They don’t have laser beams on their heads – yet. For years, biologists at Cal State Long Beach’s Shark Lab have been tagging sharks with transmitters to study their behavior, how they swim, where they migrate and their survivability. Recent discoveries have given them insight as to why there are so many great white sharks in Southern California’s waters.
How tracking works
(1) Biologists locate a shark and tag it with a tracking device and assign the shark a number. (2) Tracking devices can track the shark’s location or record and store data. (3) SPOT and PAT tags are detected by satellites, which then transmit a summary of those data to the Shark Lab via email.
Sharks may carry up to $10,000 of tracking technology.
(1) PAT tag
This transmitter has sensors for light, depth and water temperature. At a predefined time and date, it releases from the shark and floats to the surface to upload the stored data to the satellite.
(2) SPOT tag
This transmitter is attached to the shark’s dorsal fin and has a salt water switch that turns on to transmit its position to a satellite when the shark surfaces. Each satellite transmission costs $5.
(3) Acoustic tracker
Biologists began using these trackers in 2011 to tag baby great white sharks. The transmitter is the size of a AA battery and is implanted inside the body cavity. It produces an ultrasonic ping the shark can’t hear, and lasts 10 years. Acoustic receivers are anchored to the ocean floor and detect the ping when the shark is within 300 yards.
(4) Smart tag
Mounts on the dorsal fin and is equipped with an acoustic transmitter, a video logger that sees what the shark sees, a 3D accelerometer that records motion, temperature and depth sensors and a transmitter. When all data are recorded, it releases to the surface, sends a signal and is recovered.
‘Hot spot’ migration
The Shark Lab has 123 receivers in the waters along the Southern California coast that have tracked the migration of juvenile sharks since 2011. Overall, biologists have more than 200 receivers from Avila to the Mexican border that have allowed them to identify several “hot spots” where juveniles gather in large numbers, hop scotching from spot to spot.
Inside a hot spot
Studies from tracking suggest that the juvenile sharks have been staying in hot spots close to shore because the water is warmer, there are fewer predators and there is an abundance of stingrays, which are easy for them to capture in these waters.
A healthy food chain
Better fisheries management, recovery of marine mammal populations and protection of great white sharks has enabled the shark population to recover.
(1) Biologists began tagging young great whites caught in gillnets and found that over 90 percent survived if the nets were set for less than 24 hours. This shows that many of the sharks incidentally caught and released after protection in 1994 would have survived and are now adults producing their own young.
(2) Better management of coastal fisheries has also allowed recovery of many species that marine mammals like to eat.
(3) Marine mammals’ food source populations, such as squid, sardines, sea bass and stingrays, have also increased. This is a critical food source for juvenile sharks learning to eat on their own.
Source: California State University, Long Beach Marine Biology Department