Nautiluses reproduce through internal fertilization, with males transferring sperm to females using a specialized organ called the spadix. The entire process, from mating to a fully hatched juvenile, is remarkably slow. These animals take 10 to 15 years to reach sexual maturity, produce only a small number of large eggs, and those eggs need at least a year of incubation before hatching. Among cephalopods (the group that includes octopuses and squid), nautiluses have one of the most drawn-out reproductive cycles in the ocean.
Finding a Mate
Nautiluses live in deep water, typically between 150 and 700 meters, which makes observing their mating behavior in the wild extremely difficult. Most of what scientists know comes from aquarium settings and, more recently, from baited underwater cameras placed on the seafloor. What these observations reveal is a surprisingly unselective approach: males attempt to mate with any nautilus they encounter, regardless of sex. Females, by contrast, are attracted to males but actively avoid other females.
The general sequence starts with feeding. When nautiluses gather around a food source, they eat first and then turn their attention to potential mates. In at least one population (Nautilus belauensis in Palau), males perform a courtship behavior where they curl their tentacle tips along the back of another nautilus’s shell before mating. This tentacle-curling appears to be a prelude to copulation, which happens tentacle-to-tentacle. Scientists describe the overall strategy as “trial and error,” with males initiating contact broadly and mating succeeding when a receptive female is involved.
How Sperm Transfer Works
Male nautiluses use a structure called the spadix to transfer packets of sperm (spermatophores) to the female. The spadix is a modified group of tentacles that functions similarly to the hectocotylus found in octopuses and squid, though it’s a distinct structure unique to nautiluses. During mating, the male positions himself tentacle-to-tentacle with the female and passes the spermatophores directly. The female stores the sperm internally and uses it to fertilize her eggs.
Egg Laying and Incubation
Female nautiluses lay relatively large eggs compared to most cephalopods. Each egg is enclosed in a tough protective capsule that can reach about 45 mm (nearly 2 inches) in length. Females attach their eggs to hard surfaces on the seafloor, and the number of eggs per clutch is small, especially when compared to an octopus, which can lay thousands or even hundreds of thousands of eggs at once.
The incubation period is exceptionally long. According to NOAA, nautilus eggs require at least a year to develop, making them among the slowest-developing cephalopod embryos known. Water temperature plays a major role in how quickly embryos grow. In cephalopods generally, warmer water within a species’ tolerable range speeds up development, while cooler water extends it. Temperatures at the extremes of what embryos can handle cause deformities, poor hatching rates, and weak hatchlings that don’t survive long. For nautiluses, which live in relatively cool deep water, the cold environment contributes to their prolonged incubation.
The large, yolk-rich eggs are part of what makes incubation so slow. Across cephalopods, bigger eggs with more yolk consistently take longer to develop than smaller ones. Nautilus eggs are among the largest in the group, and the embryo gradually absorbs the yolk over many months as it builds its shell and body.
What Hatchlings Look Like
When a nautilus finally hatches, it emerges as a miniature version of the adult, already equipped with a small chambered shell. Unlike many marine invertebrates, there is no larval stage drifting in open water. The hatchling is fully formed and begins life on or near the seafloor, adding new chambers to its shell as it grows. Growth is slow: immature nautiluses add shell at an average rate of about 0.06 mm per day, which means it takes roughly 15 years for a hatchling to reach adult size.
Sexual Maturity and Size
Nautiluses reach reproductive maturity at around 10 to 15 years of age, when their shells measure roughly 5 to 9 inches across. There’s notable sexual dimorphism: males tend to be larger than females. In one well-studied population at Osprey Reef in the Coral Sea, mature males averaged about 132 mm in shell diameter while females averaged about 119 mm. Mature size varies widely between populations across the Indo-Pacific, ranging from 115 mm to 240 mm depending on the species and location.
Populations tend to be dominated by mature adults. At Osprey Reef, 58% of captured nautiluses were fully mature, which reflects the long time spent growing before reproduction begins and the relatively long adult lifespan once maturity is reached.
Why Reproduction Makes Nautiluses Vulnerable
Every aspect of nautilus reproduction points to what biologists call a K-selected life history: slow growth, late maturity, low fecundity, and long lifespan. This is the opposite of species that reproduce quickly and in large numbers to offset high mortality. A female nautilus invests heavily in a small number of large, slow-developing eggs rather than flooding the water with thousands of tiny ones.
This strategy works well in a stable deep-sea environment with few predators, but it makes nautilus populations extremely sensitive to overharvesting. When adults are removed faster than juveniles can mature and replace them, populations decline and recover very slowly. This vulnerability is a major reason the chambered nautilus was added to the Convention on International Trade in Endangered Species (CITES) in 2017, restricting the international shell trade that had been driving population declines across Southeast Asia and the Pacific.