UCSD - University of California - San Diego

07/28/2026 | Press release | Distributed by Public on 07/28/2026 10:10

Juvenile Great White Sharks Fled Their Nursery During Tropical Storm Hilary

Published Date

July 28, 2026

Article Content

Key Takeaways

  • Scripps Institution of Oceanography researchers led a study tracking the movements of 22 juvenile great white sharks before, during and after Tropical Storm Hilary in 2023.
  • Acoustic tags showed that many of the sharks temporarily left their coastal nursery off San Diego when the storm hit, retreating to more sheltered waters and returning once conditions improved.
  • The findings provide the first direct evidence of how juvenile white sharks respond to an extreme weather event.

In August 2023, communities across Southern California braced for Tropical Storm Hilary - the first tropical storm to directly impact the region this century. Although the storm weakened from a Category 4 hurricane before making landfall, it still brought damaging winds, record rainfall and widespread flooding across the southwestern United States and parts of Mexico.

Beneath the waves, another drama was unfolding. As the storm hit the coast, juvenile great white sharks abandoned a well-known nursery habitat off San Diego, retreating to more sheltered waters before returning after conditions improved.

A recent study by researchers at UC San Diego's Scripps Institution of Oceanography and the Shark Lab at California State University, Long Beach (CSULB) reveals how these juvenile white sharks responded to Tropical Storm Hilary, providing the first direct evidence of the species' response to an extreme weather event. Using acoustic tags to track the sharks before, during and after the storm, the team found that many temporarily left the nursery as conditions deteriorated but returned soon after the storm passed.

"To our knowledge, this is the first study to document storm-response behavior in white sharks," said Jack Elstner, a Scripps PhD student and lead author of the paper. "Our data show that many sharks in this nursery temporarily left the area as the storm arrived or just after. These findings provide new insights into how extreme weather events may impact the movements and nursery behaviors of a recovering top predator."

In Southern California, juvenile white sharks often spend their formative years in shallow coastal habitats, where their early development is supported by warm, calm waters, abundant prey (such as stingrays and small fish), and protection from larger predators. One such nursery lies off the northern San Diego beaches of Torrey Pines and Del Mar, where young sharks aggregate during the summer and fall before eventually moving on to adult habitats.

To study how the tropical storm affected this nursery, researchers tracked 22 juvenile white sharks - 13 females and 9 males - that had been tagged with acoustic transmitters. Two arrays of underwater receivers recorded more than 524,000 detections, creating a detailed record of the sharks' movements during the storm.

Before Tropical Storm Hilary arrived, researchers consistently detected 16 to 19 tagged sharks in the nursery per hour. During the storm, detected individuals declined by roughly half, dropping to as few as eight sharks before rebounding in the days and weeks that followed. Most sharks returned to the nursery within a few days and nearly every shark had returned within three weeks. Only one individual left as the storm arrived and was never detected again in San Diego that year.

The team was not always able to pinpoint exactly where these sharks went during their temporary departures, but did note a "discernible increase" in pings across La Jolla Cove. The cove is situated next to a prominent submarine canyon, giving sharks quick access to deeper water. The area was also largely protected from the storm's strong southerly winds.

"We believe this more sheltered habitat may have served as an important nearshore refuge for some individuals," said Elstner.

Researchers use a pole-mounted camera to collect video of a juvenile white shark prior to tagging it with an acoustic transmitter. Photo: CSULB Shark Lab
Two juvenile great white sharks swim along the coast of Torrey Pines on a calm day. According to Scripps PhD student Jack Elstner, young white sharks in this area typically measure between 5 and 9 feet in length. Photo: CSULB Shark Lab

When the storm hit San Diego on Aug. 20, 2023, one shark equipped with a pressure sensor was detected in La Jolla Canyon at a depth of 132 meters (433 feet) - the deepest dive recorded during the study. The researchers suggest the dive may have been an attempt to escape the turbulent conditions near the surface.

"The fact that some sharks 'tucked' into the less wave-active La Jolla Cove during the storm was an interesting finding," said Chris Lowe, leader of the Shark Lab at CSULB and a co-author of the study. "We think that some were seeking shelter from the storm, and it makes sense that not all sharks did the same things, in much the same way people respond differently. It's a key survival characteristic that humans seem to share, too."

Hilary prompted the National Hurricane Center to issue its first-ever tropical storm warning for Southern California and ultimately caused more than $900 million in damage in the U.S. The storm brought unusually hazardous coastal conditions, including high winds, record rainfall, coastal flooding and sharp drops in sea-surface temperature.

The researchers suspect the abrupt cooling had the most impact on the sharks' behavior. During the storm, sea-surface temperatures in the nursery dropped from 20°C to 13.9°C (68°F to 57°F) in less than 24 hours, closely coinciding with the sharks' temporary departure.

White sharks are regionally endothermic, meaning they can regulate their internal body temperature above ambient conditions. While adults tolerate cold water well, juveniles are more sensitive to colder temperatures and rapid changes. The researchers believe the young sharks' behavioral response likely reflected attempts to seek out warmer water until conditions improved.

As climate change increases the frequency and intensity of extreme weather events, understanding how marine species respond to rapidly changing ocean conditions will become increasingly important, noted the researchers.

"White sharks and people are increasingly using the same coastal waters in California," said Brice Semmens, a Scripps marine ecologist and co-author of the study. "Studies like this help us understand how sharks respond to rapidly changing ocean conditions and allow us to make better decisions that support both shark conservation and safe ocean use - from surfing and swimming to recreational and commercial fishing."

The study was published this spring in the journal Movement Ecology.

Satellite image of Hurricane Hilary on Aug. 18, 2023, two days before it weakened to Tropical Storm Hilary and made landfall in Baja California, Mexico, continuing across the southwestern United States. Image credit: CSU/CIRA & NOAA

A juvenile white shark swims along the San Diego coast on a calm day. Photo: CSULB Shark Lab

Additional co-authors of the study are Emily Spurgeon, Patrick Rex, Elizabeth Jahn, Zachariah Merson, Whitney Jones, Lauren Faulkner, James Anderson and Ryan Logan of CSULB, and Wave Moretto, Theodora Mautz, Rilee Sanders, Max Titcomb and Gabriel Gekas of Scripps Oceanography.

Support for this research was provided by the State of California Shark Beach Safety Program (awarded to CSULB), as well as the National Marine Fisheries Service, NOAA, Quantitative Ecology Socioeconomics Training (QUEST) Program (awarded to Scripps Oceanography). Elstner's doctoral research is supported by a National Science Foundation Graduate Research Fellowship.

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