Mesopelagic Fish Research Articles

Metabarcoding and morphological analysis of diets of mesopelagic fishes in the NW Atlantic Slope Water

Metabarcoding and morphological analysis of diets of mesopelagic fishes in the NW Atlantic Slope Water

New Documented Records of the Mesopelagic Fish Valenciennellus tripunctulatus (Sternoptychidae) in the Strait of Messina and a Review of Its Mediterranean Occurrences

The constellation fish, Valenciennellus tripunctulatus, is a small mesopelagic teleost typically found in equatorial and temperate waters worldwide, although the species has been also rarely recorded in the Mediterranean Sea (less than 20 specimens from the available literature since 1918). The Mediterranean records have been documented for the Strait of Messina, the southern Tyrrhenian Sea, the Ligurian Sea and the Adriatic Sea. The present paper offers an updated review on the occurrence of V. tripunctulatus in the Mediterranean basin and provides data on three new specimens, collected in the Strait of Messina between April 2010 and March 2024. Furthermore, we also report information from two individuals found in March 1992 and February 2017, respectively. Overall, the standard length of these specimens ranged from 24.1 to 28.2 mm, whereas weight varied from 0.18 g to 0.20 g. Morphometric and meristic data were reported, and this analysis revealed few differences between examined individuals in the number of PV (ventral series anterior to pelvic fin base) and AC (from anal fin origin to caudal fin base) photophore series. The relationship between total length and standard length (SL = 0.75 × TL + 2.98), total length and head length (HL = 0.17 × TL + 1.47) and standard length and head length (HL = 0.23 × SL + 0.88) showed high correlation values. Considering the lack of data on this species in the Mediterranean, updating morphometric, meristic, biological, ecological and distribution information is very important for taxonomic purposes and useful in understanding the characteristics of the regional population and eventual differences between Mediterranean stock(s) and those from other oceanic areas.

Vertical distribution of mesopelagic fishes deepens during marine heatwave in the California Current

Abstract Marine heatwaves can impact the distribution and abundance of epipelagic organisms, but their effect on deep pelagic communities is unclear. Using fisheries acoustics data collected in the Central California current from 2013 to 2018, we found that during the warmest years of a large marine heatwave (2015–2016), the estimated center of mass depth of mesopelagic fishes deepened by up to 100 m compared to preheatwave conditions. Using a generalized additive model, we evaluated which biophysical factors may have driven these changes and found that light, dynamic height anomaly, and acoustic backscatter explained 81% of the variability in depth. We attribute the vertical shift by mesopelagic fishes into deeper waters to heatwave-driven compression of upwelling habitat that indirectly increased the amount of light reaching mesopelagic depths. Our results suggest that mesopelagic fishes are interconnected with, and thus sensitive to changes in near-surface oceanographic conditions, which could lead to cascading effects on vertical carbon export and the availability of mesopelagic fishes as prey for top predators under future climate conditions.

Invisible threat to mesopelagic fish: Microplastics and artificial cellulose particles in bigfin lanternfish Symbolophorus californiensis from the Northwest Pacific Ocean

Lanternfishes play an important role in connecting epipelagic and mesopelagic ecosystems. Due to their global distribution, diel vertical migration, and low trophic position, they may be highly susceptible to the ingestion of microplastics (MPs) and artificial cellulose particles (ACs). However, the role of lanternfishes in these emergent pollution research remains underestimated. In this study, we compared the abundance and characteristics of MPs and ACs in the stomach and intestine of bigfin lanternfish (Symbolophorus californiensis) from the Northwest Pacific Ocean. The results showed no difference in the abundance and size of MPs between the stomach (0.28 ± 0.63 items/individual, 103.72–2946.58 μm) and intestine (0.32 ± 0.56 items/individual, 122.03–4398.17 μm). The majority of MPs were fibrous in shape, with blue and transparent being the predominant colors. Polyester (28.2 %) and polyethylene terephthalate (20.5 %) were the most common polymer types. ACs were also primary in the shape of fiber (93.2 %), with transparent being the predominant color. The abundance of ACs in the intestine (0.49 ± 0.83 items/individual) was significantly higher than that in the stomach (0.18 ± 0.43 items/individual), while similar particle sizes were observed. This study provides an important baseline on lanternfishes contamination by MPs and ACs. Understanding this impact of mesopelagic fish is crucial for enhancing our comprehension of the vertical transfer mechanism of these pollutants between epipelagic and mesopelagic ecosystems.

