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Protection in the Medes Islands marine reserve started more than 25 years ago. Dusky grouper, zebra seabream and European seabass have practically reached their carrying capacity, whereas brown meagre is still approaching population stabilization and common dentex is still increasing. One exception to these trends is gilthead seabream, which decreased probably due to fishing just outside the borders of the reserve.

These are the conclusions of an article published recently on the journal PLOS ONE; the research is based on the scientific surveillance of species of fish strongly affected by fishing practices in the Medes Islands between 1992 and 2009. The article is signed by Bernat Hereu and Miquel Zabala, from the Department of Ecology at the Faculty of Biology of the University of Barcelona, and Antoni Garcia Rubies, from the Centre for Advanced Studies of Blanes (CEAB-CSIC).

It is one of the most comprehensive studies carried out in a protected marine area on the Mediterranean coast; it is focused on six littoral fish: dusky grouper (Epinephelus marginatus), common dentex (Dentex dentex), European seabass (Dicentrarchus labrax), zebra seabream (Diplodus cervinus), brown meagre (Sciaena umbra) and gilthead seabream (Sparus aurata). Professor Bernat Hereu points out that “these fish species are good indicators of protection effects as they vulnerable to fishing, they have long lives and a common habitat and, due to protection, they are more abundant in the protected area than outside”.

What are the effects of the protection carried out in the Medes Islands?

The research compares abundance and size between some vulnerable to fishing species in the marine reserve, partial reserve and the unprotected area. Authors affirm that the effect of protection varies among species. Dusky grouper and zebra seabream, which are sedentary species, have a positive answer towards protection; they have practically reached carrying capacity. However, the effect of partial reserve is not so effective because these species do not export biomass. Dusky grouper population is extended to new areas within the reserve; that gives birth to smaller individuals. In the case of common dentex, the effect of protection is clear too: even if it does not reach carrying capacity, there is a general recovery of populations along the Catalan coast.

Gilthead seabream, threatened with fishing

Gilthead seabream is an exception as population is decreasing even in the protected areas of the Medes Islands. This phenomenon may be consequence of their movement from the protected area to the coast, named ‘spillover’. “Gilthead seabream —says Hereu— is a species that live in different habitats. In autumn, it aggregates to spawn. One of these aggregations is situated very close to the marine reserve and is well known by fishermen in the area. An overfishing of aggregations for reproduction may reduce gilthead seabream populations”. More information about gilthead seabream biology, where and when do they form aggregations, may contribute to protect them and promote their conservation.

Population recovery: a long-term process

The study alerts that the total recovery of fish populations in the Mediterranean coast lasts for decades; it opposes other studies that hold that recoveries are quicker processes. “Total recovery of populations is a long-term process”, affirms Bernat Hereu. “They are long-lived species which only reach total recovery (carrying capacity) after many years of protection”. Carrying capacity, also described in other Mediterranean marine reserves, depends on several factors related to marine coast: natural habitat, depth, substrate, currents, productivity, etc.

Antoni Garcia Rubies explains that research concludes that “those species which are more vulnerable to fishing need longer protection in order to recover totally”. “If protection is not ensured —adds the expert—, populations will be destroyed in a matter of days. The comparison between protected and exploited populations gives us an idea about how much these species are exhausted in areas open for fishing” To know these data will enable administrations to select those marine areas that most need to be protected.

Medes Islands: a reserve of high ecological value

The Department of Ecology of the UB set up these studies in the Medes Islands thirty years ago. It is a unique reserve in Mediterranean marine ecosystems due to its landscape and biodiversity richness. To be exact, the scientific works carried out by experts Joandomènec Ros (UB) and Josep M. Gili (CSIC) gave place to the creation of the Protected Area of the Medes Islands in 1983.

Now, the new study stresses the scientific value of long-term surveillance to know the evolution of the ecological status of marine ecosystems and evaluate the effect of alterations on ecosystems. Authors state that, in order to improve environmental policies in the Medes Islands, it is necessary to promote a surveillance system to control furtive fishing, foster new researches focused on species biology (reproduction aggregations of gilthead seabream, relationship between different habitats, etc. ), and develop more strategies to protect biodiversity.

The research published on PLOS ONE was first funded by the Department of Agriculture, Livestock and Fishing of the Government of Catalonia, and second by the Department of the Natural Environment of the Government of Catalonia, and was supported by the Montgrí, Medes Islands and Baix Ter Natural Park.

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