The validity of Nautilus macromphalus as the species occurring around New Caledonia was established quite early (Bonacum et al. 2011), and has recently been confirmed (Combosch et al. 2017).

Molecular studies of N. pompilius sensu lato suggest that this name covers a suite of cryptic species. Genetic studies have identified divergence between material from the following locations (1) Fiji, (2) Vanuatu, (3) American Samoa, (4) Coral Sea Islands (including Osprey Reef, Shark Reef and Bougainville Reef), (5) Papua New Guinea and the Great Barrier Reef (including Port Moresby, Admiralty Islands, Mantis Reef, Wishbone Reef, Carter Reef) and (6) Indonesia, NW Australia, Philippines and Palau (Sinclair et al. 2007, 2011; Bonacum et al. 2011; Williams et al. 2012, 2015; summarised in Nikolaeva et al. 2015; Vandepas et al. 2016).

Indonesia, Western Australia, Philippines and Palau
An application was made to the International Commission on Zoological Nomenclature (ICZN) to set aside all previous type designations for Nautilus pompilius and to designate a neotype from Ambon Indonesia (Nikolaeva et al. 2015). The commission ruled in favour of this proposal in (ICZN 2018). The species has now been redefined (Saunders et al. 2017) but may yet undergo further revisions. With Ambon, Indonesia as the type locality for N. pompilius, we assume the distribution of N. pompilius pompilius to be Indonesia/NW Australia/Andaman Islands. Approximate Bayesian Computation analysis showed that the apparent lack of genetic divergence between Western Australia and Philippine material is because of limited genetic drift in these isolated populations since their separation rather than gene exchange (Williams et al. 2015). This supports a Philippine clade as separate from an Indonesia/NW Australia clade. Habe and Okutani (1988) described a subspecies N. pompilius suluensis from near Palawan Island, Philippines. Thus we treat Philippine nautilus under the name N. pompilius suluensis. Using genomic data, Combosch et al. (2017) found little genetic differentiation between samples from the Philippines, and samples from Palau, Indonesia and NW Australia. However, the latter three locations were represented by only five specimens in total, so the data should be treated with caution. We treat Palau nautilus under the widely applied name N. belauensis. We treat material from SW Australia as N. repertus, thus using the name under which specimens from this region were originally described. While all these species/subspecies may not be valid, the names are currently available and allow us to differentiate widely spaced populations that likely need separate management.

Fiji, Vanuatu, American Samoa
Combosch et al. (2017) consider that populations from Vanuatu, Fiji, and American Samoa could represent a single species, or could represent two species, with specimens from American Samoa and Fiji comprising one species, and those from Vanuatu comprising a second. In the absence of a suitable name, we treat specimens from these three countries as Nautilus pompilius West Pacific population, but herein acknowledge that a new name is required and that this grouping may indeed comprise two or three species.

Coral Sea Islands, Papua New Guinea and the Great Barrier Reef
Combosch et al.(2017) consider populations from the Coral Sea Islands, Papua New Guinea and the Northern Great Barrier Reef to potentially comprise a single species, although, like Williams et al. (2015), they did find the Coral Sea Island population to be genetically different to specimens from the Northern Great Barrier Reef and Papua New Guinea. There are species names available from this region (e.g., N. stenomphalus, N. moretoni), but use of these names would require a full taxonomic revision since they would not be being used in their original context. Thus we treat specimens from the Coral Sea Islands as Nautilus pompilius Coral Sea subpopulation, and specimens from Papua New Guinea and the Northern Great Barrier Reef as Nautilus pompilius PNG/GBR subpopulation, despite being fully aware that these populations do not form part of the species Nautilus pompilius as currently defined (Saunders et al. 2017). Although no genetic data are available for specimens from the Solomon Islands, they may form part of the PNG/GBR subpopulation due to their geographic closeness and lack of deep-water barriers.

This species is assessed as Data Deficient because although this species could be highly susceptible to fishing pressure, there is currently no reliable well-documented evidence as to the level of fishing activity or to current population sizes.