Insight into the diet of early stages of mesopelagic fishes in the Indian Ocean using DNA metabarcoding

Despite playing a critical role in oligotrophic ocean food webs, relatively little is known about the diet of mesopelagic fishes in the Indian Ocean. These fishes are an abundant component of the micronekton assemblages and are a major energy- and nutrient-rich food source, linking the plankton which they feed on to marine predators at higher trophic levels. DNA metabarcoding, a molecular method to identify species from mixed assemblages, has not been commonly used in studies of mesopelagic fish diet, but using it to analyse gut contents can greatly improve the understanding of mesopelagic fish feeding ecology. In this study, we apply DNA metabarcoding (18S rRNA and COI) to gut contents from Stomiiformes and Myctophiformes species from 20 sampling stations covering 30 ˚ of latitude on the 110 ˚ E meridian in the Indian Ocean. In total, 174 fish specimens from 13 genera were examined. Differences in the gut contents among fish families, geographic areas and fish stages were identified. Specimens within the family Myctophidae had the most diverse diet, more so in the northern sampling stations than the south. Gonostomatidae had the least diverse diet. Overall, the most frequently identified prey items from the gut contents were calanoid copepods and halocyprid ostracods. The proportion of halocyprids were also identified to be significantly different among Myctophidae larvae and juvenile specimens, which is a potential ontogenic shift in diet towards a higher ostracod contribution in juveniles as mouth gape increases. In comparison with other plankton abundance data, Copepoda were the most abundant plankton in the gut contents of all fishes sampled throughout the latitudinal gradient, allowing them to be a potential food resource through the region. There are indications that other less abundant plankton, such as like Ostracoda and Malacostraca, may be preferentially targeted by some mesopelagic fish families.

Modeling fisheries and carbon sequestration ecosystem services under deep uncertainty in the ocean twilight zone

Mesopelagic fishes are a vital component of the biological carbon pump and are, to date, largely unexploited. In recent years, there has been an increased interest in harvesting the mesopelagic zone to produce fish feed for aquaculture. However, great uncertainties exist in how the mesopelagic zone interacts with the climate and food webs, presenting a dilemma for policy. Here, we investigate the consequences of potential policies relating to mesopelagic harvest quotas with a dynamic social-ecological modeling approach, combining system dynamics and global sensitivity analyses informed by participatory modeling. Our analyses reveal that, in simulations of mesopelagic fishing scenarios, uncertainties about mesopelagic fish population dynamics have the most pronounced influence on potential outcomes. The analysis also shows that prioritizing the development of the fishing industry over environmental protection would lead to a significantly higher social cost of climate change to society. Given the large uncertainties and the potential large impacts on oceanic carbon sequestration, a precautionary approach to developing mesopelagic fisheries is warranted.

