Mesopelagic Fish Research Articles

Assessing the potential economic effects of mesopelagic fisheries as a novel source of fishmeal

AbstractThe continuous growth of the aquaculture industry implies increased demand for efficient sources of aquafeed, such as fishmeal. Pelagic fish are a desirable source of fishmeal due to their high nutritional content. Nevertheless, several pelagic stocks that have been exploited extensively for fishmeal production face ecological limits due to commercial exploitation, and the aquaculture industry is now seeking novel, efficient, and sustainable sources of aquafeed. The mesopelagic zone, an ecosystem with many scientific uncertainties, is being considered as a potential source for fishmeal, largely owing to the abundance of mesopelagic fish and their robust nutritional profile. However, both the ecological and economic viability of commercial exploitation of mesopelagic fish are not yet well understood. To understand the conditions that would make such an endeavor economically viable in the context of global fishmeal production systems, we use a bioeconomic model that assesses the economic consequences of including mesopelagic fish as a fishmeal source. Through simulations, we assess the economic implications of this hypothetical mesopelagic fishery on major pelagic fishmeal production systems. The mesopelagic fishery can be economically profitable for harvesters, and its addition to global fishmeal production reduces fishmeal market price, thus making it more accessible to aquaculture farmers and less profitable for pelagic fishers. While this may reduce fishing pressure on pelagic forage‐fish stocks, the implications of commercial exploitation of mesopelagic on key ecosystem services remain a concern.

Mesopelagic fish assemblages in the Mauritanian Upwelling System off Northwest Africa with oxygen as a major driving force

The aims of this study were to determine the community composition and environmental drivers of mesopelagic fishes in the Mauritanian Upwelling System. Mesopelagic fish communities were sampled at 17 stations in August of 2016 off the coast of Senegal and Mauritania using a non-closing rectangular midwater trawl (RMT). This subregion is the most productive area of the Canary Current and has a pronounced and permanent oxygen minimum zone (OMZ). The sampling area was mainly composed of low-oxygenated South Atlantic Central Water, except for 1 station, where North Atlantic Central Water prevailed. Three distinct mesopelagic fish communities were identified. One community occurred in the vicinity of a coldwater eddy and was dominated by the myctophid Benthosema glaciale. In contrast, the gonostomatid genus Cyclothone prevailed in the other 2 communities and made up 62 and 51% of the total fish abundance. Our analyses revealed that the environmental factors that primarily influenced the composition of these mesopelagic fish assemblages were the oxygen concentrations at 10, 100, and 600 m depth. The present study shows that the mixing of water masses at frontal zones leads to communities representative of both water masses. In the case of the Mauritanian upwelling region, a high portion of the mesopelagic fish species were well adapted to OMZ conditions.

Hydro-acoustic classification and abundance estimation of mesopelagic fish in deep scattering layers (DSL) of the Indian Ocean

Abstract Deep scattering layers (DSL) in oligotrophic systems are typically comprised of a variety of coexisting organisms, including fish, zooplankton, jellyfish, and squid, and hence there is uncertainty about the proportion of the acoustic backscatter in these layers that can be attributed to mesopelagic fish. Here, acoustic targets were classified using a multi-frequency acoustic classification algorithm based on data collected in the Indian Ocean at 18, 38, 70, and 120 kHz during three acoustic surveys in 2018. Frequency-dependent backscattering strength information (∆Sv) was extracted from acoustic data that coincided with trawl hauls dominated by mesopelagic fish. Five ∆Sv frequency pairs were used to separate the acoustic backscattering into three broad scattering categories, i.e. mesopelagic fish, crustacean-like/tunicates, and squids/others. Results indicated that the DSL is highly diverse and dominated by mesopelagic fish, with average densities at a regional scale ranging from 12.0 (±10.9) to 26.0 (±21.7) g m−2, and proportions of the acoustic backscatter attributed to mesopelagic fish ranging from 0.5 to 0.7. These estimates are generally lower than previously estimated for other regions of the Indian Ocean. The situation may well be similar elsewhere, particularly in oligotrophic systems, with potential ramifications for global mesopelagic fish biomass estimates.

