Population structure of the Argentine shortfin squid Illex argentinus using trace elemental signatures within statolith microstructure

Ommastrephid squid are highly migratory species that are pivotal in food webs and act as links between ecosystems. The Argentine shortfin squid Illex argentinus is a nerito-oceanic squid, with a complex population structure of up to 4 seasonal spawning groups that support one of the world’s largest cephalopod fisheries. The species is characterised by long-range ontogenetic migrations, which make it available for exploitation by multiple entities as individuals pass through several exclusive economic zones and the high seas. We investigated the variation between I. argentinus seasonal spawning groups during early ontogeny and compared possible environmental conditions which individuals experience during this time. This was achieved by assigning individuals to the relevant seasonal spawning groups using statolith ageing and microstructure analysis. To determine connectivity between the groups, statolith core elemental signatures from 625 specimens were analysed using laser ablation-inductively coupled plasma-mass spectrometry. We found that single-elemental signatures revealed significant differences between the spawning groups, which also provided evidence of the putative hatching grounds for the different groups. Revealing these differences during early ontogeny provides valuable information for the introduction of future temporal and spatial conservation measures, which will require a cohesive international management strategy of the I. argentinus fishery across the Southwest Atlantic.