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The biomass of mesopelagic fishes is estimated to be on the order of or to exceed that of fishes in the epipelagic. Despite their abundance and importance as an ecological link between surface and deep ocean habitats, there is a dearth of basic life history data for mesopelagic fishes. Reproductive biology data are critical for understanding population dynamics and estimating production of a species, particularly when age and growth data are lacking. Between July 2018 and August 2022, collections were made in the western North Atlantic utilizing multiple net types to capture a broad size-range of mesopelagic fishes. Histological analysis of gonad tissue from four numerically dominant species—Argyropelecus aculeatus(Sternoptychidae),Benthosema glaciale(Myctophidae),Scopelogadus beanii(Melamphaidae), andSigmops elongatus(Gonostomatidae)—were examined to describe aspects of reproduction. We determined thatA. aculeatusandB. glacialeare gonochoristic batch spawners with indeterminate fecundity, and the standard length at which 50% of females were mature (L₅₀) was 39.45 and 33.77 mm, respectively.S. beaniiwere found to be gonochoristic, iteroparous, and likely have multi-year oocyte development with an L₅₀of 90.38 mm.S. elongatuswas confirmed as a protandrous hermaphrodite, iteroparous, and had an L₅₀of 200.45 mm. This study is the first to present regional maturity ogives for all four species and to describe detailed reproductive patterns inA. aculeatus, S. beanii, andS. elongatus.These results contribute to the data necessary for quantifying the role of mesopelagic fishes in global biogeochemical cycles and for ensuring responsible use of mesopelagic resources. 

This dataset provides an inventory of physical samples collected from zooplankton bongo and/or ring net tows conducted during the Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises, ongoing since 2018. The NES-LTER transect, located south of Martha’s Vineyard, Massachusetts, comprises standard stations L1-L11 and extends 150 km offshore. Dedicated NES-LTER cruises target all four seasons: winter, spring, summer, and fall. Samples are collected via oblique tows with a 61-cm bongo net fitted with 150- and 335-micron mesh nets, as well as a ring net with a 20-micron mesh net. During earlier spring and fall cruises along the NES-LTER Transect, in collaboration with the Ocean Observatories Initiative, samples were collected through vertical tows using a ring net with a 150-micron mesh. Samples collected are distributed among various laboratories for DNA metabarcoding, stable isotopes analysis, and morphological identification. 

This package provides a table of cruises to the Martha's Vineyard Coastal Observatory for Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER). The majority of events are single day cruises, however, samples missing an MVCO Event Number were collected on multi-day NES-LTER transect cruises aboard larger research vessels. The same sampling protocols for CTD and bongo collection are used on both cruise types. Sampling frequency is approximately monthly, with NES-LTER sampling ongoing since 2017. Cruises involve collection of water column bottle samples, surface bucket samples, and zooplankton net tow samples, as well as ship-provided data. NES-LTER transect cruises will have more extensive underway and acoustic data which can be found by searching by cruise at https://www.rvdata.us/data. The event number for each cruise is provided, along with date, vessel name, cruise identifier where applicable, link to data location (for CTD, ADCP, and other underway data), and checklist of six data types. 

This data package provides abundance data for zooplankton collected during seasonal transect cruises conducted as part of the Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) program, ongoing since 2018. Zooplankton are collected at standard NES-LTER transect stations (L1–L11) and the Martha’s Vineyard Coastal Observatory (MVCO) via oblique tows, using a 61-cm Bongo net with two mesh sizes (335 µm and 150 µm). The transect extends southward from near Martha’s Vineyard, Massachusetts, reaching approximately 150 km offshore along longitude 70 deg 53 min W, covering the continental shelf from nearshore to the shelf break, with sampling depths between 20 and 200 meters. Only the 335-µm mesh data is included here, as samples from this net are preserved on board and shipped to Morski Instytut Rybacki in Szczecin, Poland, where they are counted and identified to the lowest possible taxonomic level. Counts of taxa identified are provided by the NOAA’s Northeast Fisheries Science Center. Samples from the 150 um are preserved for other purposes and will be published as a separate data package. This second version of the data package includes staged and unstaged abundance data in volumetric (100 m³) and aerial (10 m²) units from the 335-µm net. Supplemental tables provide metadata for the cruises and stations. 

