Historical sources can provide important data for modern-day threatened species conservation, such as identifying formerly important habitat on which to focus recovery efforts. Here we reveal unique written archival material from the 1740s that provides reliable first-hand observations of the Critically Endangered angel shark Squatina squatina, extending modern knowledge of this species in Welsh waters back by over half a century. These sources clearly identify small-scale and spatially explicit areas of abundance (including of juveniles) around specific reefs that align with more recent data, further strengthening evidence that these areas are of long-term importance that should be prioritised for the global conservation of this species, which has become extinct across much of its former range. These contemporary sources also describe fisheries for angel shark and high desirability, economic value and export trade of their meat, which could suggest that population declines of this intrinsically vulnerable species commenced centuries before modern science detected this. These unique observations highlight the value that historical material can provide in prioritising resource-limited conservation efforts, as well as helping to reframe our temporal understanding of elasmobranch fish declines.