Sharks are often portrayed in media as fearsome apex predators that strike terror into anything that crosses their path. However, even these mighty hunters of the ocean have their own fears and things that they avoid.
If you’re short on time, here’s a quick answer to your question: While great white sharks have few natural predators, most shark species do exhibit fear and avoidance behaviors towards things like dolphin aggression, novel objects, fishing gear entanglements, electric fields, and the bubbles from scuba diving equipment.
In this comprehensive guide, we’ll explore the main things that make sharks turn tail and swim, or exhibit overt signs of fear and anxiety. Read on to discover the surprising weaknesses behind the tough, toothy exterior of these magnificent creatures.
Fear of Predation from Killer Whales
Attacks on Great White Sharks
Killer whales (Orcinus orca), also known as orcas, are the only known natural predator of great white sharks (Carcharodon carcharias). Orcas have been observed preying on great whites in different parts of the world, inflicting deep wounds and even consuming the liver of great whites.
One famous incident occurred in 1997 off the Farallon Islands near San Francisco, where a group of orcas was witnessed attacking a great white shark. The orcas grabbed the shark with their teeth and dragged it to the surface until it was dead.
The liver, which provides buoyancy to sharks, was precisely removed, causing the carcass to sink.
Another case in 2015 involved a juvenile great white that washed up on a South African beach. The shark had its liver cleanly excised and bite marks matching orca dentition. Several other carcasses of great whites have shown similar precise bite marks, indicating deliberate predation rather than just scavenging.
Researchers believe the strategy used by orcas is to flip sharks upside down, inducing a paralytic state known as tonic immobility. This allows the orcas to safely eat the nutrient-rich liver as great whites enter the trance-like state when flipped over.
The accuracy of the bites suggests this is a learned hunting technique within orca pods.
Avoidance of Orca Migration Routes
Studies have shown great white sharks demonstrate avoidance behaviors when killer whales are in the vicinity. One research team tagged great whites off Seal Island in South Africa and found they would immediately flee and stay away from the area once orcas were present.
In the Northwest Atlantic, researchers found seasonal co-occurrence of great whites and orcas minimal. Satellite tracking data showed great whites leaving areas like Cape Cod as orcas migrated through. One great white nicknamed Cabot swam over 500 miles in under a month to avoid orcas.
The sharks only returned to sites like the Farallon Islands once the orca pods had passed through the areas. Scientists believe the great whites can detect orca calls and have learned these acoustic signals indicate a predation risk.
There is evidence that great whites have avoided historical hunting grounds like Southeast Farallon Island since the 1997 predatory attack. The seasonal migration paths of orcas may be determining areas of overlap and avoidance for the two powerful predators.
Wary of Dolphin Aggression
Sharks have good reason to be cautious around dolphins. Despite their friendly reputation, dolphins can be quite aggressive and even violent toward sharks. Here’s an overview of the complex relationship between these two marine predators:
Competition for Food
Sharks and dolphins frequently find themselves competing for the same food sources. Both are apex predators and opportunistic feeders that prey on fish, squid, and crustaceans. When resources are scarce, the competition between sharks and dolphins can turn fierce.
Dolphins may use their intelligence and social behaviors to gain an edge over sharks when hunting. Dolphins frequently work together to herd and corral schools of fish. Their teamwork and coordination gives them an advantage that solitary sharks can’t match.
Dolphins Attack Sharks
Dolphins don’t just compete with sharks, they are also known to aggressively attack them. There are many documented instances of dolphins rammming sharks with their snouts, suffocating sharks by preventing them from swimming, and even killing young sharks by drowning them.
Some researchers believe dolphins attack sharks to eliminate competition for food. Others theorize it may be a form of play or practice of hunting techniques. Dominance and territorial displays are also possible motivations.
Whatever the reasons, sharks have learned to be wary when dolphins are around. Large sharks may flee an area when pods of dolphins move in, while smaller sharks may hide until the threat passes.
A Calculated Risk
Despite the risks, sharks don’t always avoid dolphins completely. That’s because where there are dolphins, there are often large schools of fish as well. Hungry sharks may cautiously follow or shadow dolphin pods from a safe distance, hoping to snatch some uncontrolled leftovers from the dolphins’ hunting.
Sharks also scavenge dolphin kills, feeding on injured or dead dolphins when given the opportunity. This behavior allows them access to an abundant food source while minimizing dangerous interactions.
