How to Distinguish from Similar Species:Octopus rubescens is smaller, with mantle length less than 10 cm and weight less than 200 g; its skin has small, pointed papillae but not the large skin folds found on O. dofleini.
Geographical Range: Bering Sea to California; Northern Asia, Japan (and presumably Hong Kong)
Depth Range: Intertidal to 100 (180) m
Habitat: Primarily rocky subtidal; occasionally low intertidal or on sand
Biology/Natural History: The 3rd right arm of the male of this species has a large hectocotylus, about 1/5 the length of the arm (photo). The hectocotylus is used in transferring the male's spermatophore, or package of sperm, which may be up to a meter long, to the female. The hectocotylus may be left within the mantle of the female during the process. Eggs, which look like small whitish grapes, are laid throughout the year but mainly in the winter. When the female has eggs she attaches them to the roof of a cave and guards them until they hatch (5-7 months). She may lay 35,000 to 70,000 eggs in a single clutch. Hatching is mainly in early spring, and the young are pelagic for one to several months before settling. The young are sometime seen swimming near the surface. Lifespan is thought to be 4-5 years. Prey include crustaceans (shrimp and crabs), mollusks (scallops, clams, abalones, moon snails, small octopus), and fish (rockfish, flatfish, sculpins). The octopus are often captured in crab traps, where they are trying (successfully) to steal the crabs. Females can be cannibalistic. The Seattle Aquarium recently observed an octopus catching the spiny dogfish Squalus acanthias, and in 2005 we found the picked-clean skeleton of a dogfish on the shellheap outside an octopus den (photo). The species accumulates a large pile of shells and crab carapaces outside the den, which is usually under a boulder or in a rocky crevice. They quickly kill crabs by rasping a tiny hole (1 mm or less in diameter) through the carapace (photo), probably with their radula, then presumably injecting poison, perhaps with their beak. Several species may be attracted to their shell pile (midden), including Pycnopodia helianthoides and the snail Amphissa columbiana. Predators include seals, sea otters, dogfish sharks, lingcod, and man. Parasites include the mesozoans Dicyemenna abreida and Conocyema deca, which live in the kidney.
This octopus is said to be capable of inflicting a painful bite but I have never seen anyone bitten, even when wrestling them off the rocks. They seem much less ready to bite than is O. rubescens.
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General Notes and Observations: Locations, abundances, unusual behaviors:
We have captured a large individual of this species from at least 100 m depth in the San Juan Channel. The largest I know of being seen at Rosario was one with about a 4 m span near Northwest Island.
This view shows the hectocotylus arm (right) and a normal arm (left) of a male E. dofleini which is being dissected.
This view of a dissected E. dofleini shows the salivary glands. The salivary glands of many octopus secrete poison which can be excreted through the salivary papilla in the mouth and used to subdue prey.
The carapace was collected from a shell midden outside an active den.
In experiments in the Rosario seawater tanks in summer, 2005, students Jon Mayberry and Kirt Onthank found that E.. dofleini prefers crabs over scallops. Click here for a movie showing the octopus exiting from its burrow and choosing to grab a crab rather than a scallop that was presented to it.
More detailed results from research papers by Kit Onthank, Jon Mayberry, and Nichola Marsh, 2005: Althouth the E. dofleini they captured had a clear preference for crabs over bivalves, the contents of three middens at Coffin Rocks in Bowman Bay had more bivalves than crabs. There was also substantial variation among middens in the proportion of different prey species. This suggests that different individuals may have different preferences or hunting patterns, and that bivalves may be more available to octopus in this area than crabs are. They also found that about 50% of the crab carapaces had drill marks, as seen above, while very few bivalve shells had drill marks and almost no scallops did. The literature suggests that octopus try to pry bivalves open first, and only drill them if they cannot pry them open. The large size of E. dofleini may allow it to open most bivalves and nearly all scallops without drilling them. They also found that about 25% of the scallop shells were broken in a characteristic manner--with one of dorsal extensions or "wings" of the shell broken off one valve and attached to the other valve. The valves apparently broke while the octopus was attempting to pry them open.
Figure 2 from Onthank et al., 2005: Percentage of
each prey type
from E. dofleini middens, by prey type
Authors and Editors of Page:
Dave Cowles (2005): Created original page