Young hammerhead sharks, new research

This video is called Shark Academy: Scalloped Hammerhead Sharks.

From Wildlife Extra:

Endangered juvenile sharks migrate into unprotected waters

The movements of a young female Hammerhead Shark have been tracked for the first time, revealing vulnerable gaps in the present protection plans.

Hammerhead Sharks are listed as threatened with the IUCN and numbers have declined by more than 90 percent in some parts of the world, particularly Scalloped Hammerhead sharks, found in the Gulf of California, Mexico.

These are susceptible to being caught by fishing nets while moving into the open sea, but little information exists on their exact movements, especially those of juvenile sharks as they go through the critical period of adolescence.

Current protection plans prohibit commercial fishing from large vessels within 50 nautical miles of the coast. However, findings from this study reveals the young sharks venture into the open seas to fish, meaning they are still vulnerable to being caught in fishing nets.

Researchers from the Centro Interdisciplinario de Ciencias Marinas, Mexico and the University of California, Davis, USA tagged three live juvenile hammerhead sharks in Mexico’s Gulf of California so they could be tracked through adolescence.

The results of one of these tags, which was downloaded after fishermen caught one of the sharks, revealed the female shark travelled 3,350 km, and helped pinpoint potential key sites needing protection.

She was found to swim within a school of fellow hammerheads at an offshore island during the day, but migrated away at night, diving to greater depths to feed on fish and squid, sometimes as deep as 270m.

This behaviour, the scientists believe, maximises her foraging opportunities and continuing growth, and partially explains the early migration of this juvenile female to off-shore waters for richer food. Scalloped Hammerhead Shark pups have high metabolic rates and as they grow older require higher ration levels to fulfil their energetic needs.

Study author Mauricio Hoyos from Pelagios Kakunjá (a Mexican NGO) said “The key to protecting this species is detecting their nursery grounds and protecting them in their more vulnerable stages. This is the first time ever that we have an idea of the behaviour of this life stage in this zone and this information will be important to design management plans to protect this species in Mexico.”

The research suggests that juvenile female hammerheads are trading off the risks of greater exposure to predators in the open sea, with better food sourcing opportunities.

However their ventures to the open sea means current management measures for sharks set by the Mexican government may not be sufficient for the conservation of this species.

This new information highlights hammerhead sharks may still be in danger, due to their use of both coastal and offshore waters during early life stages. The researchers say that coastal nursery grounds and offshore refuge areas for scalloped hammerheads are therefore critical habitats where protected marine reserves should be sited.

Study author James Ketchum from Pelagios Kakunjá (a Mexican NGO) said: “For the first time, we’ve seen the shift from a coastal-inhabiting juvenile to a migratory adolescent that remains mostly offshore in order to maximise growth and reproductive potential. Because of their dependence on both coastal and offshore waters during their early life-stages, we think that they may be more susceptible to fisheries than previously thought, and current protective measures in Mexico may unfortunately be insufficient.”

9 thoughts on “Young hammerhead sharks, new research

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