Ontogenetic shift or not? Different foraging trade-offs within the meso- to bathypelagic fish community.

During ontogeny, the increase in body size forces species to make trade-offs between their food requirements, the conditions necessary for growth and reproduction as well as the avoidance of predators. Ontogenetic changes are leading species to seek out habitats and food resources that meet their needs. To this end, ontogenetic changes in nocturnal habitat (vertical use of the water column) and in the type of food resources (based on stable isotopes of nitrogen) were investigated in 12 species of deep pelagic fish from the Bay of Biscay in the Northeast Atlantic. Our results revealed the existence of major differences in the ontogenetic strategies employed by deep pelagic fishes. Some species showed ontogenetic changes in both vertical habitat use and food resources (e.g. Jewel lanternfish (Lampanyctus crocodilus) and Atlantic soft pout (Melanostigma atlanticum)). In contrast, other species showed no ontogenetic change (e.g. Koefoed's searsid (Searsia koefoedi) and Lancet fish (Notoscopelus kroyeri)). Some species only changed food resources (e.g. Spotted lanternfish (Myctophum punctatum), Spotted barracudina (Arctozenus risso) and Stout sawpalate (Serrivomer beanii)), while others seemed to be influenced more by depth than by trophic features (e.g. Bluntsnout smooth-head (Xenodermichthys copei) and Olfer's Hatchetfish (Argyropelecus olfersii)). These results suggest that to meet their increasing energy requirements during ontogeny, some species have adopted a strategy of shifting their food resources (larger prey or prey with a higher trophic level), while others seemed to maintain their food resources but are most likely increasing the quantity of prey ingested. As fish species can have different functional roles during their development within ecosystems, characterising ontogenetic changes in mesopelagic fish species is a crucial step to be considered in future research aimed at understanding and modelling the complexity of deep-pelagic food webs.

Mesopelagic Mysteries: Regulating an Emerging Resource Amid Uncertainty

Mesopelagic species, which inhabit depths between 200 to 1000 m, have regained attention as potential new resources to replace and supplement the use of traditionally overfished species. Research and exploratory fishing are ongoing, yet much on the nature of mesopelagic organisms and their roles within ecosystems and the carbon cycle remains to be understood. Building on recent reports and reflecting on fisheries developments, this article examines some of the unique characteristics of the mesopelagic zone and the existing international legal framework to stimulate legal debate on the sustainable management of mesopelagic fish stocks in the high seas.

Underwater vocalizations in foraging female Antarctic fur seals (Arctocephalus gazella) in the Kerguelen Islands

AbstractIn the marine environment, many animals use sound to interact and communicate with their conspecifics or other species. Over the last decades, the development of sound recording systems has allowed a significant advance in our knowledge of sound production in marine animals. We deployed miniature sound and movement tags on Antarctic fur seals (AFS), a small otariid foraging on mesopelagic fish, to uncover potential underwater vocalizations in this species. Tags recorded underwater sounds synchronously with high‐resolution AFS movements and diving behavior, allowing us to investigate the behavioral context of vocalizations in the natural environment. We provide evidence of underwater vocalizations in foraging female AFS in a context of foraging at sea. AFS produced stereotyped calls made of low‐frequency pulses produced in series, exclusively during foraging dives. We hypothesized that these acoustic pulse series could be used as an acoustic lure to confuse or attract fish prey, however, a larger sample size is needed to study the adaptive significance of these underwater vocalizations.

