Sardine and anchovy fishermen in the Region of Murcia have long been without seeing “not a sardine” and “very few anchovies” in the waters around the Mediterranean. The main skipper of the Fishermen’s Guild of Mazarrón, Manuel Sánchez, has blamed “the voracity of bluefin tuna” for the decline of these species that, in the port of Mazarrón (Murcia), are one of the most prized catches of its waters.
In fact, Sanchez has told Europa Press that since tuna fishing has been licensed “to two fishing companies, there are very few tuna boats”, in the opinion of the major pattern, this situation has made the flowering of tuna in Mediterranean waters “is uncontrolled” which together with its predatory capacity “are ending with all the fishing grounds of sardine and anchovy” throughout the Mediterranean, “from Gerona to Almeria”.
This accumulation of circumstances has produced, according to Manuel Sanchez, that “of the 200 or 300 boxes of sardines and anchovies that were caught” in the waters of Mazarron “now we do not reach even one” complained bitterly this fisherman dedicated to purse seine fishing of these species.
The main skipper has shown “his concern” that the tuna “no longer go out to the Atlantic, they stay in the Mediterranean permanently”. Among the reasons for this change of location, Sanchez thinks that “the installation of tuna farms that ensure a ‘supply’ of food for these fish” may be among them.
On the other hand, a scientific team from the Spanish Institute of Oceanography (IEO, CSIC) and the Institute of Marine Sciences of Barcelona (ICM, CSIC) has published a study in which they analyze the effects of the proliferation of jellyfish, together with fishing and environmental factors in the decrease in the abundance of sardines and anchovies in the western Mediterranean.
The researchers blame, among other reasons, that some species of jellyfish feed on larvae and eggs of other fish. In addition, during blooms they consume large quantities of zooplankton, which means competition for food with sardines and anchovies.
Several hypotheses have been proposed to explain these changes, mainly related to fishing and climatic and environmental variability. The increasingly frequent occurrence of jellyfish blooms has also been used to explain sardine and anchovy fluctuations, although without sufficient evidence to prove it.
Some jellyfish species feed on fish eggs and larvae. In addition, during bloom episodes they consume large quantities of zooplankton, which implies a competition for food with sardines and anchovies.
This new work, published in the journal Estuarine Coastal and Shelf Science, uses statistical models to analyze a series of data from more than 10 years of sardine and anchovy abundance together with information on landings in port, different climatic indices and information on the occurrence of jellyfish blooms.
The results show that the occurrence of large blooms of jellyfish, in combination with other environmental factors, has negative effects on both sardine and anchovy and are important for predicting the abundance of small pelagics in the study area.
As explained by the researcher of the Spanish Oceanographic Institute (IEO), José Carlos Baéz, “in this scenario, in which an accumulation of human and environmental impacts are observed in the ecosystem, it is necessary to manage the resources with special caution to guarantee their conservation”. In this sense, said Baez, “it is necessary to include the potential effect of jellyfish in stock assessment models and take it into account when managing fisheries”.
For her part, ICM researcher and co-author of the paper, Marta Coll, said that “it is necessary to adopt an integrated vision of the marine ecosystem to make an adaptive and proactive management of marine resources and to guarantee fishing and its socio-economic benefits.
Finally, the skipper “does not rule out” that jellyfish may cause a decline in sardine and anchovy populations, but considers it “unlikely, there have been jellyfish long before tuna”.