Cephalopod Soup: An Underwater Phenomenon

Mother Nature is a master of the sleight of hand. Take the shallow waters off the San Diego beach known as La Jolla Shores, for example. With average visibility in the 15- to 20-foot range and a featureless sand bottom at a depth of 30 feet (9 m), it’s not much of a dive. But look again and you’ll see California’s marine life in all its glory — harbor seals, California sea lions, bat rays galore, Pacific angel sharks, horn sharks, guitarfish, thornback rays, California spiny lobsters, sculpin, ling cod, black sea bass, a variety of rockfishes, sea stars and a whole lot more. You might see the majority of these creatures on a single dive, as this normally barren sand patch magically becomes an underwater oasis teeming with life. During the winter months massive numbers of common squid invade waters at “The Shores” and the adjacent slopes and walls of the La Jolla Submarine Canyon. When the squid, also known as market squid, invade there is no telling what you’ll see.

During “squid runs,” as these massive gatherings are known, it is absolutely impossible to count the squid as “bazillions” of these foot-long mollusks fill the water column. And even when conditions create visibility that exceeds 40 feet (12 m), your field of view is often restricted to 10 feet (3 m) or less because of the density of the squid. I know this sounds like a bit of hyperbole, but those who have dived during heavy squid runs know I am reporting the truth. When Mother Nature works her magic and the squid runs are “on,” there is no better diving anyplace.

Beyond Calamari

Scientists have described more than 110,000 species of mollusks, a grouping of animals that includes the market squid (Loligo opalescens) as well as all other squids. The phylum Mollusca also includes nudibranchs, sea slugs, snails, sea hares, clams, scallops, oysters, mussels and octopods. Many of these creatures possess a hard, external shell, some type of internal shell or the remnants of a shell, but in the cephalopod mollusks — the squids, cuttlefishes and octopods — the shell is greatly reduced or even missing. As is the case in cuttlefishes, the shell in squids is relatively small and internal. Octopods have given up their shell altogether in exchange for other means of defenses.

Worldwide there are more than 600 species of cephalopod mollusks, and all are marine animals. Many specialists consider cephalopods the most intelligent of all invertebrates. The term “cephalopod” is derived from the Greek words for “head” and “foot,” and knowing that, it probably doesn’t come as much of a surprise to discover that the heads of these mollusks are rather prominent. The foot has been greatly modified into sucker-bearing arms that assist in grasping and holding onto prey. While most octopods are bottom dwellers, cuttlefishes and squids primarily inhabit the water column where they prey predominantly upon fishes, and certainly that is the case in the market squid that at times invade sandy shallow bottoms and marine canyon areas in coastal areas of central and Southern California. This same species is also known to gather and mate in bays and coastal areas in Peru, Brazil, Nova Scotia, parts of Polynesia and Brazil, Spain, Japan and many other locales ranging from the Gulf of Mexico to the Gulf of Thailand.

As is the case with other cepha-lopods, market squid have large, rather complex nervous systems. Cephalopods have the most highly developed and complex brains of all invertebrates, and the relative size of their brain is often larger than that of fishes. Much of that size is attributed to two large optic lobes, features that testify to the importance of vision in these very active, open-sea hunters. In fact, squid eyes share many characteristics with the eyes of humans, and the eyes of market squid and other species are used in teaching and research. The relatively large nerves of squids are also used in the study of multiple sclerosis and other nerve-related ailments.

Like other squids, common squid possess eight arms and a pair of longer head appendages called tentacles. The tentacles are especially well-designed for capturing prey in the open sea as the edges of the suckerlike discs found on these “elastic” appendages are lined with a hardened material called chitin that is similar in nature to human fingernails. The chitinous rings look like teeth, and they are made to grasp prey once the suckerlike disc touches the victim.

