Octopus Predation on Nautilus: Evidence from Papua New Guinea

In the Admiralty Islands, Papua New Guinea, drift shells of Nautilus pompilius and the sympatric species N. scrobiculatus are fairly common and there is no evidence that they have ever been systematically trapped or marketed. Of 1,532 drift shells examined, 57% had been bored by Octopus. The percentages are similar in both species; 57% in N. pompilius (N = 1,329), and 60% in N. scrobiculatus (N = 203). There is no significant difference in boring frequency in males (54%) versus females (46%), nor in borings in the left (53%) versus right (47%) side of the shell. Multiple borings are present in 30% of the shells, and 81% penetrate the shell wall. The great majority (98%) of the borings are located in the posterior one-half of the body chamber, where the retractor muscles, branchial cavity and visceral sac are located. These data, plus evidence of sublethal attacks in 2–8% of live-caught Nautilus, indicate that octopod predation is, and will continue to be, a significant factor in the survival of this ancient lineage.