings, but as it is, I don't feel comfortable doing that with these meager statistics, especially in the Seattle area. However, the population certainly seems healthy and abundant in Hood Canal. Ten octopuses were seen in only 400 yards of shoreline. Granted, this is a good area for octopus habitat and is located within a marine preserve, but this is still an impressive number.

We don't know what, if anything, is happening in Puget Sound proper. Dive sites such as Day Island, Three Tree Point and Keystone should have octopuses. These sites will continue to be monitored casually to see if the octopuses return during the coming year. If divers who read this should see octopuses at those sites, it would help to report them to Roland Anderson at the Seattle Aquarium. If there are none seen during this year or during next year's census, then we may have reason to worry.

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