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shark senses vision

Shark Vision: Do Sharks have Good Eyesight?

Here’s the next segment on our Shark Senses Series.  If you missed the first article, click here.  Shark vision has always seemed to be a bit of a mystery. We often hear about the mistaken identity argument related to shark-human interactions and that leads many to believe that sharks have poor eyesight. We also constantly hear about sharks amazing sense of smell, and it’s often thought that some other senses are sacrificed as a result. Is this true? Do sharks have poor vision?

A research group in Australia has been studying shark vision for years. In fact, they may be the worlds experts on vertebrate vision and have studied the eyes of literally hundreds of different species of elasmobranch (sharks, rays, skates and sawfish). Here, we’ll try to summarize their findings and explain what that means in practical terms.

Sharks lack color vision. That’s right. Sharks lack the necessary cells that process color vision and can only see in Black and White. This seems to be the case for all sharks as none of the tested animals possessed the necessary photoreceptor cells to see in color.So what’s all that talk about Yum Yum Yellow? We’ll get back to that. On a side note, rays are able to see in color.

Visual Acuity. Sharks are thought to be able to see very focused images. The fact that shark vision is monochromatic does not mean they lack visual acuity. In the human eye, we have muscles that control the shape of our lens and focuses light signals on the retina. By contrast, the lens in a sharks eye does not change shape. Rather, they have muscles that move the lens forward or backward to focus light. In both cases, the effect is the same and the retina receives a focused image. Sharks have great visual acuity and they absolutely rely on that vision for many of their behaviors. Obviously, water conditions will play a major effect on their ability to see and from what distance. In ideal conditions (the kind we get while shark diving in the Bahamas), sharks can see clearly from 10-15 meters or more.  This means while their vision is good, it’s not the first sense that keys them into their prey and becomes more important as they get closer.

Light Sensitivity. The ability to see in low light conditions varies greatly between the shark species studied. Essentially, there are 2 types of photoreceptor cells located in the retina. The cones are active in bright light conditions and the rods are active in low light scenarios. Each species will have a different proportion of these cells. Not surprisingly, deep water sharks have large eyes with a much higher proportion of low light photoreceptor cells (rods) compared to cones. Shallow water sharks have cells in the opposite proportion. In addition, sharks possess a structure called the Tapetum lucidum. This is the reflective part of the eye that lies behind the retina and causes the shining eye you may have seen in a cat or a deer in headlights. This will actually reflect the light one more time back through the retina thereby making it available to the retina a second time and increasing low light vision.

In Practical Terms. Sharks have monochromatic vision. Sharks have good visual acuity. Sharks have vision suited to the environment they live in. Given their sharp focus and black and white view of the world, do we need to worry about the color of our dive gear? In short, Yes! Sharks do tend to be interested in high contrast areas. It’s the reason we don’t like very bright accent colors on dive gear as that may peak their interest. It’s also the reason we require divers to wear gloves for our shark dives. A pale fleshy hand sticking out of a black wetsuit sleeve may be a recipe for trouble.

If you’d like to learn more about shark vision, take a look at Vision in elasmobranchs and their relatives: 21st century advances.

Shark Vision

shark vision

Images used are by Jean-Lou Justine licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

shark senses ampullae of lorenzeni

Shark Senses – How Do Sharks Hunt Their Prey?

Perfectly evolved over 500 million years and surviving 5 mass extinction events, sharks are true super predators. So how do they do it? What’s senses come in to play as sharks hone in on their prey? Here’s a quick look at each of the shark senses, and how each help make them successful predators.

Shark Senses – Long Range

Hearing. A long range and highly developed sense, the auditory system of sharks can also give important information about potential prey. This will often occur well before the animal is in visual range. They are especially tuned in to low frequency sounds, the kind made by a wounded or struggling fish, and are able to detect them often from distances greater than a kilometer away!

The Sense of Smell. It’s true, sharks have a great sense of smell. You may have heard some of those interesting little factoids such as sharks being able to smell a drop of blood in an olympic sized swimming pool. Well, it’s not far off from the truth. Sharks sense of smell (olfaction) is remarkably effective and fine tuned to pick up the amino acids in proteins, such as blood. Studies have shown sharks to be able to detect 1 part per 20 million parts water! This is likely one of the first senses that clues sharks in to potential prey items at a distance.

