Exploration naturaliste sous-marine des petits fonds rocheux du Cap Santa Clara au Cap Esterias, Province de l’Estuaire, Gabon: les poissons marins

Bien que située à moins de vingt kilomètres du centre de la capitale Libreville, la zone marine comprise entre le Cap Santa Clara et le Cap Esterias n’avait fait l’objet que de travaux scientifiques limités, essentiellement orientés vers les tortues marines, emblématiques des efforts de conservation du milieu marin au Gabon. Aucun véritable inventaire de la faune spécifique aux estrans et aux petits fonds rocheux n’avait été entrepris, et l’évidence d’une mission d’exploration s’imposait, renforcée par la probabilité de découvrir de nouvelles espèces, pour le Gabon, voire peut-être même pour la Science.info:eu-repo/semantics/publishedVersio

Frontiers in Fishwatching Series: Gobies of the North-eastern Atlantic and the Mediterranean: Gobius and Thorogobius

International audienc

Contexto socio-comportamental de la reproducción del mero Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) en la reserva marina de las Islas Medes (Mediterráneo Noroccidental, España)

20 páginas, 8 figuras, 2 tablas.[EN] The evolution of social structures and reproductive behaviours leading to actual spawning in the Mediterranean dusky grouper, Epinephelus marginatus, was studied in the Medes Islands Marine Reserve on the Spanish coast (NW Mediterranean) from February 1995 to October 1996. Density, size, sex, colour patterns, relation the bottom, swimming activity and site occupation were monitored by visual census surveys at monthly and daily scales. The main observed socio-behavioural trends were in part comparable with some patterns reported in tropical groupers, although differences exist, which might in part be related to the temperate conditions of the northern Mediterranean sea. The density of dusky groupers in the area was low in winter, and maximal in summer, from late June to late August (up to 8-fold increase); numbers rised in spring, before the beginning of reproductive activities which led to spawning by mid August, and dropped rapidly afterwards. During this long reproductive period (about 2 months), dominant males (recognized by their highly specific colour pattern) established territories in which they displayed aggressively towards neighbouring males and numerous smaller females (the species is proterogynous); the observed sex-ratio was approximately 1:7 (sexually active males versus adult females). Territoriality of males is the base of the social structuration of the reproductive population; in addition, behaviours typical of the pre-spawning period include repeated evening gathering of females in open water, and the appearance of specific colours patterns. This overall socio-behavioural pattern changed in the evenings when spawning was observed (16th - 21st of August), the males patrolling a reduced territory in which females would come to mate; spawning behaviour itself was described in Zabala et al. (1997).The complex socio-behavioural structure leading to reproduction in the Dusky Grouper should be considered in fishery management, since it could hardly develop under strong human pressure. In this respect, the contribution of Marine protected areas is determinant for the reproductive success of this species in the NW Mediterranean basin.[ES] La evolución de las estructuras sociales y del comportaimiento reproductor que condujo a la freza del mero Epinephelus marginatus, fueron estudiados en la Reserva Marina de las Islas Medes (costas españolas: Mediterraneo noroccidental) entre Febrero de 1995 y Octubre de 1996. La densidad, talla, sexo, librea, posición respecto al fondo, actividad natatoria y ocupación del espacio se estudiazron a través de censos visuales, repetidos a escala diaria y mensual. Las principales tendencias socio-etológicas observadas resultaron parcialmente comparables a algunas pautas descritas en meros tropicales, aunque subsisten algunas diferencias que podrían parcialmente atribuirse al carácter templado del mar Mediterráneo.The present work was realisewd within the frame-work of the monitoring program of the Medes Islands Marine Reserve finacied by the Fisheries ministry of the "Generalitat de Catalunya" (contract PCC 68003/9). Patrick Louisy's field work was partly supported by the G. E. m: (Groupe d'Etude du Merou).Peer reviewe

La freza del mero Mediterráneo Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) en la reserva marina de las Islas Medes (Mediterráneo Noroccidental, España)

13 páginas, 6 figuras, 2 tablas.[EN] Spawning of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) was observed for the first time in summer 1996 during scuba diving surveys in the Medes Islands Marine Reserve (NW Mediterranean). Ten spawning events were observed, which occurred at sunset, in the evenings around the new moon of August. A mature female (usually between 50 and 75 cm TL), in the standard mottled colour pattern, and a larger (more than 100 cm long) dominant male, in a conspicuous silver streaked colour-pattern, ascended up to 12 m side by side, spiralling in an anti-clockwise direction two or three times, from the bottom to shallow warmer waters, where the ova and sperm are released. Some traits of variability over this common pattern of spawning are described. Predation by saddled bream Oblada melanura, which concentrate in great numbers after each spawning suggests a very low survival of the spawned eggs.[ES] La freza del mero Mediterráneo Epinephelus marginatus (Lowe, 1834) fue observada por primera vez el verano de 1996 en el curso de trabajos de seguimiento con escafandra autónoma en la Reserva Marina de las Islas Medes (Mediterráneo noroccidental). Los 10 episodios de freza que se observaron tuvieron lugar a la puesta del sol, durante los atardeceres próximos a la luna nueva de Agosto. Una hembra madura (generalmente entre 50 y 75 cm de largo TL). en la librea críptica estandard, y un macho de talla mucho mayor (mas de 100 cm TL), exhibiendo la conspicua librea plateada de los machos dominantes, ascienden verticalmente hasta 12 m. uno junto a otro, girando dos o tres veces en espiral en sentido antihorario, desde cerca del fondo hasta aguas superficiales más cálidas, donde liberan los huevos y esperma. Se describen algunas variaciones sobre esta pauta común de freza. Una intensa depredación por parte de Oblada melanura, que se concentran en gran número tras cado episodio de freza sugiere una muy baja supervivencia de las puestas.The present work was realised within the frame-work of the monitoring programthe Medes islands Marine Reserve financed by the Fisheries Ministry of the "Generalitat de Catalunya" (contracyt PCC 68003/9). Patrick Louisy's field work was partly supported by the G. E. M. (Groupe d'Étude du Mérou).Peer reviewe