Estimations of length-weight relationships and consumption rates of odontocetes in the Mediterranean Sea from stranding data

Stranding data provide fundamental information on biometric traits of cetaceans useful to increase knowledge on ecological traits and their consumption patterns. In this study, the length weight (L-W) relationships through the power regression model (W=a×Lb) were calculated for three dolphin species (the striped dolphin, the common bottlenose dolphin and the Risso's dolphin) in several Mediterranean subregions and at the scale of the entire basin. Length (L) and weight (W) data were collected from stranding records during the period from 1983 to 2021 acquired from several databases and the literature. Starting from L-W relationships, a bootstrap method was applied to estimate the mean body weights, the daily ingested biomass (IB) and annual food consumption (AFC) rates of different dolphin species. In particular, four different equations were used to estimate the IB rates. Prey consumption by dolphin species was calculated through AFC rates and the available diet information (expressed in weight fractions) of dolphin species for different Mediterranean subregions.Considering the L-W relationships in the Mediterranean Sea, b coefficient values were equal to 2.578, 2.975 and 2.988 for the striped, the common bottlenose and the Risso's dolphin, respectively. At the Mediterranean scale, the AFC values estimated were 3913 kg (CI 2469–5306) for the Risso's dolphin, 2571 kg (1372–3963) for the common bottlenose dolphin and 1118 kg (531–1570) for the striped dolphin. Prey consumption pattern showed a clear partitioning among the investigated species, where the common bottlenose dolphin exploits neritic demersal and pelagic fishes (e.g. eel fishes, sparids), the striped dolphin exploits mesopelagic fishes and myctophids, and the Risso's dolphin was specialized on bathyal cephalopods of Histioteuthidae family.The results obtained in this study provide new information for the investigated species in several Mediterranean subregions providing a first consistent baseline to support the population dynamics modelling. At the same time, the wide uncertainty ranges of some parameters, as well as the lack of information for some species, stress the necessity of improving the data collection associated to stranding events, especially in the southern Mediterranean areas.

Parasite assemblages of lanternfishes (Myctophidae) in deep subantarctic waters: Potential indicators for ecosystem monitoring

The Agujero Azul (Blue Hole) is an oceanic region located on the edge of the Southwestern Atlantic continental shelf that is especially impacted by intense fishing activity. It harbours a high biodiversity, including the mesopelagic lanternfishes of the numerically abundant family Myctophidae. Due to their high abundance and relevance in food webs, monitoring changes in the population and community structure of mesopelagic fishes is a valuable tool to trace changes in a warming world, especially in a highly exploited ecosystem where the effects of global change have been documented. Parasite communities of the lanternfishes Gymnoscopelus nicholsi and Electrona subaspera, caught at the Agujero Azul are analyzed. The aims of this work were to assess their value as indicators of host population structure and to establish a baseline for monitoring ecosystem variations under future scenarios of global change. The connectivity with the population of G. nicholsi from around South Georgia was also evaluated by comparing their parasite faunas. A parasitological study of 170 G. nicholsi and 31 of E. subaspera showed low parasite abundance and species richness, with significantly higher levels of parasitism in larger fishes. The paucity of parasitism in G. nicholsi from South Georgia compared to Agujero Azul suggests the existence of two discrete stocks. On the other hand, comparison with literature data supports a connection between fish from the Patagonian shelf and South Shetland Islands (Antarctica). Comparison across samples from Agujero Azul showed homogeneity in parasite assemblages, regardless of the distance separating them, ensuring that parasites are reliable representatives of such physical conditions. Thus, this representability suggests that parasites can be suitable indicators to estimate the amplitude of future changes due to global warming and other anthropogenic stressors in this region. This work provides a baseline for using the parasites of G. nicholsi as indicators to trace these ongoing and predicted changes.

Comparative analysis of day and night micronekton abundance estimates in west Pacific between acoustic and trawl surveys

