Top predators are essential to the oceans

Source: www.photolib.noaa.gov/htmls/reef1373.htm Photographer: David Burdick

Gray Reef Shark (Carcharinus amblyrhynchos) Source: http://www.photolib.noaa.gov/htmls/reef1373.htm
Photographer: David Burdick

The global media was recently full of reports about the interaction that Australian pro-surfer Mick Fanning had with a shark during a competition in South Africa (see the video here). There is no doubt that the experience would have been terrifying and I’m very happy that Mick was not injured. The reactions across media and social media have been broad and varied. Many reports have reasonably pointed out that the rate of shark attacks is less than other more frequent dangers (like being killed by a cow) while some have, unreasonably in my opinion, postulated that we should “clear the ocean of sharks”.

There is no doubt that shark attacks are an emotionally charged event and that they sometimes have tragic outcomes. This has, in some instances, been used as an excuse to have shark culls. Rather than add to the chorus of voices stating how ridiculous this approach is (which it certainly is), I thought I would state something that seems to get forgotten: sharks are essential to the health of marine ecosystems and therefore essential to human life.

Why should we care about marine ecosystems? This seems like an inane question, but many people either don’t care or don’t understand how important healthy oceans are to our lives. Approximately 50% of the oxygen we breathe is produced in the ocean – can you skip every second breath? Over one billion people worldwide rely on seafood as their primary source of protein. Much of our food and pharmaceuticals relies on marine-based products. Basically, we can’t live without healthy marine ecosystems.

Why should I mention that? Because ecosystems rely on balance. When they are out of balance, they are unhealthy and become less productive. One of the services that top predators such as sharks provide to marine ecosystems is this balance. They control the species which would otherwise rapidly expand and dominate systems, lowering species diversity and productivity. A very good example of this in a terrestrial ecosystem is wolves in Yellowstone National Park in the USA. Wolves were hunted to local extinction in the area because they were thought to prey on livestock in the surrounding farmlands. In the absence of the wolves, however, elk populations expanded to the point where massive ecological damage was being done to the forests by grazing elk. Since reintroduction of the wolves, the forests have once again become healthy.

Another of the services that sharks perform is to “clean-up” marine ecosystem. Again, a terrestrial example that most people would be familiar with is lions in Africa catching the sick, diseased or old animals from herds. By removing these weaker individuals the lions are strengthening the herd as well as increasing the per capita resources available to the herd (by reducing its size).

Indeed, there is now a plethora of information on the benefits of top predators to the health and function of different ecosystems. We don’t seem to doubt this information for terrestrial systems, but our fear of sharks makes us irrational when it comes to marine systems. If one person is attacked by a shark the media goes crazy and we hear phrases like “shark cull”. If someone is killed by a cow…….. well, you’d never hear about it.

The reality is that in marine ecosystems the top predators are often sharks and these ecosystems cannot function properly without them. Humans need marine ecosystems to survive. Ergo, without sharks we can’t live as we currently do. While interactions with sharks can be terrifying and even tragic, we need to accept that the oceans are their habitat and we humans need them.

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One thought on “Top predators are essential to the oceans

  1. […] a recent post I explained how top predators are essential for healthy ecosystem function. Being a marine […]

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