Oarfish aren’t necessarily rare in the way most people assume. They live in one of the least explored parts of the ocean, hundreds of meters below the surface, where humans almost never go. The handful of sightings we get each year, usually sick or dead animals washing ashore, create the impression of extreme rarity. But the truth is more nuanced: we simply have almost no way to observe or count them in their natural habitat.
They Live Where We Can’t Easily Look
Oarfish spend their lives in the mesopelagic zone, a band of open ocean roughly 200 to 1,000 meters deep where sunlight doesn’t reach. This layer sits between the sunlit surface waters (where familiar fish like sardines and anchovies live) and the deep ocean floor. NOAA describes the mesopelagic as “probably the least explored part of the ocean,” and that’s key to understanding oarfish rarity. It’s not the pitch-black bottom that gets explored by submersibles and remotely operated vehicles. It’s a vast, featureless middle zone with no seafloor landmarks to attract research missions.
Animals in the mesopelagic often migrate vertically, rising toward the surface at night to feed on plankton and krill, then descending during the day to avoid predators. Electronic tagging of other deep-diving species like swordfish and bigeye tuna has shown that many fish routinely descend to 300 to 400 meters daily. Scientists long underestimated how much life moves through this vertical column, and oarfish are part of that hidden community. There’s strong evidence that oarfish rise toward shallower water to spawn, which may be one of the few times they come close enough to the surface for anyone to spot them.
Sightings Are Almost Always Dead Fish
When oarfish make the news, it’s nearly always because one has washed up on a beach or been found floating at the surface. A specimen that washed ashore in California made headlines partly because it was only the 20th oarfish documented on California’s coast since 1901. That’s roughly one every six years across the entire coastline of a major U.S. state.
In the rare instances oarfish are seen in shallow water alive, they’re typically sick, dying, or caught in strong currents that pushed them out of their normal depth range. Healthy oarfish have little reason to approach the surface during daylight, so live encounters are extraordinarily uncommon. Most of what scientists know about oarfish anatomy and biology comes from necropsies of stranded specimens, and researchers at Scripps Institution of Oceanography have noted that each one represents a valuable and unusual opportunity for study.
Their Body Isn’t Built for Easy Study
Oarfish are the longest bony fish in the ocean, with a maximum reported length of 36 feet, though most are closer to 10 feet. Despite their impressive size, their bodies are fragile and ribbon-like. They lack the heavy musculature of open-water predators, and their long, thin profile makes them poor candidates for conventional fishing nets or tagging equipment. They don’t school in dense groups. They don’t congregate around reefs or seamounts where researchers could reliably find them.
Their swimming style is also unusual. Oarfish appear to spend much of their time oriented vertically in the water column, head pointed toward the surface and tail hanging down. In this position, their long dorsal fin provides propulsion. Scientists believe this posture allows them to spot the silhouettes of prey items above them. They’re filter feeders that use protrusible mouths to suck in plankton, small squid, fish, and tiny crustaceans, then strain them through gill rakers. This solitary, drifting lifestyle spread across vast stretches of deep ocean means individual oarfish are scattered thinly and hard to locate.
We Know Almost Nothing About Their Numbers
No reliable population estimate for oarfish exists. The mesopelagic zone is enormous, spanning most of the world’s oceans, and surveying it for a single species that doesn’t aggregate is essentially impossible with current technology. Oarfish could number in the tens of thousands or far more, and we’d have no way of knowing. Their absence from scientific data doesn’t reflect actual scarcity so much as the limits of deep-sea observation.
Even their reproductive biology is barely understood. One research team in Japan managed to artificially inseminate oarfish eggs using a recently dead pair of mature fish caught in a set net. The larvae behaved unusually, spending more than half their time in a downward-facing posture. Mature oarfish with developed reproductive organs have been found stranded at the surface, supporting the idea that they rise from the deep to spawn. But whether they spawn seasonally, year-round, or only under specific conditions remains unclear. Eggs have been identified near the Marshall Islands in summer and mature adults captured in Japanese waters in winter, suggesting the spawning window could be long.
Rare to Us, Not Necessarily Rare in Nature
The distinction matters. Some species are genuinely rare because their populations are small, their habitat is shrinking, or they reproduce slowly. Oarfish may face none of those pressures. They have no commercial fishing value, their deep-water habitat isn’t directly threatened by coastal development, and they aren’t targeted by any fishery. The real barrier is access: they live in a place humans rarely visit, in a posture and at a density that makes accidental encounters unlikely.
What makes oarfish feel so mythical is the combination of their enormous size and their near-total invisibility. A 36-foot fish that almost no living person has seen in its natural habitat is the kind of animal that fuels sea serpent legends. But the ocean below 200 meters is home to countless species we rarely see. Oarfish just happen to be the most spectacular one.