Micronekton organisms are a central component of the trophic organization in the pelagic ecosystem, being prey to top predators and participating in the export of carbon from the surface to the deep layers. Despite their importance, the abundance estimates and species distribution of micronekton remain largely uncertain. This study aimed to compare and assess two sampling methods classically used for the estimation of micronekton abundance in mesopelagic acoustic scattering layers: scientific echosounder and trawl sampling. Measurements of 38 and 70 kHz hull-mounted echosounders were examined with biological trawl samples from 8 surveys in the South-West tropical Pacific. A model of acoustic observation was built from the trawl sampling species composition and forward scattering models. Predicted and observed acoustic responses are compared to assess the variability and the difference between the acoustic and trawl sampling methods in various scattering layers, for day and night periods. The difference between methods decreased with depth and with increasing abundance of fish with swimbladders caught in trawls. Notably, this difference was found to be minimal in the nocturnal deep scattering layer (mesopelagic zone, depth>200 m). This study emphasizes potential lower estimates of organisms’ abundance by trawling and a bias towards mesopelagic fish. Understanding the differences between methods and their variability within different scattering layers is essential for studying micronekton and improving the precision of biomass estimates.

Growth and natural mortality of Maurolicus muelleri and Benthosema glaciale in the Northeast Atlantic Ocean

Mesopelagic fish are considered a possible future fisheries resource, but the biological sustainability of their potential exploitation has not yet been assessed. Sustainability should be evaluated at the population level, for which accurate stock-specific life-history parameters are required. Here, we use a length-based model to estimate life-history parameters related to growth and natural mortality, and their uncertainty, for the assessment of Northeast Atlantic populations of Maurolicus muelleri (Gmelin, 1789, Mueller’s Pearlside) and Benthosema glaciale (Reinhardt, 1837, glacier lantern fish). We compare three different approaches to estimate natural mortality rates and provide recommendations for future data collection and monitoring programs. For M. muelleri, we estimated an asymptotic length of 57.98 mm and a von Bertalanffy growth constant of 1.28 year−1, while for B. glaciale, we estimated an asymptotic length of 78.93 mm and a von Bertalanffy growth constant of 0.41 year−1. Estimates of natural mortality rates for M. muelleri were around 1.29 year−1 and 1.80 year−1 based on empirical formulae with the estimated growth parameters and maximum age, respectively, and around 1.51 year−1 with the length-converted catch curve method for B. glaciale estimates ranged between 0.5, 0.68, and 0.75 year−1, with the three respective methods. Due to limited data availability, the estimated uncertainty of the provided life-history parameters is large and should be considered in the evaluation of the sustainability of potential mesopelagic exploitation following the precautionary approach.

Assessing mesopelagic fish diversity and diel vertical migration with environmental DNA

Mesopelagic fishes are an important component of the world’s oceans in terms of their abundance, biomass, and ecosystem function. These fishes are important contributors to the biological carbon pump via their feeding and behaviors, whereby they facilitate the transfer of carbon from shallow waters to the deep sea. Several species undertake diel vertical migration, feeding in shallower waters at night and moving to deeper waters during the day. This process actively expedites the downward flux of carbon. However, carbon budgets and climate models require accurate information regarding the depth distributions and migration patterns of these fishes, and environmental DNA (eDNA) analyses can provide this information. Here, we utilize eDNA approaches, generating taxonomically-informative COI and 12S reference barcodes for 80 species of mesopelagic fishes, which can be used for species-level identification of eDNA sequences. Using these, along with a publicly available barcodes database, we compare results from eDNA analysis with traditional net sampling, and explore the ability of eDNA techniques to detect diel vertical migration in fishes from samples collected in Northwest Atlantic Slope Water. We found that eDNA and net samples often resulted in different species identifications, demonstrating that eDNA can detect species that would otherwise be missed with traditional methods. In our eDNA samples, we also detected more species (12) in our shallowest depth category (0 - 100 m) from night samples than from day samples (3). This is consistent with increased diversity in shallow waters at night due to diel vertical migration. Based on the variability observed in sample duplicates, we suggest that future mesopelagic eDNA studies incorporate larger sample volumes and scaled-up sampling efforts. We also note the potential applications of eDNA analysis in addressing ecological questions related to predator-prey relationships identification of foraging hotspots, and carbon flow through the ocean’s midwaters.

