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Predators & defenses | |||
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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 beaks & biting, considered here, and WITHDRAWAL & INKING, considered in another section . | |||
Research study 1 |
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Beaks in octopuses are large, sharp, and formidable-looking. A bite is invariably accompanied by injection of toxins from the posterior salivary glands that act quickly to paralize and/or kill prey such as crabs. Although used to kill and dismantle prey during hunting and feeding, beaks are not as commonly used in defense as their appearance might suggest. An exception is the feisty Indo-Pacific blue-ringed octopus Hapalochlaena lunulata, whose toxin has been known to kill humans. On our coast, there are several references to divers, snorklers, and aquarium staff being bitten while handling the small west-coast red octopus Octopus rubescens including, in a few instances, injection of toxin. Similarly, at least one report notes that giant octopuses Enteroctopus dofleini will also bite in defense of (human) attack, mostly on hand and wrist areas. The account describes a lot of bleeding and prolonged healing. The fact that most close contact by humans with both of these cold water-inhabiting species is done in protective suits, including gloves, may explain why reports of biting are relatively few. NOTE a description of a bite on the back of the hand from a specimen of Octopus rubescens caught in Puget Sound, Washington includes the following: localised pain commencing 10min after the bite, accompanied by swelling at the wound site and a “fiery” pain extending up the forearm. The victim bathed the hand in NOTE in the cases described the toxin appears to have only minor topical effects, such as localised necrosis and prolonged healing. As the main or perhaps only component of tetrodotoxin is a protein, then any treatment that destabilises protein is likely to be a useful prophylactic for an octopus bite. This would include immersion of the affected part in hot water (as hot as possible, but not so hot that scalding occurs) and treatment with mild acid such as vinegar
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![]() Research study 2 |
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NOTE the otoliths, or balance-receptor stones, are quite soft NOTE 73 octopuses are collected, weighed, and their beaks dissected out. Twelve measurements on the beak are selected that are convenient and easy to take. Five are on the upper beak and 7 on the lower beak. Each of the 12 measurements is then plotted against live mass (using log-transformed values to produce linear relationships), and the one that gives the best fit as measured by correlation coefficient r is selected (the parameter chosen produces an r value of 0.97) |
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Research study 3 |
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Analyses of stomach contents of 250 Steller sea lions in the Gulf of Alaska indicate the presence of 4% by volume cephalopod prey (mainly octopuses and squids). The author uses the presence of beaks to estimate numbers of cephalopod prey and the volume of identifiable cephalopod matter in relation to volume of all stomach contents to obtain the % volume represented. However, owing to the ease of digestibility of cephalopods (absence of hard parts), this latter is likely to be an underestimate at best. In the case of cephalopods a better substitute for such visual estimations would have been to employ a similar technique to that used in Research Study 2 above. |
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