Vertical movement and behavior of the ocean sunfish, Mola mola, in the northwest Atlantic

Pop-up satellite archival tags (PSATs) were attached to 31 ocean sunfish, Mola mola. in the Northwest Atlantic between 2005 and 2008, in order to examine their vertical movement and behavior. Tags remained attached from 7 to 242 days, with a mean attachment period of 107.2 ± 80.6 (SD) days. Fish spent greater than 30% of their time in the top 10 m of the water column, and over 80% of time in the top 200 m. The maximum depth recorded by any fish was 844 m. Temperatures experienced by tagged fish ranged from 6 to 30 °C. Vertical behavior of M. mola changed over short-term and seasonal scales. Ocean sunfish in northeastern US waters in the summer months inhabited shallower depths and spent more time at the surface than those that moved south in the winter and spring. This shift from shallow to deeper depths was especially apparent when fish entered the Gulf Stream, where they spent little time at the surface and dove to depths of 400-800 m. A diel pattern was observed in vertical behavior. Tagged fish spent more time at depth during the day and inhabited shallower waters at night. There was no observed relationship between the amount of time per day that fish spent in cold water (< 10 °C) and the amount of time fish spent near the surface (0-6 m), indicating a lack of evidence for M. mola basking at the surface as a mechanism for behavioral thermoregulation.