When hunting, squids tend to face their prey as they move forward. The arms curl back around the hunter’s head as the attack begins. From a distance that is usually greater than the length of the body of the squid, the tentacles are rapidly thrust forward and these armed clubs strike the prey. In a successful attack, as the extended tentacles recoil, the numerous small hooks on the tentacles pierce the flesh of the victim, ensnaring the prey. The tentacles quickly drag the victim back toward the eight arms that further ensnare and rip into the prey. If the prey is a fish, the squid will bite the victim with its beaklike radula breaking the fish’s spine. If the victim is a shrimp or other shelled creature, the radula will be used to penetrate the shell. When a squid bites, it also delivers an immobilizing toxin that affects nerve cells and motor muscles of its prey, and once the prey is sufficiently subdued the squid will consume its unfortunate victim.

The ability of many cephalopods to emit a blast of ink is well-known, and it is not uncommon to see market squid emit a cloud of ink when a predator is pursuing the squid. Sometimes the ink is shaped somewhat like the shape of a squid body. The ink cloud is known as a pseudomorph, or “false body,” and it is theorized that the shape is intended to fool a predator into attacking the ink cloud as the squid makes a hasty escape. The ink also contains chemicals that irritate the eyes, dull the sense of smell and inhibit the ability of predators to maintain their orientation and balance.

Jet propulsion is a hallmark of torpedo-shaped squids and other cephalopods. All squids can swim forward, backward and sideways with equal rapidity as they “jet propel” themselves by squirting powerful streams of water through a highly directable opening called a siphon. They also use their tail fins for added thrust. Sometimes market squid hover almost motionless in the water column, but within the blink of an eye they can be at full speed and have darted several yards away.

Colorful Courtship

Common squid normally travel and live together in schools that inhabit the deep waters of the open sea where they play a major role in the lives of many pelagic creatures as part of the food web. Stomach content analyses reveal that blue sharks, pilot whales, billfish, tunas and many more open fishes prey heavily upon these squid. But when common squid gather to mate and lay their eggs they do so in much shallower surroundings.

Heavy runs involving millions upon millions of squid can last a month or longer.

Though this belief has come into question in recent years, many specialists believe that market squid only live for one year, just long enough to reach sexual maturity and reproduce. There is no question that during mating runs the adults are driven by strong instincts that encourage them to mate, and the mating action is rather frenetic. Most mating takes place at night. Courtship and copulation are accompanied by rapid flashes of color as the adults pulsate in dazzling displays. Body colors rapidly change from creamy white to deep purple, red, green and brown via the use of prismlike cells known as iridocytes.

When a male latches on to a female, his tentacles often blush scarlet and his arms are curled, a message that many specialists consider a warning to other males.

Females also swim energetically while flashing colorful signals believed to communicate their eagerness to mate. During copulation the male quickly and adeptly passes a packet of sperm underneath the mantle (the part of the animal where all of the organs are located) of the female by using an arm known as a hectocotylus. The female uses the sperm packet to fertilize her eggs, and she soon looks for just the right spot to plant her egg casing, which is about six to 10 inches (15 to 25 cm) long and contains roughly 200 squid eggs.

In U.S. waters mating runs of market squid commonly occur in Monterey, California, as well as the Channel Islands and along the coast of Southern California in places like La Jolla Shores where a sandy bottom is near deep water. In many of these areas during heavy runs the egg casings are so densely packed that they obscure the sea floor as the once brownish bottom is transformed into a creamy white, shag carpet of egg casings. After five to seven days, you can see the bright red eyes of the unhatched young within the translucent casings. In another seven days or so, the eggs will hatch and the newborn mollusks instinctively head for deep water. But only a few of these embryonic creatures will survive long enough to reach adulthood and reproduce. The squid are heavily preyed upon by a wide variety of carnivorous fishes and crustaceans from the moment the fingernail-sized young hatch.

The Food Chain in Action

Very soon after mating the dazzling color displays slow considerably and then cease, and the squid take on a sickly looking appearance. Their once brilliant bodies turn a pallid hue and their tentacles become grossly disfigured. All throughout the runs the sea floor is a stew of freshly planted egg casings and dead and dying adults. The demise of the adults attracts a diversity of scavengers and predators that come to gorge themselves. Interestingly, the seemingly vulnerable egg cases are not heavily preyed upon. Some specialists suspect that this is due to the presence of proteins that prove repulsive to predators.

