Spatial distribution of early life stages of fish along horizontal and vertical gradients in the canary current large marine ecosystem

ABSTRACT The Canary Current Large Marine Ecosystem (CCLME) is among the most productive upwelling systems globally, supporting high fish biomass and biodiversity. We examined horizontal patterns of early fish stages along a 241-nautical-mile transect and vertical distributions down to 800 m at four of 11 stations, within the strong permanent upwelling area of the CCLME in December 2019. An inshore–offshore transition of the larval assemblages was observed, shifting from dominance of European pilchard (Sardina pilchardus) within the upwelling domain to an offshore assemblage dominated by mesopelagic families such as Myctophidae, Phosichthyidae, and Gonostomatidae. Mesoscale activity near the 3000 m isobath significantly influenced larval distribution patterns. A distinct vertical structuring was evident, with transforming stages of mesopelagic taxa contributing increasingly toward deeper layers. The gonostomatid Cyclothone prevailed between 400 and 800 m, showing no evidence of diel vertical migration, unlike other mesopelagic fish species. Size distributions of Cyclothone revealed a clear ontogenetic vertical pattern, with larger individuals occurring at greater depths, while transforming stages comprised a substantial proportion of total sampled net biomass within the deeper strata (up to 34.9%). These findings are discussed in the context of the ecology of this genus and its importance to the carbon flow in the mesopelagic zone.