Use of otolith natal elemental signatures as natural tags to evaluate connectivity among open-coast fish populations

Variation of trace elemental composition in fish otoliths has been successfully used to reconstruct the environmental history of fish, including the movement of early life stages among populations and habitats. Past studies have focused primarily on estuarine-dependent species, and information has been very limited for species that spawn along open coastlines, where spawning locations are not discrete and environmental gradients are less extreme. In this study, we used defined natal otolith elemental signatures from pre-pelagic larvae of the viviparous kelp rockfish Sebastes atrovirens taken from the natal source along the open coast of California and the offshore Channel Islands to identify the dispersal patterns of recently recruited individuals from the Channel Islands. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we chemically analyzed the otolith core (the portion of the otolith corresponding to the period of time prior to larval release) of recruits and compared the elemental signatures to spatially restricted natal otolith elemental signatures in southern California. Linear discriminant function analysis (DFA) revealed that the natal elemental signature of the mainland California location was not apparent in the elemental signatures of Channel Island recruit cores, suggesting a lack of exchange among the locations for the recruitment year. Several recruits had core elemental signatures that differed from all defined natal locations, suggesting that they originated from an uncharacterized site. These data demonstrate the use of natal otolith chemical data within a limited geographic area to identify larval dispersal patterns, with particular focus on sources that do not contribute to the defined locations.