• European Marine Science
• Open Access close
• BJ close

This study aims to test whether exploitation affects tunas and tuna-like species displaying contrasting life history traits similarly. We first collected information on life history of 10 commercial Atlantic species and then compared this information using multivariate analysis. On one hand, tropical tunas are characterised by small to medium size, rapid growth, early age-at-maturity, long spawning duration and short life span. These species, therefore, display a rapid turnover, characteristic of r-selected species. On the other hand, temperate tunas display differing life history traits, i.e., large size, slow growth, late age-at-maturity, short spawning duration and long life span. The turnover of these species is slow and present characteristics similar to 'K-selected' species (with a conservative strategy adapted to a colder and more variable environment). We, then, selected the two tuna species displaying the most contrasting life histories, i.e., skipjack (SKJ) and bluefin tuna (BFT), and investigated their respective responses to various levels of exploitation, using simulation modelling. If fishing activity starts at age I (a situation which is close to the actual exploitation pattern), differences in life history traits make the BFT population much more fragile to exploitation and less productive than SKJ. However, if the fisheries only target adults, both SKJ and BFT populations are able to sustain high F. Spawning stocks and yields of BFT also display conspicuous long-term fluctuations, resulting from the combination of year-to-year variations in the recruitment and a long life span. This variability makes it difficult to detect overfishing or depletion risks in the BFT population. Because of its short life span, SKI does not display such long-term variations in its SSB. Our simulations also showed that current management measures based on a minimum size limit are much more critical for BFT than SKJ. This difference stresses the importance of taking account of differences in life history traits into management measures.

The giant clam Tridacna maxima has been largely overexploited in many tropical regions over the past decades, and was therefore listed in appendix II of the Convention of International Trade in Endangered Species (CITES) in 1985. In French Polynesia, several atolls and islands harbor the world's highest stocks of giant clams in very shallow and accessible areas, which are therefore highly vulnerable to fishing pressure. The local fishery authority (i.e., Direction des Resources Marines or "DRM") implemented several management schemes in 2002 to control and regulate fishing pressure. However, for further decisions DRM was missing a sensitivity analysis on the effectiveness of the possible management actions. Here, we report on the use of a deterministic Viable Population Analysis (VPA) and spatially-explicit age-based population model that simulated the 30-year trajectory of a Tridacna maxima stock under different management approaches. Specifically, given various scenarios of intra-island larval dispersal, we tested which of No-take-Areas (NTAs), rotational closures, size limits, quotas, and restocking schemes would lead to the highest future stocks in Tubuai and Raivavae, two exploited islands of the Austral archipelago. For both islands, stock abundances were estimated in 2004/2010 and 2005/2010 respectively, and natural mortalities were assessed previously only in Tubuai. When compared to field data, the model successfully predicted the 2010 stocks for Tubuai, but proved to be less reliable for Raivavae, where natural mortality rates may well be different from those on Tubuai. For Tubuai, the spatial model suggested that reducing fishing effort (through fixed quotas) and banning fishing below the 12 cm size limit (as currently implemented) were the most effective management actions to sustain T. maxima populations into the future. Implementing NTAs was of poor effectiveness. NTAs increased giant clam stock inside the protected area, but also increased overfishing in the neighboring areas, and were ineffective overall.