Spies of the deep: An animal-borne active sonar and bioluminescence tag to characterise mesopelagic prey size and behaviour in distinct oceanographic domains

Mesopelagic fishes, a central component of marine trophic networks, play a fundamental role in marine ecosystems. However, as they live in highly inaccessible environments, little information is currently available on their distribution and abundance. The emergence of biologging technologies has made it possible to use deep-diving predators as bio-samplers of their environment in under-sampled regions. In this work, we deployed an innovative miniaturised sonar tag that combines active acoustics with high-resolution GPS, pressure, movement and light sensors on Southern elephant seals, a deep-diving predator feeding on mesopelagic prey. Seals were also equipped with Conductivity-Temperature-Depth tags. Salinity and temperature depth profiles were used to define oceanographic domains, allowing us to explore distribution and ecology of mesopelagic prey targeted by seals and the seals’ foraging behaviour. We highlighted strong vertical differences in prey characteristics and behaviour, with larger, more evasive and less bioluminescent prey in deeper waters. Moreover, prey encountered in warmer waters were found deeper, were more evasive and displayed a more marked diel vertical migration behaviour compared to prey encountered in colder waters, suggesting that prey accessibility and characteristics differ according to oceanographic domains. This study highlights the usefulness of the sonar-bioluminescence tag to infer mesopelagic prey distribution and habitat when deployed on deep-diving predators such as elephant seals.

Model of mesopelagic fish predation on eggs and larvae shows benefits of tuna spawning under full moon

AbstractMost mesopelagic fish are small planktivores that migrate up at nightfall to feed in the safety of darkness and descend to depth at dawn to escape visual predators. However, the trophic roles can reverse since mesopelagic fishes also predate eggs and larvae of their predators. We use the Atlantic bluefin tuna as a model species to test the hypothesis that fishes in the open ocean synchronize spawning to moon‐lit nights (when mesopelagic fishes avoid near‐surface waters) to increase offspring fitness. Our analysis over two decades of field observations shows that tuna spawn most intensively the week before full moon. This fits predictions from a mechanistic model where spawning around full moon increases offspring fitness by two orders of magnitude due to low predation from mesopelagic fishes. Circalunar patterns of food availability can also favor fitness of offspring spawned the days before full moon. Our findings suggest that mesopelagic fishes may have an important impact on pelagic fish through predation of early life stages and cause an evolutionary drive to synchronize spawning to the lunar cycle.

New Records of Three Mesopelagic Fish Species from Southwestern Taiwan

New Records of Three Mesopelagic Fish Species from Southwestern Taiwan

An overview of the impacts of fishing on seabirds, including identifying future research directions

Abstract Knowledge of fisheries impacts, past and present, is essential for understanding the ecology and conservation of seabirds, but in a rapidly changing world, knowledge and research directions require updating. In this Introduction and in the articles in this Themed Set “Impacts of fishing on seabirds”, we update our understanding of how fishing impacts seabird communities and identify areas for future research. Despite awareness of the problems and mitigation efforts for >20 years, fisheries still negatively impact seabirds via the effects of bycatch, competition, and discards. Bycatch continues to kill hundreds of thousands of seabirds annually, with negative population-level consequences. Fisheries for forage fish (e.g. anchovy, sandeel, and krill) negatively impact seabirds by competing for the same stocks. Historically, discards supplemented seabird diets, benefitting some species but also increasing bycatch rates and altering seabird community composition. However, declining discard production has led to potentially deleterious diet switches, but reduced bycatch rates. To improve research into these problems, we make the following recommendations: (1) improve data collection on seabird–vessel interaction and bycatch rates, on fishing effort and vessel movements (especially small-scale fleets), and on mitigation compliance, (2) counter the current bias towards temperate and high-latitude ecosystems, larger-bodied species and particular life stages or times of year (e.g. adults during breeding), and (3) advance our currently poor understanding of combined effects of fisheries and other threats (e.g. climate change, offshore renewables). In addition, research is required on under-studied aspects of fishing impacts: consequences for depleted sub-surface predators, impacts of illegal, unreported and unregulated fishing, artisanal and emerging fisheries, such as those targeting mesopelagic fish, have received insufficient research attention. Some of these shortfalls can be overcome with new tools (e.g. electronic monitoring, remote sensing, artificial intelligence, and big data) but quantifying and addressing fishing impacts on seabirds requires greater research investment at appropriate spatio-temporal scales, and more inclusive dialogue from grassroots to national and international levels to improve governance as fishing industries continue to evolve.