Shark Senses – Mid Range

Vision. Contrary to some myths out there, sharks actually have good eyesight, as far as fish are concerned. They lack color vision and only see in black and white, but still possess the visual sensory equipment to produce focused images. Water conditions play a big role and low light or murky water will have a big impact on their visual acuity. Take a look at our blog focused on Shark Vision for more details.

The Lateral Line – Mechanosense. Sharks have evolved another sense that is quite foreign to humans. The lateral line system is a series of canals located throughout the sharks body with openings to the skin. It allows for water to enter and is very sensitive to picking up water movements. Because of this, sharks are able to tune in to the vibrations caused by wounded or struggling fish, again helping them to hone in on potential prey.

shark lateral line

Shark Lateral Line System – illustration by Chris Huh

Shark Senses – Close Range

Ampullae of Lorenzini – Electrosense. Another sense unfamiliar to us is electrosense, the shark’s ability to detect the weak electrical field given off by all living things. This highly tuned sense is thanks to countless small pores located throughout the sharks skin, mostly concentrated around the snout, and called the ampullae of Lorenzini. These gel filled pores help amplify these weak electrical signals allowing sharks to detect prey even if it’s completely hidden, such as in the sand. It’s effective at close range, typically within 1 meter or less.

shark senses ampullae of lorenzeni

Shark Electroreception – illustration by Chris Huh

Touch. Obviously a close range sense, sharks will often bump potential prey items before taking a bite to get a better sense of what they’re dealing with. Lacking hands, it’s common for sharks to investigate items in the water column by hitting with their snout or even “feeling” with their mouths. This is the reason for the often described bump and bite scenario, and also a reason that we let divers know they cannot let sharks bump into them, as it’s often followed by a test bite.

Taste. Like us, sharks have taste buds in their mouths, making it the final sense involved in determining if a shark has found it’s next meal, or made a mistake. We have no idea what tastes good to a shark, but given the frequency that shark-human interactions only end in a single bite, and our terrestrial nature, it seems we are certainly not on the top of the shark menu.

 

megamouth shark encounter

Ultimate Shark Encounter: Megamouth

What’s your ultimate shark encounter?  Was it seeing a massive Great White shark?  Perhaps a Great Hammerhead cruising in the shallows.  Or a big Tiger Shark prowling the reef?  There’s no doubt divers have had their fair shark of amazing shark encounters over the years.  What’s exciting now, most are equipped with some form of underwater imaging gear and some of those most special shark encounters can be shared with us all!  Take a look:

megamouth shark encounter

Megamouth Shark Encounter

Read about the fascinating Greenland Shark.

great white shark aquarium

Great White Sharks fail in aquarium captivity

Take a look at this brief but interesting look at the history of Great White Sharks in captivity.



We believe strongly that putting people face to face with live animals like this is very significant in inspiring ocean conservation and connecting people to the ocean environment. We feel like white sharks face a significant threats out in the wild and our ability to bring awareness to that is significant in terms of encouraging people to become ocean stewards.

great white shark dies
Source: Why there aren’t any great white sharks in captivity – Vox

Read about SeaWorld ending their captive orca program.

Read about Shark Fight: Scientists Complain about Rival Great White Tagging

smalltooth sawfish

Endangered Oceans: Smalltooth Sawfish

The smalltooth sawfish is one of the most unique shark species found in warm tropical waters. It has been on the endangered species list since 2003 because of drastic reductions in their population. Unlike other shark populations decimated by the shark finning industry, this species is threatened primarily through habitat destruction and bycatch.

Here’s a video put together by NOAA:

Video Transcript

Sawfish are large shark-like rays that are found in tropical and subtropical seas, rivers, and creeks, and can grow to 15 feet.

It gets its name from its long, saw-like nose called a rostrum which is lined with modified scales that look like teeth, 22-29 on each side.

