Taxonomy

Rarity

The California moray is common where it lives, but a diver has to know how to look. It is a nocturnal predator that spends the day tucked deep in a rocky-reef crevice with only its head showing, and it will not be swimming past a snorkeler in open water. A visitor to Catalina Island or a reef around La Jolla, San Diego, who slows down and peers into holes will find one soon enough. Researchers at UC Santa Cruz trapped and tagged 462 individuals in a few weeks at Two Harbors, on Catalina, and a follow-up study at the Blue Cavern marine protected area recorded 1,736 captures of 1,336 individual eels between 2015 and 2018. The IUCN listed the species as Least Concern in 2011. It is not commercially fished and is only rarely caught by pier anglers. It faces no known population-level threat beyond general habitat degradation. A diver who does not look into the holes will not see one, even on a reef that holds many.

Seasonality

Location

The California moray is the only member of the moray family that lives north of Baja California. Its range runs from Point Conception, Santa Barbara south through the coast of Baja California to Magdalena Bay, and the species has also been recorded around the Galapagos Islands. Population density is highest around the Southern Channel Islands and Catalina, and Catalina is where most of the research on the species has been done.

Adults live inside cracks and holes in rocky reefs and boulder fields, from tide pools down to about 130 feet, most often shallower than 65 feet. Juveniles use tide pools before moving deeper as they grow. The reef is home in a literal sense. A recent tracking study reported that adult California morays have high site fidelity, meaning they stay in the same general area throughout their adult lives. A moray a diver photographs in a particular hole is likely to be found there again, or in a hole next door, in later summers.

The range limit is where the biology gets strange. The California moray is a warm-water fish living at the cold end of what its family can tolerate, and a hypothesis in the recent literature is that morays in Southern California do not reproduce there at all, because the water is too cold for the eggs and larvae to develop. Instead the spawning takes place in the warmer water off Baja California. The larvae, called leptocephali, are transparent and shaped like willow leaves. They drift north on currents for as long as a year before settling to a reef. More young morays settle on California reefs in El Niño years, when the water off the coast warms. The moray in a Catalina crevice may be a fish that started life in Mexico and washed up as a larva.

Deep Dive

The first thing to know is that the California moray is breathing. A moray with its mouth open and closing steadily, showing its teeth, is not warning off the diver in front of it. Morays lack the bony gill covers that most fish flare to pump water past their gills, so they have to open and close the mouth over and over to move water in and out. This gives every moray a look that reads as menacing to a person, when the fish is only breathing. The species is not aggressive by default. It sits in its hole with its head out because that is how it breathes and watches for prey, and it stays there while divers photograph it from a foot away all day long.

The animal is built for the crevice life. It has no scales, no pectoral or pelvic fins, and no visible sensory row along its side that most fish have, called the lateral line. A thick yellowish mucus coats the skin and protects it from scraping along rough rock. The eyes are small and the eyesight is poor, and the moray navigates and hunts almost entirely by smell. It grows to about 5 feet long. The largest documented individuals are believed to live 22 to 26 years. Some estimates push past 30. Growth is slow, and a large moray in a diving spot is a fish that has been there for a long time.

At night the California moray leaves its hole and hunts. It is a serious predator on the kelp reef, and its diet has been studied in unusual detail thanks to the Mehta Lab at UC Santa Cruz. A 5-year study at Two Harbors, on Catalina, found that kelp bass accounted for about 64 percent of prey items recovered from trapped morays. The animal is a kelp-bass specialist that fills in with octopus, spiny lobster, small crabs, red rock shrimp, sea urchins, and small reef fishes when the chance comes up. Larger morays drop the smallest prey out of their diet and add larger prey, so a 4-foot moray hunts a different reef than a 2-foot moray in the same cove. Cannibalism, moray on moray, has been recorded, but only during the 2015 warm-water year and the year after. A follow-up study inside the Blue Cavern marine protected area found that protected morays were larger, more abundant, and more strictly specialized on kelp bass than morays living outside the boundary.

The most striking thing about how a moray eats is not visible from the outside. The moray, like the other members of its family, has a second set of jaws deep in its throat. That second set is small and mobile, with its own teeth, and when the moray bites into a struggling fish with its front jaws, the throat jaws shoot forward into the mouth, clamp onto the prey, and drag it back down the throat. Biologists Rita Mehta and Peter Wainwright described this throat-jaw system in detail in a 2007 Nature paper, working with a related tropical moray. It is the first case ever documented in a vertebrate of a second set of jaws that both restrain and swallow prey. The reason it evolved is practical. Most bony fish suck prey in by opening the mouth fast and pulling in a rush of water, but a moray inside a narrow crevice has no space for that. So the moray bites, and the throat jaws haul the meal in, in a ratcheting motion that biologists have compared to the way a snake swallows.

The bite is where the moray earns its reputation. The plain version of the story is this: California morays are not venomous, and they do not seek out divers. When a bite happens, it is almost always because a diver reached blindly into a hole where a moray was sheltering, or because a diver was hand-feeding fish and the moray, which sees badly and smells for food, could not tell the bait from the hand. Bites are described in the medical literature as deep puncture wounds prone to infection from bacteria in the moray's mouth. In the wild, at rest, the fish is docile. Reef dive operations at Catalina and elsewhere routinely photograph the same individuals year after year. Some morays are identifiable to local guides by scars and coloring. The Mehta Lab's research program depends on the same fish being in the same crevice season after season. Almost every recorded bite comes from a hand pushed blindly into a moray's hole, or from a diver offering food by hand. A diver who avoids both is left alone.

There is a different side to the moray, and a snorkeler at the right site can see it. The California moray keeps company with a small red shrimp called the red rock shrimp, which cleans parasites and dead skin off the moray in exchange for a safe home in the moray's crevice. During a cleaning the moray opens its mouth and lets the shrimp pick at its teeth.