International audience; Millions of people’s livelihoods rely on artisanal fisheries. However, in many regions fishers are increasingly facing ciguatera poisoning, a seafood-borne illness. The toxin, produced by benthic dinoflagellates, can spread through marine food webs and to humans by direct consumption. Ciguatera risk can play a major role in fisher’s activities but has never been considered in any marine spatial plans thus far. To fill this gap, we examined if integrating ciguatera in systematic conservation plans could affect these decisions. We developed through map-based interviews, a novel seven-step framework to collect and map local knowledge on ciguatera risk and fisheries activities with two innovations: (i) better mapping of fishing grounds by combining geomorphological habitat and fishing gear information, and (ii) integrating ciguatera risk directly into systematic spatial planning designs and scenarios conceived to maximize benthic habitat conservation while minimizing impacts to fishers. The approach is illustrated for Raivavae Island, in French Polynesia, Pacific Ocean. We found that integrating ciguatera zones significantly improved prioritization solutions with a 24–38% decrease of costs to fishers compared to scenarios based solely on fishery data. This framework was designed for scientists and managers to optimize the implementation of conservation plans and could be generalized to ciguatera-prone areas.; Des millions de personnes dépendent de la pêche artisanale. Dans de nombreuses régions cependant, les pêcheurs font de plus en plus face à des intoxications alimentaires dues à la ciguatéra, suite à la consommation de produits de la mer contaminés. La toxine, produite par un dinoflagellé benthique, peut se répandre dans les réseaux trophiques marins et affecter les hommes suite à la consommation de poissons ou invertébrés. Le risque de ciguatéra peut jouer un rôle majeur dans les pêcheries lagonaires, mais il n’a encore jamais été pris en compte dans la planification spatiale marine. Pour combler ce manque, nous avons examiné si intégrer la ciguatéra dans la planification systématique de la conservation allait affecter les résultats. Nous avons développé une méthodologie en sept étapes pour collecter et spatialiser les savoirs locaux sur la ciguatéra et les activités de pêche via des entretiens basés sur des cartes, incluant deux innovations : (i) cartographier plus précisément les zones de pêche en combinant des informations sur les instruments de pêche et les habitats et (ii) intégrer le risque de ciguatéra directement dans le design de planification, celui-ci étant conçu pour maximiser la conservation des habitats benthiques tout en minimisant l’impact pour les pêcheurs. L’approche est illustrée par l’île de Raivavae, en Polynésie française, dans l’Océan Pacifique. Nos résultats montrent qu’intégrer les zones à ciguatéra a significativement amélioré le design des plans de conservation, avec une diminution de 24-38% des coûts infligés aux pêcheurs par rapport aux scénarios basés uniquement sur des données de pêche. Cette méthodologie est destinée aux scientifiques et gestionnaires afin d’optimiser la mise en œuvre de plans de conservation, et elle pourrait être généralisée à toutes les régions concernées par la ciguatéra.

Small-scale spatial and temporal variability in animal abundance is an intrinsic characteristic of marine ecosystems but remains largely unknown for most animals, including coral reef fishes. In this study, we used a remote autonomous unbaited video system and recorded reef fish assemblages during daylight hours, 10 times a day for 34 consecutive days in a branching coral patch of the lagoon of New Caledonia. In total, 50 031 fish observations belonging to 114 taxa, 66 genera and 31 families were recorded in 256 recorded videos. Carnivores and herbivore-detritus feeders dominated the trophic structure. We found significant variations in the composition of fish assemblages between times of day. Taxa richness and fish abundance were greater in the early morning and in the late afternoon than during the day. Fourteen taxa displayed well-defined temporal patterns in abundance with one taxon influenced by time of day, six influenced by tidal state and seven influenced by both time of day and tidal state. None of these 14 taxa were piscivores, 10 were herbivore-detritus feeders, three were carnivores and one was plankton feeder. Our results suggest a diel migration from feeding grounds to shelter areas and highlight the importance of taking into account small-scale temporal variability in animal diversity and abundance when studying connectivity between habitats and monitoring communities.

Lanternfishes (Myctophidae) are among the most abundant, widespread, and diverse fish groups in the world ocean. They account for a significant part of oceanic fish biomass and play crucial roles in various ecosystem processes, including carbon sequestration and nutrient recycling. However, despite the increasing risks they face (e.g. global warming, plastic pollution, and exploitation of deep-sea resources), many aspects of the lanternfishes ecology still remain poorly known. Here, we investigate the species composition, vertical migration, and trophic ecology of lanternfishes in the Southwestern Tropical Atlantic (SWTA) and the influence of physicochemical factors on their horizontal structuring. We show that lanternfishes are a highly diverse and an abundant fish family of the SWTA, comprising at least 33 species and contributing 40% of all fish collected (in number). We reveal that some of these species may differ in their patterns of prey composition and migratory behaviour, leading to multidimensional niches, underestimated trophic links (e.g. gelatinous organisms), and several mechanisms to avoid competitive exclusion. At least 73% of the lanternfish species reported here seem to migrate to the surface to feed at night. Additionally, they are a central food source for mesopelagic and bathypelagic predators, thereby connecting shallow and deep-sea ecosystems. Finally, we show that the structure of lanternfish assemblages is not strongly affected by environmental conditions analysed here (i.e., throughout the thermohaline structure and current systems), leading to weak horizontal assemblage separation. International audience WOS:000724705600001

