Danger Underwater

Stay aware and take precautions to avoid potential attacks by sea life.

danger underwater

Contrary to what you see in the movies, sharks, barracudas, giant octopuses and other dangerous creatures aren’t always lurking in the ocean waiting to launch a fatal attack on divers. Such incidents are relatively rare; divers are more likely to suffer a painful sting from a jellyfish or to get entangled in a kelp forest.

However, there is a potential for injury from sea creatures that divers should not ignore. Before they enter the water, they should learn everything they can about the dive area’s ocean life and be prepared to avoid or deal with the results of any encounters.

Dangerous dive locales

The degree of danger from sea creatures varies by region.

When divers from Scripps Institution of Oceanography at UC San Diego are working off the coast of southern California, “The hazardous marine life we’re most often concerned with are stingrays and their defensive barb below their caudal fin, and sea urchins with their many sharp spines, which can be painful and can contribute to infection,” said Christian McDonald, diving safety officer.

Stingrays and jellyfish are equipped with stinging cells called nematocysts. Although these stings are often very painful, they are rarely fatal off the U.S. West Coast. The deadliest jellyfish species, the big box, lives in the tropical waters in the Pacific and the Indian Ocean.

Divers working in the Sea of Cortez off the Baja Peninsula may have to contend with the extremely aggressive Humboldt squid. “They’ve got little hooks on the suckers of their tentacles that will actually dig into flesh, and they’ve been known to attack divers,” said Jim Gunderson, director, Divers Alert Network (DAN) training. One researcher who is studying the squid “wears a suit of armor and looks like a Star Wars stormtrooper. His hoses for his unit are wrapped in metal so they cannot physically bite and cut off the hoses.”

The same species of animals may behave differently in one area than they do in another. Despite an increasing number of white juvenile sharks frequenting the southern California coast, most don’t bother divers. The last fatal white shark attack in the area took place about 15 years ago, said McDonald.

fire coral and similar plants


Fire coral and similar plants have nematocysts that can cause burns, irritation or inflammation. ISTOCK.COM/IFISH

But white sharks off the west coast of Australia are more aggressive. Scripps’ research partners in that area require divers to wear shark shields on their ankles, which deter attacks by emitting an electrical charge that disorients the sharks.

In remote sites in the Central Pacific, Scripps’ divers may have to contend with gray reef sharks and snappers. “We’ve been encouraged to get out of the water a few times while collecting small fish or grasses for analysis,” McDonald said. “But in general, they tend not to be that interested in what we’re doing.”

Divers should also learn to recognizes life forms in the ocean that look like harmless plants but are sessile organisms. Anemones, hydrozoans, fire coral and similar plants have nematocysts that can cause burns, irritation or inflammation.

The biggest danger divers face from actual ocean plants is entanglement. “In the big kelp forests in southern California, for example, and in other areas, you have long strands of bull kelp that grow incredibly fast and are incredibly strong. They’re very fibrous, and you cannot pull on them long ways and break them. When you get entangled in them, you have to start cutting your way out. That’s why all commercial and public safety divers carry at least one and ideally more than one cutting implement,” Gunderson said.

Protection and preparation

No matter how slight the danger from sea life appears to be, pre-dive briefings should cover the sea life that could sting, entangle, or otherwise harm divers and suggest ways to mitigate those risks.

Along the Pacific Coast, for example, where divers might encounter a stingray, lion mane jellyfish or Portuguese Man o’ War, they can wear long-sleeve shirts, gloves, a thicker wetsuit or drysuit, and a full facemask and/or helmet to reduce the chance of getting stung.

Scripps encourages its divers to do the “stingray shuffle” as they walk along the ocean floor, said McDonald. Stingrays strike when they are startled, so if divers make themselves heard by shuffling it gives the stingray the opportunity to swim away.

Fish like sharks, barracudas or jacks typically attack divers only when they’ve been antagonized or when they’re protecting something such as a brood of eggs. “I’ve had fish attack my fins, but then I realized there’s a brood of eggs nearby. I back off, and they go back to guarding their eggs,” said Gunderson.

Divers should never stick their hands into holes when they don’t know what’s inside. “It could be a stonefish or lionfish in there; they have venomous spines on their backs that will cause serious pain and potentially further injuries,” he said.

Gunderson advises divers approaching a big hole in a wreck not to go in at the center. “You always want to start on one side. If something’s in there and it wants to escape, you don’t want to block their escape,” he added.

The medical crew supporting divers should also be equipped to deal with possible attacks. Their kits should contain a pair of tweezers to remove any tentacles or spines (from a sea urchin, for example) as well as washing agents like saline and vinegar.

DAN offers a program, First Aid for Hazardous Marine Life, a component of the Diving First Aid Professional Divers (DFA Pro) first aid course, which teaches participants how to identify potentially hazardous marine life, how to avoid them, and how to provide first aid when injuries do occur. It covers techniques like pressure immobilization, which can mitigate the risk of a dangerous toxin (like venom from a cone snail) being pushed through the body before the diver can be taken to a hospital for more advanced care.

While divers might not face the deep-ocean dangers that Hollywood suggests, being prepared for the worst-case scenarios helps ensure that they will be able to deal with and survive almost every potential hazard.