Capabilities that Only Predators Have for Managing Ecosystems

Contributed by Marielle Grenade-Willis

Sharks, and predators in general, have been getting a bad rap these days. Between the latest admission from Trump that he hates sharks, and uproar over New Zealand’s zealous “conservation” campaign to eradicate introduced predators by 2050, there’s a lot to be said about the misnomer of being called a “predator”. Predators such as wolves, lions, bears, and sharks are integral ecosystem managers, and as Caroline Fraser puts it in Yale School of Forestry and Environmental Studies’ Yale Environment 360:

“While no one disputes the importance of photosynthesis and nutrient cycling, experts on predation have become increasingly convinced that ecosystems are ruled from the top.”

Take for instance the gray wolf in Yellowstone whose reintroduction not only controlled the population of ungulates such as elk and moose from overgrazing stream-side vegetation, but also provided food for other scavenger communities within the national park.

Sharks especially have an immense impact on how marine animal communities and ecosystems are shaped. A 2010 study published in Ecology Letters found that shark populations were dwindling in three distinct areas of the world: the Northeast Atlantic, Mediterranean/Black Sea, and Northwest Pacific. By reviewing ten years of scientific data on sharks, analysts were able to pinpoint that the catching of sharks by fishing boats affects the equilibrium of the marine food chain. The Lenfest Ocean Program’s review of the study demonstrates that the decline of sharks by the fishing industry contributes to the increase in meso-predators such as smaller sharks, dolphins, and turtles who further deplete resource species like bony fish and invertebrates. Sharks were also shown to replenish and keep plant communities in tact such as in the case of seagrass meadows in Shark Bay, Australia where the presence of tiger sharks kept marine animals like dugongs and turtles from overgrazing the ocean floor.

Not only do sharks keep marine habitats healthy, but they have also been found to practice philopatry, which is the pattern nonhuman animals have of staying in or returning to the same geographic area. Pew marine fellow and shark scientist Demian Chapman “found evidence that at least 31 shark species around the world exhibit fidelity to a particular site for mating, feeding, or giving birth.”

Science about shark behavior, like their affect on marine ecosystems and their allegiance to certain areas for key survival stages, is paramount to their conservation so that we can reframe how predators are caricatured as “scary” or a “nuisance” in our modern society and understand how much our presence affects their habits. According to the IUCN, a third of shark species are threatened with extinction and as leading shark scientist Rachel Graham says:

“There still are sharks left, and so with many of the species, there is time to reverse what we’ve done to them. Think back to when turtles were thought of as jewelry boxes and fodder for soup. Today if there’s any mention of turtle slaughters, it becomes big news. So I think there’s a big chance for changing how people feel about sharks and rays. As people learn more about them, they see that their slaughter is unsustainable and morally wrong.”