Weight-length relationships of 3 demersal fish species from Lebanese marine waters, eastern Mediterranean

International audienceWeight‐length relationships (WLRs) were estimated for 3 demersal species, from the Lebanese marine waters, eastern Mediterranean, namely Coelorinchus caelorhincus (Risso, 1810), Scorpaena elongata Cadenat, 1943 and Stephanolepsis diaspros Fraser‐Brunner, 1940. The specimens were collected using trammel and gill nets from June 2012 to October 2014. The values of parameter b of the WLRs W = aLb ranged from 2.922 to 3.708. Pronounced sexual dimorphism in WLR was observed for S. diaspros and none showed a WLR‐based geographical pattern of distribution. WLRs reported in this study should be applied only within the observed length ranges

Population biology of the little gulper shark Centrophorus uyato in Lebanese waters

International audienceA total of 38 individuals of the heavily exploited little gulper shark Centrophorus uyato were collected from Lebanese coastal waters using bottom longlines and trammel nets of different meshes at depths ranging from 115 to 600 m between May 2013 and February 2014. Their total lengths were between 45 and 94 cm and their total mass was from 870 to 6700 g. The sex ratio was not significantly different from 1:1, with 20 males and 18 females, but bathymetric sexual segregation occurred. Catch per net setting (CNS) was used as a relative abundance index to detect spatial distribution; trammel nets showed largest CNS ranging from 4·9 to 5·45 kg per unit effort in the north and south, at depths from 120 to 200 m, during spring and summer. The mass-length relationships demonstrated negative allometric growth (b < 3) (males: MT  = 0.3585LT2·071 , r2  = 0·94; females: MT  = 0.0239LT2·735 , r2  = 0·64). The condition factor as well as the gonado-somatic and hepato-somatic indices of C. uyato in the study area were also calculated. The results are discussed in relation to the distribution, growth and reproduction as well as the management of C. uyato

A case study of artificial reefs as a potential tool for maintaining artisanal fisheries in the French Mediterranean Sea

International audienceThe aim of this study was to obtain information allowing an initial assessment of the potential of French Mediterranean artificial reefs (ARs) as a management tool to aid artisanal fishermen. The study focuses on 3 ARs located along the Gulf of Lion coastline in the French Mediterranean Sea. At the end of spring 2012, experimental fishing with trammel nets was conducted at ARs and natural rocky areas (NRs) at various distances from the ARs/NRs (0, 300 and 900 m). The yields of fish and invertebrates were analyzed at the AR sites to identify significant changes along a distance gradient and to determine whether there was a significant difference between ARs and NRs. The AR yields of species preferring rocky substrates were generally higher between 0 and 300 m from the ARs than beyond 300 m, whereas the yields of species preferring sandy substrates or of invertebrates did not differ between 0 and 900 m from the ARs. Furthermore, the AR yields were equal to the NR yields or were between 1.5- and 1.8-fold higher than the NR yields. Overall, this study indicates that success varied by species, fishing locality and distance from the reef. ARs could be a potentially effective tool for enhancing artisanal fishing along the French Mediterranean coasts. However, it would be necessary to establish management measures to avoid overexploitation. For instance, in terms of the configuration of the AR areas in a given locality, a no-take area could be established within a radius of 300 m around the ARs

Potential use of marinas as nursery grounds by rocky fishes: insights from four Diplodus species in the Mediterranean

International audienceThe construction of marinas along the shoreline has caused substantial habitat destruction within the sheltered coastal areas previously used as nursery grounds by many fish species. However, although the negative ecological impacts of these constructions have been reported extensively, their potential roles in the functioning of the coastal zone remain largely unknown. Here, we surveyed the juveniles of 4 Diplodus species in 5 marinas located along the French Mediterranean coast to assess whether rocky fishes can successfully settle inside these artificialized coastal areas. Inter-specific differences in the spatiotemporal use of the various artificial habitats provided by marinas were investigated between April and August over 2 consecutive years. We also tested the potential benefit of pegging additional artificial habitats (Biohuts) on docks and pontoons to increase their value as fish nursery grounds. Our results suggest that although variations in marina and artificial habitat preferences exist between species, Diplodus juveniles repeatedly colonize marinas. Their average abundances on added Biohut habitats were twice as high as on nearby bare surfaces. This suggests that increasing the complexity of the vertical structures of marinas can considerably enhance their suitability for juvenile rocky fishes, especially at the youngest stages, when mortality is highest. Therefore, as long as marina water quality is well controlled, ecological engineering within these man-made habitats might reduce the ecological consequences of urban development by providing suitable alternative artificial nursery grounds for rocky fishes

Biogeochemical characterization of the riverine particulate organic matter transferred to the NW Mediterranean Sea

