Developing a sea ethic.

By Richard Plate and Marta Calosso ~ Photos By Marta Calosso

In 2008 we wrote an article for Times of the Islands providing an introduction to Aldo Leopold’s land ethic. Briefly, Leopold suggested that humans increase their sense of ethics to include “soils, waters, plants, and animals, or collectively: the land.” The article suggested ways in which we might translate Leopold’s ideas into a sea ethic. In this article, we look more closely at one specific aspect of Leopold’s ethic — what he called “thinking like a mountain.”

Leopold introduces this idea by describing an experience he had in the early 1900s as a forest ranger, coming upon a wolf mother and several cubs. “In those days,” he explains, “we had never heard of passing up a chance to kill a wolf. I thought that because fewer wolves meant more deer, that no wolves would mean hunters’ paradise.”

Wolves remain one of the most feared predators for many in the western United States because of their ability to harm humans and human property (e.g., cattle). But wolves also seem to evoke fear that goes beyond these potential threats and have a long history in human perception as the archetypal monster in the wilderness.

Can you think of any marine species that evoke a similar fear? If you were asked this question, say 150 years ago, you likely would have answered “whales.” While whales have benefitted for several decades from public awareness campaigns and as the center of many marine shows and major motion pictures, their sheer size prompted stories from sailors about the flesh-hungry leviathans that awaited humans in the deep sea.

Encounters between whaling ships and their prey fueled these ideas. Turks & Caicos Islands historian H.E. Sadler describes an encounter in which a TCI whaling ship failed to avoid a tail strike from the hunted whale, “Some of the men jumped overboard in time, but others were scattered by the blow which smashed the boat in half.”

But whales probably weren’t the first animals to come to mind when I mentioned “monster in the wilderness.” Today a different class of animals holds the title of most feared creatures of the sea: sharks.

Thinking like an ocean

After emptying his rifle into the pack of wolves, Leopold walked down to the wolf mother just in time to “watch the fierce green fire dying in her eyes.” He realized then that wolves too had an important role to play in the larger picture, thinking about the ecological function of those wolves — controlling the deer population.

Without the top-down control from the wolves, the deer population would continue to grow until there was eventually nothing left to eat. The result would be a forest largely defoliated by deer and deer dying of starvation. Leopold came to suspect that “just as a deer herd lives in mortal fear of wolves, so does a mountain live in mortal fear of its deer.”

Today we know that not only do wolves act as a top-down control on deer populations, but they also pick out the weak, the sick, or the old as their targets. Analogous functions can be seen in many apex predators, the term used to describe species whose adults are generally not preyed upon by other species. Typically, apex predators sit at the end of long food chains, so population changes in apex predators cascade through the rest of the ecosystem.

As you may have guessed, many species of sharks are apex predators. Like wolves, they tend to feed on easy-to-capture prey, such as weak, sick, very old or very young individuals. By feeding on sick or weak fish, sharks not only help keep diseases under control, but also allow more fit individuals to survive and reproduce. More fit adults will produce more fit young, and so on.

Sharks also play a role in maintaining biodiversity in the ocean, by preventing explosion of single species that might cause other species to die out. So when we make changes to their populations, we can expect to see further changes in the ecosystems where they hunt. These changes are unpredictable, but here’s an example of what the effects can look like.

A study published in Science magazine in 2007 showed that major reductions in large shark species in the North Atlantic resulted in increased populations of their prey species, including cownose rays (a type of stingray). With the depletion of several large shark species in the North Atlantic, cownose ray populations have been shown to have increased as much as 1,000% in some places.

Cownose rays feed largely on mollusks, including scallops. Scientists have suggested that the collapse of the scallop industry in Chesapeake Bay can be attributed to the increased predation pressure from cownose rays. This is what is meant by the cascading effect: a decrease in large sharks leads to an increase in their common prey (cownose rays) which then leads to a decrease in scallops. Other scientists have linked the decline in mollusks to decreased water quality in coastal systems. Mollusks are filter feeders, meaning they filter their food out of the water. With fewer mollusks around, less water gets filtered.

So it is not only the marine ecosystems that benefit from sharks. Humans benefit too. We might say, following Leopold, that while cownose rays may live in mortal fear of sharks, coastal systems live in mortal fear of too many cownose rays.

From fear to fascination

Dr. John Claydon observes a pregnant nurse shark resting on the seagrass.

Sharks are impressive predators, powerful and elegant as they swim through their domain with absolute confidence. But these days that confidence is misplaced. In truth, sharks are not apex predators any longer. They have yielded that role, like so many other apex predators, to humans.

