Predation of pop-up satellite archival tagged albacore (Thunnus alalunga)

• Pop-up satellite tagged albacore were predated.
• Shortfin mako and porbeagle sharks are identified as the likely predator.
• The observed predation rate is thought to be elevated due to irregular post-release behavior.

Three out of eight albacore (Thunnus alalunga) tagged with pop-up satellite archival tags (PSATs) in the greater Bay of Biscay area of the North East Atlantic were predated as indicated by missing light level data, sudden increases in temperature, and substantial changes in depth profiles. Recorded stomach temperatures and differences between stomach and ambient water temperatures were consistent with shortfin mako (Isurus oxyrinchus) and porbeagle (Lamna nasus) sharks. Vertical behavior in the form of diel migrations, deep dives and extensive periods spent close to the surface during day and night time was again consistent with Lamnid sharks. The observed predation rate was considered to be elevated due to irregular post-release behavior as opposed to symptomatic of natural mortality.