Unverified reports and drift shells are known from the Chesterfield Reefs, Coral Sea Islands and off the Great Barrier Reef (Ward 2008), but this species is probably endemic to New Caledonia and the Loyalty Islands (House 1987) and the range map is based on the limited data currently available. Shells found in a cenote in the Loyalty Islands were aged at ~6,800 years old (Landman et al. 2014). Molecular phylogenetic work indicates that allopatric populations of the congeneric species Nautilus pompilius represent distinct phylogenetic species (Bonacum et al. 2011) so a restricted distribution for this species is not unreasonable. This species occurs in depths to 800 m and is found as shallow as 20 m in some areas off southern New Caledonia (Jereb 2005).

The population size for this species is not known, but the sex ratio of nautiluses generally is known to be highly biased in favour of males, with typically only 25% of any given nautilid population being female (Saunders et al. 1987). The recorded sex ratio of individuals in east Australia was 83 male:17 female (Dunstan et al. 2011a). A high male sex ratio has also been recorded in the Philippines (Haven 1977), Palau (Saunders and Spinosa 1978) and Papua New Guinea (Saunders et al. 1991). Individuals of other nautilus species have been tracked using radio telemetry (Dunstan et al. 2011c) and mark and recapture (e.g., Saunders et al. 1987) studies. These have found that animals move up to 3 km per day, with mean movement rates of about 1 km per day. Longer distant movements have also been recorded with animals recaptured up to 150 km from their release site. This suggests that subpopulations extend over a large area even though the population size might be small.

Nautiluses live on the steep sides of coral reefs and adjacent substrates (Jereb and Roper 2005, Saunders and Ward 2010). They are probably best characterised as mobile bottom-dwelling fore-reef scavengers and opportunistic scavengers (Jereb and Roper 2005, Saunders and Ward 2010, Dunstan et al. 2011a); they will also take small crustaceans such as crabs. They themselves are preyed upon by sharks and other fishes and, in some regions, by octopuses that drill into the shell (Saunders et al. 1991). Attacks from triggerfish and groupers have been observed on numerous occasions (Saunders et al. 2011). A maximum of ten eggs are laid per batch, and experiments in aquaria have indicated that eggs take more than a year to hatch (Barord and Basil 2014). Juveniles hatch at 25–30 mm diameter growing to 6 or 7 cm diameter within a year. Whilst most research has been conducted on Nautilus pompilius sensu lato, it is likely that all species have similar longevity (15–20 years) exhibiting slow growth and slow fecundity. Dunstan et al. (2011b) suggest, as have others previously, that these characteristics make nautiluses particularly vulnerable to over-exploitation. The coral reef habitat in New Caledonia has been impacted in places by mining activities which dominate economic production in New Caledonia (David et al. 2010).

Slow growth, low fecundity and the uneven sex-ratio of Nautilus species make them susceptible to overfishing even where levels of exploitation are relatively low. Hence Nautilus macromphalus is potentially threatened by fishing activity, but the extent of the current fishing pressure on the population is not documented. The reef habitat of N. macromphalus is threatened by degradation (particularly siltation) due to mining activities (David et al. 2010). It may also be threatened by future climate change.

Nautilus macromphalus is taken mostly by artisanal fishers (Jereb 2005) and the shells are sold locally. Anecdotal reports of fishing pressure conflict by as much as an order of magnitude, with estimates for take for 1998 and 1999 varying between 1,000 and 10,000 shells (Aguiar 2000). Trade in Nautilus has been known for at least 150 years, with Bennett (1859) reporting that "A vessel arrived at Sydney from New Caledonia with several tons of these shells, which were disposed of as an article of trade to the Navigator [Samoa] and Friendly islands [Tonga]". In 2006, mining accounted for 94% of export values, providing 11% of GDP. Fisheries and aquaculture by comparison accounted for 0.3% of GDP (David et al. 2010) with Nautilus production apparently insignificant.

The CITES trade database (CITES 2020) reports trade statistics to genus only, but does indicate the exporter and the origin of the wildlife. Only one nautilus was listed as exported from New Caledonia 2017–2019, although nine other specimens were traded by other countries with their origin listed as New Caledonia.

There are no current conservation actions for this species, however, UNESCO listed the "Lagoons of New Caledonia: reef diversity and associated ecosystems" on the World Heritage List in July 2008. Although nautiluses are not found in the lagoons themselves, the increased management and environmental awareness is likely to have a positive impact on Nautilus habitat and conservation. The family Nautilidae was listed under CITES Appendix II in 2017 and includes all Nautilus and Allonautilus species. Monitoring of population trends, harvest trends and trade trends is required. Habitat monitoring is also required.