Assessing the trophic ecology of Southern Ocean Myctophidae: the added value of DNA metabarcoding

Lanternfishes (Myctophidae) are key components of mesopelagic fish communities globally. In the Southern Ocean, incomplete information on myctophid diets limits our understanding of their energetics, interactions, and wider ecosystem impact. Traditional microscopic methods of diet analysis have relatively coarse prey resolution and possible taxonomic and observer biases. Deoxyribonucleic acid (DNA) metabarcode sequencing promises higher taxonomic and temporal resolution, but uncertainty remains in comparing this with microscopy-based analyses. Here, we applied 18S DNA metabarcode sequencing to stomach contents from 20 Electrona antarctica individuals that had previously been examined via microscopic analysis. Across all fish analysed, crustacean and gastropod taxa dominated the prey identified via both methods, with broad agreement between methods on the relative abundance of different prey items. DNA metabarcode sequencing recovered greater taxonomic diversity and resolution, particularly for soft-bodied prey items and small crustaceans. DNA sequencing results also more clearly differentiated diet between individuals collected from different environments. Overall, our findings illustrate how DNA-based methods are complementary to, and consistent with, traditional methods and can provide additional, high-resolution data on a range of trophic interactions.

Seasonal patterns in the mesopelagic fish community and associated deep scattering layers of an enclosed deep basin

Mesopelagic fish constitute the most abundant vertebrate group in the marine environment. The current work reports on results of three seasonal acoustic cruises carried out in the Gulf of Corinth, a relatively small, deep, isolated basin located in the Central Mediterranean (Greece) that presents some unique geomorphological and ecological features. The aim of this study was to describe seasonal echo-types and the vertical distribution of the Deep Scattering Layers (DSLs) as well as to relate them with specific species or species groups. Mesopelagic fish dominated the pelagic ecosystem as confirmed by biological sampling with different gears during daytime and nighttime. In total, at least 15 species were caught, belonging to the families Myctophidae, Paralepididae, Sternoptychidae and Stomiidae, while the—elsewhere very abundant—families Gonostomatidae and Phosichthyidae were completely absent. Common echo-types included: (a) shoals and schools formed by the silvery lightfish Maurolicus muelleri, usually located along the shelf break (80–225 m), (b) a non-migrant thin DSL found at 150–280 m throughout the deep parts of the Gulf, dominated by juvenile half-naked hatchetfish Argyropelecus hemigymnus, and (c) one thick, partially migratory DSL at 250–600 m, mainly consisting of myctophids. The echo backscatter characteristics and species composition of the DSLs as well as the length distribution of the populations were found to differ seasonally. Species-specific and size related patterns in the vertical distribution of fish were detected both during daytime and nighttime. Overall, the Gulf of Corinth seems to sustain high densities of mesopelagic fish that constitute the basic food resource for the abundant dolphin populations that inhabit the area.

Simulating impacts of fishing toothfish on the pelagic community in the Cooperation Sea, Southern Ocean

