On Locking Eyes with a Shark

Off the Mornington Peninsula in Victoria, Australia, 43-year-old diver Marshall Yu was approached by a 13-foot great white. He recalls being frozen in place as the behemoth shark, curious, came right for him. 

Through the brief news circulation following the event, much adding expected sensationalism, Yu’s quote stands out. “I didn’t see any aggression,” he said. “I made eye contact with it. (The shark) was pretty cute.” 

It may seem unbelievable that, during an unexpected encounter with such a large predator, one would even recognize the eyes, let alone comment on their beauty. But Yu is not alone in this thought. 

Charles Darwin kept a journal from 1831-1836 chronicling his voyage along the southern hemisphere. In an August 28 entry he speaks on a shark’s eye with undeniable revery:  “Caught by a hook a specimen of genus Squalus: Body “blueish grey”; above, with rather blacker tinge; beneath much white:--Its eye was the most beautiful thing I ever saw.—pupil pale “Verdegris green,” but with a lustre of a jewel, appearing like a Sapphire or Beryl.—Iris pearly edge dark.—Scelerotica pearly.” 

Not every shark species has a pale green pupil around a Sapphire jewel with a pearly sclera. All are different, and in What You Should Know About Sharks, Ocean Ramsey argues this visual difference may affect their overall vision and, by extension, behavior. 

“They all have unique eyes, beautiful and complex, and highly adapted to their specific ecological niche,” Ramsey writes. “Take tiger sharks, for example. Tiger sharks have an amber-yellow eye, like the color you see in the water in low morning and evening light. I can’t prove it exactly, but I think this coloring may provide an advantage. I have observed that tiger sharks like to approach with the sunlight perhaps because most animals avoid looking into the bright sunlight. It’s possible the color of their eyes helps with this approach in this type of low light. However, I’ve also observed that tiger sharks do not have the best eyesight. They don’t seem to notice small objects like many other species do, which might explain why, in addition to their foraging behavior and size, they are one of the species more suspect in adverse interactions in tropical waters.”

So, a shark’s eyes can stand out to a human. But can a human’s eyes stand out to a shark? Is Yu correct in saying he made mutual eye contact with the great white? According to shark experts, also yes. 

While sharks lack the cells to process color vision, they do not lack visual acuity. Human eyes use muscles which control the lens shape and can focus light signals. Though shark lenses do not change shape, they can move forward and backward to focus light. In this sense, many sharks have been documented with a near-equal quality of vision as humans and rely on this strong sense for much of their activities and behavior. 

A 2021 study published by the Journal of Ecotourism considered eye contact between humans and approaching Caribbean reef sharks, examining specifically whether an interruption, such as glancing at a camera or regarding where to retreat, would affect a shark’s behavior. In the field, divers maintained or interrupted eye contact with them, finding that the sharks came significantly closer to the divers when eye contact was interrupted and also reduced their speed. 

“I don’t usually wear a mirrored scuba mask because I get a better response when the sharks can see my eyes,” Ramsey writes. “I also no longer wear mirrored lenses because they reflect light at random which can be eye catching in a bad way depending on my position. I’ve had a shark in the Bahamas rush at the reflection from my mask which I was able to block off at the last moment.”

Many types of sharks ambush their prey, and they can’t sneak-attack something that is aware of them. Thus, they have become evolutionarily wired to make and sense eye contact. 

“The majority of the time, sharks rely on eyesight when hunting and are very sensitive to the eye line of prey and other predators,” Ramsey writes. “It’s for their own safety and success to be able to identify if a potential prey item is aware of their presence, and to identify where the front or eyes of a prey item or another predator are located and looking.” 

Looking a shark in the eye is one of Ramsey’s favorite things to do. Much can be gained by studying how a shark scans its domain and what catches its attention. It allows divers to realize how much detail each species can and cannot see. It helps them understand what can attract unnecessary attention or cause confusion—a safety protocol when interacting with sharks. 

Sharks, in identifying prey, in establishing dominance, are constantly surveilling the blue surroundings for an eyeline. But is this all it is, a simple prey-or-not binary, a checkbox of dominant or submissive? According to the people who are in the water with them every day, there might be something more going on here. 

“Any time I have the experience where I get to lock eyes with a shark it’s almost as if time stops,” says Marina Praet, a safety diver at One Ocean Diving. “It’s as if you are able to communicate without words and peacefully coexist in their home. It truly shifts your perspective on sharks as a whole because you get to see them as more than an animal. You get a glimpse into their personality and have a chance to understand them on a deeper level.”

Predator & Prey

Interactions between marine predator and prey species vary at every trophic level in the surrounding ecosystem. Both the stability of the trophic level and the community depend heavily upon these interactions and the total abundance of all predator and prey species in the food chain. As seen across the seven seas, changes in abundances of species in any trophic levels have a great effect on the ecosystem as a whole. Lower trophic levels are composed of mainly detritivores, who are responsible for recycling nutrients in the ecosystem. Higher trophic levels include consumers and apex predators. The trophic level system as a whole works together and is of utmost importance to community structure and balance among all levels. Changes in abundance of higher trophic level species of predators can impact the profusion of their prey at lower trophic levels, causing a cascade of events that takeover the ecosystem and are detrimental to balance in the community. One example of this effect is shown off the Pacific coast in the 1900s where sea otter populations severely diminished due to overhunting for the fur trade. As the populations of sea otters diminished, the abundance of their main prey source, sea urchins, experienced unrestrained growth. The immense populations of sea urchins devastated local kelp and algal supplies, creating colossal issues for primary production, nutrient recycling, habitat degradation, and coastal erosion in this ecosystem. Subtle changes to predator and prey relationships can cause severe effects that resonate throughout the entire marine community. Consequently, understanding these relationships may provide beneficial information about ecosystem heterogeneity which may aid in protecting and conserving biodiversity in these fragile marine systems.

