Elemental signatures reveal the geographic origins of a highly migratory shark: prospects for measuring population connectivity

摘要

ABSTRACT: Distinguishing individual natal origins of highly dispersive species is essential for quantifying the extent of connectivity among spatially separated groups. Variation in the chemical composition of calcified structures has been used to determine natal origins of many organisms but the utility of this approach to sharks and rays has only recently been examined. We evaluated the ability to accurately classify young-of-the-year scalloped hammerhead sharks Sphyrna lewini to their putative natal origins using vertebral elemental signatures and assessed individual, temporal, and spatial variation in vertebral chemistry. Vertebrae were collected from sharks captured in artisanal fisheries along the Pacific coast of Mexico and Costa Rica in 2007 to 2009. Elemental signatures were measured using laser ablation inductively coupled plasma mass spectrometry. Elemental signatures were spatially distinct and served as reliable site-specific markers. Intra-annual variation in natal signatures was detected among and within sites. Natal signatures also differed across years within sites. Inter-annual variation was driven by a single year (2008) and site-specific signatures were similar for 2007 and 2009. Classifications to geographic origins exceeded chance expectations and discrimination among sites was achieved with 39 to 100% success. Classification accuracy improved when data were analyzed at finer spatial and temporal resolution (i.e. year, season, month). Vertebral elemental signatures can successfully distinguish among sharks that have occupied different locations across broad spatial scales, from 10s to 1000 km. Identification of connectivity patterns and key areas of use through intrinsic natal signatures may propel more tractable, spatially explicit approaches to the conservation and management of elasmobranch populations.