Socio-behavioural context of reproduction in the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) in the Medes Islands Marine Reserve (NW Mediterranean, Spain)

The evolution of social structures and reproductive behaviours leading to actual spawning in the Mediterranean dusky grouper, Epinephelus marginatus, was studied in the Medes Islands Marine Reserve on the Spanish coast (NW Mediterranean) from February 1995 to October 1996. Density, size, sex, colour patterns, relation the bottom, swimming activity and site occupation were monitored by visual census surveys at monthly and daily scales. The main observed socio-behavioural trends were in part comparable with some patterns reported in tropical groupers, although differences exist, which might in part be related to the temperate conditions of the northern Mediterranean sea. The density of dusky groupers in the area was low in winter, and maximal in summer, from late June to late August (up to 8-fold increase); numbers rised in spring, before the beginning of reproductive activities which led to spawning by mid August, and dropped rapidly afterwards. During this long reproductive period (about 2 months), dominant males (recognized by their highly specific colour pattern) established territories in which they displayed aggressively towards neighbouring males and numerous smaller females (the species is proterogynous); the observed sex-ratio was approximately 1:7 (sexually active males versus adult females). Territoriality of males is the base of the social structuration of the reproductive population; in addition, behaviours typical of the pre-spawning period include repeated evening gathering of females in open water, and the appearance of specific colours patterns. This overall socio-behavioural pattern changed in the evenings when spawning was observed (16th - 21st of August), the males patrolling a reduced territory in which females would come to mate; spawning behaviour itself was described in Zabala et al. (1997).The complex socio-behavioural structure leading to reproduction in the Dusky Grouper should be considered in fishery management, since it could hardly develop under strong human pressure. In this respect, the contribution of Marine protected areas is determinant for the reproductive success of this species in the NW Mediterranean basin

Spawning behaviour of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) in the Medes Islands Marine Reserve (NW Mediterranean; Spain)

Spawning of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) was observed for the first time in summer 1996 during scuba diving surveys in the Medes Islands Marine Reserve (NW Mediterranean). Ten spawning events were observed, which occurred at sunset, in the evenings around the new moon of August. A mature female (usually between 50 and 75 cm TL), in the standard mottled colour pattern, and a larger (more than 100 cm long) dominant male, in a conspicuous silver streaked colour-pattern, ascended up to 12 m side by side, spiralling in an anti-clockwise direction two or three times, from the bottom to shallow warmer waters, where the ova and sperm are released. Some traits of variability over this common pattern of spawning are described. Predation by saddled bream Oblada melanura, which concentrate in great numbers after each spawning suggests a very low survival of the spawned eggs

Socio-behavioural context of reproduction in the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) in the Medes Islands Marine Reserve (NW Mediterranean, Spain)

The evolution of social structures and reproductive behaviours leading to actual spawning in the Mediterranean dusky grouper, Epinephelus marginatus, was studied in the Medes Islands Marine Reserve on the Spanish coast (NW Mediterranean) from February 1995 to October 1996. Density, size, sex, colour patterns, relation the bottom, swimming activity and site occupation were monitored by visual census surveys at monthly and daily scales. The main observed socio-behavioural trends were in part comparable with some patterns reported in tropical groupers, although differences exist, which might in part be related to the temperate conditions of the northern Mediterranean sea. The density of dusky groupers in the area was low in winter, and maximal in summer, from late June to late August (up to 8-fold increase); numbers rised in spring, before the beginning of reproductive activities which led to spawning by mid August, and dropped rapidly afterwards. During this long reproductive period (about 2 months), dominant males (recognized by their highly specific colour pattern) established territories in which they displayed aggressively towards neighbouring males and numerous smaller females (the species is proterogynous); the observed sex-ratio was approximately 1:7 (sexually active males versus adult females). Territoriality of males is the base of the social structuration of the reproductive population; in addition, behaviours typical of the pre-spawning period include repeated evening gathering of females in open water, and the appearance of specific colours patterns. This overall socio-behavioural pattern changed in the evenings when spawning was observed (16th - 21st of August), the males patrolling a reduced territory in which females would come to mate; spawning behaviour itself was described in Zabala et al. (1997).The complex socio-behavioural structure leading to reproduction in the Dusky Grouper should be considered in fishery management, since it could hardly develop under strong human pressure. In this respect, the contribution of Marine protected areas is determinant for the reproductive success of this species in the NW Mediterranean basin

Spawning behaviour of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae) in the Medes Islands Marine Reserve (NW Mediterranean; Spain)

Spawning of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) was observed for the first time in summer 1996 during scuba diving surveys in the Medes Islands Marine Reserve (NW Mediterranean). Ten spawning events were observed, which occurred at sunset, in the evenings around the new moon of August. A mature female (usually between 50 and 75 cm TL), in the standard mottled colour pattern, and a larger (more than 100 cm long) dominant male, in a conspicuous silver streaked colour-pattern, ascended up to 12 m side by side, spiralling in an anti-clockwise direction two or three times, from the bottom to shallow warmer waters, where the ova and sperm are released. Some traits of variability over this common pattern of spawning are described. Predation by saddled bream Oblada melanura, which concentrate in great numbers after each spawning suggests a very low survival of the spawned eggs