It uses its “saw” packed with electro-sensitive organs and teeth to locate, stun, and kill prey.

And although it’s been around for over 50 million years, it is now endangered.

Two major threats exist for this species: bycatch in various fisheries, and loss of juvenile habitat.

Its toothed rostrum can easily become entangled in fishing lines and nets.

Young sawfish use shallow habitats that are lined with mangrove forests, as important nursery areas. Many such habitats have been displaced by concrete seawalls  or lost entirely due to development of the waterfront.

The smalltooth sawfish was listed as endangered in 2003.  NOAA’s National Marine Fisheries Service has worked to develop and implement a recovery plan for the species.  The major steps for recovery include: reducing bycatch in fisheries, protecting important habitats, and educating the public.

Guidelines were also developed for fishermen to safely handle and release any sawfish they might catch.

Today, NOAA Fisheries continues to study this species. Through this research, they hope to help develop the next steps in conservation and management that will save this endangered species. You can help bring them back from the brink of extinction by protecting shoreline habitats and reporting sawfish sightings or encounters to the International Sawfish Encounter Database.

smalltooth sawfish shark research

Image ID: fish1952, NOAA’s Fisheries Collection
Location: Atlantic Ocean

Check out Ocean Today by NOAA for more great information.

howard hall filming a bull shark

Bull Sharks – knows no bounds

Description

Bull shark, Carcharhinus leucas, from the CARCHARHINIDAE family. Depending on where you are in the world, you might also hear it referred to as a Ganges shark, Zambezi shark, ground shark, shovelnose, freshwater whaler, swan river whaler or slipway grey.

As its name suggests, a bull shark is large, stout and unpredictable. They are distinguished from other sharks by their stout appearance. Male bull sharks grow to an average size of 7 feet (2.5 m), whereas the females are bigger, with an average length of 11 feet (3.5 m). They weigh about 200 lb (90kg), 290lb (130 kg) respectively.

Bull sharks are wider and heavier than other requiem sharks of comparable length, and are grey on top and white below. The second dorsal fin is smaller than the first. The bull shark’s caudal fin is longer and lower than that of the larger sharks, and it has a small snout, as well as lacking an interdorsal ridge. This species reaches maturity at about 6 years and lives to be least 14 years.

Location

bull shark carcharhinus leucas

Range of the Bull Shark

They’ve been spotted as far north in the Atlantic as coastal Massachusetts and as far south as Brazil. In the Indian Ocean, you can find them from Africa and India to Vietnam and Australia. They tend to avoid the cold waters of the Pacific. They can be a common sight in big rivers. There have been reports of bull sharks as far as 1000 miles (1600km) down the Amazon. They were also sighted in the Mississippi. It’s one of only two species of shark that can live in freshwater — the other is the rare river shark.

The ability to be able to survive in both freshwater and saltwater also gives it a benefit that has been driven by evolution. Because the majority of sharks are only able to survive in saltwater, the bull shark has evolved to have their offspring in the fresh water where other sharks cannot enter. The fresh water acts as a protective area where the young are able to grow and mature without the threat of larger sharks preying on the younger bull sharks.

Diving with The Bull shark

Bull sharks like to dwell in shallow coastal waters (less than 100 feet in depth) , so you can be sure to encounter them more frequently, than say, an Oceanic whitetip. The fact that they are considered territorial animals assures that you are bound to catch one with your underwater camera. Bull sharks are a sight to behold and are a truly unforgettable experience for any scuba diving enthusiast.

wild dolphin swim with epic diving in bimini bahamas

The Bottlenose Dolphin

The bottlenose dolphin is the most common member of the Delphinidae family. Recent molecular studies showed that the genus contains two species, the common bottlenose dolphin (Tursiops truncatus) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus).

Like the name “bottlenose” suggests, this species of dolphin has a short, stubby beak. Its sleek, conical body varies in color from a light to slate grey on the upper body to a pale to pinkish grey on the bottom part. Their coloration ranges from light gray to black with lighter hues on the belly. Inshore and offshore individuals vary in color and size. Inshore animals are smaller and lighter in color, while offshore animals are larger, darker in coloration and have smaller flippers.

