Fine-scale movement patterns and habitat preferences of ocean sunfish (Mola mola) off the coast of southern California

Ocean sunfish (Mola mola) are a common inhabitant of southern California waters and comprise the largest bycatch component (29% of total catch) of the California drift gillnet fishery for swordfish. Reducing bycatch of ocean sunfish requires an understanding of their movement patterns and habitat preferences, both of which are poorly known. I used temperature and depth-sensing acoustic transmitters to quantify the fine-scale movement patterns and habitat preferences of ocean sunfish near Santa Catalina Island, California. Eight ocean sunfish were tracked continuously over 24–72 h periods, during which oceanographic data were collected every 2 h. Geographical position and depth of tracked fish were analyzed in relation to oceanographic data and time of day. Ocean sunfish traveled a mean distance of 26.5 ± 5.2 km (mean ± SD) per day. Horizontal movements were characterized by a significant decrease in rate of movement during the 6-h period following sunset (0.78 ± 0.26 km h−1) as opposed to daytime periods (1.26 ± 1.16 km h−1). (Abstract shortened by UMI.)...