Biology of One of the Most Abundant Mesopelagic Fish in Icelandic and Surrounding Waters: The Krøyer's Lantern Fish <i>Notoscopelus kroyeri</i> (Malm, 1861)

ABSTRACT Myctophids play an essential role in the marine ecosystem, linking the surface to the mesopelagic layer through diel vertical migration, and contributing to carbon sequestration. However, basic knowledge of their biology and distribution is still limited. Here, we described the length and age distribution, growth and otolith morphometrics for one of the most abundant myctophid fish of the Northeast Atlantic, the Krøyer's lantern fish Notoscopelus kroyeri (Malm, 1861). Individuals were sampled opportunistically by pelagic trawls during the International Ecosystem Summer Survey in the Nordic Seas (IESSNS) conducted in July 2020 and 2021. We provide the length–weight and otolith–fish size relationships and the size distribution for 336 N. kroyeri individuals collected along Iceland's south and west shelf, the Iceland Basin, and the Irminger Sea. Fish were primarily distributed along the Reykjanes Ridge and the continental shelf at depths between 0 and 550 m. Three size groups, corresponding to three different age groups, with individuals from 2 to 9 years old, were detected across sampling areas. We found positive allometric growth during both sampling years. Linear regressions were significant between otolith length, width and area, and fish length and weight, with adjusted r 2 values ranging between 0.93 and 0.94. This study provides new information on the biology and distribution of one of the most abundant mesopelagic species in south Icelandic and surrounding waters.