Bottlenose dolphins range from 6.0 to 12.5 ft (1.8 to 3.8 m) in length, with males slightly larger than the females. Adults weigh from 300-1400 lbs (136-635 kg). This is a long-lived dolphin species with a lifespan of 40-45 years for males and more than 50 years for females.

They are known to have a complex communicating system that includes whistles and sounds that resemble moans, trills, grunts, squeaks, and creaking doors. They make these sounds at any time and at considerable depths. Sounds vary in volume, wavelength, frequency, and pattern. The frequency of the sounds produced by a bottlenose dolphin ranges from 0.2 to 150 kHz. The lower frequency vocalizations (about 0.2 to 50 kHz) are likely used in social communication. Social signals have their most energy at frequencies less than 40 kHz. Higher frequency clicks (40 to 150 kHz) are primarily used for echolocation.

They are considered highly intelligent, and have been observed to use tools. In one instance they place a marine sponge on their rostrum, presumably to protect it when searching for food on the sandy sea bottom

Location

Bottlenose dolphins live in temperate and tropical waters worldwide, especially where the water temperature is between 22 and 29 degrees Celsius. In general, the coastal ecotype seems to be adapted for warm, shallow waters. Its smaller body and larger flippers suggest increased maneuverability and heat dissipation. These dolphins frequent harbors, bays, lagoons, and estuaries.

That is why they have a vast presence here in the Bahamas, especially at Bimini where we do most of our sighting trips.

Swimming with the Bottlenose dolphin

They make excellent diving buddies. They show curiosity towards humans in or near water. They often approach divers and encourage a friendly interactions. Like the Spotted dolphin, they have a distinct swimming style, making them an interesting and delightful sight. Here at the Bahamas, they are numerous, so odds are you will be swimming with a lot of Bottlenose dolphins. At the end of the day, we guarantee you will be smiling from cheek to cheek.

Check out our information page on Atlantic Spotted Dolphin.

swimming-with-dolphin-bimini-bahamas

Atlantic Spotted Dolphin

The Atlantic spotted dolphin (Stenella frontalis) belongs to the Delphinidae family. They are usually  5-7.5 ft (1.6-2.3 m) long and weigh about 220-315 lbs (100-143 kg). Interestingly,their average lifespan has not been estimated, although it is general knowledge that they live more than 20 years. They have a robust or chunky body with a tall, “falcate” dorsal fin located midway down their back. The rounded “melon” is separated from the moderately long beak by a distinct crease. The coloration and patterns vary with age, life stage, and geographic location.

They are born without spots, they are dark gray on their backs graduating along their sides to a white belly. At approximately four years of age they begin to get spots. The older adults become so fused with spots their bellies appear almost black with white specks.

Atlantic spotted dolphins are usually found in groups of fewer than 50 individuals, but have been occasionally seen in larger groups of around 200 animals. Since they are mammals, they need to visit the surface often to replenish oxygen. They generally make dives of about 30 ft (10 m) or less for 2-6 minutes, but are capable of reaching depths of 130-200 ft (40-60 m) and have been recorded holding their breath for up to 10 minutes.

They lead very complex social lives. They exhibit numerous social behaviors like companionship, affection, aggression and playfulness. Regardless of the relationship when two dolphin are swimming together they will be in almost constant physical contact with each other.

They have an unique swimming style. It is often described as acrobatic due to their frequent “breaching”, jumping, and other aerial activities at the surface. They are capable of swimming at very fast speeds and often approach vessels to “bowride”.

Location

This species is found only in the Atlantic Ocean, from southern Brazil to the United States (New England) in the west, and to the coast of Africa in the east. They relish warm waters of the Caribbean and are a common sight here. Although they are widespread, their abundance has still not been estimated by official studies, though the general presumption is that their numbers are potentially large.

Although they are sometimes caught in fisherman nets, they are not considered endangered.

Swimming with the Atlantic Spotted dolphin

Because of their tame temper and general appeal for humans, we offer a thrilling opportunity to experience the Spotted dolphin up close as you swim alongside them. They are very responsive and eager to come close to meet you. They are especially playful with kids. Since they have a natural habitat at Bimini, Bahamas, you are bound to meet numerous playful specimen. Your good time is guaranteed.