Unveiling vertical migration patterns of the mesopelagic fish Ceratoscopelus warmingii in cold seep ecosystems: A trophic niche perspective

Ceratoscopelus warmingii, a common mesopelagic fish in cold seep ecosystems, plays a crucial role in transferring energy and materials between different water layers, thereby influencing deep-sea carbon cycling and storage. In August 2023, we collected samples from four depths (75 m, 400 m, 500 m, and 600 m) in cold seep waters to analyze the trophic niche characteristics of C. warmingii using stable isotope techniques. The results indicated significant differences in δ13C and δ15N values among the water layers, with mean δ13C and δ15N values of −19.85 ‰±0.33 ‰ and 8.41 ‰±0.62 ‰, respectively. Indicators of trophic structure showed distinct vertical differentiation, with the width of the trophic niche decreasing as depth increased. At 75 m and 400 m, the consistency of CR and NR indicators and high trophic niche overlap indicated similar food sources, confirming vertical migration behavior. In contrast, at 500 m, the MNND and SDNND values suggested a more stable trophic structure, while at 600 m, changes in feeding sources pointed to a distinct population. The Standard Ellipse Area of Overlap (SEAc) was highest between 75 m and 400 m, while the divergence of trophic ecological niches at 600 m, with different food sources, suggests that cold seep ecosystems at this depth provide a relatively stable trophic structure for C. warmingii and support the formation of an independent population. In cold seep ecosystems, C. warmingii employs adaptive trophic strategies to optimize survival under varying habitat conditions at different depths. This vertical trophic differentiation reduces intraspecific competition and enhances population stability in deep-sea habitats. This study enhances our understanding of the trophic niche and vertical migration of C. warmingii in cold seep ecosystems, significantly contributing to our knowledge of biodiversity, energy flow, and material cycling in these unique environments.

Distribution patterns of micronektonic crustaceans (Decapoda, Euphausiacea, and Lophogastrida) in the tropical and subtropical Atlantic Ocean

Large pelagic crustaceans are a main component of the micronekton community in the deep-sea having an important role in the food webs and the biological carbon pump. However, they are scarcely studied in comparison to other groups such as mesopelagic fish. Here, we analyse day/night and bathymetric variability in taxonomic composition, abundance, and biomass across a latitudinal transect in the Atlantic Ocean from off Brazil (15°S) to the Canary Islands (25°N). A total of 95 species were identified belonging to 9 different families, of which Euphausiidae was the most abundant family and Acanthephyridae the family contributing the most to the total biomass. We found distinct assemblages associated with Atlantic ecoregions related to the environmental variables. Diel vertical migrations were detected along the entire transect, even crossing the oxygen minimum zone, likely due to the metabolic adaptations of these organisms.

Climate damage from fishing the mesopelagic zone exceeds its economic benefits

Abstract Mesopelagic fish represent an opportunity for fishing companies and food production, but their exploitation carries substantial environmental risks related to these populations’ role in the oceanic carbon pump. We assess the economic viability of mesopelagic fishing from a private economic perspective, focusing on costs and revenues accruing to the fishing industry, and a public economic perspective, considering impacts on society at large, notably climate change. We develop a stylized model, which we apply to four pelagic trawling fleets in the European Union. We find that a mesopelagic fishery operated with current excess capacity in the four fleets considered is profitable from a private perspective, but the climate impacts potentially outweigh the private economic benefits. This implies that strict governance arrangements are needed to safeguard the sustainability of the mesopelagic zone. Considering long-term dynamics, we explore potential natural limits to an expanding mesopelagic fishery. First, a growing fishery will reduce biomass level, affecting profitability. Second, an increase in mesopelagic production may lower the price, also limiting potential for expansion. For the time being, however, it is unlikely that the fishery will reach a scale level where such feedbacks can be expected, making effective governance arrangements even more crucial.

Otolith morphology of mesopelagic fishes collected from the Irminger Sea, North Atlantic Ocean

A large series of otoliths of 16 mesopelagic teleost fish species from the Irminger Sea, North Atlantic Ocean, are described morphologically to investigate the ontogenetic and intraspecific variation. The results show that the surface morphology of the otoliths between young and adult specimens is variable, especially in the alepocephaliform (Normichthys operosus, Sagamichthys schnakenbecki, Xenodermichthys copei) and astronesthine (Borostomias antarcticus) species. The diagnostic features of the otoliths can be used to confirm the identity of the species, especially in myctophids, where confusion between Benthosema glaciale and Myctophum punctatum may be possible. A SEM-based iconography of the otoliths of all studied species is presented.

