Christopher Lowe, professor of marine biology at California State University, Long Beach (CSULB) and director of its Shark Lab, along with a group of his students are researching great white shark nurseries, health and movements. Their work was featured this summer in the Discovery Channel’s Shark Week premiere program, “Great White Invasion.”
The episode follows Lowe and his students as well as researchers in South Africa and Australia as they seek to learn more about great white shark populations.
The CSULB Shark Lab has been collaborating with the Monterey Bay Aquarium for eight years on studying young great white sharks, Lowe said. “It looks like in the last 10 years, the number of sharks that are caught incidentally in the fishery is increasing despite the fact that there are fewer fishers out there and there is less fishing than there was back in the ’80s and ’90s. Based on that evidence, we think the white shark population is increasing in California and you would expect that, if all the conservation and management strategies put into place are working.”
CSULB is part of the aquarium’s white shark rapid response team. “If a commercial fisher captures a baby white shark in our area, which constitutes basically Santa Barbara to Dana Point, my graduate students go out and meet with the fishermen and assess the shark,” Lowe explained. “Then we take measurements of the shark and a few tissue samples and we put tags on the animals, either acoustic tags and/or satellite tags, and then we let them go.
“Over the last eight years, we’ve tracked almost 20 pups. Then last summer we began our acoustic telemetry study where we’ve been surgically implanting acoustic tags in these babies. The tags have a battery life of 10 years. We have acoustic listening stations off many of the ocean piers from Morro Bay down to San Clemente and they’re constantly listening for these tagged sharks.
“Last summer we tagged four baby white sharks off Malibu and we detected all four of them up into the fall and early winter months,” he noted. “Then they all went down to Baja, which is a common pattern that we’ve seen from most of the sharks that we’ve tagged over the last eight years. They all tend to hang around Southern California during the summer and fall months, but usually by November and December, they all head south.”
The baby white sharks often remain close to shore in the summer, but sometimes move further out into the offshore island channels, he said, but the reasons for these movements remain a mystery.
Although rare events, on occasion young white sharks die in the nets and the fishers give them to the lab for research, Lowe said. “We’ve also been looking at contaminant levels in the sharks that have died. Because many of these babies are spending a lot of time around the more polluted parts of Southern California waters, which includes the Palos Verdes Peninsula, we’ve actually found amazingly high levels of contaminants (e.g., DDT, PCBs, and mercury) in many of these pups who may only be a couple of months old. We were scratching our heads trying to figure out how these babies could have such high contaminant loads. We’ve measured some of the highest mercury loads in the muscles of these baby sharks that have ever been measured in any shark anywhere in the world. But these are babies and it doesn’t make sense for such young animals to have such high contaminant loads.
“One of our theories is that the moms are probably offloading contaminants to their young. It passes from the food web to the moms, and the moms are eating things that have really high contaminant levels like marine mammals,” said Lowe.
His wife, Gwen Goodmanlowe, also is a marine biologist who specializes in marine mammals. She and former graduate student, Mary Blasius, published a study in 2008 in which they found remarkably high amounts of DDT and PCBs in Southern California seals and sea lions, which likely resulted from massive dumping in the mid-20th century of these chemicals from sewer system outfalls off the Palos Verdes Peninsula.
Lowe explained that white sharks give birth to live pups who develop as embryos from a yolky egg. The embryos use up their yolk long before they’re born, but the mothers continue to produce unfertilized eggs which the embryos eat while in the uterus to help them grow. Lowe believes the egg yolks contain contaminants passed along from the mother’s food sources.
“This is really the first time that a study of this nature has ever been done,” he said. “The shocking part is that despite the fact that the population seems to be recovering from overfishing because of better management, there may be other more insidious things that are affecting the population, like the effects of these contaminants on these young pups. We know how these contaminants affect humans and other mammals. They cause cancers, reproductive failure and suppress immune function, but in sharks, it’s not really well understood how these contaminants affect their physiology. While the population may be doing better because of protection from overfishing, we may be slowly poisoning them. We just don’t know at this stage of the game.”