• Sharks and Tuna
• Monitoring the Mako
• In the Beginning
• Shark Tracks

 cont'd

The tracking also revealed that the animals exhibited most of their movement up and down the water column during daylight hours. This may be due to, the scientists say, the sharks' reliance on vision for locating prey, and is reflected in their greater depth penetration during daylight hours.

All of this information, they hope, will provide scientists with a better understanding of the mako's fine-scale movements and will provide fishery managers with data that accurately depict how habitat areas are used by the animals. In the end, Sepulveda hopes this will eventually translate to reduced juvenile mako bycatch.

"This is the first time that this has ever been done so everything is new and interesting," said Dickson, Sepulveda's former advisor. "These new data generate more ideas because now you have something to really base your hypothesis on."

The project's success has led to a follow-up study on thresher sharks, which, like the previous study, is funded by the California Sea Grant College Program. Sepulveda and new Scripps graduate student Dan Cartamil are updating their methods by employing "archival" tags that record a long-term series of movement information.

The square, paper-clip-sized electronic recording tags, attached on the thresher's dorsal fin, stay with the animal and record data for months at a time. Larger threshers are likely to be caught offshore by commercial fishers while smaller fish will most likely be landed by sport fishermen. Recovered tags are returned to the laboratory where the information is downloaded onto computers.

The information is so valuable that the researchers are offering fishermen a $50 reward for each returned tag. Sepulveda and Cartamil believe the cost is well worth it, as the data will significantly broaden their knowledge about the activities of southern California sharks.

The expanded database will be important for predicting shark movement patterns and identifying possible areas or depths that can be considered thresher "hot spots." Ultimately, Graham and Sepulveda hope it will factor into future protection of the animals.

"Both of Chugey's projects are giving us new scientific information," Graham said. "A Ph.D. student needs to demonstrate that he or she can apply scientific methods and acquire data through research, and this gives them the potential to discover something important. Chugey Sepulveda has done this."

SCRIPPS INSTITUTION OF OCEANOGRAPHY