Predators & defenses


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Withdrawal & inking


Defenses of octopuses and their relatives can be divided into passive and active. Topics relating to passive defenses include , HIDING AWAY, NOCTURNAL BEHAVIOUR, COLOUR CHANGE/CAMOUFLAGE, and MAKE BODY SEEM LARGER, considered in other sections.  Active defenses include withdrawal & inking, considered here, and BEAKS & BITING, considered in another section. 

There are actually only a few references to inking as a defense in west-coast cephalopod species that are not anecdotal.

Research study 1

There are many potential predators of west-coast octopuses. For example, of 39 octopuses Enteroctopus dolfleini collected in the Clayoquot Sound, British Columbia by researchers from Simon Fraser University, 19 are found to have missing or partly missing arms and 26 have scar damage.  Little is known, however, of which predator from a long list of potential ones is actually most important, or whether inking acts to protect against attacks by large predators such as seals, sea lions, and other mammals, let alone from attacks by large fishes and sharks. Hartwick et al. 1978 J Fish Res Bd Can 35: 1492.

photograph of a Humboldt squid stranded and moribund releasing ink

CLICK HERE to see a video of ink release in a stranded and moribund Humboldt squid Dosidicus gigas.

NOTE the video replays automatically

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In the absence of of any specific studies on function of inking and withdrawal in defense of west-coast octopuses, consider what potential functions may be served by inking from the following list, then CLICK HERE for explanations.

The ink acts to hide or obscure the intended prey from the predator.

The ink acts as a dummy or decoy to distract the predator.

The ink acts to anaesthetise the predator's sensory perception.

Research study 2

schematic describing flight in squids Todarodes pacificusAn unusual strategy of fast withdrawal by squids to escape from predators is to take to the air.  It is commonly referred to as flying but, as it does not involve propulsion, it is really just gliding.  It is not clear how often “flying” has evolved in squids, but several tropical species are reported to do it, and one photograph of squids Todarodes pacificus gliding above the ocean surfaceeastern north-Pacific species Todarodes pacificus is quite adept at it.  A researcher at Hokkaido University, Japan provides the first description of flying behaviour in Todarodes.  Squids of up to 20-25cm total length swim or jet to the ocean surface, fill their mantle cavities one last time, and jet free of the water.  Seawater is expelled as a trail of droplets that continues until the mantle cavity is mostly or completely empty (see photograph and graphic).  Body shapes change to maximize lift. These include extending and flaring the posterior fins, and opening the arms and tentacles.  Inter-arm membranes are drawn tight to form a kind of wing.  Flights are brief (about 3sec), but reach speeds of 11m per second at heights of 3m and over distances of 30-35m.  On re-entry the squids tuck in their posterior fins and re-fold their arms to minimise impact shock.  Although not known for sure and never observed, it seems likely that squids fly to escape potential predators. Yamamoto 2015 Report Hokkaido UniversityPhotograph courtesy Jun Yamamoto, Hokkaido.  Schematic courtesy

NOTE distribution extends from Japan to the west coast of North America  

Research study 3
  photograph of a dead Octopus bimaculoides apparently suffocated by its own ink clogging its ctenidiaIs an octopus's ink toxic to itself? This question arises in response to a report from biologists at Illinois College, Jacksonville that three juvenile octopuses Octopus bimaculoides exhibited stressful and eventually incapacitating symptoms after being shipped by air from California in plastic travel bags. On examination, each affected individual’s ctenidia were found to be clogged with mucousy ink. After suction cleaning and irrigation with fresh seawater, all recovered. One later died following narcotisation and surgery, with ink-clogged ctenidia being once again evident (see photograph). In answer to the question posed above, the authors suggest suffocation resulting from stress as the probable cause of mortality, rather than ink toxicity. It would not be evolutionarily likely for an octopus to be especially sensitive to chemicals in its own ink. Bennett & Toll 2011 J Am Ass Lab Anim Sci 50 (6): 943.