Abstract
The low fecundity, late maturity, long gestation and long life span of Nautilus suggest that this species is vulnerable to over-exploitation. Demand from the ornamental shell trade has contributed to their rapid decline in localized populations. More data from wild populations are needed to design management plans which ensure Nautilus persistence. We used a variety of techniques including capture-mark-recapture, baited remote underwater video systems, ultrasonic telemetry and remotely operated vehicles to estimate population size, growth rates, distribution and demographic characteristics of an unexploited Nautilus pompilius population at Osprey Reef (Coral Sea, Australia). We estimated a small and dispersed population of between 844 and 4467 individuals (14.6–77.4 km−2) dominated by males (83∶17 male∶female) and comprised of few juveniles (<10%).These results provide the first Nautilid population and density estimates which are essential elements for long-term management of populations via sustainable catch models. Results from baited remote underwater video systems provide confidence for their more widespread use to assess efficiently the size and density of exploited and unexploited Nautilus populations worldwide.
Highlights
Nautilids have existed for over 500 million years [1,2,3] in a diverse and worldwide distribution
There was some indication of a seasonal trend for sampling maxima towards the middle months of the year; catches within the 95% confidence interval of mean catch rates (6.4 trap21) were returned throughout all months, with February being the only month without sampling effort (Fig. S1)
Trapping data show a male:female sex ratio of 83:17 from animals mature enough to determine sex and an age distribution of 0.002% juvenile Nautilus, 42% sub-adult and 58% mature individuals
Summary
Nautilids have existed for over 500 million years [1,2,3] in a diverse and worldwide distribution. Most reported trade comes from the Philippines fishery but trade is emanating from Indonesia and New Caledonia [17,18,19,20,21]. Recent studies on the Philippines fishery has shown declines in catch per unit effort of around 80% in 10–20 years, with relatively low effort by 3–4 local fishermen in each locality [19]
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