Many species of sharks have declined rapidly over the last few decades, some declining by more than 80% in 20 years due to overfishing. Unlike other fish, sharks are particularly vulnerable to exploitation because they grow slowly, mature late in life, and reproduce infrequently, giving birth to only a few pups each time.

If sharks continue to be killed at the present rate, many shark populations may be permanently damaged or even disappear. But sharks lack the furry cuteness of a harbor seal or the playful charisma of a dolphin. They are seen as killing machines despite the fact that humans are very rarely their targets. Consequently, shark conservationists have a difficult time garnering public support for their cause. In fact, sharks are not the “killing machines” that have been portrayed in movies and books. They are simply predators who have managed to persist since before the dinosaurs.

Sharks in the Turks & Caicos Islands

The Turks & Caicos Islands are home to a number of shark species, including reef, nurse, lemon, tiger, hammerhead, and bull sharks. There are no regulations that formally protect sharks in TCI waters. However, sharks are not the primary target of any fisheries.

The Caribbean reef shark (Carcharhinus perezii) is the most commonly seen on reefs, where it can be found swimming gracefully in the water column. Measuring up to 3 metres (10 feet) long, it is one of the largest apex predators in the reef ecosystem.

The nurse shark (Ginglymostoma cirratum) usually sleeps under ledges during the day, and it is active in the night. The name comes from the feeding habit of biting down and slowly sucking the prey (generally crabs, lobsters, and mollusks). During mating season, adult nurse sharks aggregate in large numbers (up to 50 individuals) over seagrass flats off some TCI cays.

Marta Calosso holds a young lemon shark prior to tagging in the waters off South Caicos.

While adult lemon sharks (Negaprion brevirostris) mostly live on reefs and are rarely encountered, baby lemon sharks are commonly found in mangrove habitats all over TCI. Lemon shark populations are dependent on shallow coastal habitat, often fringed by the red mangroves that act as “nursery areas.” Advantages of nurseries include abundance of food and protection from larger predators. Unfortunately, nursery areas are often vulnerable habitats due to their proximity to land and exposure to human activities (e.g. increase of coastal development). Appropriate management of these important areas is a conservation priority and more information on the use of nurseries by apex predators such as lemon shark is needed.

Juvenile lemon sharks have been a research focus at the School for Field Studies, Center for Marine Resource Studies in South Caicos for several years. Our aim is to look at potential nursery areas for lemon sharks around South Caicos. Specifically, we are assessing the distribution of juvenile lemon sharks, their sizes, their growth rates and residency over time. Finally, we are looking at all of these factors in comparison to other lemon shark study sites in the world.

Present knowledge of lemon sharks originates from only a few locations and therefore may not be representative of a species with such a wide distribution (western Atlantic, eastern Pacific, and west coast of Africa). For a more comprehensive understanding of lemon sharks, further research in alternative locations such as the TCI is needed. This would enhance our ability to conserve this threatened species, especially in the face of rapid development occurring worldwide.

Putting it into practice

We are not suggesting that you attempt to befriend the next shark you see. We hope that seeing them elicits caution and awe, not fear. Leopold’s epiphany did not lead him to go live with wolves. But he did stop shooting them. And he became a proponent of ecosystem level wildlife management (i.e., valuing species for their contribution to the health of the ecosystem).

Developing a sea ethic means seeing sharks not as menacing monsters, but as valuable members of the marine community. There are some who think that a sharkless ocean would mean a swimmer’s paradise. That is because they base their views on fear and misperceptions, and they have not learned to think like an ocean.

Scholars disagree about whether our fear of sharks stems from deep-seated psychological tendencies or mass-media coverage of sharks that has largely emphasized sensationalism over accuracy. In truth both probably play a role.

Whatever the cause, these fears are based largely on misperceptions. We might take a lesson from Leopold for hints about getting past these fears and understanding sharks for what they are: important members of marine ecosystems.

It’s worth noting here that there are over 350 species of sharks, most of which do not fit the fear-inspiring vision that most people picture. For example, the cigar shark tops out at six inches, hardly material for the next Hollywood thriller. Globally, we’ve averaged about five fatal shark attacks per year for the last several years. According to the International Shark Attack File at the University of Florida this means that you are about 100 times more likely to die from a lightning strike than from a shark attack.  However, you are only slightly more likely to die from a sand-hole cave-in at the beach than a shark attack. For more interesting statistics, see www.flmnh.ufl.edu/fish/sharks/attacks/relarisk.htm.