Check out our information page on Bottlenose Dolphin.

shark diving with caribbean reef sharks

The Caribbean Reef Shark

Description

diving with caribbean reef sharksCaribbean reef shark, Carcharhinus perezi, belongs to the family Carcharhinidae. It has a robust, streamlined body typical of the requiem sharks, and is often mixed with dusky or the silky shark. Distinguishing characteristics include dusky-colored fins without prominent markings and a short free rear tip on the second dorsal fin. The snout is rather short, broad, and rounded, without prominent flaps of skin beside the nostrils. The eyes are large and circular, with nictitating membranes (protective third eyelids). There are 11–13 tooth rows in either half of both jaws. The teeth have broad bases, serrated edges, and narrow cusps; the front 2–4 teeth on each side are erect and the others increasingly oblique.

They are somewhat smaller than those of a Bull Shark or a Tiger shark, measuring 2–2.5 m (6.5–8 ft) long; the maximum recorded length is 3 m (10 ft). They weigh about 70 kg (150 lb).
Although they are very numerous in the Caribbean, extensive hunting has made an impact on their presence, and they currently have a status of ‘nearly threatened’ by the IUCN Red list of threatened species. It is valued for its meat, leather, liver oil, and fishmeal. Its liver oil is one of main ingredients in modern cosmetics.

Location

Caribbean reef sharks range throughout the tropical western Atlantic and Caribbean from North Carolina to Brazil and are the most common reef shark in the Caribbean. This shark species is most commonly found in water shallower than 30 m (98 ft), but has been known to dive to 400 m (1300 feet). It can be found swimming around the reef’s outer edges. Especially in the Caribbean, their quantity is abundant and you can sure as a shark’s tooth count on meeting one.

Diving with the Caribbean Reef Shark

The Caribbean Reef Shark is known to be relatively passive and typically doesn’t pose much of a threat to scuba divers, snorkelers, swimmers, or other humans it comes into contact with. They are also known for their threat display, in which they swim in a short, jerky fashion with frequent changes in direction and repeated drops of the pectoral fins.

nurse shark diving bahamas

Nurse Sharks – a bottom dweller

Description

nurse shark diving bahamas

Nurse shark in the sand

Nurse shark, Ginglymostoma cirratum, from the Ginglymostomatidae family.

Its body is yellow-brown to gray-brown, with or without small dark spots and obscure dorsal saddle markings. Mouth is set forward of eyes and is relatively high up on the head – maintaining a more forward position. Noticeable barbells are present, along with nasoral grooves (though there are no perinasal grooves). Spiracles are minute. Dorsal fins are broad and rounded, with the first dorsal being considerably larger than the second. Dorsal fins are set relatively far back along the ventral surface. The upper lobe of the caudal fin is considerably longer than the lower lobe. The caudal fin itself comprises roughly one quarter of the overall body length.

They can get quite large with a length of up to 4.5 meters (15ft) as adults. These large creatures reach weights as high as 150 kilograms (330 pounds). Typically, they live to between 25 and 35 years of age.

Unlike most sharks, which require constant motion to move water over their gills and maintain a sufficient internal blood pressure, the nurse shark often remains motionless along the bottom – actively pumping water over its gills through the continual opening and closing of its mouth.

Location

They prefer warm seas and range through the Atlantic and east Pacific. This species is often found along reef sites, within mangrove channels, and on sand or sea grass flats. They are often observed at depths of a meter or less within the intertidal zone, though they are known to range down to depths of at least 12 meters.

Diving with Nurse sharks

Nurse sharks have long elegant lines, and, since they move sluggishly, you don’t have to worry about scaring them away. Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. They can be a special sight when encountered in such groups. Nurse sharks are generally considered to be a docile shark species. Virtually every tallied attack has been provoked, so unless one tries to pull its tail, you will have a safe close encounter, should you meet one.

Check out this nurse shark ID guide from The Shark Trust.

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