Diel movement patterns of ocean sunfish Mola mola off southern California

Ocean sunfish Mola mola are a seasonally common inhabitant of southern Californian waters, and comprise the largest bycatch component (29% of total catch) of the California drift gillnet fishery for swordfish. We used temperature and depth-sensing acoustic transmitters to quantify the fine-scale mov...

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Bibliographic Details
Published in:Marine ecology. Progress series (Halstenbek) 2004-01, Vol.266, p.245-253
Main Authors: CARTAMIL, Daniel P, LOWE, Christopher G
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Biological and medical sciences
Fundamental and applied biological sciences. Psychology
Marine
Mola mola
Sea water ecosystems
Synecology
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Summary:Ocean sunfish Mola mola are a seasonally common inhabitant of southern Californian waters, and comprise the largest bycatch component (29% of total catch) of the California drift gillnet fishery for swordfish. We used temperature and depth-sensing acoustic transmitters to quantify the fine-scale movement patterns of ocean sunfish near Santa Catalina Island, California. Eight ocean sunfish were tracked continuously over 24 to 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 26.8 plus or minus 5.2 ( plus or minus SD) km d super(-1). Horizontal movements were characterized by a significant decrease in rate of movement (ROM) during the first 6 h of night (median ROM = 0.76 km h super(-1)) (SD = 0.31) as compared to the remaining nighttime period (median ROM = 1.00 km h super(-1))(SD = 0.39), whereas daytime ROM (median ROM = 1.22 km h super(-1)) (SD = 0.58) was significantly higher than either nighttime period. Horizontal movements were highly directional, with angular concentration values (r) as high as 0.765 over the duration of entire tracks. Nocturnal vertical movements were confined to the surface mixed layer and thermocline, while diurnal vertical movements were often characterized by repeated dives below the thermocline. A significant relationship was found between maximum dive depth and the post-dive period spent in the mixed layer, suggesting that ocean sunfish may behaviorally thermoregulate between deeper daytime dives. The observed depth-distribution patterns of ocean sunfish indicate that lowering the depth of gillnets in the water column could significantly reduce bycatch of this species in the California drift gillnet fishery.
ISSN:0171-8630
1616-1599
DOI:10.3354/meps266245