Data and code: The European eel's spawning thermal band migrated poleward while its larval transport stayed insensitive to the spawning front's position (1982-2025)

Analysis code and derived data accompanying a single-author study testing the dominant explanation for the European eel (Anguilla anguilla) recruitment collapse: that ocean warming displaced its Sargasso Sea spawning ground poleward and broke the larval-transport route to Europe. What the study finds. The 22 to 24 °C spawning thermal band migrated poleward at roughly 0.4° per decade over 1982-2025, while the SST-gradient front that marks the spawning ground moved much less (+0.095° per decade, not significant). In an eddy-resolving Lagrangian transport model, the fraction of larvae delivered to Europe is governed by larval swimming behaviour rather than by front latitude, at every swim speed tested and across three independent current products. The much-cited front-to-recruitment correlation does not survive de-trending. What the study does not claim. It excludes one specific mechanism, a poleward shift of the surface front breaking transport. It does not claim to explain the collapse, which these data are underpowered to attribute. The front result is a power-limited null, meaning no detected movement rather than proof of a fixed front. The one oceanic pathway that is not excluded is a decline in drift-route productivity (corridor chlorophyll -5.3% per decade, corroborated by net primary production -3.3% per decade), which is reported as a surviving candidate. Contents. All analysis and modelling code, the derived outputs behind every headline number, frozen climate-index snapshots for byte-reproducible attribution, the open ICES Eggs and Larvae Database extract used for larval validation, and the manuscript. Raw third-party reanalyses are public and are obtained via the included pull scripts rather than redistributed. The restricted Miller et al. (2015) compilation is used only as a corroborating benchmark and is not redistributed. No core result depends on it. The bundle includes a claim-to-evidence map (docs/EVIDENCE-MAP.md) linking each stated claim to the script, the output file and the number, and a Makefile target that regenerates the manuscript figures from committed derived data. License: code MIT, data and text CC-BY-4.0.