Feeding Habits and Prey Composition of Six Mesopelagic Fish Species from an Isolated Central Mediterranean Basin

Mesopelagic fishes hold an important position in marine food webs, serving as a link between lower trophic levels and top predators and transferring energy from their deep mesopelagic habitat to shallower oceanic layers. Despite their ecological importance, research on mesopelagic fishes’ diet and feeding habits in the Mediterranean Sea is far from thorough. The present work attempts to assess the preying patterns and diet composition of four myctophid (Benthosema glaciale, Ceratoscopelus maderensis, Myctophum punctatum, Notoscopelus elongatus) and two sternoptychid (Argyropelecus hemigymnus, Maurolicus muelleri) species from the Corinthian Gulf (Ionian Sea, Greece), sampled during pelagic trawl surveys in 2018 and 2019. Stomach vacuity was high for myctophids caught during daytime, a pattern which sternoptychids did not follow. Estimated trophic indices revealed high dietary diversity (Shannon’s H’ index) for most investigated species, but a narrow trophic niche breadth (Levins’ normalized Bn index). Copepods and various marine crustaceans were dominant in all diets, classifying them under the zooplanktivorous trophic guild, while A. hemigymnus exhibited high concentrations of particulate organic matter in their stomachs and N. elongatus exhibited consumption of fish. Diet overlap was significant among most studied mesopelagic species, as indicated by Shoener’s S index and confirmed by both the multidimensional scaling ordination and a hierarchical cluster analysis. Information on mesopelagic fishes’ diet composition in this poorly studied part of the Mediterranean is useful in further assessing and parameterizing marine food webs and midwater trophic interactions, as well as in quantifying the ensued energy transfer to top predators of commercial interest or conservation concerns.

Total mercury concentrations in Tasman Sea mesopelagic fish: Exploring biotic and abiotic drivers

Understanding mercury (Hg) concentrations in mesopelagic and mid-trophic fishes is important for assessing Hg accumulation in oceanic ecosystems and higher-order predators. This study measured total Hg (THg) concentrations in the whole body of 16 abundant mesopelagic fish species sampled in two distinct sites within the Tasman Sea. Across all species, total Hg concentrations ranged from 0.02 to 0.48 μg g−1 dry weight (0.01 to 0.15 μg g−1 wet weight). Total Hg concentrations varied with vertical migration patterns, with shallower migrators exhibiting higher THg. Females typically had statistically higher THg concentrations than males. Positive correlations between THg concentration and standard length were observed for some but not all species. At the community level, THg concentrations correlated positively with estimated trophic position and foraging habitat, as inferred by stable isotope values. These findings contribute to our understanding of Hg cycling in oceanic ecosystems and the potential for biomagnification in oceanic top-order predators.

Ichthyocenosis of the upper epipelagic layer in the Pacific waters of Russia during japanese sar-dine «renaissance» in the beginning of the 21<sup>st</sup> century

Dynamics of integral parameters for the species structure in ichthyocenosis of the upper epipelagic layer in the Pacific waters off the Kuril Islands in 2019–2023 is discussed in compare with previously published data since 2004 in context of a new bloom of japanese sardine Sardinops melanostictus. Results of trawl surveys are clustered using the method of multi-dimensional scaling. Species composition in the trawl catches in 2004–2013, before the time of mass expansion of subtropi-cal migrants, as japanese sardine and chub mackerel Scomber japonicus, was distinguished by domina-tion of mesopelagic fishes of families Myctophidae and Microstomatidae and pink salmon Oncorhynchus gorbuscha. From 2014 to the present, the dominant positions in the ichthyocenosis were held by japanese sardine and chub mackerel, with a decreasing role of the latter. In the last pentade (2019–2023), the species structure of pelagic ichthyocenosis in the Pacific waters of Russia has not undergone fundamental changes. At the same time, the tendency has increased for uneven distribution of biomass between the species of fish community in favor of japanese sardine. The polydominance index decreased significantly (P < 0.05, t-test 4.33) from 4.85 ± 0.44 in 2004–2013 to 2.37 ± 0.21 in 2019–2022, and the index of evenness of species structure decreased from 0.41 ± 0.04 to 0.15 ± 0.02 (P < 0.05, t-criterion 5.25). Growth of domestic and foreign catches of japanese sardine in the second decade of the 21 century is a sign of this species bloom beginning.

