Scientists use drones to track white sharks along California beaches

The beach forecast today is cloudy, with a risk of sharks. At least that’s the prediction UC Santa Barbara researchers would like to be able to provide. They are leading a project to predict when and where great white sharks will appear near a beach.

The goal is to develop forecasting tools that can help predict which times of year, times of day or ocean conditions are likely to be more or less stormy. The team sought to understand what small-scale factors affect shark behavior at all life stages. “Predicting when sharks will appear is sort of the holy grail in shark science,” said Douglas McCauley, a professor in UCSB’s department of ecology, evolution and marine biology. “But even early information can help us make better decisions: is today a better day for surfing or beach volleyball?”

For the moment, the presence of sharks is still difficult to predict. But some first steps towards this goal were shared in a report published in the Advances in Marine Ecology Seriesafter a two-year study at Padaro Beach in Carpinteria, California. Lead author McCauley and his team used aerial drones to observe how the presence of sharks varied according to different oceanographic conditions. Water temperature, season and time of day appear to be most correlated with shark density off the coast, they found. This information can help inform shark conservation and swimmer safety.

A shark’s schedule

Some things in nature are easy to predict: the ebb and flow of tides, the emergence of cicadas, the changing fall foliage. But the movements of white sharks are difficult.

Many factors influence the decisions of an animal as complex and intelligent as the shark, especially in an environment as dynamic as the ocean. Where sharks appear is determined by their life stage, feeding behavior, oceanographic conditions, and long-term patterns associated with climate change.

To assemble their forecast model, the team used aerial drones to count the number of white sharks near the beach, then measured as many other ocean features as possible. This included temporal factors, such as time of day and season, as well as physical characteristics, such as swell and wave height, water visibility, surface and seafloor temperatures. They also took into account biological factors such as the amount of plankton in the water (an indicator of the fertility of the food web these sharks depend on).

The drone aspect of this project was relatively new. The group has used all sorts of methods to count sharks over the years: asking divers to count them as they swim, counting sharks with sonar and marking them with tags. But for this study, the team sent a drone to follow a pre-programmed one-mile flight path just outside the surf line. “One of the strengths of this method is that you can cover a lot of ground in these surveys, and because the sharks have no idea that there is a drone overhead, they are easier to count,” explained co-author Neil Nathan, a science project at UCSB’s Benioff Ocean Science Laboratory. “A disadvantage is that you can only really visualize the surface layer of the ocean.”

To address these blind spots, researchers at UC Santa Barbara collaborated with experts from Professor Chris Lowe’s Shark Lab at CSU Long Beach. Lowe’s team has been studying white sharks in this region for years, providing additional data streams through tagging efforts and sonobuoys. Coupling this visual and acoustic data gives a better picture of these population trends over time, but this was not part of this particular study.

Finally, the authors combined shark sightings and oceanographic factors with mathematical models to determine which combination of variables best predicted the number of sharks present on the beach on a given day.

Warm waters for small sharks

Ocean temperature and time of year were among the very few factors that seemed to correlate well with where and when sharks appeared. White sharks are actually warm-blooded; they can keep their cores a little warmer than the water around them. But they still feel cold, especially the smallest ones, who lose heat more quickly. The researchers found that small white sharks tended to avoid colder temperatures near the seafloor and were slightly more attracted to warmer surface waters.

There were also many more sharks in summer, which corresponds well with the temperature results. That said, they still observed a few juveniles even in November and December. Before that, researchers thought the young were heading south to warmer climates for the winter.

Most of the individuals at Carpinteria were juveniles, indicating that the beach is an important breeding habitat for baby white sharks. But there are also older sharks. The largest sharks measured up to 15 feet.

Drones spotted more sharks near the surface late in the afternoon. Again, this may be because they are trying to warm up in these warmer surface waters. “Compared to deep water, (the surface) is like a hot tub for these sharks after the sun has warmed it all day,” Nathan said. It’s the same part of the ocean that we love to play, swim and surf in. Eight times more sharks were seen directly at the surf break than further offshore, he added.

Share the waves

This is a good time to remember that Californians have experienced, on average, only three “shark incidents” per year since 1950. And the California Department of Fish and Wildlife defines an incident as “any documented case where a shark approached and touched a person in the water. It turns out that sharks make very good neighbors.

McCauley grew up on the beaches of Southern California, but he doesn’t remember seeing a single shark from shore or in the water during the decades of his youth. Seeing 10 to 15 per day is a welcome sight; this means the state’s wildlife is recovering.

White shark populations have been hit hard by gillnets for decades, as have birds and marine mammals. The state has phased out many types of gillnets and is now considering potentially eliminating the last form of gillnet allowed. These policy changes, along with additional protections for marine mammals, have done much to repair our coastal ecosystem. “A generation later, I was blown away to drop my kids off for their first days of surf camp in Carpinteria and see baby shark fins just outside the surf line,” McCauley said.

Californians know the importance of finding safe ways to share our common home with wildlife. What happens in the waves is similar to how we use science to coexist with terrestrial predators, like mountain lions or bears. “Right now, coexistence is generally going well, because people on these beaches seem to be much more interested in sharks than the other way around,” McCauley said.

In fact, one of the most exciting things to come out of this project was the collaboration with the community. “Everyone was curious to see the scientists flying a drone on the beach,” said Samantha Mladjov, lead pilot of the SharkEye drone and co-author of the study. “The only thing everyone wanted to know was, ‘What did you see: were there a lot of sharks today?’ Should I go surfing or running?”

Due to interest and curiosity, the team quickly implemented an automated SMS notification system that shared the day’s survey results in real time. “We believe data empowers us and helps us make safer, smarter decisions,” Nathan said. “Our goal in this program is to provide data that helps people fall more in love with the ocean. It helps them understand it better, feel safer, even if the likelihood of an incident with a shark is exceptionally weak.”

The team invites community members to view live data at SharkEye.org and sign up to receive free text notifications from the Shark Survey Program. McCauley and Nathan also encourage people to follow ongoing discussions about gillnet fishery reform, which can help build momentum for wildlife recovery along our beaches and coasts.