In the middle of the bathing season, with a generous sun and thousands of people on the beaches of San Sebastián, in mid-August the yellow flags were raised after the presence of a family of blue sharks (tintorera) was observed in the port of San Sebastián. A few days before, a shortfin mako shark had been seen near the bay. Their habitat is not so close to the beaches, but from time to time they come close to the coastline. In recent years, in addition to blue sharks and mako sharks, other species of sharks have been sighted in these areas in this environment, such as the basking shark, the porbeagle, the hammerhead shark and some thresher sharks. “The presence of these sharks is a good indicator, it means that the ecosystem is healthy,” explains oceanologist Maite Erauskin-Extramiana. A scientific team from the Azti technology center, a leader in marine and food research, has placed electronic tags on 14 blue sharks to understand their behavioral patterns in the Bay of Bizkaia and the migrations that these sharks make.
There are several studies on the behavior of these sharks on the coasts of Brazil and the United States. It has also been found that they usually arrive in the Bay of Biscay from Ireland, but there is no research on their behavior while they are in the waters of the Cantabrian Sea, before to continue the route to the Canary Islands and the Azores Islands, and then migrate to the other side of the Atlantic. The truth, says Erauskin-Extramiana, is that “the Bay of Bizkaia is an area of interest for these species, where numerous juveniles and some adult individuals have been sighted.”
The blue shark is a pelagic shark, with a slender body. It usually reaches 2.5 meters in length and is bluish on the dorsal side and whitish on the ventral side to better camouflage itself, while the mako shark, more robust and very hydrodynamic, a very fast swimmer, can reach up to four meters and weigh 750 kilograms. . They are not dangerous species, assures the Azti oceanologist: “We must demystify the bad reputation they have. We humans are not in their diet, far from it. They are curious, they approach, but at no time aggressively, except when they feel cornered. It is beautiful to see them, appreciate the tranquility with which they swim. In Bermeo (Bizkaia) there is a group that usually organizes trips to the sea to see them up close. It is an activity that I recommend to everyone.”
A project led by Azti seeks to understand the behavioral patterns of these sharks, the use of habitats they frequent and the migrations they make, in order to “promote harmonious coexistence with human and fishing activities,” reports this technology center. “It is important to know the location and season preferences of sharks, as this will allow us to develop management measures aimed at reducing bycatch mortality of these species,” says Erauskin-Extramiana. The blue shark, above all, is a shark that is often accidentally caught in longline fishing nets.
A scientific team made up of around thirty researchers has placed tags on 14 blue shark specimens between July and August of this year, half female and half male, to monitor their movements on the Cantabrian coast. Nine have been given conventional plastic marks (yellow for females and green for males) and their measurements and weight are recorded, as well as the position where they have been marked. Azti has already received notification that some of these individuals have already been sighted in surrounding waters, which allows “obtaining information about the movement they have made and whether they have made large-scale migrations,” says the oceanologist.
Five other sharks are given satellite-controlled tags. “They are immobilized from head to tail, a genetic sample is taken and the satellite tag is placed on a fin. These devices have a release time of six months or one year. During this time they store data on pressure, temperature and light that will later be used to know what environmental variables they prefer, what temperature ranges they like best. Once released, with this data the migration patterns they have carried out can be reproduced,” explains Erauskin-Extramiana. So far no tag has been placed on a shortfin mako.
The blue shark is a large predator, very important for the ecosystem, and at the same time of great interest for fisheries. It is the most fished shark in the world and tourism is also booming to get to know this blue shark up close, adds the scientist: “Maintaining stable and healthy populations of these species in the ecosystem is essential for the ocean and for human beings.” humans”.
Between February and August of next year, the tags that these sharks will release will begin to be collected and all the recorded information will begin to be processed. The German collective Ocean Collective and the Caila Diving and Fishing & Sailing Basque Country associationand is financed by the European Maritime, Fisheries and Aquaculture Fund of the EU and the Basque Government.
Azti assures that the decline in shark populations in the oceans is a cause for “growing concern due to their vulnerability and overexploitation in fishing.” Both the capture of blue shark and shortfin mako are regulated by the International Commission for the Conservation of Atlantic Tunas (ICCAT), which has established fishing maximums and, in the case of mako, a prohibition on retention on board fishing vessels. Although this is a pilot project that will last one year, it is planned to continue until the end of 2024.
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