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Dusky grouper

The dusky grouper, Epinephelus marginatus, is an emblematic fish of the Mediterranean. Since 1992, the Paul Ricard Oceanography Institute has supported the action of the Grouper Research Group (GEM - Groupe d’Etude du Mérou) to protect this species. A moratorium banning underwater fishing and line fishing of the grouper was introduced in 1993 and has been renewed until 2023.

Reproduction of the dusky grouper
Are the juveniles found on the French coasts evidence of climate warming ? Until the late 1980s, observations of the dusky grouper revealed the absence of individuals of less than one kilogram along the French Mediterranean coasts. According to scientists, the dusky grouper reproduced in the southern Mediterranean, and part of the population migrated northwards in successive waves.

The discovery of juveniles of a few hundred grams, then of an individual of a few grams in 1991, at Les Embiez (near Toulon, S.E. France), contradicted this hypothesis. These specimens constitute irrefutable proof of the reproduction of grouper along the north-western coasts of the Mediterranean, probably due to the impact of climate change.

Individual identification
For research on animal behaviour patterns, it is often necessary to be able to recognise each individual. The method of identification is based on the pattern and shape of two groups of patches around the eye. These patches are characteristic for each individual and do not change significantly with time.

Census surveys
The GEM organizes and coordinates census surveys of the dusky grouper in which the divers of the Institute participate on a regular basis. The aim of these campaigns is to count and assess the size of the grouper present at the site. In most cases the campaigns are repeated at intervals in order to monitor patterns of change in the populations.

The census surveys of populations of grouper are undertaken by scuba divers associated with snorkel divers, both in Marine Protected Areas (MPA) and in non-protected sites.

In general, a very sharp increase in these populations has been observed in the Marine Protected Areas (e.g. the number of grouper was multiplied by 8.5 between 1993 and 2011), and a significant but considerably lesser increase outside the MPAs.

These changes are linked on the one hand to the protection moratoriums in force since 1993, and on the other hand to climate warming, which now allows the reproduction of this species along the north-western coasts of the Mediterranean.

The campaign sites
MPAs :
-  Port-Cros National Park, every 3 years since 1993.
-  Porquerolles, every 2 years since 2008
- Scandola Nature Reserve, first survey in 2011
-  Cerbère – Banyuls Marine Nature Reserve, every 5 years since 2001
-  Bouches de Bonifacio Nature Park, at irregular intervals since 2000
-  Côte Bleue Marine Park, 2006

Outside MPAs :
-  La Ciotat, every 2 years since 2007
-  Monaco, 1995, 1997, then every 3 years since 2006
-  Coasts of Les Maures, every 2 years since 2010
-  Calanques of Marseille, in collaboration with the French Underwater Research and Sports Federation (FFESSM), every year since 2004

-  Grouper Research Group (GEM)
The Paul Ricard Oceanography Institute is very active within the GEM, founded in 1986 at the initiative of marine protected area managers, scientists and members of the FFESSM : a member of the Institute is the Secretary General of the association (Dr. Patrick Lelong), and members take part in census surveys, organize symposia, etc.
To know more about the GEM (in French) :

- Port-Cros National Park

LELONG P., 1993
Présence de juvéniles du mérou brun (Epinephelus guaza) sur le littoral méditerranéen français. In : Qualité du milieu marin - Indicateurs biologiques et physico-chimiques. C.F. Boudouresque, M. Avon, C. Pergent-Martini (eds), GIS Posidonie Publ., France, pp : 237-242. Download (in French, Abstract in English)

LELONG P., 1999
Identification individuelle du mérou brun, Epinephelus marginatus (Lowe, 1834) par les taches céphaliques. Mar. Life, 9 (2) : 29-35. Download (in French, Abstract in English)

LELONG P., 2005
Capture d’un macabit, Epinephelus merra Bloch, 1793 (Poisson, Serranidae), en Méditerranée nord-occidentale. Mar. Life, 15 (1-2) : 63-66.