Generation, Characterisation and Identification of Bioactive Peptides from Mesopelagic Fish Protein Hydrolysates Using In Silico and In Vitro Approaches.

This study generated bioactive hydrolysates using the enzyme Alcalase and autolysis from mesopelagic fish, including Maurolicus muelleri and Benthosema glaciale. Generated hydrolysates were investigated for their bioactivities using in vitro bioassays, and bioactive peptides were identified using mass spectrometry in active hydrolysates with cyclooxygenase, dipeptidyl peptidase IV and antioxidant activities. In silico analysis was employed to rank identified peptide sequences in terms of overall bioactivity using programmes including Peptide Ranker, PrepAIP, Umami-MRNN and AntiDMPpred. Seven peptides predicted to have anti-inflammatory, anti-type 2 diabetes or Umami potential using in silico strategies were chemically synthesised, and their anti-inflammatory activities were confirmed using in vitro bioassays with COX-1 and COX-2 enzymes. The peptide QCPLHRPWAL inhibited COX-1 and COX-2 by 82.90% (+/-0.54) and 53.84%, respectively, and had a selectivity index greater than 10. This peptide warrants further research as a novel anti-inflammatory/pain relief peptide. Other peptides with DPP-IV inhibitory and Umami flavours were identified. These offer potential for use as functional foods or topical agents to prevent pain and inflammation.

Diet of non-breeding leach’s storm-petrels (Hydrobates leucorhous) in the sub-polar frontal zone of the North Atlantic

In order to understand the drivers of the distribution and abundance of pelagic seabirds it is necessary to know what they eat, yet there remains little detailed, geo-referenced information on the diets of pelagic seabird. In particular, due to sampling difficulties, information is lacking for non-breeding stages, smaller species, such as storm-petrels, and remote oceanic areas, which may include important diversity hotspots. In this study, we aimed to characterize the trophic ecology of Leach’s storm-petrels foraging in the vicinity of the North Atlantic Current and Evlanov Seamount Marine Protected Area using a combination of survey methods. On a cruise undertaken in June 2017 to characterize the distribution and ecology of seabirds in the region, nineteen Leach’s storm-petrels were caught, sampled and released unharmed. Regurgitations and faecal samples were collected, as well as blood and feather tissues for stable isotope analyses. Of the 12 males, 6 females and 1 unsexed bird, 84% were in active flight feather moult, suggesting they were non-breeders. Prey species, assayed via molecular metabarcoding, were dominated by mesopelagic fish, principally lanternfishes (Myctophidae) and hatchetfishes (Sternoptychidae), but also included cephalopods and crustaceans. Additionally, almost half of the birds had microplastics in their regurgitates. Stable isotopic ratios did not differ significantly between sexes. Our results, combined with those of previous studies, suggest that within the oceanic North Atlantic, Leach’s storm-petrels feed at a similar trophic level to much larger seabirds, targeting mesopelagic fishes that are a key component of the North Atlantic pelagic food web.