International audienceA large amount of terrestrial organic matter is annually delivered by rivers to the continental shelf, where this material is either degraded, buried or transferred to the deep sea by hydrodynamic processes such as storms. The relative amount of terrestrial organic matter in the marine sediments is often determined by analysing the stable isotopes (δ 13 C and δ 15 N) and the C / N ratio of organic matter because the various particulate organic matter (POM) sources have distinct isotopic compositions. With the objective to refine and better interpret POM sources in the marine environment , we have characterized monthly terrestrial POM delivered by eight rivers discharging to the NW Mediterranean Sea: the Rhône, Hérault, Orb, Aude, Têt, Fluvià, Ter and Tordera rivers. These rivers were simultaneously sampled from November 2008 to December 2009 and the concentrations of total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PN), as well as their stable isotopic ratios (δ 13 C and δ 15 N) were determined. During the survey, three rainstorm events with winds coming from the E–NE and the S–SE impacted the NW Mediter-ranean. Depending on the direction of incoming winds, the fluvial response (amount of water discharge and TSM) was different. Rivers draining the Alps (Rhône River) and Central Massif (Hérault, Orb, and Aude rivers) were mostly im-pacted by rainstorms associated with winds coming from the S–SE, while rivers draining the Pyrenees (Têt, Fluvià, and Ter rivers) and the Montseny Massif (Tordera River) were impacted by rainstorms associated with winds coming from the E–NE. In addition, the spatial evolution of water discharges shows a different hydrological regime of the Rhône River, with relatively constant and high water stages and TSM concentrations when compared to coastal rivers, characterized by long periods of low water stages. TSM concentrations are positively correlated to water discharges (high water flows resuspended riverbed sediments) but show an inverse relationship with POC and PN relative contents (mostly due to dilution and by low availability of light in river waters during flood events). TSM in most of the coastal rivers have on average 2.5–3 times higher POC and PN mean contents than the Rhône River (8.5 and 1.5 %, respectively, for coastal rivers compared to 3.6 and 0.5 %, respectively, for the Rhône River). This discrepancy may be caused by the long drought periods in small coastal Mediterranean watersheds that enhance the eutrophication in studied coastal rivers. The δ 13 C ratios of organic matter also reflect this discrepancy between high and low water stages with values ranging from −33.2 to −24.5 ‰. The enriched 13 C values (−26.3 ± 0.4 ‰ for the Rhône River and −26.9 ± 1.2 ‰ for coastal rivers), measured during high water stages, express mostly a mixture of terrestrial source (plant remains and soils) whereas depleted 13 C values (∼ −30 ‰) associated with low water stages exhibit a source with predominant freshwater algae. The high δ 15 N mean values (> 8 ‰) found in Têt, Ter and Tordera rivers may underline the importance of denitrification processes as a consequence of the eutrophication and anthropogenic impact

Movements and spatial distribution of an endangered fish (Sciaena umbra) within a marine protected area

Abstract The brown meagre (Sciaena umbra) is an endangered species, which requires specific protection measures to ensure its conservation. These measures need to be informed by high-quality scientific knowledge on their space use patterns. Here, we used acoustic telemetry to assess its seasonal movement patterns and habitat use within a marine protected area (MPA). Our results suggested that S. umbra is a highly sedentary species (home range < 1.0 km2) and, therefore, the MPA is extensive enough to protect the local population. Their population was discretely distributed in two main areas within the MPA, which was likely a result of habitat segregation and density-dependent movements. The temporal variability of their movements further uncovered when and where spawning occurs (mainly, but probably not only, in the fully protected area in June) and indicated that spillover of this species is limited but still possible. Overall, we highlight the importance of MPAs in the recovery of S. umbra, we advocate the need to perpetuate the current national fishing bans and extend it to other countries in the Mediterranean region, and we emphasize that considering the fine-scale movements of S. umbra in future management actions is key to achieving a successful recovery of their populations

Seasonal influence on the bathymetric distribution of an endangered fish within a marine protected area

The spatio-temporal variability of fish distribution is important to better manage and protect the populations of endangered species. In this sense, the vertical movements of a vulnerable and protected species, Sciaena umbra, were assessed in a marine protected area (the Réserve Naturelle Marine de Cerbère-Banyuls, south of France) to study the variability of their bathymetric distribution at different time scales. Twenty adults were marked with acoustic transmitters and acoustically monitored over 2.5 years. This revealed that some individuals remained at shallow waters (< 8 m) all year round, while others presented vertical segregation at deeper waters during the cold months (mean depth of 22.5 ± 0.04 m) and all aggregated in shallow waters during the warm months. The brown meagre was more active during the night, except in June and July when peaks of activity were observed at dusk. These patterns are likely associated with foraging and reproductive behavior during the cold and warm periods, respectively, and likely regulated by water temperature and the depth of the thermocline. Here, we provide valuable information on when and where in the water column critical periods of S. umbra life cycle are expected to occur, which should be considered in management and protection plans