Sub-annual cohort representation among young-of-the-year recruits of the western stock of Atlantic bluefin tuna

•The fate of bluefin tuna recruits from the Slope Sea spawning region is unknown.•Developed a daily ageing method based on literature review and a precision trial.•US Atlantic juvenile bluefin tuna hatch dates occurred mainly in early-April.•Matched Gulf of Mexico spawning but occurred earlier than observed Slope Sea spawning.