Patterns in the distribution of myctophid fish in the northern Scotia Sea ecosystem

The mesopelagic fish community of the northern Scotia Sea was investigated during the austral autumn using multi-frequency acoustics, opening and closing nets and pelagic trawls fished from the surface to 1,000 m. The Family Myctophidae (15 species in 5 genera) dominated the ichthyofauna, with larval notothenids caught over the South Georgia shelf and bathylagids and stomiids abundant in deeper hauls. The biomass of myctophids was estimated to be 2.93 g wet weight 1,000 m-3, with Electrona carlsbergi, E. antarctica, Protomyctophum bolini, P. choriodon, Gymnoscopelus braueri, G. fraseri, G. nicholsi and Krefftichthys anderssoni, being the most abundant species. Analysis of community structure indicated a high level of depth stratification within the myctophids, with evidence of diurnal vertical migration in some, but not all, species. Length-frequencies of G. braueri, G. nicholsi, E. antarctica and K. anderssoni were multimodal, suggesting that all life stages may be present in the northern Scotia Sea. In contrast, P. choriodon, P. bolini, G. fraseri and E. carlsbergi had unimodal distributions despite having multi-year lifecycles, indicating that they probably migrate into the region from warmer areas to the north.