According to a new IEO study in which the ICM has participated, predation of eggs and larvae by these animals that are part of the gelatinous plankton is contributing to reduce the abundance of small pelagic fish.
A new study involving researchers from the Spanish Institute of Oceanography (IEO-CSIC) and the Institut de Ciències del Mar of Barcelona (ICM-CSIC) has revealed that jellyfish proliferations -together with fishing and environmental factors- are contributing to the reduction of sardine and anchovy abundance in the western Mediterranean.
The last decade in the western Mediterranean has seen a significant decline in sardine (Sardina pilchardus) biomass, abundance and catches, as well as strong fluctuations in anchovy (Engraulis encrasicolus) populations.
Several hypotheses have been proposed to explain these changes, mainly related to fisheries and climate 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 support this.
Some jellyfish species feed on fish eggs and larvae. In addition, during blooms they consume large quantities of zooplankton, which compete with sardines and anchovies for food.
This new study, published in the journal Estuarine Coastal and Shelf Science, uses statistical modelling to analyse more than 10 years of sardine and anchovy abundance data 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 jellyfish blooms, in combination with other environmental factors, has negative effects on both sardine and anchovy that are important for predicting the abundance of small pelagics in the study area.
"In this scenario, in which an accumulation of human and environmental impacts on the ecosystem is observed, it is necessary to manage the resources with special caution to ensure their conservation," explains Jose Carlos Baez, researcher at the IEO and first author of the study. In this sense, the scientist adds that "it is necessary to include the potential effect of jellyfish in stock assessment models and to take it into account when managing fisheries".
Marta Coll, researcher at the ICM-CSIC and co-author of the paper points out 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 be able to guarantee fishing and its socio-economic benefits".