In the midday sun, a black sand beach, gentle surf and the smell of rottenness. There are 137 sea lion carcasses scattered, alone or in groups. Sometimes up to 150 meters separate one and the other. They are swollen, in an advanced state of decomposition. The most probable thing, the scientists present at the site observe, is that they died offshore and floated dragged by the northern currents to this point on the coast of Baja California Sur, the beach of San Lázaro. Pending laboratory analysis, the main hypothesis to explain the largest incident of this type in northern Mexico points to red tide poisoning, a natural phenomenon caused by the proliferation of algae.
The alert jumped on September 3. “Wow,” thought biologist Aurora Paniagua, president of the Mmares association, when the warning came. I had never heard of anything close in size. Neither she nor any of her colleagues from the Marine Mammal Stranding Network, a collective platform in charge of monitoring animals stranded on beaches and trying to save those still alive. Since 2012, nearly 300 cases have been reported in the area, from gray whales to common dolphins. “They are mostly individuals. Sometimes, between two and five and, in rare cases, more than 10. Seeing wolves and that number had never touched me ”, explains Paniagua. Before the episode on the beach of San Lázaro, the largest incident of this type on the north coast of Mexico that the consulted associations recall did not reach 100 copies.
The day after the report, Paniagua and a dozen people, including scientists and inspectors from the Federal Attorney for Environmental Protection (Profepa), left La Paz for Magdalena Island, located four hours from the regional capital, at the end of a wide spoon-shaped bay. Fishermen from the coast crossed them by boat. They got on several 4x4s and a four-engine and began to travel the more than 50 kilometers of beach. “It was finding you one corpse after another,” recalls Paniagua, by phone from La Paz.
Using a yellow tape, protected with scarves or masks, they measured the thickness of the neck and the size of each animal, from the nose to the tip of the tail. When they finished with one, they marked it with white spray so as not to repeat themselves. Taking samples to find out what had happened was not easy. Of the 137 dead animals, only four were fresh enough. They were cut open with a scalpel to extract bits of liver, kidney and brain. They stayed that way for seven hours.
From the outset, the biologists observed that no corpse had fishing net marks. Baja California Sur is an area rich in marine fauna and is among the main fishing producers in the country. In 2017 it was placed in third place with a production of more than 110,000 tons. It is not strange that sea lions, especially the younger ones, approach the nets, attracted by the prospect of easy food, and get trapped. But both the scientists present on the ground and Profepa rule out that possibility. “No marks of anthropogenic origin caused by nets or blows and cuts caused by some type of vessel were observed in them,” the agency declared. it’s a statement released this Sunday, ten days after the first alert was sent to the associations.
In addition to the absence of marks, neither the number of bodies nor the type of specimen found on the beach of San Lázaro agrees with this hypothesis. Among the 137, only one female was found. The rest were males between five and nine years old, weighing an average of 200 kilos and measuring around 2.4 meters in length. In addition, they sported the typical crest on their heads. The biologist Fernando Elorriaga, a CICIMAR researcher at the National Polytechnic Institute, points out that this homogeneity reinforces the hypothesis of intoxication: “These males feed in certain areas and could have consumed a contaminated resource. There is a segmentation by sex of feeding areas and that is why other groups did not fall ”. The only female, says the scientist, “could have arrived alive and perhaps was not part of the event.”
California sea lions eat tons of food each year. In the area, the most common is that their diet is composed of sardines, anchovies and hake. The hypothesis of intoxication ventures that the animals would have ingested contaminated species and that would have caused them a cerebral arrest while swimming. Domoic acid, the toxin on which suspicions center, affects the nervous and gastrointestinal systems. “It was a very acute event. In a very short time it hit all these animals, so the degree of decomposition is similar, ”explains Elorriaga. The researcher estimates that the corpses could have floated between 10 and 15 days to reach the beach of San Lázaro, but calls not to jump to conclusions before knowing the results of the tests. Although Profepa has avoided confirming the toxin hypothesis, sources in the region confirm to this newspaper that it is the “most viable option.”
Algal blooms that generate toxins such as domoic acid are known as “red tides” because the pigment of these organisms can produce discoloration in the water, usually red. In recent years there has been an increase in this type of phenomenon. The combination of factors that cause them is an open debate, without definitive scientific evidence. Even so, Conabio, a public body dedicated to the study of biodiversity, points out that the increase in ocean temperature, associated with climate change, may be one of them. Some of these toxins, if consumed by humans, can cause diarrhea, vomiting, amnesia and even death.
On occasions, the authorities have decreed a ban on the consumption of certain types of mollusk or fish to avoid incidents. For now, Profepa has opted for caution. “The environmental authorities may apply the corresponding measures for the protection of this species and the ecosystem,” he said in his statement. Along the same lines, Fernando Elorriaga points out that the red tide may be as far away as California, in the United States. “There is no certainty that it was in this area. It could have been at a great distance and that the corpses arrived here by currents ”, says the biologist. Aurora Paniagua, from Mmares, agrees on the difficulty of locating the contaminated patch: “Sea lions swim long distances. The problem with red tide is that it can be seen in animals, but to find out where it is, you would have to take water samples. ”
To solve the mystery, Profepa has taken part of the samples from the corpses to its central laboratories. The civil and academic associations involved, including the Whale Museum Rescue Center and the Autonomous University of Baja California Sur, have theirs stored in formaldehyde and alcohol cans. As part of the stranding network, they work voluntarily and do not charge from the Government for their monitoring activity. In La Paz, they do not have the capacity to analyze the remains and have had to communicate with laboratories in central Mexico and the United States. With the coronavirus lockdown still in place in certain parts, some institutes remain closed or have limited activities, making it difficult to determine when they will have the results.
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