 The study uses natural chemical traces to determine the individual experience temperatures and expressed field metabolic rates of Atlantic bluefin tuna during their first year of life, revealing that they exhibit a preference for cooler temperatures to avoid warm ones that limit metabolic performance. Based on IPCC projections, historically important spawning and nursery grounds for bluefin tuna will become thermally limiting due to warming within the next 50 years, but limiting global warming to below 2°C would preserve habitat conditions in the Mediterranean Sea for this species. The approach used in the study provides predictions of animal performance and behavior that are not constrained by laboratory conditions and can be extended to any marine teleost species for which otoliths are available. This article was authored by Clive Entruman, AII'd articulate, Lisa A. Kerr, and others.