Reef sharks are a significant part of the ecosystem of coral reefs around the world. Species such as the Caribbean Reef Shark and the grey reef shark, play a big role as predators in and around coral reefs. However, there has become a worry in regards to the number of reef sharks that live in the wild. What is causing this, and what does this mean for coral reefs?

What Are Reef Sharks?

There are several different species of reef sharks, each associated with specific oceans and areas. The Caribbean Reef Shark is found in the tropic regions of the Western Atlantic Ocean, while the Indian and Pacific Oceans are home to Blacktip Reef Sharks and Grey Reef Sharks. 

These sharks spend their time in and amongst the coral reefs. They are agile predators and feed off fish and cephalopods. 

According to the World Wildlife Fund, reef sharks are an important part of the ecosystems of many coral reefs. They are one of the major top predators, balancing and maintaining a healthy and stable food web. This means that the reef is healthy and working in harmony, meaning that the corals and marine life are less likely to get ill from the stressors of global warming and water pollution. 

Why Are They At Risk?

A recent study has found that reef sharks across the globe are in decline, with some reefs not having sharks in them at all.

The study, published in Nature in July 2020, surveyed 371 reefs across 58 countries. They found that in the coral reefs surveyed, 20% contained no sharks at all. In the coral reefs that did have sharks, the population was scant with some reefs having a worryingly low number of reef sharks. 

But what is causing this worrying decline of reef sharks?

Fishing

A major cause of the decline of sharks around the world is fishing. According to the World Wildlife Fund, there is a huge demand for shark fins and meat, and the fishing of sharks for this is not managed correctly. They are also fished for leather and liver oil.

According to an article in eLife Science, two-thirds of all species of sharks are vulnerable because of overfishing. This is mainly because shark fins are seen as one of the most valuable types of seafood. Sharks are also affected by fishing nets and equipment that trap them. This means that the true number of sharks that are killed in the oceans by humans every year is not fully known because many sharks are caught by accident and then discarded in the sea. 

Global Warming 

Fishing is not the only cause of the decline of reef sharks. A study was conducted by researchers at the James Cook University and the University of Massachusetts that looked into how higher temperatures affect shark embryos and the health of baby sharks. 

The study found that when shark eggs were growing in warmer water, the embryo grew quicker, using up the yolk in their sac faster. This meant the sharks hatched sooner and came out undernourished and smaller. 

This means that as the oceans get warmer, the health of the sharks will decline, and means that many species of sharks might become extinct. 

Damage to the Ecosystem 

According to the World Wildlife Fund, reef sharks are threatened by the damage to the ecosystem that they live in. Pollution and coastal development mean that coral reefs are damaged and plants are harmed. 

Mangrove plants are used by reef sharks as a nursery and these plants help protect the young sharks. Without these, the young reef sharks are vulnerable to predators. 

What Does The Decline of Reef Sharks Mean for Coral Reefs?

A coral reef is an extremely fragile ecosystem. When one aspect of the reef is harmed, the whole system is threatened. If coral reefs lose their sharks they are losing one of the main predators in their ecosystem. This causes an imbalance in the food chain, meaning that the stability of the reef is rocked. 

When the overall diversity of a coral reef changes, the coral reef becomes unstable. Corals can become stressed and vulnerable and therefore more likely to suffer from bleaching and other diseases. 

If there are no sharks in coral reefs, there is nothing eating bigger predatory fish. These fish eat herbivores that eat the algae. If the bigger fish have no predator and are therefore eating more herbivores, there is then more algae amongst the coral reefs. 

If there is an abundance of algae in the area, the growth of corals is affected. The ecosystem will shift and become dominated by algae. 

What Can Be Done to Protect Reef Sharks?

As we can see, reef sharks are a really important part of the ecosystem of coral reefs. Without them, the whole habitat is threatened and at risk of collapsing. 

Thankfully, scientists and charities are working towards protecting these reef sharks and therefore supporting the coral reefs of the oceans. 

The International Union for Conservation of Nature has categorized the Caribbean reef shark as ‘Near Threatened’ because of the overfishing in the area. Reef sharks are protected in marine protected areas in Brazil and, according to Wikipedia, the fishing of this species is banned in United States waters. However, the International Union for Conservation of Nature has pointed out that there needs to be an increase of law enforcement against illegal fishing to fully protect these sharks.  

Illegal fishing is a common occurrence around the world and more needs to be done. Having a law and not following through with it has the same effect as not having a law at all. The sharks that are so important to coral reefs are still getting fished. 

We must also look into regulating fishing and what equipment is used so reef sharks are not being killed accidentally. A lot of equipment used in fishing does not discriminate with what is being caught, and many vulnerable species get wrapped up and die in the nets. 

In order to protect the reefs, we must also reject the consumption of shark meat and fins.