1. Do not swim at night, dawn, or dusk.
This is the time when sharks are most active – they are a nocturnal creature. The dark also interferes with their ability to distinguish humans from regular prey.
2. Swim in a group
Sharks are less likely to attack a group: there is safety in numbers. When there is a group, they will usually target the individuals on the furthest edge or stragglers, so it is important to stay close and not wander too far off. Even those on the edge have a distinct advantage by being with a group: every person is an extra set of eyes, and the chances of spotting a threat before succumbing to it are exponentially higher.
People usually swim where they know shark attacks are unlikely. Either they are not otherwise attracted to the area by water conditions, or their regular prey is elsewhere, or measures such as nets are in place to minimize sharks. Swimming in a group by default sets you in a place where shark attacks are less likely to happen.
No measures provide certain protection, however. Nets are not 100% effective; they are also facing controversy for the sea life they kill including and beyond sharks and so are not a universally accepted means of protection. Even with a hundred sets of eyes a shark can and will pass by unnoticed because our eyes are usually looking above the water, not below.
3. Avoid Seals
Do not swim when seals or other prey are present. You may see these smaller, innocent looking fellow mammals and feel almost a sense of ease. They are almost a kin to us, they are small, no one ever heard of a ‘seal attack’. This is a misleading sense of ease: where there is prey, there is a hunter, and the seal is known as a favorite of the Great White in particular.
If you swim near a group of seals, not only are you almost certainly swimming with a large Great White, but you are greatly increasing the chance that it will mistake you for a slow, vulnerable seal on the edge of the group.
4. Do not swim in murky water or just after a rain storm.
A storm washes fish from the rivers and various animal bodies from their banks and the shore. It creates a murky environment where the astute senses sharks have give them a massive advantage in capturing less capable prey. It also makes it harder for them to identify what exactly the prey item is, and when on the hunt they cross the warm, electromagnetic signal emitting body of a human, they will not be able so well to distinguish it from any of the other food; their cautious side takes the back seat while their curious and hungry side takes a bite.
There are various means of shark deterrents both in existence and being developed. These mainly target surfers, the most common being wearable or designed to attach to a surfboard with minimal intrusion on balance. Most work to confuse or overpower the sharks highly tuned senses by one of two means: scent or electromagnetic fields.
Sharks have an extremely good sense of smell, often quoted as being able to detect one drop of blood in an Olympic-sized swimming pool. Deterrents focused on odor typically attempt to both mask the wearer’s scent and to make a clear distinction that the wearer is not a usual prey item.
Sharks have a sense that humans do not: electroreception (or electroception). With this sense, sharks can detect and accurately locate living creatures even without being able to see or smell them. No creature is more sensitive to electric signals than a shark, and that is why this power can be used against them in creating electromagnetic deterrents.
Sharks use electroreception to locate prey in dark or murky conditions or even buried beneath the sand. This ability is called electrolocation
Sharks have one more very important and highly attuned sense that they use to hunt, and so one more opportunity for a deterrent: their sight. Sharks are color blind but still have fantastic vision.
Researchers have found that, while the human eye has 3 cones (responsible for seeing red, green, blue), a shark eye has only one, very strongly suggesting that sharks do not see in color. This means they rely on contrast and tend to be attracted to high contrast items. This explains why they have a known preference for yellow: especially in murky water yellow has a high contrast.
Unfortunately, those high contrast colors such as yellow and orange, are the very same colors that stick out to human eyes and are necessary and useful colors for safety equipment.
Imagine yourself lost at Sea, your ship went down and you are all alone. The only thing you have is your life jacket, but you managed to in an SOS with your location. If that life jacket is black, you might be safer from sharks, but you almost definitely will not be seen. If the life jacket is bright orange, you might be more attractive to a hungry shark, but you also are much more likely to be seen by a rescuer. As we described above, a shark has plenty of other ways to find you; a human rescuer does not, and, considering how big the ocean is and how small we are, I think most of us would rather increase the chance to be seen by a rescuer. That said, it would be nice if all life rafts etc. were all a less provocative color below and bright on top.
While on the topic of sight, look beyond sharks and you will find that one of the deadliest creatures in the ocean is the sea snake, particularly the Sea Krait. This black and white striped snake is feared even by most sharks, who recognize and avoid it. The black and white pattern is something that can be very clearly distinguished by the contrast oriented eyes of the shark. In 2013, an Australian company called “Shark Attack Mitigation Systems (SAMS)” developed a wet suit designed to imitate this pattern in order to deter sharks, and in tests it seemed to reduce the chance of an attack versus a plain design.
It should be noted that none of these deterrents are 100% effective; many are not even close, so it is always best to rely on the more basic tips and only to use deterrents as a supplement, not as a sole means of protection.
You cannot avoid sharks completely, not if you want to swim in a natural body of water. Sharks dominate the oceans and several species even many rivers and lakes throughout the world, including Bull Sharks. There is not a part of the Ocean sharks avoid, they will swim in (and hunt in) water as shallow as 3 feet and across the 36,201 foot Mariana Trench. On top of this, most shark attacks occur within 100 feet of the shore! Swimmers think they are alone, but beneath the surface there are all forms of life, and any regular ocean swimmer is almost guaranteed to have had a shark eye them and decide not to bite at some point without them knowing it was ever there.