Spatial and temporal boundaries to gene flow between Chaenocephalus aceratus populations at South Orkney and South Shetlands

The black-fin icefish Chaenocephalus aceratus is among the most abundant fish species on the Antarctic continental shelves of the Scotia Arc, and Bouvet Island. We genotyped 11 microsatellite loci in C. aceratus population samples from South Orkney, southern South Shetlands, and Elephant Island (northern South Shetlands) collected in 2002 and 2006. This investigation further develops a previous study on the species reporting the presence of one panmittic population in southern South Shetlands and Elephant Island, with genetic differentiation between year classes. Our results reveal a more complex pattern of differentiation than shown previously, as genetic differences occur both at the temporal level at Elephant Island and at the geographic scale between southern South Shetland-Elephant Islands and South Orkney population samples. In particular, the magnitude of genetic differentiation at the temporal scale, the relatively high effective population size (N-e) and high gene flow indicate that genetic differentiation is not only driven by geographic distance. At present, our results should be taken into account when defining conservation measures and management boundaries in regions where fishery is still open or where other Antarctic fish species are still exploited.