Ecosystem heterogeneity is controlled by various factors, living and nonliving, throughout marine environments. Although the factors controlling ecosystem heterogeneity fluctuate based on varying locations and conditions, studies have revealed patterns in the processes of marine organisms in maintaining the diversity of ecosystem arrangements. Almost all ecosystems have been modified or controlled by a single species and their existence may be traced back to the dependence upon a single organism. Apex predators are prime examples of organisms that aid in preserving heterogeneity. As the top tier of the food chain, apex predators control the balance and efficiency of the trophic levels underneath them. Sharks are amazing apex predators that act as the doctors of the sea, or the white blood cells of the sea, that kill of the sick, weak, dying, and injured so that the strong individuals have more resources and therefore can survive and reproduce. This removal of the weak and sick species in lower trophic levels helps maintain the ecosystem’s overall health. Shark’s ecological role is to maintain strong and healthy ecosystems and not let sickness and disease overrun the population of species in lower trophic levels. Without sharks in our global ecosystems, there would be a detrimental chain reaction felt in every level of the food chain. Lower trophic level organisms would become uncontrolled and consume too much of their prey, leaving an insufficient amount of food for survival and this cascade of events would eventually reach every level of this complex food chain.

Other than ecosystem balance, health, and population control, sharks also maintain proper nutrient recycling in our oceans. We get 70% of oxygen from the ocean, thus ocean health is vital to human health. Sharks are necessary for ecosystem heterogeneity, healthy fish populations, food webs, trophic level systems, whole ecosystems, and the world’s oxygen supply. Therefore, sharks are a necessity and demand protection and preservation in our oceans.

The Overfishing of Sharks

In order to properly understand and conserve any aspect of marine life, the demographic and diversity of a species or ecosystem must be studied. Sharks are among the top apex predators in the ocean and provide scientists with various outlooks on an ecosystem’s trophic networks, health, and biodiversity. These aspects are associated with shark populations due to the elasmobranch’s importance as keystone species in marine ecosystems, meaning that they protect the diversity of a food chain by maintaining levels of predatory fishes and thus, every organism at every trophic level. Without sharks, food chains would collapse, and biodiversity would be lost. At every trophic level, the consumption by a predator species keeps the populations of prey species in check, but without a top apex predator, such as sharks, each level would be left unrestricted. Thus, the target species of sharks would be plentiful and soon take over their prey species in the trophic level below them, wiping them out and contributing to a cascade of this effect at every level. This trophic cascade, and depletion of shark populations as a whole, has been seen throughout ecosystems across the globe due to finning, overfishing, pollution, and habitat loss.

The oceans’ biodiversity is under immense threat from marine pollution and habitat loss, but the most ominous is arguably the overarching effects of overfishing. Overfishing is detrimental to marine landscapes due to fishing tactics, such as longlining, that ruin fragile habitats. Lines, nets, and other fishing-related debris are also among the top contributors to ocean pollution, contributing to over half of the plastic pollution found in the Great Pacific Garbage Patch. In addition, overfishing noticeably facilitates the immense loss of fish species biodiversity and population sizes and impacts species that interact with those target species in marine ecosystems. Thus overfishing, apex predator or not, is arguably one of the worst contributors to marine community degradation and loss of biodiversity.

The key to protecting against the overfishing of any apex predator is to understand the species at risk. To successfully conserve and protect vulnerable ecosystems and marine organisms from overexploitation and loss of biodiversity, their migrations, reproduction periods, and risk factors need to be understood. For many species of sharks, much research has been done to understand their migratory patterns, where and why they are at risk, and their common reproduction grounds. Migration to warmer waters during autumn and winter seasons is common in several species of sharks in the Pacific waters because most sharks are ectotherms; meaning they need to be in warm temperatures to regulate their body temperatures. Certain nomadic patterns of several species of sharks suggest that some yearly migrations to warmer southern waters might be due to mating tendencies and nursery purposes. Studies suggesting shark migrations to various known nurseries and mating grounds surrounding the Hawaiian Islands by specific species such as the Scalloped Hammerhead Shark and Galapagos Shark have been recorded for several years. These migrations aimed at reproductive purposes are vastly significant for conservation resolves due to the increased risk that the influx of populations of both adult and juvenile sharks face in mating and nursery areas.

Marine Protected Areas are locations in which fishing and hunting are banned so that the species there can mate, reproduce, and live significantly less affected by human life than in other areas around the world. The implementation of MPAs in the Pacific could help the shark population on the mend and create a healthier and more sustainable ecosystem overall. The Hawaiian Islands are home to many small conservation areas such as Hanauma Bay and many restricted fishing areas along the coasts but implementing major MPAs could significantly benefit Hawaii’s local marine life even further. The implementation of Papahānaumokuākea Marine National Monument has helped heal and maintain amazing biodiversity in the remote Pacific region. Conserving and protecting more local waters should be of utmost importance to our local government to help save and heal our local ecosystems and marine life populations that face threatening and injurious factors every day.