Occurrence of the bigeye thresher shark, Alopias superciliosus (Lowe, 1841) (Elasmobranchii, Alopiidae) in the southwestern Gulf of Mexico

The bigeye thresher shark Alopias supeciliosus is a large epipelagic and mesopelagic species, and it has a wide distribution in the Atlantic. However, its record in the Gulf of Mexico is sporadic. A single adult female of A. superciliosus, measuring 360 cm total length and about weight 165 kg, was caught by artisanal fishers in Salinas Roca Partida, Veracruz, Mexico, on July 14, 2020. This study reports the first occurrence of this species in the southwestern of the Gulf of Mexico, which extends its geographical distribution in Mexico.

Exploring the Use of Environmental DNA (eDNA) to Detect Animal Taxa in the Mesopelagic Zone

Animal biodiversity in the ocean’s vast mesopelagic zone is relatively poorly studied due to technological and logistical challenges. Environmental DNA (eDNA) analyses show great promise for efficiently characterizing biodiversity and could provide new insight into the presence of mesopelagic species, including those that are missed by traditional net sampling. Here, we explore the utility of eDNA for identifying animal taxa. We describe the results from an August 2018 cruise in Slope Water off the northeast United States. Samples for eDNA analysis were collected using Niskin bottles during five CTD casts. Sampling depths along each cast were selected based on the presence of biomass as indicated by the shipboard Simrad EK60 echosounder. Metabarcoding of the 18S V9 gene region was used to assess taxonomic diversity. eDNA metabarcoding results were compared with those from net-collected (MOCNESS) plankton samples. We found that the MOCNESS sampling recovered more animal taxa, but the number of taxa detected per liter of water sampled was significantly higher in the eDNA samples. eDNA was especially useful for detecting delicate gelatinous animals which are undersampled by nets. We also detected eDNA changes in community composition with depth, but not with sample collection time (day vs. night). We provide recommendations for applying eDNA-based methods in the mesopelagic including the need for studies enabling interpretation of eDNA signals and improvement of barcode reference databases.

Synthetic and Semi-Synthetic Microplastic Ingestion by Mesopelagic Fishes From Tristan da Cunha and St Helena, South Atlantic

Mesopelagic fishes were sampled around Tristan da Cunha and St Helena in the South Atlantic from the RRS Discovery at depths down to 1000 m. Sampling was part of the Blue Belt Programme, a marine survey of British Overseas Territories funded by the United Kingdom Government. Thirteen species of mesopelagic fishes identified from 30 specimens were compared with two species (two specimens) collected from rock pools or surface water near the shore. The digestive tracts of all fishes were examined for microplastics. Additionally, one specimen of Opostomias micripnus (Günther, 1878) was analyzed after recovery from the stomach of a commercially fished species, Hyperoglyphe antarctica (Carmichael, 1819). One specimen of Anoplogaster cornuta was found to have ingested a bearded sea devil (Linophryne sp.), a cock-eyed squid (Histioteuthis sp.), a bolitaenid octopus, Japetella diaphana, remains of unidentifiable fish, crustaceans, and possibly salps. These prey items were also examined for microfibres. Both Histioteuthis sp. and Linophryne sp. had ingested fibers and these were considered “ingested particles” for A. cornuta. Neither shallow water dwelling species had ingested microplastics, whilst 11 of the 13 studied mesopelagic species were found to be contaminated. Overall, 66.7% of mesopelagic fishes were found to contain microfibres. Anthropogenic fibers were common especially viscose, a semi-synthetic material which is associated with sanitary products as well as other items.

Undesirables in Mesopelagic Species and Implications for Food and Feed Safety—Insights from Norwegian Fjords

The increase in the global population demands more biomass from the ocean as future food and feed, and the mesopelagic species might contribute significantly. In the present study, we evaluated the food and feed safety of six of the most abundant mesopelagic species in Norwegian fjords. Trace elements (i.e., arsenic, cadmium, mercury, and lead), organic pollutants (i.e., dioxins, furans, dioxin-like polychlorinated biphenyls, and polybrominated flame-retardants), and potentially problematic lipid compounds (i.e., wax esters and erucic acid) were analyzed and compared to existing food and feed maximum levels and intake recommendations. Furthermore, contaminant loads in processed mesopelagic biomass (protein, oil, and fish meal) was estimated using worst-case scenarios to identify possible food and feed safety issues. While most undesirables were low considering European food legislation, we identified a few potential food safety issues regarding high levels of fluoride in Northern krill, wax esters in glacier lanternfish, and long-chain monounsaturated fatty acids in silvery lightfish. Our estimates in processed biomass indicated high levels of undesirable trace elements in the protein fraction, frequently exceeding the maximum levels for feed ingredients. However, in fish meal, almost no exceedances were seen. In the oil fraction, dioxins and furans were above the maximum levels, given for food and feed ingredients. The present study is crucial to enable an evaluation of the value of these species; however, more data is needed before proceeding with large-scale harvesting of mesopelagic biomass.