In essence, sharks weigh the risks versus rewards when dolphins are near. Their wariness helps protect them from aggression, while opportunism allows them to benefit from the dolphins’ hunting abilities.
The dynamic between sharks and dolphins is complex, spanning competition, predation, scavenging, and uneasy coexistence. Caution serves sharks well in navigating interactions with these highly intelligent and potentially dangerous marine mammals.
Unsettled by Novel Objects
Cautious Investigation
Sharks tend to be wary of unfamiliar objects and will often investigate them cautiously before deciding whether they pose a threat. When encountering something new in their environment, sharks will frequently circle and bump the object with their snout as they try to determine what it is.
They may also swim around the perimeter of the object while watching it closely with their eyes. This investigative behavior allows sharks to gather sensory information about novel items to determine if they should be avoided or might offer a potential food source.
While cautious, sharks do not seem to exhibit overt signs of fear when checking out novel objects. Their behavior appears more curious than frightened as they rely primarily on their senses of smell, vision, and electroreception to inspect unfamiliar things.
However, if the object elicits a painful or startling reaction when bumped or touched, the shark will likely flee the area quickly. Novel biotechnology devices used for shark research, like camera tags, often evoke this kind of evasive response at first until the shark determines the object is not an active threat.
Possible Signs of Curiosity
In some instances, sharks even seem to display curiosity about new items they encounter. While not definitive, potential signs of curiosity in sharks may include:
- Approaching novel objects slowly with pectoral fins splayed outward as if to enhance sensory perception.
- Changing position to view the object from different angles.
- Gently mouthing or bumping the item repeatedly as if experimenting with it.
- Returning to the object intermittently as if drawn to it.
These behaviors suggest sharks may not only investigate novel things to evaluate danger, but also to satisfy sensory curiosity and gain knowledge about new aspects of their domain. However, their wariness means sharks will abandon interest in unfamiliar items if they detect indications of threat.
While novel objects can pique their curiosity, sharks tend to prioritize caution over indulging their inquisitiveness. Their survival instincts make them ready to flee at the first signs of potential peril.
Fishing Gear Entanglements
One of the major hazards facing shark populations around the world is accidental entanglement in fishing gear left behind by commercial fishing vessels. Over 640,000 tons of fishing gear is left in our oceans every year.
This “ghost fishing gear” continues catching fish and marine wildlife long after it has been abandoned.
Sharks are especially vulnerable to getting tangled up in drifting gill nets, lobster and crab pots, and longlines. Their teeth and rough skin make it difficult for them to free themselves once caught. Entanglement often leads to severe injury, starvation, and death.
Causes and Statistics
The vast majority of abandoned fishing gear is due to accidental loss from storms, gear conflicts, or intentional dumping of old equipment. Hundreds of thousands of sharks and other marine animals die grisly deaths wrapped in this underwater debris every year.
Experts estimate that over 10 million open-ocean sharks are killed annually by entanglement in longlines alone. The problem may be even more severe closer to shore.
One study of entanglement rates in Australian waters found that 26% of captured grey nurse sharks had signs of prior entanglement in nets, lines, strapping, or other debris. Capture in protective beach meshing and drum lines used to control sharks is also an enormous source entanglement.
Efforts to Reduce Entanglement
There are growing efforts to clean up or avoid abandoned fishing gear in the world’s oceans. The National Oceanic and Atmospheric Administration has guidelines for marking fishing equipment properly so it can found and retrieved if lost.
New technologies like biodegradable gear and acoustic tracking devices could reduce accidental loss.
Some conservation programs train volunteer divers to locate and remove marine debris. Yet the overall scale of ghost fishing gear accumulating in offshore waters makes it difficult to coordinate large-scale removal efforts.
Without better tracking and regulations, entanglement will continue to haunt shark populations for decades to come.
The Bottom Line
Like marine turtles, seals, dolphins and whales, sharks often suffer gruesome fates after encountering lost or active fishing equipment meant for other species. Entanglement is an overlooked threat facing sharks that needs more attention and innovative solutions.
With more awareness and cooperation between conservationists and the fishing industry, we can make the oceans safer for sharks and other marine life.
