The Directorate-General for Fisheries and the Marine Environment of the Ministry of Agriculture, Fisheries and Food presented the results of the fish censuses of the Freu de Sa Dragonera Marine Reserve, one of the two Balearic marine reserves under shared management with the Ministry of Agriculture, Fisheries and Food. The results show that all the indicators used in the evaluation of the fishery resources on rocky bottoms have responded in some way positively to protection. The creation of the marine reserve of Sa Dragonera was declared in 2016 by the Govern, and the State extended it in 2020 in the outer waters. The results were presented during the monitoring commission of this reserve, which was held this Friday in Andratx.
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The fish census campaign was carried out in July 2020, 3 years and 9 months after the declaration of the reserve, by 4 diving biologists who covered an area of 2.5 ha of rocky bottoms in a total of 51 hours of immersion. All indicators constructed from 20 recorded vulnerable species have shown temporary increases (from 2016 vs. 2020) or higher values within the marine reserve. Species richness, for example, has increased by 40% in shallow waters and by 81% in deep waters, reaching values of up to 8 species/250 m2 by 2020. This value is considered very high in the geographical context of the Balearic Islands, and is currently higher, for example, than those recorded in the deep-water stations of the northern marine reserve of Menorca (4-5 species/250 m2) or the marine reserves of El Toro and Malgrats (5-6 species/250 m2).
The total biomass of vulnerable species has increased by 138% in shallow waters with average values of 11.4 kg/250 m2, almost double the data recorded in the 2018 campaign; and has grown by 340% in deep waters, standing at 25.3 kg/250 m2.
The results in shallow waters respond to factors such as the good state of the populations of species of lower trophic level (diplodus spp.) that are increasing all along the Balearic coastline due to changes in the fleet of small gears, both quantitative and qualitative, and also in the uses of recreational fishing from land and from boats. On the other hand, the effects of protection also come into play, which indicate that the area between Cala Llebeig and Cap Llebeig will be one of the so-called ‘hot spots’ of diversity and biomass in the not too distant future. The biomass of demersal species has multiplied by a factor of x4.4 between 2016 and 2020 between 20 and 25 metres deep, and up to x13 times in the case of higher trophic level species. The current values of total biomass (25.3 kg/250m2), with only 4 years of partial protection, are already among the high values of other sites with more years of protection, such as Illa dels Porros in the northern marine reserve of Menorca (18kilos/250m2). Even so, it is still far from exceptional values such as those of Toro Island with a total biomass of 48 kg/250 m2.
It is still too early to talk about carrying capacity or virgin biomass, since only 4 years have passed since the reserve was declared a reserve. The recent declaration of the outer waters will make it possible to elucidate these concepts and their influence on inland waters.
The RM of the Llevant de Mallorca maintains its richness, density and biomass
The monitoring commission of the Llevant de Mallorca-Cala Rajada Marine Reserve was also held this Thursday afternoon. This is the other marine reserve of fishing interest under shared management with the Ministry of Agriculture, Fisheries and Food. The fish census campaign was carried out between the 1st and 8th of June 2021, at 6 sites in the integral reserve and in another two located outside the reserve. The objective was to intensify the information from the integral reserve area. Statistical analyses of the four indicators assessed (species richness, density of individuals, total biomass of vulnerable species and biomass of high trophic level vulnerable species) showed no differences between the 6 sites within the integral reserve, nor between the integral reserve and the control area.
The median richness of vulnerable species within the integral reserve is 4.25/250m2, a value already observed between 2016 and 2020, but higher than that recorded between 2008 and 2010. The median density within the integral zone is 43 individuals/250m2, virtually unchanged from the 2020 data.