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Student researchers study why sharks gravitate to certain areas at the beach

Published August 10, 2020

Sharks – big and small, spotted or white – are omnipresent off the coast of California. From Santa Barbara to San Diego, they roam the waters searching for food, breeding grounds and social interaction. 

Now, with the research done by students in Cal State Long Beach’s Shark Lab and under the guidance of Director Chris Lowe, more is being learned about sharks’ behavior and the likelihood of an attack. This research was featured in Scientific American magazine and on local television stations.

Graduate student Patrick Rex has been researching juvenile white sharks for the past 18 months. He said younger sharks, which range from 4 to 9 feet long, are skittish and tend to stay away from humans and larger prey but will gravitate to warmer waters near the shore. 

“They are extremely vulnerable to predation by larger sharks,” he said. “The best thing to do for their self-preservation is to avoid confrontation with any larger than them.” 

And that seemingly includes humans. Rex said they have not witnessed aggressive behavior between juvenile sharks and humans throughout their research that spanned from Santa Barbara to San Onofre. Most of the activity this summer has been around Carpinteria. 

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“As sharks get larger, they may get a little more curious about humans and may come closer,” said Rex, who is pursuing his master’s degree in biology, adding that most sharks gather 150-250 feet off shore, but some have been spotted so close “that their bellies are almost scraping the sand.” 

Rex and other Shark Lab students used drones to survey the sharks’ behavior with five different groups of beachgoers: waders, swimmers, bodyboarders, suffers and stand-up paddle-boarders. Rex said they don’t know what exactly precipitates an attack but have not documented aggressive behavior between juvenile white sharks and humans in their research.

“At this point (in their lives), their diet consists of stingrays, small fish, squid and demersal fish,” Rex said. We are far from being on their menu for them.” 

students launch drone off boat

Rex is using his surveys to figure out where, when and what water-user group (surfers, swimmers, etc.) might be likely to encounter a juvenile shark and under what conditions. He also is looking at environmental parameters, such as water temperature, wind and wave height, that will better help him understand “when and where encounters may occur.” 

“This will help lifeguards better advise the public on when they may encounter sharks and educate the public about when they need to be most mindful of sharks,” Rex added. 

Re-population of leopard sharks

Great white sharks get all the publicity, but leopard sharks are one of the most common sharks along the coast of California. Easily identified by their silvery-bronze skin with dark oval patterns, these fish diminished in recent years because of over-fishing. 

Graduate student Jack May is looking at how the leopard shark is making a comeback following California’s ban on nearshore gill-net fishing in Southern California by tracking its movement. He said that knowing where and when leopard sharks might be vulnerable is important for future management strategies.

leopard shark

May uses drones to survey the area for leopard sharks and then hover over each group or “aggregation” of sharks to collect video for later analysis.

“This allows me to count how many sharks are present, look at how they are dispersed in relation to seafloor water temperature and estimate the sizes (of the fish) in an aggregation,” May said. 

He has documented female leopard sharks forming relatively dense groups in shallow water during warm months that not only allows them to increase their body temperatures, but ultimately decrease the time to takes for them to brood their pups. 

Through his data, May hopes to understand whether there are trends in what temperatures the sharks prefer relative to temperatures that were available. It also could be a safety issue. 

“Leopard sharks may not only be seeking warmer waters but there could be a social component where each individual is potentially safer when being surrounded by individuals of the same species,” May said. “Sea lions have been observed hunting and eating leopard sharks and there is less of a chance of any individual being eater if they stay in groups where there are more watchful eyes scanning for danger.” 

May, who is earning his master’s in biology, eventually will compile the data from temperature loggers and create temperature maps of the seafloor at the aggregation site. 

Finding patterns in the environment

Graduate student Emily Spurgeon uses an underwater robot to track juvenile sharks along the coast of California. The yellow torpedo-shaped autonomous underwater vehicle (AUV) that the Shark Lab acquired last year, uses transmitters to listen for tagged young sharks and locate them. 

“Hopefully, I can determine patterns or trends in the environment that the sharks may be queuing in on,” Spurgeon said. 

Spurgeon said what she has learned is that juvenile sharks, unlike their older counterparts, tend to stay in a relatively small area, while adult sharks continually migrate several miles over a 24-hour period unless they are at a feeding site. 

“It’s interesting to think about how a small area is capable of sustaining them for however long they decide to stay,” she said. 

But that hasn’t been the most revealing part of her research. Spurgeon said that tracking these elusive fish can be difficult. 

“Although we do our best, technology has its limitations with how it can perform inn an ocean environment as we have in California,” she said. 

Still, Spurgeon is grateful for the opportunity the AUV has afforded her in her research. 

“To be a part of a lab that that not only is continuously pushing the boundaries of what is possible to study, but it also allows me to use cutting-edge technology (AUV) is setting me up very well to be in a competitive position for a career in marine biology,” she said.

shark fin sticking out of water