Caught in the Current
Climate change may be cause of record shark sightings
By Savannah Welch | November 19, 2020
The Shark Lab at California State University, Long Beach tagged a record 49 sharks off Southern California this year — three times as many sharks as the year prior.
With rising ocean temperatures shifting animal migration patterns, the sudden spike in numbers raises new questions about the extent of climate change.
“It's a little bit too early to tell what the long-term ramifications of climate change, as far as white sharks on our shores are, but we are starting to see a shift,” CSULB graduate student Patrick Rex said. “This might be the first year that we see a year-round shark population — just sharks that don't leave.”
Shark season in Southern California begins in March and typically ends in the fall as lower temperature cues prompt sharks to migrate south, Chris Lowe, the director of the Shark Lab, said. Over the lab’s last 12 years of white shark research, scientists have found five major hot spots for shark activity: Santa Barbara/Ventura, Santa Monica Bay, Long Beach/Huntington Beach, Dana Point/San Onofrey and San Diego. Summer seawater temperatures along Southern California’s coast typically hover around 68°F, while northern beaches are a temperature of 52°F.
“This summer, we had sharks at this aggregation site all summer long into the fall,” Lowe said. “We had new individuals coming and going, but we also had a large number of individuals that we tagged remain there for months. And that's something we haven't seen before.”
According to the 2019 Annual Climate Report by the NOAA National Centers for Environmental Information (NCEI), the global annual temperature has risen 0.13°F per decade since 1880 and over twice that rate at 0.32°F since 1981. Since sharks follow food sources and fish species migrate with changing temperatures, marine life and ocean ecosystems bear the brunt of climbing temperatures.
“It's possible that Baja simply got too warm this year and it pushed more sharks north,” Lowe said. “The other possibility is that for whatever reason, we had beaches and habitats that had more food. Right now, a lot of our research is really drilling in and trying to answer that question.”
Rex, a student at the Shark Lab, is conducting a two-year study investigating behaviors between humans and sharks. Researchers understand general migration patterns, but still need further data on shark activity once they choose a spot and how close they are to the shore, Rex said. The focus of his research is determining who is most likely to encounter juvenile white sharks, when, where and how the sharks will behave around humans.
“I went out on Sunday and saw 13 different individual sharks, which is outrageous,” Rex said. “The most I'd ever seen in 2019, I think in one beach, was four.”
This year, the lab received a four million dollar grant from the state of California to expand the lab’s research throughout Southern California and develop an educational outreach program. Advances in technology have greatly improved the capacity to gather data on shark patterns and behavior. The device that makes Rex’s research possible: the DJI Phantom 4 Pro V2.0 drone.
From the Researchers
White Shark Tagging and Technology
In a typical day of gathering data, Rex starts at 8 a.m. and will pilot the drone from the coast. He flies over 500 yards from shore, traveling north, south and then down the coastline to monitor who’s using the beaches and scan for juvenile white sharks. The lab’s drone has 13 extra batteries, with each battery lasting for 20 minutes at a time. Knowing when humans are using the beach helps in understanding shark behavior and interactions along the coastline, Rex said.
“By using this drone survey, we realized we could kill two birds with one stone,” Lowe said. “We could count how many sharks are out there, but we can also count how many people are out there.”
Jack May III is another graduate student at the Shark Lab and a fellow at the USC Wrigley Institute for Environmental Studies. May studies leopard shark activity off Catalina Island at the USC Wrigley Marine Science Center. May creates temperature maps of leopard sharks to determine shark size, location and the aggregation area. When he’s not analyzing his own data sets, May helps Rex conduct juvenile white shark research.
“It's just been insane that we've been able to keep going back there for month after month after month and [are] still finding untagged individuals,” May said.
May said when tagging sharks, the crew uses an underwater camera to identify whether the sharks are male or female. The tagging boat, guided by the drone, locks location and maneuvers up to the sharks. The acoustic tag is typically on a full spear or harpoon and is deployed near the dorsal fin. The tags correspond with a receiver in the water, so when a shark passes by, it “pings” and alerts that a shark is in the area. The lab will also deploy satellite tags, like Smart Position or Temperature Transmitting (SPOT) tags, which display a shark’s location whenever they break the surface for more than 90 seconds.
“We'll just keep at that for a few hours, so long as we have drone batteries and tags and sharks to play ball, we just basically continue that process of identifying male or female, deploying a tag and then trying to find another one,” May said.
Rex’s drone missions survey between Santa Barbara and San Diego, counting how many sharks are spotted along the coastline, estimating the size of those sharks and correlating their appearance to environmental conditions. The lab also uses an autonomous underwater robot to measure environmental factors, such as temperature and oxygen levels.
“The thing that we've learned about sharks is that they don't stay put — they move incredible distances,” said Dr. Culum Brown, a professor at the Macquarie University Department of Biological Science in Sydney, Australia. “That has been an amazing experience to be part of, that kind of revolution driven by technology.”
Seven shark attack deaths were reported in Australia in 2020. The last time Australia saw seven shark attack fatalities was 1934.
The Taronga Conservation Society Australia conducts comprehensive reviews of shark reports. This year, the agency reported 22 "unprovoked" shark cases, or cases in which a shark is in its natural habitat and attempts to bite a person without human engagement. Brown said roughly 20-25 shark bites are reported every year.
“Last year or the year before, we had two or three bites that would ordinarily have been fatal, but there just happened to be a paramedic or a nurse or a doctor right there on the scene,” Brown said. “That has made a big difference.”
Both on land and at sea, climbing temperatures are greatly affecting Australia’s environment. Last year’s brushfire crisis burned more than 83 million acres.
“One of the things that's clearly happening — and you can see this from the number of interactions that are happening in Tasmania — is quite a few more sightings than usual and more interactions than usual,” Brown said. “The southeast corner of Australia is a hotspot for global warming already.”
The Behavior, Ecology and Evolution of Fishes Laboratory, or Fish Lab, at Macquarie University conducts shark and fish tagging. There is some overlap between the Fish Lab and the Shark Lab, Brown said. Lowe and Brown will co-supervise students on research and the same technology is used in both facilities. One of the closest species to the California horn shark is the Port Jackson shark, which is found in Sydney, Brown said.
“Our students talk to each other online,” Brown said. “They're all trying to solve the same sort of problems and answer the same questions.”
The Fish Lab conducts research on shark movement, social networks and cognition of ocean species. While researchers continue to investigate the long-term ramifications of climate change, the shift in migration patterns highlights the role humans have played in climate fluctuations.
“Whenever we're talking about sharks and rays, they're still one of the most threatened and endangered group of animals on the planet,” Brown said. “We do way more damage to them than they do to us. We just need to keep that in mind.”