A single fin slicing through the surface of the water. The glimpse of a shadowy shape as big as your board in the curl of a wave. If images like these swim into mind—if the iconic baaa DUM, baaaaa DUM of Jaws fills your ears—if your heart seizes in terror when you think of sharks, you’re far from alone. Humans’ relationship with these magnificent predators is one of morbid fascination: sharks awe and terrify us in equal measure. Of course, surfers needs must be wary of what lurks below, but sharks deserve our respect as amazing predators whose presence is vital to the health of oceanic ecosystems.
Most people think of sharks, especially great white sharks, as apex predators. And while that’s not entirely true (orcas have been known to prey on even great whites) sharks are predators who often top their food chains, and therefore, a sea change in a shark population can domino outward in a series of dramatic consequences. Not only do sharks contribute to the strength of their prey species’ gene pool by weeding out the weak and infirm, the very presence of sharks affects the breeding and feeding behavior of their prey species, which in turn contributes to the maintenance and management of foundational species such as coral and sea grass. A chilling and recent example of such a change culminated in 2004 just off the Atlantic seaboard. A catastrophic reduction in great shark populations resulted in an explosion of rays, who then proceeded to decimate the hundred-years-old bay scallop fishery in North Carolina.
It’s just not true that sharks are immune to disease and cancer or that shark cartilage cures cancer. On the other hand, scientific minds are interested in the way that sharkskin appears designed to repel microbes. Material called Sharklet, made to mimic the effect of sharkskin with microscopic ridges and grooves, was shown in laboratory tests to retain 94% fewer MRSA bacteria than a smooth surface. On their home turf, or rather, surf, shark predation may be linked with infectious disease transmission. When prey species normally exist at low populations kept in check by predation, they tend to have less resistance to diseases and parasites that rely on high population density to proliferate. Take predators out of the picture, population densities go up, and suddenly those parasites and diseases have room to roost. So even though there are no known cases in which a decline in specific shark populations have led to oceanic equivalent of an apocalyptic outbreak, who wants to be the person to find out the hard way?
Sharks <3 Coral Reefs
Or, rather, sharks are important to the health and resilience of reefs. A study conducted on the relationship between sharks and reefs in the atolls off Australia’s northwestern coast shows that when sharks are overfished, the reef suffers. Because coral isn’t the first thing that comes to mind when folks answer the question, “What do sharks eat?” the link may not seem obvious. But as it turns out, fewer sharks mean that mid-level predators, whose populations would normally be kept in check by shark presence and predation, proliferate, and feed on the herbivorous fishes that would normally feed on algae. With fewer algae-eating fish around, algae can overwhelm coral, leading to the overall decline of the reef. The report’s conclusion? “Healthy populations of reef sharks should be a key target of management strategies that seek to ensure the future resilience of coral reef ecosystems.”
By running the circle of aquatic life and keeping the population of herbivorous fishes and sea life in check, sharks directly contribute to the health of “blue-carbon” vegetated coastal habitats like sea grass, saltmarshes, and mangroves. These environments can capture carbon and sequester it in the seabed forty times faster than rainforests, but only if they’re able to thrive, which they can’t do if they’re being decimated by sea turtles grazing at will in the absence of the sharks who would eat them. Fear-driven measures like shark culls and other policies that drastically impact apex predator populations can thereby have disproportionate, unintended implications for climate change.
Thank you, Jaws, for all you do to make our planet safer and healthier!