Restricted vertical and cross-shelf movements of longtail tuna (Thunnus tonggol) as determined by pop-up satellite archival tags

Abstract

The global catch of longtail tuna (Thunnus tonggol) has almost tripled over the past two decades, with recent stock assessments suggesting overexploited stocks. Nine longtail tuna were tracked for 2–115 days with pop-up satellite archival tags off eastern Australia (27.5°S 153.4°E to 27.5°S 153.4°E) to better understand their movements, habitat specificity, and post-capture mortality. Fish primarily utilised coastal waters of 0–25 m (maximum 90 m) and water temperatures of 23–28 °C (17.1–28.5 °C). All fish moved north for distances of up to 654 km, with three fish moving to a known spawning area where their vertical movement behaviour changed abruptly. Their occupation of shallow waters and a lack of diel vertical migrations differ markedly to the habits of oceanodromous Thunnus species. This may be due to the absence of a swim bladder and highly evolved heat exchanging vascular networks that may limit their niche breadth. The tagging data may help improve stock assessment model inputs and subsequent outcomes to guide the development of science-based conservation and management measures.