Distribution and diel vertical migration of mesopelagic fishes in the Southern Sargasso Sea — observations through hydroacoustics and stratified catches

Abstract

Vertical distribution patterns and relative abundance of mesopelagic fish species and other major taxonomic groups were investigated through vertically stratified trawl sampling and hydroacoustic analyses along the subtropical convergence zone from 52° W to 70° W in the oligotrophic Sargasso Sea. Persistent stationary layers and several migrating components of different scattering characteristics were detected. The results reveal varying vertical migration patterns, including different times of onset of diel vertical migration in different depths and a migrant pathway emerging daily from the lower deep scattering layer (DSL) at dusk and migrating through the upper DSL without affecting its composition. Fish species identification was made based on morphological characteristics and confirmed by genetic barcoding analyses of subsamples. In total, 5022 fish specimens from 27 families, 62 genera and 70 species were caught. In terms of relative abundance (A) and biomass (M), catches were dominated by species of the families Myctophidae (A=59.1%, M=47.4% of total fish catch) and Melamphaidae (A=22.5%, M=17.1%). Myctophidae and Stomiidae were the most species-rich families with 31 and 12 species, respectively. Catches at the two easternmost stations were dominated by Scopelogadus mizolepis and Nannobrachium cuprarium, while Bolinichthys photothorax and Ceratoscopelus warmingii were the most abundant species in catches from the two westernmost stations. This study provides insights into distribution and vertical migration behaviour of mesopelagic fish in the Sargasso Sea and adds to our understanding of the mesopelagic community in this large oceanic area.

Variation in mesopelagic fish community composition and structure between Mediterranean and Atlantic waters around the Iberian Peninsula

“…Sternoptychidae and species of genus Cyclothone exemplified the non-migrators and the gonostomatid S. elongatus partial vertical migrators. These results are in line with the feeding migrations patterns previously reported in the Atlantic and Mediterranean (Goodyear et al, 1972;Badcock and Merrett, 1976;Bernal et al, 2015;Drazen and Sutton, 2017;Contreras et al, 2020;Czudaj et al, 2021;Marohn et al, 2021).…”

What determines the vertical structuring of pelagic ecosystems in the global ocean?

“…S6). In addition to the mesopelagic communities commonly observed between 300m and 600m, deeper mesopelagic communities are visible between 500 and 800m during the day, as reported in other regions (22)(23)(24)(25)(26). To assess whether this could explain the deeper DSL observed in the DP group, we added two deep mesopelagic communities (one migratory and one residents) to the model, in addition to the two previous shallow mesopelagic groups.…”

Fine-scale movement data of the endangered Bermuda petrel highlights surface foraging and greater nocturnal flight activity

“…Similarly, they may also feed while sitting on the water through surface-seizing or scavenging, and less frequently, by searching for prey underwater [21,22]. Because of their mesopelagic-prey specialization, including mainly fish (mostly Myctophids) and cephalopods [17] that are available by means of diel vertical migration [23], petrels are also expected to forage at night [10,17,18], thus supporting the idea of a marked nocturnality [10,18,24]. Furthermore, because of their morphology (e.g., body size, long wing, lack of laterally compressed legs) and physiological characteristics, Pterodroma petrels are not regarded as proficient divers unlike shearwaters or diving-petrels [15,19,22,[25][26][27] (see references in [28]).…”