The bycatch of these organisms damages the nets and hinders the fishing activity, which is creating unrest in the Catalan fishermen's associations.
The waste of artisanal fishermen in the Cap de Creus (Girona) has revealed an "unusual" abundance of brittle stars -a type of echinoderm related to starfish- of the species Astrospartus mediterraneus that is causing havoc in the fishing sector of the area.
Until now, the information on the species was very scarce, although the collaboration between the scientific and fishing sectors has made it possible to extend it considerably. In fact, thanks to this it has been possible to establish for the first time the ecological requirements of the species in Cap de Creus.
"The information gathered is important because it provides information on the biology of the species and recognizes the sudden increase in specimens of the species and the problem it is causing for fishermen in the area, which has also been reported in other fishermen's associations along the Catalan coast," explains Marina Biel, one of the authors of the study.
The details of the distribution and habitat preference of the species are included in an article of the Institut de Ciències del Mar (ICM-CSIC) recently published in the journal Continental Shelf Research. The authors highlight the importance of the new publication as it deals with an emblematic species of the Mediterranean.
An expanding species
In 2018, fishermen reported an "unusual" abundance of this starfish, which they were catching accidentally on an increasingly regular basis. This was interfering with their activity, as the nets were filling up with these stars to the point of making the fishermen's work notably difficult.
Given this scenario, and taking advantage of the collaboration framework established with the ICM-CSIC thanks to the RESCAP i MITICAP projects, the species was monitored between the months of April and August 2018, with more than 140 trips to the sea with the fishermen. During these outings, underwater robots were used to determine the ecology and population status of the species.
"Collaboration with fishermen has allowed us to become aware of this phenomenon and to investigate it. Without this exchange of information, it would probably have been overlooked by the scientific community," explains co-author Janire Salazar.
The results of the study show a preference of the species Astrospartus mediterraneus for rocky substrates with the presence of gorgonians - a type of coral - and steep slopes. They also reveal that most are relatively young organisms, which fits with the perceptions of fishermen and could indicate the beginning of a massive outbreak of the species, which also seems to be expanding in other parts of the Catalan coast as the Gulf of Lion, where significant increases have been detected by the guilds of Llançà, Roses and Palamos.
"If so, it is possible that the population densities that have been observed continue to increase and this may become a chronic situation, so it is necessary to monitor the population closely in order not to endanger the fishing activity," says Andreu Santín, another of the authors of the study.
In fact, following its publication, several fishermen's associations on the Catalan coast associated with the Life ECOREST project (which continues with the scientific-fishing collaboration established in the RESCAP and MITICAP projects) have expressed their willingness to monitor the evolution of the species given the interference it causes in their activity. The fact is that the fishermen spend many hours removing the brittle stars from the nets, which often have to be renewed because they have been damaged due to the capture of this species.