Search

The reef manta ray (Mobula alfredi) is a highly mobile and plankton-feeding species, classified vulnerable to extinction on the IUCN Red List for Threatened Species. Knowledge on their spatial ecology and the extent of their dispersal remain incomplete, especially within island-fragmented habitats as found in New Caledonia. Satellite telemetry was used to investigate the horizontal movement ecology of reef manta rays in New Caledonia. A total of 21 manta rays were tagged with pop-up satellite archival transmitting tags (21 Fastloc and 2 MiniPAT) that remained deployed for a duration ranging from 3 to 180 days (mean ± SE = 76.7 ± 50.3). Rays presented a strong site fidelity and an important affinity for coastal waters. Long-distance migrations (> 300 km) were also observed, mainly through coastal and shallow water paths. Horizontal movements were compared to a home range area and classified into four distinct patterns: Fidelity, Excursion, Fidelity + Relocation and Relocation. The most dominant pattern was Fidelity where manta rays remained within their home range for the whole duration of the tag deployment. Our findings may assist the design of more appropriate management strategies for the species in New Caledonia and other regions worldwide.

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements. Vertical habitat use by sharks, rays, and skates varies globally and has implications for their conservation and management.

Current best-practice policy recommendations for managing fish stocks are achieved by a mixture of maintaining modest fishing mortality (restricting effort, times and gear), marine reserve networks and not subsidizing unprofitable fisheries. A seldom evaluated question is how effective these proposed approaches are for maintaining all fish stocks and biodiversity elements in marine seascapes? Both recommended and unrecommended fishing practices fragment habitats and reduce metapopulation connectivity with potentially unexpected seascape-level consequences. To better understand these outcomes, we pooled and evaluated fish community data into two seascape groupings for comparisons of biomass and life-history characteristics. These were remote baseline reefs (>9 hr from regional cities and >4 hr from human habitation, n = 584 locations) and those emulating best-practice seascapes (BPS, n = 140). BPS were a mix of high-compliance marine reserves (fishable biomass = 892 ± 696 (±SD) kg/ha, n = 95; >5 km2 and >15 years of closure) and fished seascapes (478 ± 395 kg/ha, n = 45) that had biomass near the maximum sustained yield (MSY) estimates for coral reefs. The fish communities in the BPS locations differed considerably from the remote baseline by having 49% of the median and 32% of the mean biomass, smaller community-weighted body sizes, and faster growth and mortality rates. Most of the declines were associated with high biomass taxa that included carnivorous jacks (Carangidae), snappers (Lutjanidae), groupers (Serranidae) and triggerfish (Balistidae), which were reduced to between 11% and 28% of the mean baseline. Surgeonfish (Acanthuridae) and parrotfish (Scarinae) were an exception in being reduced to only 48 and 53% of the baseline's mean biomass, respectively. As expected, community-level body sizes and age values were larger and trophic level higher, while growth and mortality were lower in baselines than BPS seascapes. After evaluating the different environmental

Three isoenergetic diets differing in their fishmeal/soy protein concentrate (SPC) ratio were assessed on the tissue growth and energy budget of juvenile crabs Scylla serrata in postmolt stages (PMolt) and in intermolt stages (IMolt). The average growth rates on a dry matter basis were 2.064 ± 0.324% and 0.492 ± 0.08% initial BW.day−1 during PMolt and IMolt stages, respectively. The efficiencies of the feed conversion (FCE, %), protein retention (PRE, %) and energy retention (ERE, %) were similar for the three experimental diets. However, FCE, PRE and ERE in PMolt stages were four to five times higher than in IMolt stages. The feed intake, energy and protein required for growth in PMolt stages were obviously higher than in IMolt stages. The energy budgets (% total energy intake) were marginally affected by diet but were significantly affected by the molt stage. The maintenance energy was lower in PMolt stages (49.84 ± 4.9%) than in IMolt stages (83.33 ± 2.45%). The excess in maintenance energy in IMolt stages represents the portion set aside for the next molt: shell energy content (4.97 ± 0.31%) and energy for ecdysis (±28%). Conversely, recovery energy was significantly higher in PMolt stages (34.39 ± 0.99%) than in IMolt stages (8.33 ± 1.7%). In conclusion, SPC sustained good tissue growth and good feed utilization and can be used as a main source of dietary protein for crab juveniles in captivity.

The relationships between shore fish assemblages from habitats neighboring coral reefs have received little attention in the Indo-Pacific. The present study is based on the extensive sampling (539,000 fish; 898 taxa) of three fish assemblages: reefs, mangroves, and soft-bottoms in a large bay of New Caledonia. Species area curves indicate that sampling was nearly exhaustive in all three habitats (262 species in mangroves, 342 on soft-bottoms, 594 on reefs). Combinations of life-history traits were used as proxies of ecological functions. The species and functional overlaps were highest between soft-bottoms and mangroves and lowest between mangroves and reefs. These overlaps were lower than most recent studies in the Indo-Pacific, a result probably linked to the extent of the sampling in the present study. The life-history traits of species found exclusively in one habitat as opposed to several habitats were not a random selection within the species pool. Overlapping species were mostly large species that fed on nekton, large invertebrates, or plankton; exclusive species were mostly sedentary, solitary, and of small size, except for plankton-feeding species, which mostly had large home ranges and formed large schools. Herbivores were seldom found in several habitats. Functional redundancy was correlated to species richness, and was highest in reef fish assemblages. Functions common to several habitats had very seldom the same relative redundancy, implying that these functions had not the same importance for each assemblage. Functions exclusive to one habitat generally had low redundancy. These functional attributes and species overlap suggest that these three assemblages have a low level of interaction, despite the fact that they share extensive boundaries. These findings may have important applications in the management of shore fish assemblages.

Lagoon soft-bottoms are key habitats within coral reef seascapes. Coral reef fish use these habitats as nurseries, feeding grounds and transit areas. At present, most soft-bottom sampling methods are destructive (trawling, longlining, hook and line). We developed a remote, unbaited 360 degrees video sampling method (RUV360) to monitor fish species assemblages in soft bottoms. A low-cost, high-definition camera enclosed in a waterproof housing and fixed on a tripod was set on the sea floor in New Caledonia from a boat. Then, 534 videos were recorded to assess the efficiency of the RUV360. The technique was successful in sampling bare soft-bottoms, seagrass beds, macroalgae meadows and mixed soft-bottoms. It is easy to use and particularly efficient, i.e., 88% of the stations were sampled successfully. We observed 10,007 fish belonging to 172 species, including 45 species targeted by fishermen in New Caledonia, as well as many key species. The results are consistent with the known characteristics of the lagoon soft bottom fish assemblages of New Caledonia. We provide future users with general recommendations and reference plots to estimate the proportion of the theoretical total species richness sampled, according to the number of stations or the duration of the footage.

The worldwide decline of coral reefs necessitates targeting management solutions that can sustain reefs and the livelihoods of the people who depend on them. However, little is known about the context in which different reef management tools can help to achieve multiple social and ecological goals. Because of nonlinearities in the likelihood of achieving combined fisheries, ecological function, and biodiversity goals along a gradient of human pressure, relatively small changes in the context in which management is implemented could have substantial impacts on whether these goals are likely to be met. Critically, management can provide substantial conservation benefits to most reefs for fisheries and ecological function, but not biodiversity goals, given their degraded state and the levels of human pressure they face.