Aversion to Electric Fields
Shark Deterrent Devices
Sharks have specialized sensory organs called the ampullae of Lorenzini that allow them to detect electric fields emitted by potential prey. Various shark deterrent devices have been developed that take advantage of this sensitivity by emitting electric pulses to overload a shark’s ampullae and deter an attack.
Popular consumer products like the Shark Shield Freedom7 emit a three-dimensional electrical field around swimmers that causes spasms in sharks that approach within 10 meters.
Larger commercial shark deterrent systems are also deployed to protect beaches, surfing competitions, and offshore infrastructure. For example, the Clever Buoy system uses sonar to detect sharks and then sends out electrical pulses to drive them away before they enter swimming areas.
Studies find these electric deterrent devices can reduce the risk of a shark attack by up to 60%.
Sensitivity Varies by Species
However, not all sharks have the same sensitivity to electric fields. Smaller shark species like spiny dogfish and smooth dogfish tend to be less sensitive while larger, more powerful sharks like great whites, tigers, and bull sharks are more easily deterred.
Their ampullae organs are also concentrated in different areas of their heads and bodies, meaning shark deterrent devices need to emit omni-directional fields to be effective against different species.
Within a species, younger juvenile sharks have been found to be less responsive to electric pulses than larger adults. Scientists hypothesize younger sharks may have yet to fully develop their electroreception abilities.
More research is still needed to fine-tune shark deterrent technologies against specific species and life stages.
Fear of the Bends
Just like human divers, sharks can suffer from decompression sickness, commonly known as “the bends.” This dangerous condition occurs when sharks ascend too quickly after diving to great depths, causing nitrogen bubbles to form in their blood and tissues.
Sharks have an excellent sense of pressure using their lateral line system, allowing them to precisely control their buoyancy. However, accidents still happen. Researchers have found evidence of the bends in several species of sharks, including great whites, tiger sharks, and mako sharks after rapid ascents from deep dives.
Symptoms
The most common symptoms of the bends in sharks include:
- Erratic spiraling while swimming
- Difficulty maintaining balance and orientation
- Gas emboli in fins, tail, or eyes
- Paralysis, convulsions, or death in extreme cases
These effects can range from mild disorientation to mortality depending on severity. Oceanic whitetip sharks seem especially susceptible, with over 20% showing signs of decompression sickness in one study after being caught on longlines and pulled rapidly to the surface.
Avoidance Behaviors
To reduce their risk of getting the bends, sharks demonstrate several avoidance behaviors:
- Taking longer to resurface from deep dives
- Ascending at slower, more controlled speeds
- Frequent stops during ascent to recompress
- Extended rests near surface after deep dives
For example, satellite tracking indicates whale sharks can take over an hour to fully surface from dives approaching 5,000 feet (1,500 m). This suggests they linger at depths to decompress before completing their ascent.
Species | Reported Depth | Typical Ascent Time |
---|---|---|
Whale shark | 4,921 ft (1,500 m) | ~1 hour |
Tiger shark | 3,281 ft (1,000 m) | ~45 minutes |
As these examples show, sharks clearly take precautions to avoid decompression issues despite anatomical and physiological adaptations for deep diving. Researchers continue investigating various species’ ascent behaviors to better understand the risks of the bends.
Evolutionary Influences
Experts hypothesize that sharks’ fear of the bends is an evolutionary adaptation selected over millions of years. Individuals that surfaced more cautiously after deep dives likely survived and reproduced at higher rates than those more susceptible to decompression sickness.
Over many generations, sharks may have evolved excellent barosensitivity and precise buoyancy control as key survival traits for frequent vertical movements. Their intricate physiological regulation during ascents supports this theory and demonstrates an instinctual fear of the bends.
Conclusion
While sharks deserve their reputation as fierce apex predators in many situations, this guide has revealed some of the main things that make them turn tail and swim. Learning more about the fears and avoidance behaviors of different shark species can help us understand how to safely coexist with these captivating creatures when our paths cross.
From thebubble streams of scuba divers to novel objects like floating debris, sharks react warily to unfamiliar situations they perceive as threats. Their fear of dolphin aggression and the debilitating effects of fishing gear entanglements also influence their behavior in nature.
Understanding the factors that intimidate mighty sharks gives us a glimpse into the risks they calculate when going about their daily lives. This knowledge reminds us that they have vulnerabilities like any other wild animal despite their domineering image in popular imagination.
Their avoidance of feared stimuli is key to their survival as a species.