2025 Volume 89 Issue 3 Pages 181-193
Vertical movement of skipjack tuna Katsuwonus pelamis provides fundamental information for considering fishing effort and eliminating the effect of fishing location on catch per unit effort. Vertical movement of skipjack tuna associated with the surface-type fish aggregating devices (FADs) on the coast of Wakayama, Japan, was examined using the archival tag records. Based on nine fish that were recaptured around the surface-type FADs where they had been released on 24 June 2020, the elapsed period between release and recapture was from 3 days 19 h to 10 days 20 h. Skipjack tuna remained shallower than 20 m in depth for 91.2–99.5% of the time during both the nighttime and daytime. The differences in mean swimming depth between nighttime and daytime were as small as 0.3–3.7 m. Overall, the results of the present study suggested that there was no clear pattern of vertical movement between nighttime and daytime in skipjack tuna associated with the surface-type FADs on the coast of Wakayama. The peritoneal cavity temperatures were generally above 22°C regardless of the ambient temperature, suggesting that skipjack tuna maintained its body temperature to maintain its metabolism.
