![]() ![]() Our results show that the life history of G. This approach allows the prediction of the exact mantle length (ML) and mass when the species changes its ecological role. Here, the life history of Gonatus fabricii, the most abundant Arctic cephalopod, is reconstructed by the analysis of individual ontogenetic trajectories of stable isotopes (d13C and d15N) in archival hard body structures. One important parameter is the change in ecological role (habitat and diet) associated with individual ontogenies. Consequently, they are under-represented in the Arctic ecosystems assessment models. Eye lens stable isotope analysis represents an additional tool for researchers and managers to use natural isotopic markers to accurately assess natal origins and hatchery contributions to fish populations.Ĭephalopods are important in Arctic marine ecosystems as predators and prey, but knowledge of their life cycles is poor. Rainbow Trout formed over ten layers at age‐0, decreasing to an estimated one to two layers during subsequent years. These high carbon and sulfur isotopic values were retained in the core, despite subsequent lens layers showing a dietary shift to natural prey items post‐stocking. ẟ15N proved to be a less useful indicator for natal origin than sulfur and carbon. The stable isotope values of eye lens cores from stocked Rainbow Trout were >15‰ higher for ẟ34S, and >4‰ higher for ẟ13C than naturally reproduced fish. We compared isotopic values for stocked and naturally reproduced Rainbow Trout Oncorhynchus mykiss in the North Platte River (WY, USA), and found that the metabolically inert core of the eye lens retained hatchery feed values as the fish grew post‐stocking. We investigated the utility of eye lens stable isotope analysis as a natural marker to determine natal origins, specifically the differentiation of stocked versus naturally reproduced individuals. Natal origin determination can be critical to understanding the movement, recruitment, and stock discrimination of fish populations.
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