GEM: “when the grouper goes, everything goes”

The GEM, Mérou Study Group, was born from a simple idea: to share the experiences of managers of Marine Protected Areas, to compare and cross-check their data, choosing a key species which becomes a good indicator of the quality of the environment. And it is quite naturally the brown grouper that has been designated. In 1986, there were only six active members, from the Lavezzi, Scandola and Banyuls Nature Reserves, then from the Port-Cros National Park. But very quickly, the network grew, more and more biologists, managers, members of the FFESSM, hunters or freedivers, journalists, photographers, joined the movement. Today, there are more than 120, French but also from other countries around the Mediterranean.

Initially, the GEM Of course, it aims to measure the evolution of grouper ecosystems and populations in MPAs, taking into account its knowledge and conservation objectives. “But the missions, explains Philippe Robert, president of the GEM, are developing more and more outside protected areas, as in La Ciotat or on the Côte du Massif des Maures for example. And it is interesting to note that the growth of brown grouper populations is (very) observable everywhere, even if the pace is sometimes slower elsewhere, because of a smaller population at the start and always with some well-known poaching risks. . "

Since the birth of the GEM, census operations had already been carried out in Corsica, but the mission carried out this summer in the waters of Scandola was the first of this scale. “Previously, explains Jean-Michel Cottalorda, only a few counts had been carried out on site by our Corsican colleagues, Jean Marie Dominici and Jean-Michel Culioli. And in 1975, a few months before the classification in Scandola Nature Reserve, a first count (very important zero state) had also been carried out by about fifteen divers and freedivers, also over a large week, in this area then overfished and overhunted (COMETES mission). Results: no corb and only 6 brown groupers! "

Thirty-five years later, the grouper resumed its rights: more than 600 individuals were counted this summer in the Reserve. “And while all the results have not yet been analyzed,” says Jean-Michel Cottalorda, “we can already indicate that all age and size classes have been observed in significant quantities. Both small groupers of 10 to 20 cm (1 to 2 years) and individuals exceeding 100 to 120 cm (more than 40 years probably for some individuals). Display and reproductive behavior have been observed several times in the central zone of the Reserve and baby groupers of 3,5 to 5 cm (a few months) have also been observed on the periphery of the reserve, proof of effective local reproduction. . "

"Without a doubt, insists the biologist Jo Harmelin, who from the beginning has participated in the GEM adventure, the moratorium for the protection of the grouper which prohibits it from spearfishing and hook fishing on our Mediterranean coasts. French (with some adjustments in Corsica), is responsible for this gradual return of the grouper on all our coasts offering habitats for this species. “Beyond the regulations, the work of awareness, information, and awareness on the part of many submarine hunters have also played their part. Scientists also do not rule out the likely effect of global warming which now favors reproduction in the northern part of the western Mediterranean basin. “Overall, concludes Philippe Robert, the context is therefore rather favorable for the brown grouper to gradually regain the balance of its populations according to the habitats and prey available. For example, there is a marked slowdown in the growth of the population of Port-Cros, very probably linked to the availability of habitats around the island. "

The study of the behavior and ecology of marine species began with in situ observation, therefore with scuba diving, scuba diving or apnea. “It is therefore a very recent phenomenon, insists Philippe Robert. And even if we are starting to understand key elements of the life of this fish (diet, reproduction methods, population dynamics, etc.), there is still a lot to learn from this species, both for its biology and for its ecology. . Among the many areas of research, we can cite: the modalities of sexual change in relation to the age structure of the local populations, the more precise conditions of reproduction, larval development, the feasibility of aquaculture of this fish, certain inter relations with other predators in the ecosystem… ”Geneticists are also studying the genetic differences between our brown groupers, and those of Brazil or Uruguay.

The group is also keen to learn more about other grouper species, which are increasingly numerous on our coasts and for which very little information is currently available. And Scandola, here again, represents an exceptional study site because we can meet there, in addition to the brown grouper (Epinephelus marginatus), 4 other species of grouper: the very beautiful king grouper (Mycteroperca rubra), the badèche ( Epinephelus costae), gray grouper (Epinephelus caninus) and cerniers (Polyprion americanus). “Apart from the Lavezzi (where they are much rarer), explains Jean-Michel Cottalorda, this configuration only exists much further south of the Mediterranean. Some of these species have occasionally been fished in Corsican funds by professional fishermen for a long time. But in recent years, scientists can now observe some of them more and more often in Scandola. Diving clubs sometimes also observe them on the outskirts of the reserve. "

25 years after the creation of GEM, its members are still working hard. “We are working for the future and not just for the next few years,” points out Philippe Robert. The national and regional authorities have so far followed us in our objectives and our proposals for measures of knowledge and management of these emblematic species. The moratorium system is by definition called into question regularly, which also makes it possible to adjust the proposals for measures linked to the possible evolution of the context and the living environments of this fish. It would however be regrettable and even catastrophic if these protections, offered on a temporary but renewable basis, were interrupted without other accompanying measures. We know of several examples, on land and at sea, where the end of the protection of a species or an environment, very quickly leads to a return to the initial state of poverty. "

But Philippe Robert is confident: “taking into account, he said, the ecological but also economic issues that this fish represents, particularly for scuba diving, we are optimistic that everyone, in their levels of responsibility and use of the marine environment , adheres to this idea of ​​a desirable, balanced and sustainable return of the grouper to our coasts. Everyone can understand that for coastal marine life, when the grouper goes, everything is fine. "