Most shark species are either high up or at the top of the food chain; they act as controllers and indicators of the population numbers of the species below them.
Sharks As Controllers
Commercial fishing practices, finning, trophy hunting and destruction of habitat, are all factors which result in the decline of sharks. It is reasonable to assume that the removal of such predators will affect the population numbers of their prey species as well as those further down the food chain. Examples of such effects have been documented in other ecosystem interactions; for instance the Sea Otter was almost hunted to extinction off the West Coast of North America, this led to a population explosion of sea urchins (the otters main food source), which in turn led to a dramatic decrease in Kelp (the sea urchins food source). The Kelp provided the Pacific Herring with breeding grounds, with this area vastly depleted the Herring disappeared and without them the salmon, tuna, sea lions, sharks, dolphin and whales also left the area. To try and better understand the larger scale impact that removing sharks may have, I would like to direct everyone to Peter Benchley’s short story titled “The Day All the Sharks Died” as it appears in his book Shark Trouble – which I also urge everyone to read in its entirety!
Sharks as Indicators
The loss or lack of sharks from certain areas are indicators of the balance of the ecosystems, provided the sharks have not been fished out of certain areas it is reasonable that the disappearance of sharks from an area is as a result of or in addition to the destruction of a suitable habitat. The fact that shark species are so diverse and inhabit every ocean on the planet makes them key players essential to the ocean environment. It is important to remember how vital the functioning of the ocean ecosystem is to earth itself. With phytoplankton being the greatest consumer of carbon dioxide which it uses for the process of photosynthesis, oxygen is the by-product of this process and it is estimated that 70 % of the oxygen in our atmosphere is produced by phytoplankton!