There is increasing attention to the use of Antarctic toothfish (Dissostichus mawsoni) and Patagonian toothfish (Dissostichus eleginoides). Understanding the responses of toothfish and other species to fishing activities favors the sustainable use of natural resources. We developed an end-to-end model OSMOSE-CooperationSea to simulate the food web dynamics in the Cooperation Sea and evaluate the impact of toothfish fishery. Fishes and cephalopods played important roles in the energy pathways from krill species and other zooplankton species to toothfish and Weddell seal (Leptonychotes weddellii) whose trophic levels were higher than 5.0. Adélie penguin (Pygoscelis adéliae), Crabeater seal (Lobodon carcinophaga), and Baleen whales were strongly krill-reliant. The spawning stock of toothfish decreased more quickly than the recruitments with increasing fishing pressure. Fishing impacts on the recruitments of toothfish were hysteretic due to the fishing selectivity. The model considered an ontogenetic diet shift of toothfish that mesopelagic fish was influential to toothfish juveniles. The overexploitation of toothfish stock might result in a trophic cascade that mesopelagic fish biomass increased and krill biomass declined. Adélie penguin, Crabeater seal, and Baleen whales preyed on more small fishes in response to the decline of krill biomass. Considering the impacts of changes in Antarctic krill availability, the biomass of Adélie penguin, Crabeater seal, and Baleen whales declined with a heavy toothfish fishery. The study highlights the importance of precautionary and ecosystem-based management to toothfish fishery.

Could Deep-Sea Fisheries Contribute to the Food Security of Our Planet? Pros and Cons

Hundreds of millions of people on the planet are affected by malnourishment. This contributes to the vulnerability of large swaths of the population worldwide. Children under five years old and adolescent girls are especially disproportionately vulnerable to diseases and even death in less developed countries. Today, by providing a substantial share of global protein intake, as well as fatty acids and micronutrients, fisheries contribute to global food security. As fish stocks in the upper sea levels are increasingly over-exploited, there is a surge in discussion on the potential contributions of deep-sea fisheries for global food and nutrition security. Some mesopelagic fishes show potential in providing important nutrients. Another way of supplying food security might be in using mesopelagic fish as fish feed. However, fishing in the mesopelagic zone could lead to severe ecological repercussions, especially because the impact on the biological carbon pump is uncertain. This paper highlights and juxtaposes different perspectives regarding exploitation pathways of the fish riches of deep seas, and reviews best practice model projects that deal with uncertainties related to fishery management in the mesopelagic zone. The review concludes that due to the essential role of the mesopelagic zone in the global biological carbon pump and complex interaction patterns between pelagic and mesopelagic species, exploitation of the fish riches of the mesopelagic zone must be based on comprehensive data and rigorous analyses. In the face of the current uncertainty on the respective mechanisms, the authors endorse an international moratorium on deep-sea fisheries and/or the rather small-scale exploitation of mesopelagic biomass.

Development and Seasonal Variations of the Larvae of Three Mesopelagic Fishes near Coral Reefs in the Red Sea

This work aims to describe the larval stages and the seasonal variation in the abundance of three mesopelagic species whose larvae are surprisingly abundant near coral reef areas in the Red Sea. The larvae were collected monthly using a plankton net (500 µ) from three coastal coral reef areas surrounding Sharm El-Sheikh on the Egyptian Red Sea coast between January and December 2015. The identification of larvae was based on the morphological and meristic characteristics according to the available literature. The larvae of this species were divided into preflexion, flexion, and postflexion stages and they were also categorized according to their size into relevant size classes. Mesopelagic fishes were represented in the collection by four species belonging to four families: Vinciguerria mabahiss (Family: Phosichthyidae), Benthosema pterotum (Family: Myctophidae), Astronesthes martensii (Family: Stomiidae; subfamily: Astronesthinae), and Trichiurus sp. (Family: Trichiuridae). In general, a total of 3678 larvae were collected, of which 1191, constituting about 32% of the total fish larvae, belonged to mesopelagic species. The most abundant species was V. mabahiss, with 677 larvae that constituted 18% and 57% of the total larvae and mesopelagic fish larvae, respectively. The second most abundant species was B. pterotum, which was represented by 485 larvae (13% of the total larvae and 40% of the mesopelagic fish larvae). A. martensii was represented by the lowest number of larvae (29 larvae, 2%). Most larvae of the three species were small and in the preflexion stage, whereas larger larvae are absent. They are highly abundant in the cooler months of the year between November and April. The high number of preflexion larvae may indicate that the three mesopelagic species spawn in the colder times of the year.