Researchers at UC Santa Barbara (UCSB) in California are using drones to help project when and where great white sharks show up near specific beaches.
Forecasting what times of year, what times of day and what ocean conditions are more or less likely to attract sharks can help experts make informed decisions about shark conservation and beachgoer safety, according to a new report published in the Marine Ecology Progress Series.
“Predicting when sharks will turn up is something of a holy grail in shark science,” says Douglas McCauley, a professor in UCSB and lead author of the study.
But great white shark movement is hard to predict, admits McCauley, who explains that there are many factors that dictate the whereabouts of sharks, such as their life stage, the behaviour of their food, oceanic conditions and long-term patterns associated with climate change.
Keen to find out more, McCauley and colleagues spent two years studying shark activity at Padaro Beach in Carpinteria, California. They used aerial drones to count the number of white sharks near the beach and then measured as many other features about the ocean as they could.
The study looked at temporal factors, such as the time of day and season, as well as physical characteristics, including swell and wave height, water visibility, and surface and seafloor temperatures. They also considered biological factors, such as the amount of plankton in the water.
Unlike previous shark-counting studies – such as divers recording them as they swim, sonar counts and marking them with tags – the drones offered the researchers regular and reliable counts using 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 there is a drone overhead, they are easier to count,” explains co-author Neil Nathan, a project scientist at UCSB.
“A disadvantage is that you can really only image the surface layer of the ocean.”
To offer a more comprehensive picture of shark population patterns, the researchers gathered additional data from tagging efforts and acoustic buoys from Professor Chris Lowe’s Shark Lab at CSU Long Beach.
Using this data, the authors combined shark sightings and oceanographic factors with mathematical models to see what variables best predicted how many sharks there were at the beach on any given day.
What did the drones discover?
The study found that shark density was most clearly affected by water temperature, season and time of day.
Sharks, especially the smaller ones (which lose heat faster), tend to avoid colder temperatures close to the seafloor and were slightly more attracted by warmer surface waters.
There were also significantly more sharks in summer – another observation that supports the temperature theory. There are exceptions to the rule, with some juveniles observed at Carpinteria in November and December.
Most of the sharks spotted in the study area were juveniles, suggesting that the beach is an important nursery habitat for baby white sharks. Again, there are exceptions, say the researchers, who spotted a number of larger sharks, including some that measured up to 15 feet.
The drones located more sharks near the surface in the late afternoon, another clue that they are trying to warm up in these balmier surface waters. "Compared to water at depth, [the surface] feels like a jacuzzi to these sharks after the sun warms [... it] all day,” says Nathan, adding that eight times more sharks were recorded at the surf break, compared to farther out to sea.
What do these observations mean?
“Everyone was curious about the scientists flying a drone on the beach,” says Samantha Mladjov, lead SharkEye drone pilot and study co-author.
“The one thing everyone wanted to know was, ‘What did you see: Are there a lot of sharks out there today? Should I go for a surf or a run?’”
Keen to keep the community informed, the team set up an automated text notification system that shared the results of the day's survey in real time.
“We think data is empowering and helps us make safer, smarter decisions,” says Nathan.
"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 and feel and be safer, even though the probability of an incident with a shark is exceptionally low.”
According to the California Department of Fish and Wildlife, California has experienced an average of three 'shark incidents' (defined as 'any documented case where a shark approached and touched a person in the water') per year since 1950.
“Right now, co-existence is largely going well, as people at these beaches seem to have much more interest in the sharks than vice versa,” says McCauley, adding that Californians are familiar with the importance of finding safe ways to share our mutual home with wildlife.
Check the live data on SharkEye.org and sign up for free text notifications from the shark survey program.
More wild stories from around the world
