Bad times for sardines and anchovies. Bad news is piling up for these two species, one of the most commercialized in the Mediterranean. They are traditional victims of overfishing, climate change affects their populations and their diet is getting worse, like their health, affected by microplastics. To this range of factors that paint his future black now adds one more. A study promoted by the Spanish Institute of Oceanography (IEO) and published in the magazine Estuarine, Coastal and Shelf Science has revealed that the number of captures and abundance of these fish falls in the years with the highest proliferation of jellyfish. The massive presence of these organisms can affect the decrease of up to 45% in the number of individuals who, in addition, are more malnourished.
How has science found the correlation between jellyfish, sardines and anchovies? The starting point is the PELWEB project, financed by the Ministry of Science and Innovation. Directed by researchers Marta Coll (from the Barcelona Institute of Marine Sciences) and José María Bellido (from IEO-CSIC), its main objective was to study the reasons for the impoverishment of populations of small pelagic species such as sardines and anchovies. in the western Mediterranean, from Cabo de Gata in Almería to Cabo de Creus in Girona. In the study series of both species, it is observed that their number has fallen since 2001, as well as that their size is smaller and their health worse. Today it is almost a miracle to find a specimen of seven or eight years – their life expectancy – and finding a two-year-old is almost impossible due to overfishing, which does not allow them to grow.
To search for solutions, scientists proposed hypotheses from various points of view: the effects of climate change, fishing pressure, the decline in the quality of their food or contamination by microplastics. To do this, they took advantage of the IEO maritime campaigns, in which the Mediterranean coast is traveled in scientific vessels every summer. And, in parallel, they collected samples in the main fish markets for 18 months. The four hypotheses were confirmed, the last one a few months ago, when Coll’s team published a study showing how tiny plastics appear in almost 60% of the specimens. “And the more quantity their stomachs have, the sicker they were” -says the researcher- “because the individuals showed worse physical condition and a greater number of parasites”.
The team pitched a fifth idea. What if the upward trend in the number of jellyfish has an impact on the populations of anchovies and sardines? That is where the figure of the researcher José Carlos Baéz appeared, based at the IEO of Fuengirola, in Malaga, where anchovies find their refuge while, together with sardines, they are the basis of gastronomy. With surprise, he says that this week he has seen the Malaga slipway dotted with stranded jellyfish. The image is recurrent in summer, but in winter it is an exception that begins to cease to be so. It is the button that shows the increase in the population of the species in the Mediterranean, especially the so-called carnation jellyfish (pelagia noctiluca), which wreaks havoc in the summer season and fishing nets. “Overfishing of its predators, such as tuna or swordfish, has favored its development,” says Báez. He has also done the increase in sea temperature as a result of climate change. And in an increasingly placid environment with fewer risks, they multiply.
Very voracious jellyfish
For the last three years, this researcher has led the work to resolve hypothesis number five. They pulled data from historical series -until 2001- and also had a precedent in the Bay of Bengal, in the Indian Ocean, where the breakdown of the ecosystem also caused jellyfish to proliferate. There it was found that they fed on small fish larvae. Would it be repeated in the Mediterranean? The data shows yes. “The proliferation of jellyfish negatively affects the populations of sardines and anchovies,” says Báez.
The scientist explains that there are two main reasons. One, that organisms develop in the vicinity of submarine canyons, where thousands of individuals create huge swarms. It is just the place where the anchovies spawn, something that the jellyfish take advantage of to ingest the eggs or the fry. “They are very voracious, they eat a lot,” adds Báez. And as there are more and more swarms, their incidence is greater. The study data shows that they have caused a 45% decrease in the abundance of sardines, whose catches have fallen by 10%. In the case of anchovies, the number of individuals fell by 42% and the tons caught by up to 63%. The second is that jellyfish also feed on plankton. And their greater presence makes it difficult for sardines and anchovies to feed. For this reason they are more malnourished, worsening their physical condition.
There’s a solution? “At this point inertia is very difficult to break, but it can be done. It would be enough to restructure the ecosystem,” says Báez. In order for each element of the gear to return to its place, his team proposes the need to end the overexploitation of jellyfish predators, such as tuna, sharks or swordfish, as well as recover turtle populations. Also eliminate contamination or allow populations of sardines and anchovies to recover with less fishing pressure. “Historically, many discarded juveniles have been thrown away, they have been fished where they shouldn’t or in their nurseries, although it happens less now. It would be enough for the laws to be complied with”, adds Marta Coll. Jellyfish also play a role here, since the study emphasizes that “they could be an important inhibitor for the recovery of fish populations in depleted ecosystems.” One more challenge for science and, above all, for sardines and anchovies, whose future is, to say the least, pessimistic.
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