Waiting for the enigmatic smalltooth sandtiger shark in the Canary Islands

Since last summer, when the Canary photographer Francis Pérez performed the best and longest observation ever made of the smalltooth sandtiger shark (Odontaspis ferox), the researcher at Spanish Institute of Oceanography (IEO) Pedro J. Pascual is preparing to monitor this enigmatic species, which for five years has been observed in the Marine Reserve of the Calm Sea on the island of El Hierro.

Last summer, on 7 and 8 August, the enigmatic smalltooth sandtiger shark was seen for the fifth consecutive year in the coast of El Hierro (Canary Islands), and the underwater photographer Francis Pérez was able to make the best observation worldwide until yet.

This unknown shark, included in the IUCN Red List as vulnerable, lives at depths between 400 and 1000 metres and, only females, every two years, emerge in coastal waters to give birth their calves.

The smalltooth sandtiger had never seen alive until, in 1999, he was observed in the coast of the Colombian island of Malpelo. "His presence generated an avalanche of divers who wanted to see and photo the animal," said Pascual. "In the beginning he was very humble, letting even touch, and now when he detects a diver, runs away, and he is no longer seen for several years," Pascual adds.

He was first observed in El Hierro in 2006 and, since then, appeared every summer. However, the shark had been cited in Canarian waters before. There have been several catches of this species, especially in the western islands where there is a steep and rocky slope. These catches are usually at depths around 500 meters deep along the insular slope or underwater mountains. Some specimens are larger than four meters and weigh over 400 kilograms.

The smalltooth sandtiger sightings on the island of El Hierro match with the most delicate moment of the species: the birth of their calves. "The smalltooth sandtiger is a species with very slow growth. He can live more than 40 years, his reproduction is biennial and each female gives birth two calves each time, making the moment even more delicate," says Pascual.

What happened in Malpelo shows the stress that diving can cause to this enigmatic species. "On this island it could happen the same if we do not manage and temporalize this activity," says Pascual. Currently, there is no other place on earth where you can watch the smalltooth sandtiger and it is important not to lose the opportunity to learn a little more about this species. Pascual suggests that "we should set a maximum time of observation, establish quotas and make a waiting list for diving in this area."

Reproduction

The smalltooth sandtiger has a curious reproductive strategy. Unlike most fishes, this shark produces very few offspring, but those are independent from birth. He is ovoviviparous, that is, their young are born from an egg but this is developed and hatched in the womb. In addition, the embryos practice the adelfofagia or intrauterine cannibalism; this means that the biggest of the litter is fed by his brothers in the late stages of development. The surviving cave can grow to over a meter after birth.

The delivery has never been observed and according to Pascual would be "spectacular" if it could be filmed. Most shark species share the same strategy: they do not give birth where they live. No one knows exactly why, but the most accepted hypothesis is that in this way they avoid predation by other sharks of the same species. The few things that are kwown about the biology of smalltooth sandtiger is largely by the extrapolation of the knowledge that we have of a close relative: the sand tiger (Cacharhinus taurus). This species is quite common in aquariums around the world.

Monitoring

Pedro J. Pascual, a shark expert, has written several books about these animals and, now, he is finishing one about Sharks and Rays in the North Atlantic, which will be soon published.

Pascual did not want to lose the unique opportunity to study the smalltooth sandtiger and, despite financial difficulties to carry out this project, he is preparing to monitor the shark for the possible arrival at the coast of El Hierro.

First, the idea is to continue with the identification of the specimens of El Hierro's population, thanks to the exceptional photos and films that the photographer Francis Perez took last summer. Pascual will try, together with the photographer, to observe the birth, research the reproductive seasonality and demonstrate that, as it is thought, it occurs once each two years.

In a second phase of these studies, they will mark the specimens sighted with temperature and depth sensors. These instruments provide a continuous record of information that could define the habitat of the animal.

"The main project, and the idea that accompanies all its actions, is to raise awareness and convey the idea that sharks are not dangerous enemies and disseminate a clear and unequivocal message that promotes their protection and conservation," Pascual says.