Investigating the potential for a commercial fishery in the Northeast Atlantic utilizing mesopelagic species

During three cruises in the Mid Atlantic Ridge area in 2016 and 2017, we studied the biomass of mesopelagic fish and its potential as a source of protein and oil for animal feed and human consumption. We collected samples of mesopelagic species down to a depth of 600 m, studied fish behaviour, identified and quantified the species composition of the catches, analysed the chemical composition of the catch samples, and evaluated the presence of unwanted substances. Results showed that Maurolicus muelleri (Mueller’s pearlside) and Benthosema glaciale (Glacier lantern fish) were the most abundant fish species in our samples and catches containing 80% fish can be a good source of protein and marine lipids including eicosapentaenoic acid (C20:5n3) and docosahexaenoic acid (C22:6n3). Unwanted substances, except for Cd and As, were present at levels far lower than the limits set by European Union regulations. However, our experiments identified challenges that may limit the efficiency of commercial operations in the Northeast Atlantic. Combined real-time optical and/or multifrequency acoustic systems will be needed to improve species identification and ensure cost-effective fishing operations. Also, selective trawls that target only fish and release unwanted species are needed to secure high-quality oils and proteins.

Mesopelagic Species and Their Potential Contribution to Food and Feed Security—A Case Study from Norway

The projected increase in global population will demand a major increase in global food production. There is a need for more biomass from the ocean as future food and feed, preferentially from lower trophic levels. In this study, we estimated the mesopelagic biomass in three Norwegian fjords. We analyzed the nutrient composition in six of the most abundant mesopelagic species and evaluated their potential contribution to food and feed security. The six species make up a large part of the mesopelagic biomass in deep Norwegian fjords. Several of the analyzed mesopelagic species, especially the fish species Benthosema glaciale and Maurolicus muelleri, were nutrient dense, containing a high level of vitamin A1, calcium, selenium, iodine, eicopentaenoic acid (EPA), docosahexaenoic acid (DHA) and cetoleic acid. We were able to show that mesopelagic species, whose genus or family are found to be widespread and numerous around the globe, are nutrient dense sources of micronutrients and marine-based ingredients and may contribute significantly to global food and feed security.

Exploring the economic viability of a mesopelagic fishery in the Bay of Biscay

The study analyses the economic viability of the mesopelagic fish exploitation. Operating characteristics of the selected bottom-trawl fleet operating in the Bay of Biscay were analysed on a trip basis, from the technical, financial and market perspectives. The results show that, while this activity is technically possible, it cannot be considered a viable financial alternative to the existing commercial fisheries. However, the landing obligation of the European Union Common Fisheries Policy, to become fully operational in 2019, provides an economic incentive in the form of alternative trips. The fishing effort is to be limited by this regulation. Thus, the discouraging opportunity costs of fishing mesopelagic species might be alleviated by the effort limitation. Additionally, the existing markets might expand, and new opportunities for commercial fisheries of mesopelagic species might be created. The sustainability of exploitation and its impact on the ecosystem services associated with these species should be considered in their management.

CHANGES IN SPECIES COMPOSITION AND ABUNDANCE OF FISH LARVAE FROM THE GULF OF TEHUANTEPEC, MEXICO

The larval fish abundance and species composition of the Gulf of Tehuantepec are described based on the analysis of samples obtained from oblique zooplankton tows during summer 2007 and spring 2008. Changes in species composition and abundance between both periods were also described. A total of 145 taxa were obtained from which 73 were identified to species level, 43 to genus and 29 to family. The larval fish assemblage of the Gulf of Tehuantepec showed distinctive characteristics from other regions of the American Pacific, such as: A) a dominance of coastal-pelagic species (mainly Bregmaceros bathymaster); B) high diversity and abundance of shallow demersal species even along the oceanic stations of the study area; and C) a low proportion of mesopelagic species, an unusual condition in areas with narrow continental shelf. The diversity estimations suggest that Gulf of Tehuantepec is one of the most diverse ecosystems of the American Pacific, even as compared with other regions considered of highest diversity such as the Gulf of California. The high abundance, as well as the presence of the larval, juvenile and adult stages of B. bathymaster, suggests the importance of this region as a reproductive, nursery and recruitment for this species. Cambios en la composición de especies y abundancia de larvas de peces en el Golfo de Tehuantepec, México Se describen la composición de especies y abundancia de larvas de peces del Golfo de Tehuantepec a partir del análisis de muestras obtenidas en arrastres oblicuos de zooplancton. Así mismo, se describen los cambios en composición y abundancia entre un periodo de verano y uno de primavera. Se obtuvieron 145 taxa de los que 73 se identificaron a nivel especie, 43 a género y 29 a familia. La comunidad de larvas de peces del Golfo de Tehuantepec mostró rasgos distintivos de otras regiones similares del Pacífico Americano, tales como: A) dominancia de especies pelágico-costeras (particularmente Bregmaceros bathymaster); B) alta diversidad y abundancia de especies demersales someras aún en las estaciones mas oceánicas del área de estudio; y C) una proporción menor de especies de peces mesopelágicos, condición poco común en áreas con plataforma continental estrecha. Las estimaciones de diversidad ubican al Golfo de Tehuantepec como uno de los ecosistemas más diversos del Pacífico americano, aún comparándolo con regiones consideradas de alta diversidad a nivel mundial como es el caso del Golfo de California. La abundancia y la presencia de estadios larvales, juveniles y adultos de B. bathymaster reflejan la importancia de esta zona como área de reproducción, crianza y reclutamiento de esta especie.