Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science

Pop-up satellite archival tags (n = 31) were deployed on Yellowfin Tuna Thunnus albacares in the Gulf of Mexico for periods ranging from 14 to 95 d. Differences in diel vertical behavior were assessed by comparing time spent at temperature relative to the surface temperature ( T). Pooled samples revealed that 31% of darkness hours, 20% of twilight hours, and 12% of daylight hours were spent in the uniform-temperature surface layer (i.e., T = 0). Total time spent above 100 m was less during daylight (90.0%) than during darkness (99.8%), suggesting greater exploration of deeper depths during daylight hours. Maximum depth visited ranged from 208 to 984 m, and minimum temperature visited ranged from 5.4◦C to 11.8◦C. Only a small proportion of total time was spent at temperatures colder than 8◦C below the surface temperature. Horizontal excursions for the majority of individuals were less than 100 km from the point of release; however, three individuals moved distances of 411–1,124 km, suggesting that this species has the capability to move relatively long distances within the Gulf of Mexico. The T values are provided in tabular format and serve as direct input variables for use in habitat standardization models. Subject editor: Michelle Heupel, James Cook University, Queensland, Australia *Corresponding author john.hoolihan@noaa.gov Received January 7, 2014; accepted June 8, 2014 211 D ow nl oa de d by [ 71 .4 6. 64 .2 22 ] at 0 8: 36 0 2 N ov em be r 20 14