What did population growth and urbanisation have to do with an increase in shark attacks in Réunion between 2011 and 2019, if anything? Was there a relationship?
Let me explain.
In the lead up to this period, the island of Réunion was experiencing significant population growth in the north and west. Development pressures were particularly acute here.
More people meant more houses and more roofs. There were more paved surfaces, more roads. At the same time there was less undisturbed soil and less vegetation.
There was a theory that this led to increased water runoff in the west and potentially altered the salinity around stream and river mouths.
Additionally, faster runoff may have been bringing more sediment to the estuaries.
Most sharks live in salt water and can not survive in fresh water.
But there is one species that can survive in fresh water – the bull shark.
They can control the proportions of salt and water they store in their bodies.
Bull sharks are known for using rivers as nurseries for their young. River mouths are usually rich in food and relatively free of other shark species.
Bull sharks have been recorded hundreds, even thousands of kilometers up major rivers around the world.
They are also known to like murky, brackish water.
So the theory goes like this: a rise in population in the west and north has led to more urbanisation, more built structures and fewer natural retarding structures.
A greater volume of fresh water at the mouths of rivers and streams have decreased the salinity of the water.
Also, faster runoff can carry more sediment, making the water murkier.
These conditions create an ideal environment for bulls sharks.
The theory is just that at this stage. But is worth considering.
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