Our ocean giants

Our ocean giants are the species at the top of the food chain, also known as the apex predators, which roam the oceans with little to fear except us.

Sharks, whales and dolphins are all crucial to the health of the oceans but they are under threat from intensive fishing and marine pollution. These huge creatures live for a long time and grow slowly, but they don’t have many offspring in their lifetimes so their populations do not bounce back well from overfishing.

Sharks are killed in their millions for their fins, they get caught in fishing nets along with dolphins, and whales are still hunted in some places. They are all also affected by marine pollution, impacted by plastic in the oceans and changing water quality from oil spills and noise from shipping.

Hong Kong Shark Fin_Leff
Shark fins Source: http://fxn.ws/1MBBzhc

Marine food webs are carefully balanced and so removing the top predators has a knock-on effect on the rest of the ecosystem. These top predators are called ‘keystone’ species and they’re really important for keeping the ocean healthy. Apex predators keep the populations of their prey species in check, without them disease in fish populations is more common and one species can overtake an area more easily, so apex predators keep the diversity of marine species higher.

Marine+trophic+pyramid
Marine trophic pyramid Source: http://bit.ly/1yTvQTC

Part of the problem is that there is a lot that we don’t know about how the ocean responds to pressure from humans, and this means that it’s quite likely that it will respond in a way we can’t predict if we push it too far.

The difficulty with protecting ocean giants is that they are migratory and roam huge distances. Some also dive very deep so it’s hard to know where they are and this means designating vast Marine Protected Areas is not the most effective way of protecting them. One thing we can do though is to work out where these giants go to breed and feed, and protect these areas. These are often nutrient rich areas where currents rise up to the surface from the depths, or different currents swirl together mixing the nutrients they are carrying making it an area which is rich in fish and therefore the perfect meeting place for keystone species.

In the UK the Wildlife Trusts have identified 17 ‘megafauna hotspots’ where this occurs and proposed them as ideal new MPA sites to help protect UK ocean giants. You can find the different sites here.

So removing these ocean giants is unbalancing the ocean ecosystem like a wobbling Jenga tower. Protecting them by enforcing strict catch limits based on the best available evidence on the population size, limiting whaling for scientific purposes,  reducing consumer demand for shark fin soup and minimising the amount of plastic entering the ocean will help restabilise the ocean ecosystem through the recovery of our ocean giants.


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