First marlin archival tagging study suggests new direction for research

Decades of billfish tagging studies have been hindered by below-par conventional tag recovery rates and high rates of premature satellite pop-up tag shedding. With hopes of obtaining long-term tracking data, we performed the world's first archival tagging study on an istiophorid, surgically implanting 99 archival tags into the peritoneal cavity of striped marlin (Kajikia audax) off the coast of Baja California, Mexico. Marlin were also tagged externally with a conventional tag before release. Ten archival tags (10.1%) were recovered with days at liberty (DAL) ranging from 400 to 2795. Nine recoveries were from Mexican waters, whereas one marlin was recaptured off Ecuador. In total, 100% of the light stalks on the archival tags failed, with nine failing within the first 3 months of deployment; because the light data are used to estimate the geographic position of the tagged fish, tracking data were compromised. The absence of conventional tags on all recaptured marlin indicates that studies of marlin using conventional tags have been hindered by tag shedding rather than tagging-associated mortality or underreporting. Our high recapture rate and long DAL suggest istiophorid science could be greatly advanced by archival tagging if new tag designs or methods can eliminate tag failure.