Abstract
Averaged demographic data from previously unfished populations of Nautilus and Allonautilus (Cephalopoda) provide a baseline to determine if a population is undisturbed and in “equilibrium” or is in “disequilibrium” as a result of fishery pressure. Data are available for previously undisturbed local nautiloid populations in Papua New Guinea, Australia, Indonesia, Fiji, Palau, American Samoa, New Caledonia and Vanuatu (total n = 2,669 live-caught, tagged and released animals). The data show that unfished populations average ~75% males and ~74% mature animals. By contrast, unpublished, anecdotal and historical records since 1900 from the heavily fished central Philippines have shown a persistent decline in trap yields and a change in demographics of N. pompilius. By 1979, a sample of fished live-caught animals (n = 353) comprised only ~28% males and ~27% mature animals. Continued uncontrolled trapping caused collapse of the fishery and the shell industry has moved elsewhere, including Indonesia. In addition, we show that estimated rates of population decline are offered by unpublished tag-release records in unfished Palau. These data show that patterns of trap yields and demographic differences between fished and unfished populations in relative age class and sex ratios can indicate disequilibria wrought by fisheries pressure that can render local populations inviable. Given adequate samples (n ≥100 live-caught animals), a threshold of <50% males and mature animals in fished populations should signal the need to initiate curative conservation initiatives. The current trajectory of uncontrolled nautiloid fisheries can only mean trouble and possibly extinction of local populations of this ancient, iconic molluscan lineage.
Highlights
One of the most iconic of marine invertebrates, the chambered nautilus includes two genera of nautiloids (Nautilus Linnaeus, 1758 and Allonautilus Ward and Saunders, 1997), whose pedigrees have roots dating back hundreds of millions of years
It has become apparent that pressure from the shell-trade industry is causing local depletions and fisheries collapses of Nautilus populations in the central Philippines and that large-scale trading in shells is occurring in Indonesia, even though Nautilus pompilius is protected there [11, 12, 13]
Since 2008, the U.S Fish and Wildlife Service along with the National Marine Fisheries Service has been evaluating whether Allonautilus and Nautilus species should be regulated under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) [14, 15]
Summary
One of the most iconic of marine invertebrates, the chambered nautilus includes two genera of nautiloids (Nautilus Linnaeus, 1758 and Allonautilus Ward and Saunders, 1997), whose pedigrees have roots dating back hundreds of millions of years. We have assimilated demographic parameters from 16 previously unfished populations of Nautilus and Allonautilus in Papua New Guinea, Australia, Indonesia, Fiji, Palau, American Samoa, New Caledonia and Vanuatu (combined n = 2,669 live-caught animals) to characterize undisturbed nautiloid populations in terms of age groupings and sex ratios (Figs 1 and 2; Table A in S1 File).
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