Higher risk of fatality by predatory attacks in earlier ontogenetic stages of modern Nautilus pompilius in the Philippines: evidence from the ontogenetic analyses of shell repairs

Abstract

The shell repair scars of modern Nautilus pompilius in the Philippines presumably due to sub-lethal predatory attacks were examined throughout ontogeny ranging from hatching to maturity, revealing the higher risk of fatality in earlier ontogenetic stages. The examinations throughout ontogeny demonstrate that: (1) sub-lethal predatory attacks by other organisms have no preferred position through ontogeny; (2) the sizes of shell repair scars are similar throughout ontogeny and, therefore, the width and length of shell repair scars relative to shell diameter decrease from hatching towards maturity; and (3) the proportion of sub-lethal predatory attacks within 10 mm increments of shell diameter are similar irrespective of shell diameter or decrease approaching maturity. The numbers of the irregular, radiating, black shell repair scars, indicating injury to the soft parts at shell breakage, decrease at a diameter >80 mm and none were found at <56 mm in shell diameter. Furthermore, the rarity of juvenile trapping data might be related to the higher fatality from predatory attacks in earlier ontogenetic stages, providing crucial information for the conservation of N. pompilius.