DNA metabarcoding and morphological taxonomic (microscopic) analysis of the gut contents was used to examine diet diversity of seven species of fishes collected from mesopelagic depths (200-1000 m) in the NW Atlantic Ocean Slope Water during Summer 2018 and 2019. Metabarcoding used two gene regions: V9 hypervariable region of nuclear 18S rRNA and mitochondrial cytochrome oxidase I (COI). V9 sequences were classified into 14 invertebrate prey groups, excluding fish due to predator swamping. Ecological network analysis was used to evaluate relative strengths of predator-prey linkages. Multivariate statistical analysis revealed consistently distinct diets of four fish species in 2018 and/or 2019:Argyropelecus aculeatus, Chauliodus sloani, Hygophum hygomii, andSigmops elongatus. Three other species analyzed (Malacosteus niger, Nemichthys scolopaceus, andScopelogadus beanii) showed more variability between sampling years. COI sequences were classified into eight invertebrate prey groups, within which prey species were detected and identified. Considering all predator species together, a total of 77 prey species were detected with a minimum of 1,000 COI sequences, including 22 copepods, 18 euphausiids, and 7 amphipods. Morphological prey counts were classified into seven taxonomic groups, including a gelatinous group comprised of soft-bodied organisms. The ocean twilight zone or is home to exceptional diversity and biomass of marine fish, which are key players in deep sea food webs. This study used integrative morphological-molecular analysis to provide new insights into trophic relationships and sources of productivity for mesopelagic fishes, including identification of key prey species, recognition of the importance of gelatinous prey, and characterization of differences in diet among fish predators in the NW Atlantic Slope Water. 

This dataset lists the inventory of physical samples from zooplankton net tows conducted on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises, ongoing since 2017. The NES-LTER transect lies south of Martha’s Vineyard, Massachusetts. Dedicated NES-LTER cruises target summer and winter seasons, with samples collected in oblique tows with a bongo net fitted with 150 and 335 micron mesh nets, as well as a ring net with a 20 micron mesh net. Additional cruises along the NES-LTER Transect, including spring and fall cruises with the Ocean Observatories Initiative, collect samples in vertical tows using a ring net with 150 micron mesh net. Samples are shared with different labs for purposes including DNA metabarcoding, stable isotopes, and morphological identification. 

Zooplankton are sampled on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises in summer and winter seasons in oblique tows with a bongo net equipped with two mesh sizes (335 micron and 150 micron). Tows are conducted at standard stations L1 to L11 along longitude 70 deg 53 min W extending southward from near Martha’s Vineyard, Massachusetts, to approximately 150 km offshore. Counts for taxa morphologically identified from the 335 micron net were provided by the Northeast Fisheries Science Center of the NOAA National Marine Fisheries Service. Counts were divided by volume and multiplied by depth sampled for abundance as per meter squared. The first version of this data package provides the abundance of 14 taxa from the 335 micron net for cruises in 2018 - 2020 in a described data table, as well as a supplemental table for the tow metadata. 

Fish diversity and ecology in the ocean’s mesopelagic zone are understudied compared to other marine regions despite growing interest in harvesting these potential resources. Otoliths can provide a wealth of taxonomic and life history information about fish, which can help fill these knowledge gaps; however, there has been relatively little research to date on the otoliths of mesopelagic species. Here, a species-specific image library was assembled of sagittal otoliths from 70 mesopelagic fishes belonging to 29 families collected in the western North Atlantic Ocean. Images of adult sagittal otoliths from 12 species were documented and photographed for the first time. The fish were identified to species with a combination of morphological characters and DNA barcoding. Regressions between otolith size and fish length are presented for the six species with the largest sample sizes in this study. This otolith image library, coupled with otolith-length and width to fish-length relationships, can be used for prey identification and back-calculation of fish size, making it a valuable tool for studies relating to food webs in the important yet poorly understood mesopelagic zone. In addition, the 44 fish barcodes generated in this study highlight the benefit of using an integrative taxonomic approach to studies of this nature, as well as add to existing public databases that enable cryptic species and metabarcoding analyses of mesopelagic species. 

This package provides a table of day cruises to the Martha's Vineyard Coastal Observatory for Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER). Sampling frequency is approximately monthly, with NES-LTER sampling ongoing since 2017. Cruises involve collection of water column bottle samples, surface bucket samples, and zooplankton net tow samples, as well as ship provided data. The event number for each cruise is provided, along with date, vessel name, cruise identifier where applicable, link to data location (for CTD, ADCP, and other underway data), and checklist of six data types. 

These data represent the diet composition of small pelagic fishes assessed by the Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) project. The six species of fish in this dataset represent a subset of the species collected in bottom trawls conducted by the NOAA Fisheries Northeast Ecosystems Surveys from Cape Hatteras to the Gulf of Maine. Sampling occurred in the Spring and Fall seasons. Fish were frozen and stomach content analyses were conducted by the Fisheries Oceanography and Larval Fish Ecology Lab at the Woods Hole Oceanographic Institution. Data are counts and length measurements for prey items examined under a dissecting microscope. Prey species were matched to the lowest taxonomic level in the Integrated Taxonomic Information System (ITIS) for scientific name and taxonomic serial number. The dataset was supplemented with geospatial and temporal information from NOAA Fisheries trawl databases.