Ichthyoplankton assemblages and physical characteristics of two submarine canyons in the south central Tyrrhenian Sea

Ichthyoplankton assemblages in the south central Tyrrhenian Sea are not known in spite of this being an intensely fished area. There are two large canyons in this region: Dohrn, in the Gulf of Naples, and Cuma, at the south end of the Gulf of Gaeta. In this study, we provide the first description of summer ichthyoplankton assemblages in the vicinity of the two canyons and present the physical features and Lagrangian particle tracking analyses at the time of the sampling. We identified fish larvae of 19 families and fish eggs of 8 families. The most abundant species was Engraulis encrasicolus, which was found at densities comparable to other known spawning grounds of the western Mediterranean. Mesopelagic species, such as Gonostomatidae and Myctophidae, were also abundant, especially at the Cuma Canyon. The notochord and standard length of the E. encrasicolus larvae ranged from 2.06 to 10.47 mm and was significantly smaller at the Cuma stations than at the Dohrn stations, suggesting the presence of sub-populations with different spawning phenologies. The passive particle tracking analyses and the examination of currents confirmed distinct circulation features between the two sampled regions and in relation to depth and proximity to the canyon heads. These results uncover previously unknown rich assemblages of fish eggs and larvae and have conservation and management implications given the proximity of these canyons to a marine protected area and to an intensely fished continental shelf.