It is not uncommon for divers to encounter normally wary bat rays that have eaten so many squid that they rest in a comatoselike state on the sea floor. Those bat rays that can still swim are often so listless that they bump into divers’ lights and then settle down to the sea floor next to the diver instead of bolting away. Horn sharks, angel sharks and many other predatory fishes are commonly seen as they rest on the sea floor trying to digest their food — often with partially eaten squid and squid parts dangling from their mouths.

Lobsters, crabs, sea stars, sea urchins and snails leave the protective crevices of nearby reefs to forage on the dying adults, and near the surface a variety of sea birds commonly join in to pursue the squid. But even with all of this feeding activity, in some places the bodies of dead and dying squid stack up on top of one another in piles a foot thick or thicker.

High up in the water column the feast continues for sea lions and harbor seals that prey upon the still-living adults. At times, pilot whales and blue sharks join the fray. Blue sharks rarely venture so close to shore in shallow waters, but the allure of so much food draws these open-sea sharks into the shallows to feed.

On the Run

There is no way to tell how long a squid run will last. Sometimes the runs last for more than a month, and other times for only a few days. If you have the chance, whatever time you might spend diving in a squid run is guaranteed to provide incredible insight into the fascinating inner workings of the marine kingdom and provide some diving memories that will last a lifetime.


No thank you, I couldn’t possibly….

During the late 1970s, while working on a film for the National Geographic Society about sharks, I made a series of night dives during a squid run at California’s Catalina Island, and during that shoot we hit the mother lode of all squid runs. Market squid, as their name implies, are heavily sought after by commercial fishermen. During that shoot the squid were so numerous that several dozen commercial boats were catching their daily 10-ton limits within two or three hours. With so many squid it wasn’t surprising to also encounter a lot of blue sharks that came to feast, which was exactly what we were hoping to film.

The lights of our boat attracted the squid and at times we could see more than a dozen blue sharks feeding under the boat. We entered the water with our cameras rolling, and as far as we could tell our presence in the middle of the fray didn’t phase the sharks at all. They swam through the squid mouth agape, literally stuffing themselves with squid. It was a common sight to see lethargic sharks swimming around with half-eaten squid hanging out of their mouths — they simply couldn’t swallow another bite.


Timing is Everything

Squid runs are somewhat predictable. In central California the runs generally occur during the fall and early winter. As you move toward Southern California, the runs tend to occur during the winter and occasionally into the early spring. Not easy to predict is exactly where the squid will choose to gather, at what depths and whether the weather and water conditions will be favorable.

Sometimes the squid mate and lay their eggs over bottoms that are just deeper than 30 feet (9 m) below the waves, and the action can be heavy from 30 to 130 feet (9 to 39 m). Other times the squid gather off the same beaches but all of the mating and egg-laying activity occurs in water that is deeper than safe sport diving allows. And as is the case with all natural phenomena, the intensity and duration of the runs varies considerably.


Tips to Remember

For some divers, the idea of descending into a squirming soup of dying squid and frenzied predators is sheer madness. Others might look upon it as an exciting opportunity to witness the marine realm in action. If you’re up for it, diving a squid run can indeed be rewarding. Here are a few tips for safe “squid running”:

Find out what the pros know. Most central and Southern California dive operators can clue you in to when and where the squid are running. Inquire about guided trips.

Make sure your skills are up to par. If you aren’t experienced in night or low-visibility diving, consider getting advanced or specialty training.

Evaluate and respect the weather. Even if the squid are running, the weather and sea conditions might not be right, so don’t push it.

Lighten up. If you’ll be diving at night, be sure to have the appropriate primary and backup dive lights. Keep in mind that your dive light acts as a “squid magnet.” If you become uncomfortable with the numbers of squid surrounding your light, cover it for a few seconds and the action will dissipate.

Stay close. To avoid becoming lost in the fray, you and your buddy should plan to remain within reach of each other.

Monitor your gauges. Even though you might be sitting motionless on the bottom for most of the dive, in the excitement of the squid run you’ll likely burn air more quickly than you realize.

Don’t be afraid to back out. After the initial shock of so much activity all around you, it’s likely that you’ll enjoy the excitement, but you and your buddy should agree ahead of time that it’s OK to abort the dive if either of you feel uncomfortable.

Story and Photos by Marty Snyderman