Abstract. Nitrogen (N) and phosphorus (P) availability, in addition to other macro- and micronutrients, determine the strength of the ocean's carbon (C) uptake, and variation in the N : P ratio of inorganic nutrient pools is key to phytoplankton growth. A similarity between C : N : P ratios in the plankton biomass and deep-water nutrients was observed by Alfred C. Redfield around 80 years ago and suggested that biological processes in the surface ocean controlled deep-ocean chemistry. Recent studies have emphasized the role of inorganic N : P ratios in governing biogeochemical processes, particularly the C : N : P ratio in suspended particulate organic matter (POM), with somewhat less attention given to exported POM and dissolved organic matter (DOM). Herein, we extend the discussion on ecosystem C : N : P stoichiometry but also examine temporal variation in stoichiometric relationships. We have analyzed elemental stoichiometry in the suspended POM and total (POM + DOM) organic-matter (TOM) pools in the upper 100 m and in the exported POM and subeuphotic zone (100–500 m) inorganic nutrient pools from the monthly data collected at the Bermuda Atlantic Time-series Study (BATS) site located in the western part of the North Atlantic Ocean. C : N and N : P ratios in TOM were at least twice those in the POM, while C : P ratios were up to 5 times higher in TOM compared to those in the POM. Observed C : N ratios in suspended POM were approximately equal to the canonical Redfield ratio (C : N : P = 106 : 16 : 1), while N : P and C : P ratios in the same pool were more than twice the Redfield ratio. Average N : P ratios in the subsurface inorganic nutrient pool were ~ 26 : 1, squarely between the suspended POM ratio and the Redfield ratio. We have further linked variation in elemental stoichiometry to that of phytoplankton cell abundance observed at the BATS site. Findings from this study suggest that elemental ratios vary with depth in the euphotic zone, mainly due to different growth rates of cyanobacterial cells. We have also examined the role of the Arctic Oscillation on temporal patterns in C : N : P stoichiometry. This study strengthens our understanding of the variability in elemental stoichiometry in different organic-matter pools and should improve biogeochemical models by constraining the range of non-Redfield stoichiometry and the net relative flow of elements between pools.

ABSTRACTUnderstanding aspects of the biology of early life stages of marine fish is critical if one hopes to reveal the factors and processes that impact the survival and recruitment (year class) strength. The Peruvian anchovy (Engraulis ringens) is a key species in the Humboldt current system, and the present study provides the first description of the embryonic and larval development of this species reared in captivity. Embryonic and early exogenous feeding stages of larvae were illustrated in detail at 18.5°C. Hatching was completed within 42 and 48 h post‐fertilization at 18.5 and 14.5°C, respectively. Mean ± 95% C.I. standard length (LS) at hatch (3.40 ± 0.10 mm at 18.5°C and 2.76 ± 0.34 mm at 14.5°C) was significantly different between the two temperatures. Larval behaviour was assessed at 18.5°C; at the onset of exogenous feeding [3 days post‐hatch (dph)], larvae were fed small, motile dinoflagellates, Akashiwo sanguinea. At 7 dph, larvae started to feed almost exclusively on zooplankton (rotifers and Artemia nauplii). Larval activity increased with age, and the first sign of schooling was noted at 31 dph (18.56 mm LS) at 18.5°C. Temperature had a significant effect on size‐at‐age, but not on body shape (depth to LS ratio). The size‐at‐age data for larvae (this study) was used to parameterize a temperature‐corrected von Bertalanffy growth function for Peruvian anchovy, the accuracy of which was assessed for juveniles and adults (literature values).