The great white shark has been a financial bonanza to the TV and movie industries, and yet we know very little about the real animal — until now. On Thursday, two researchers from California’s Marine Conservation Science Institute announced their findings from a years-long study that involved placing satellite tags on four adult female sharks caught offshore Guadelupe Island, Mexico. The research was published today in Animal Biotelemetry.
In the past, it was impossible to track the entire two-year migration and breeding cycle of the wide-ranging female great white shark. The batteries simply wouldn’t last long enough. However, lead author Dr. Michael Domeier revealed that modern batteries with much longer lives have finally allowed biologists to track the entire life sequence.
Just getting the tags on the great white sharks sounds like a bear. But Domeier suggested that sharks have more to fear from humans than the humans have to fear from sharks. Because of stress, “the shark’s life is in our hands during the short time it takes us to capture and tag each individual,” he explained to a local TV news station.
The satellite tags allowed the researchers to track the great white sharks from their mating ground offshore Guadalupe Island. Once they got pregnant, the female sharks traveled a great distance into open ocean, far away from the males. This “offshore gestation phase” lasted roughly 15-1/2 months — most of the shark’s 18 month pregnancy.
They would then return to waters offshore Baja, California where they ultimately gave birth in the warmest months from April to August.
Here, the great white sharks are at their most vulnerable. The pregnant females, or females that have just given birth to young pups, seem to be drawn to a potentially hazardous coastal region at just the wrong time. That makes them vulnerable to commercial fishing, including nets, and the pups are most at risk because they aren’t yet strong enough to break free of many potential traps.
The males, by contrast, seem to be at a reduced risk, because they spend the smallest amount of time in the area.
Because of the long period of time it takes to carry and deliver the young, the females return to the mating site offshore Guadalupe Island every two years, while males return each year.
All in all, it’s a fascinating peek into the great white shark lifestyle that we didn’t previously know much about.
That comes fast on the heels of research published in March, when Australian and British researchers offered evidence that great white sharks must eat several times more food than earlier scientists had believed.
Are you surprised that we still had so much to learn about the great white shark?
[feeding great white shark photo courtesy BrockenInaGlory via Wikipedia Commons]
[swimming great white shark photo courtesy Terry Goss and Wikipedia Commons]