Hammerhead Shark

Hammerhead Shark
Hammer from Cocos Island, Costa Rica” by Barry Peters licensed under CC BY 2.0

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Introduction

  • Scientific name: Sphyrnidae spp.
  • Easily identified due to their unique head which is shaped like a flattened hammer
  • The wide shape of its head allows for more sensory organs which makes the hammerhead shark an effective ocean hunter
  • 3 out of 9 hammerhead species can be found in the Coral Triangle, they are all considered vulnerable and endangered by the International Union for Conservation of Nature (IUCN)

Distribution

The hammerhead shark species are found in tropical and temperate waters all over the world. Out of all the hammerhead sharks, only the great hammerhead is considered to be nomadic. This means that they do not like to stay in a single location and they like to travel to different places in search of food and warmer waters. However, it is observed that they prefer to remain within the underwater continental shelf and do not like being in the open ocean.

Hammerhead sharks can be found in all CT3 countries (Indonesia, Malaysia, and the Philippines)

Why they are important

The hammerhead sharks, like most sharks, are considered to be apex predators. They are at the top of the food chain and they prevent populations of other species from overpopulating and disrupting the balance of the ecosystem. Hammerhead sharks also remove sick and weak members of different prey populations; thus preventing the spread of diseases and ensuring that only healthy fish remain.

Loss of a shark species in a local marine ecosystem means that different species may overpopulate which can cause the food chain to collapse.

Biology

Hammerhead sharks are known to have a strong sense of sight and smell, and can detect electrical or magnetic fields. The position of the eyes on the edges of the wide head allow for a 360 degree view of the world around them and the head of a hammerhead shark contains several thousand sensory organs called the Ampullae of Lorenzini. These are specialized pores that can detect electrical fields created by their prey and are useful for finding one of their favorite foods – rays – that try to hide by burying themselves in the sand. The wide head of a hammerhead shark is also used to hold rays in place by pinning them against the sea floor while the shark can feed on the ray itself.

Hammerhead sharks reproduce once a year and produce 12-15 pups. The Great Hammerhead shark is known to produce 20-40 pups.

Even though hammerhead sharks live in the water, they need to be constantly moving in order to keep oxygen-rich water flowing over their gills to avoid drowning. Unlike other fishes, sharks do not have swim bladders that can give them buoyancy. They use their large pectoral fins to move them up and down the water column. Their large liver also contains a lot of oil which is lighter than water and helps given them additional buoyancy when swimming.

Threats

The demand for shark fin for food is pushing them to extinction; a lot of sharks that are caught for the shark fin trade are often caught just to have their fins cut off while the rest of the shark is untouched. They are tossed back into the sea without the capability to swim and drown shortly afterwards. Hammerhead sharks are also prone to being accidentally caught in fishing gear and end up as by-catch. They are often caught by commercial fishermen who are using longlines. Sharks will often drown before fishermen are able to release them back into the water.

Demand for shark cartilage for use in medicine is also putting sharks at risk; it is believed that shark cartilage has cancer fighting properties because there is a belief that sharks do not get cancer. This is the myth that is fueling the shark cartilage industry; there have been several cases where sharks have been found with cancerous tumors. Harvesting of sharks for their cartilage, liver and fins are adding to the decimation of the world’s shark population. It is estimated that 100 million sharks are killed every year around the world, a number that far exceeds what many populations need to recover.

According to a report done on shark utilization by the World Wildlife Fund (WWF), fishermen primarily focus on three hammerhead sharks within the Coral Triangle. The scalloped hammerhead (Sphyrna lewini) and the great hammerhead (Sphyrna mokarran) are both listed as endangered while the smooth hammerhead (Sphyrna zygaena) is listed as vulnerable.

What you can do

Don’t eat shark fin soup.
Demand for shark fin soup is one of the primary reasons for the overfishing of sharks. The fins themselves are relatively tasteless but are considered to be an important part of the dish.

Don’t use medicine that is made from shark cartilage.
Research has also failed to find any direct benefit of consuming shark cartilage to fight cancer or arthiritis. Spread awareness about myths surrounding the benefits of shark cartilage in order to prevent more shark deaths.

Inform the authorities of illegal hunting or sale of hammerhead sharks.
Hammerhead sharks are protected in all CT3 countries (Indonesia, Malaysia, and the Philippines). Share the information on social media to raise awareness about illegal shark meat in local markets.

Laws that protect Hammerhead Sharks in the CT3:

Quiz

What would be an example of an ecosystem collapse once the sharks are gone?

Answer in the comments section below!