Exploitation of mesopelagic fish stocks can impair the biological pump and food web dynamics in the ocean

The demand for marine living resources is increasing at an unprecedented scale because of the need for continuous food provision to the world’s population. The potential of already exploited fish stocks to meet this demand is limited. Therefore, mesopelagic fish have recently become attractive potential targets for fisheries because of their vast conjectured biomass. However, the role of mesopelagic fish in marine ecosystems is poorly understood. Before developing commercial exploitation plans, the relationship between mesopelagic fish and other groups in the marine food web and biogeochemical cycles should be analyzed quantitatively. In this study, we coupled a one-dimensional biogeochemical model (North Atlantic Generic Ecosystem Model) with a higher-trophic-level food web model (Ecopath with Ecosim) for the Sargasso Sea in the North Atlantic to investigate changes in carbon export and trophodynamics under two mesopelagic fish harvesting scenarios. The coupled model represented the marine food web from plankton to fish and mammals, vertical carbon export dynamics, and their interaction with fisheries. The results showed that when mesopelagic fish were not harvested, they contributed approximately 6% of the total carbon export in the surface waters, but up to 40% of the total carbon export below 400 m. Harvesting mesopelagic fish altered the energy transfers within the food web as well as to fisheries. The ecological footprint of fisheries increased significantly. Due to declining competition in the food web, epipelagic fish increased to exert elevated grazing pressure on phytoplankton; hence, phytoplankton-mediated carbon export decreased. The total carbon export decreased by 14% due to the decreases in mesopelagic fish- and phytoplankton-mediated carbon exports. The simulated increase in zooplankton- and non-mesopelagic fish-mediated carbon exports (up to 92% and 96%, respectively) did not compensate for the total decrease in carbon exports under harvesting scenarios. The findings of this study highlighted that mesopelagic fish not only have a direct control on carbon dynamics by their metabolic releases and diel vertical migration, but also strong indirect controls through prey-predator interactions within the food web. Therefore, the implications of harvesting mesopelagic fish should be carefully considered from a holistic perspective.

The impact of oceanographic factors on the composition and abundance of mesopelagic fish communities in the central and equatorial Atlantic

This paper presents an overview of the composition and abundance of pelagic fish communities collected during the 43rd cruise of the R/V ′Akademik Sergey Vavilov' on the transect in the central Atlantic, from the Azores to the Equator, in autumn 2016. Samples were taken only at night with a Samyshev-Aseev modified Isaacs-Kidd non-closing midwater pelagic trawl (SAMT) at 18 stations from two depth of 0–200 and 0–700 m. The study recorded 112 species of juvenile and adult mesopelagic fishes belonging to 20 families at the sampled stations. The statistical analysis indicated notable disparities in the fish communities that were caught at depths of 0–200 and 0–700 m. Our study suggests that there are notable differences in pelagic fish associations between the North Atlantic anticyclonic gyre zone and the equatorial jets region, at both depths analyzed. These differences are most likely the result of variations in hydro-physical and other environmental parameters. It has been observed that deep-sea fish communities in the equatorial and central North Atlantic are capable of inhabiting at the same time multiple habitats that exhibit varying physical and chemical structures of water masses. This phenomenon highlights the remarkable ecological adaptability of the species that make up mesopelagic deep-sea communities, as well as their wide geographical distribution. The higher abundance and diversity of mesopelagic fishes observed at stations located above the Mid-Atlantic Ridge may be due to a general decrease in depth over the ridge compared to the surrounding regions and/or local circulations occurring over its crests. Thus, the tops and slopes of seamounts may become unique concentrations of mesopelagic fishes for a limited time due to their topography.

Impact of increased fishing on long-term sequestration of carbon by cephalopods

Fish and other metazoans play a major role in long-term sequestration of carbon in the oceans through the biological carbon pump1. Recent studies estimate that fish can release about 1,200 to 1,500 million metric tons of carbon per year (MtC year-1) in the oceans through feces production, respiration, and deadfalls, with mesopelagic fish playing a major role1,2. This carbon remains sequestered (stored) in the ocean for a period that largely depends on the depth at which it is released. Cephalopods (squid, octopus, and cuttlefish) have the potential to sequester carbon more effectively than fish because they grow on average five times faster than fish3,4 and they die after reproducing at an early age4,5 (usually 1-2 years), after which their carcasses sink rapidly to the sea floor6. Deadfall of carcasses is particularly important for long-term sequestration because it rapidly transports carbon to depths where residence times are longest1,6. We estimate that cephalopod carcasses transfer 11-22 MtC to the seafloor globally. While cephalopods represent less than 5% of global fisheries catch7, fishing extirpates about 0.36 MtC year-1 of cephalopod carbon that could otherwise have sunk to the seafloor, about half as much as that of fishing large fish8.

