Wednesday, October 27

Scientists warn that a mysterious disease has wiped out 70% of Galicia’s gull population in 10 years


The seagull population has fallen so much in the last decade in Galicia that the criteria applied internationally place this species in the category of vulnerable, prior to considering it in danger of extinction. Scientists who work with seabirds estimate the collapse at 70% in that period of time and warn that, although the causes are most likely multiple, there is a disease that they have not yet managed to unravel that is causing havoc in the colonies of these animals.

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Álvaro Barros, doctor in Biology and member of the Animal Ecology Group of the University of Vigo, recalls that in 2019, in a single field day, the corpses were counted by the hundreds in the Sisargas Islands, an archipelago of the Costa da Morte that hosts one of the colonies of yellow-legged gulls (Larus Michahellis) Most important in the world. It is in this specific species, which breeds and lives all year round in Galicia, where the population decline has been noted. The census drawn up of the specimens that are on the coast of the province of A Coruña that goes from Malpica to the border with Lugo put numbers to the fall: it counts 2,674 pairs -2,306 of them in the Sisargas- currently, in front of the around 8,900 there were a decade ago. In the 90s there were about 13,000.

The situation is “worrying and leads the species to a threatening situation,” says Sergio Paris, head of the census and technician at the Center for University Extension and Environmental Disclosure of Galicia (CEIDA), an entity supported by the Oleiros City Council, the University of A Coruña and the Xunta. The figures for the population decline that are calculated can be extrapolated to the rest of Galicia, he assures. In the case of land included in the Parque Nacional das Illas Atlánticas, collect their own data and they show the same accelerated decline: between 2006 and 2019, the number of breeding pairs was reduced by 70%.

Both Barros and Paris ask for attention and resources to find out why the seagulls are dying. And when they do, they are aware that they encounter an additional problem: these birds have a “bad reputation” and are “annoying” for humans, especially those that have settled in urban areas. “We have to get away from the idea that they are the rats of the air,” asks Paris. Barros adds that it is not “sympathy” that should guide nature conservation work. In this case, the first challenge is to understand what happens to these animals. “Those of us who are dedicated to seabirds are very pissed off because we don’t really know what is happening. Probably several factors are involved,” explains the expert from the University of Vigo.

He believes that it is possible that there was an “oversized” population of seagulls in the past because the species “makes good use of all ecological niches.” It is closely associated with humans and has benefited from food found in landfills and discards from fishing. The former have been closed since the 1990s and the latter have been reduced with new laws. That led, Barros continues, to a drop in the number of these birds. But when it was expected that the figures stabilized, what happened was that the fall “was accentuated”: “And that is no longer explained by the disappearance of landfills,” he emphasizes. The first alerts about a disease that paralyzed these birds occurred ten years ago.

Paris agrees in the analysis. The decline, he says, became “exponential” and has been noted above all in the last five years. Scientists link it to this mysterious paralyzing syndrome, which causes death because they stop being able to eat. Periodically an episode of this disease jumps to the media due to the appearance of hundreds of dead birds. The most recent was at the beginning of September in the Vilagudín reservoir, in Cerceda (A Coruña). The Xunta prohibited fishing for fear that it was due to the presence of some toxic substance in the waters.

The CEIDA expert explains that, although some analyzes have been carried out, it is not known what the cause is. Several hypotheses have been raised: that it is botulism -a disease caused by a bacterium, of which some strains affect humans-, that there is a toxin or that it is due to chemical contamination. Álvaro Barros assures that the case has the ornithologists “half crazy”. Affected birds have been found in Galicia, but also in Portugal, in the Cantabrian area, in the British Isles and even in the Mediterranean, but no clear results have been obtained on the origin. “We are puzzled and eager for someone to find an explanation,” he says. He regrets that, if the species were “more emblematic”, “all the cards would have been put on the table”.

On the effects of this drop in the number of seagulls in the ecosystem, scientists agree that they are “difficult to predict”. Paris compares it to the impact of removing an operator who puts a part off an assembly line: “It’s just a screw, but the whole chain still gets out of control.”

“It’s not the gull coronavirus”

One of the technicians of the Parque Nacional das Illas Atlánticas, Vicente Piorno, explains that on the island of Sálvora they are carrying out an experiment to save the seagulls they find sick and to identify the cause. Botulism and red tide biotoxins have been initially ruled out in their analyzes. Also “quite a few viruses and some bacteria”, but the results remain “inconclusive”. He points out another hypothesis that has been raised in the scientific field: that paralysis is related to a deficiency of vitamin B, which seagulls obtain through phytoplankton. Next year, Piorno says, they will test again considering this possibility, but for now the syndrome “remains a mystery.” He says he has the impression that “there is something in the ecosystem”: “It is not simply a virus. This is not the gull coronavirus.”

Regarding the recovery, it indicates that between 50% and 60% of the animals that collect weak, with signs of paralysis and with diarrhea recover with hydration therapy.

An “apparently indestructible” species

Sergio Paris demands that a complete study of the seagull population be carried out. The latest census is one for all of Spain that has not been updated since 2009, he says. He also asks that efforts be made to investigate the disease and recalls that it is the Xunta that has the powers in matters of nature conservation.

The CEIDA technician reports that the data on the decline of specimens has been received with skepticism in some areas because the animal is very common, it breeds on the roofs of buildings and is seen daily. “It may seem impossible, but if the trend continues, in a few years it will become a species considered threatened,” he says. Scientific criteria already place it as vulnerable, although this does not have a reflection for now in the lists of protected species of the administrations.

Barros, for his part, remembers “faces of astonishment” among fellow ornithologists when he began to speak to them of the sharp decline in the colonies. “The yellow-legged gull is an all-rounder; it feeds on debris from terraces, mosquitoes, worms, barnacles, fish … it eats grass if it needs to. It is apparently indestructible. If this species is doing badly, he has to sound the alarm “, he defends. The Galician Ornithology Society, of which he is a member, sent a letter to the Department of the Environment, but “there has been no response of any kind.” The category of vulnerable, he remarks, supposes that there is time to reverse the problem, but “we must act now.”



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