“Tiger sharks will sink if they stop swimming.”

“If you look at the nurse shark and the tiger shark, this belief is already proven false: these, and a few other shark species, can stop swimming whenever they want. They breathe by way of buccal pumping, actively ‘inhaling’ water by using cheek muscles to draw it into the mouth and over the gills. This allows sharks to stop moving but continue breathing… Most kinds of sharks, then, won’t die if they stop swimming.”

“The tiger shark (Galeocerdo cuvier) is a large, apex predator… Tiger sharks are known to rest on the bottom like many other large requiem sharks. Individuals have been observed lying motionless on the seafloor for extended periods, indicating that they are capable of buccal pumping and do not need to swim continuously to ventilate their gills.”

“For two reasons, says James Kitchell, professor of zoology at UW–Madison. First, sharks lack the swim bladder that most fish use to adjust their buoyancy. Swimming creates lift that prevents sharks from sinking… Sharks, however, use a ramjet ventilation system that requires them to swim to force water to the gills. However, nurse sharks do have mechanisms to move water through their gills, and thus do not need to swim constantly to ‘breathe’.”

“Sharks have two methods of breathing… The second method is called ‘buccal pumping’… Many of these sharks make obvious use of this technique by lying completely still on the seabed, sucking water in through spiracles… So, while most sharks will be 100% fine if they stop swimming, a few iconic species such as great white sharks, whale sharks, hammerheads and mako sharks would suffocate without forward motion or a strong current flowing towards their mouths. In answer to our titular question – NO, most sharks will not drown if they stop swimming.”

“Sharks don’t have a swim bladder, so they need to sleep on the sea bed or on support structures, such as reefs, as they aren’t naturally buoyant. This ensures that they won’t sink… Certain species of sharks, like great whites and hammerheads, will actually drown themselves if they stop swimming. However, other species, such as nurse sharks and tiger sharks, don’t suffer the same fate… In buccal pumping, nurse sharks can let in water using their cheek muscles, then draw it into their mouths and push it toward the gills. This allows the sharks to stop moving, but keep breathing.”

“The tiger shark is one of the largest shark species. Like other sharks, it does not have a swim bladder and is slightly negatively buoyant. Its large, oil-rich liver provides some lift, but when the shark is not swimming it will gradually sink unless supported by the bottom or another surface.”

“Do sharks have swim bladders like other fish? No. Sharks lack swim bladders and instead rely on their large, oil-filled livers for buoyancy. … Because they lack swim bladders, sharks cannot hover motionless in midwater like many fish. If they stop swimming, they gradually sink.”

“Elasmobranchs don’t have a swim-bladder, and they must find other ways to regulate their buoyancy; this is achieved via several methods. The primary aspect that gives sharks and rays buoyancy is a large liver filled with low-density oil… It is not only liver oil that gives elasmobranchs buoyancy and several factors contribute to over-all lift. … One shark that uses air gulping to an entirely different end is the sandtiger shark (Carcharias taurus). Sandtigers gulp air at the surface, holding it in their stomachs … This retention of air allows the shark to hover almost motionless at a depth of its choosing.”

The post aggregates scientific literature on which shark species are obligate ram ventilators (those that must keep swimming to breathe). In the excerpts cited, bull sharks are described as showing “continuous swimming as well as some resting behavior,” and it notes that “the oxygen supply capacity at rest was not enough to support energetic demands at rest… The use of buccal pumping (active ventilation) was not a sustainable or likely hypoxic coping strategy for either species.” Tiger sharks are not listed among the obligate ram ventilators in the compiled literature, implying they do not strictly require continuous swimming for oxygen.

“The amount of gas in the swim bladder enable fish to control their ability to ‘float’ and ‘sink’ in the water column. … Cartilaginous fish, like sharks and rays, do not have swim bladders to give them buoyancy.”

“Sharks Don’t Have Swim Bladders—Here’s Why. Unlike bony fish, sharks are cartilaginous fish, meaning their skeletons are made of cartilage, not bone. Because sharks lack swim bladders, they cannot simply ‘float’ in the water column. Instead, most species must keep swimming to maintain their depth, or they will slowly sink.”

“Buoyancy: Like other carcharhinid sharks, the tiger shark has a large liver filled with low-density oils that provide buoyancy, but it is still slightly negatively buoyant and will sink slowly if it stops swimming. Resting behavior: Tiger sharks have been observed resting on the seabed, indicating that they can maintain respiration while stationary, probably through buccal pumping and favourable currents.”

In reporting on tag data from juvenile sand tiger sharks, the Aquarium notes: “Using acceleration and depth data that were collected from eight juvenile sand tigers within PKD Bay during summer 2011, we determined the sharks spent the majority of their time slowly swimming near the bottom of the bay, but swam more actively and toward the surface at night.” It adds, “They even spent some time resting motionlessly on the bottom!” This shows that at least some large, negatively buoyant shark species can rest motionless on the bottom instead of sinking uncontrollably when they stop swimming.

“Most sharks are ‘negatively buoyant,’ meaning they tend to sink rather than float. They compensate for this in two ways: They have a large liver filled with oil that provides some buoyancy, and they generate lift with their pectoral fins as they swim. If a shark stops swimming, it will slowly sink, although some bottom-dwelling species can rest on the ocean floor.”

“Sharks and rays are negatively buoyant, meaning that if they stop swimming, they will sink. They do not have a swim bladder like many bony fishes. Instead, they stay afloat with the help of large, oil-filled livers and the lift generated by their bodies and fins as they swim.”

Discussing swimming and energy use in sharks, the article notes that some species such as shortfin mako sharks have very high oxygen demands and are adapted for continuous, fast swimming: “This means that to swim continuously, and at high speeds, these sharks need to be energy efficient… their oxygen consumption while swimming is more efficient than that of most other species because they have some of the highest oxygen demands of all sharks in the sea.” By contrast, it describes other shark species (e.g., deep-sea sharks) as generally slow-moving and not constantly swimming at high speed, underscoring that continuous swimming is not a universal requirement for all shark species.

At 02:46–02:53 the narrator states: “Contrarily, sharks don’t really have swim bladders and they’re also negatively buoyant. This means that they’re heavier than the weight of the water that they displace which means that they’ll naturally sink.” Later, at 04:24–04:32: “Sharks such as great whites can’t use buccal pumping [and] continue to move so as to get oxygen into their systems… on the other hand, there are other sharks that don’t have to necessarily move in order to maintain their oxygen supply.”

In general marine biology descriptions, tiger sharks (Galeocerdo cuvier) are described as negatively buoyant, like most pelagic sharks, because they lack a swim bladder and depend on an oil-rich liver and hydrodynamic lift from swimming. Standard accounts note that if a tiger shark stops swimming in open water it will gradually sink, although, like other large coastal sharks, it can rest on or close to the seafloor in shallow areas.

“It’s a widespread belief: if sharks stop swimming, they die. But is that actually true?… If you look at the nurse shark and the tiger shark, this belief is already proven false. These and a few other shark species can stop swimming whenever they want… This allows sharks to stop moving but continue breathing… Most kinds of sharks then won’t die if they stop swimming.”