A Pilot Study on the Diel Vertical Migration Pattern of Mesopelagic Fishes in the Southern and Central South China Sea

The diel vertical migration of mesopelagic fishes in the southern (S-May station and S-Nov station) and central (C-Jun station and C-Dec station) South China Sea was investigated through a series of continuous field surveys conducted in May, June, November, and December 2017. These surveys employed a combination of mid-water trawl and acoustics techniques. The diel migration process, vertical distribution, acoustic migration proportion, and migration pattern of mesopelagic fishes were analyzed. The results revealed that mesopelagic fishes initiated an upward migration before sunset, with the process concluding within 30–120 min after dark. Subsequently, they commenced a downward migration before dawn, which terminated within 10–50 min after sunrise. The mesopelagic deep-sea layers of mesopelagic fishes at the S-May, S-Nov, C-Jun, and C-Dec stations ranged from 360 to 700 m, 350 to 680 m, 350 to 520 m, and 300 to 700 m, respectively. The acoustic migration proportions of mesopelagic fishes at the corresponding stations were found to be approximately 44.5%, 25.7%, 29.8%, and 58.0%, respectively. There were seasonal and regional differences in the vertical migration and distribution patterns of mesopelagic fishes in the South China Sea. A total of 228 species were identified, including 203 fish species, 23 cephalopod species, and 2 shark species. Among these, a subset of 43 fish and cephalopod species exhibited extensive diel vertical migrating behavior. Specifically, this subset comprised 23 lanternfish species, 8 cephalopod species, and 12 other fish species. Lanternfishes were the predominant diel vertical migratory species, while cephalopods also played a significant role in diel vertical migration. The diel migration behavior was found to be slight for Diaphus lucidus, Melamphaes microps, Argyropelecus affinis, and six other fish species. Non-migratory behavior was observed in Sternoptyx obscura, Argyropelecus sladeni, Sternoptyx diaphana, and 13 other fish species. The diel migration habits of 178 additional species of fish, cephalopods, and sharks could not be definitively determined.

Economic trade-offs of harvesting the ocean twilight zone: An ecosystem services approach

The mesopelagic or ocean twilight zone (OTZ) in the ocean contains huge numbers of fish in a relatively pristine environment and may therefore attract interest as a commercial fishery. In this study we evaluate in economic terms, the likely trade-offs between the different services provided by the mesopelagic layer in the Bay of Biscay and the societal benefits of its commercial exploitation. Benefits arise mainly from the likely use of this group of species as raw material for producing fishmeal and fish oil. Costs are derived from the loss in climate regulating and cultural, services, but also from the loss in the provisioning service of other commercial species. To do so we compare the current non-exploited status with a situation in where mesopelagic fishes are harvested at levels capable of producing the Maximum Sustainable Yield. Results suggest that if mesopelagic fishes are harvested, a mean value of 1.2 million Euro loss in a year will be created in the Bay of Biscay, although in a range between 42 million Euro loss and 48 Euro million benefits. This uncertainty comes, mainly, from the limited existing knowledge of the mesopelagic fishes’ biomass but also from the uncertainty on the biomass of the rest of the species of the studied ecosystem. The large range indicates that a better understanding of the mesopelagic ecosystem is needed, however, results also show that ecosystem services under no exploitation provided by the OTZ could be more valuable than the fishmeal and fish oil that potentially could be obtained from the fishes harvested in this sea layer.