Chasing Great White Sharks—From Guadalupe to a Huge, Mystery Population off California

Michael Domeier and Nicole Nasby Lucas have been studying great white sharks together for over 20 years. They began their work off Guadalupe Island in 1999. Since then, they have compiled a huge database of great whites off the coast of this 94 square mile island that sits about 160 miles from Baja California. And this database includes some of the world's best known white sharks, including Lucy, a 17-foot female with a mangled tail fin, and Deep Blue, who at an estimated 50 years old and 20-foot long, is thought to be one of the biggest great whites known. Domeier and Nasby Lucas, from the Marine Conservation Science Institute, started tracking sharks by accident, Domeier said. He had been looking to study a population of bluefin tuna around Guadalupe Island with satellite trackers.

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"Unfortunately, by the time I was able to purchase the tags and organize a trip to Guadalupe Island, the bluefin had vanished," he told Newsweek. "However, we came across a number of great white sharks." Guadalupe Island has a huge and stable population of great whites. The waters around the volcanic island provide warmth and a steady flow of nutrients into the surrounding waters, making them food chain hotspots. Around Guadalupe Island, great white sharks can enjoy feasting on seals, sea lions and tuna. Their satellite tracking system soon threw up some surprises. "The very first tag came off in the middle of the ocean, between the mainland and Hawaii," Domeier said. "I immediately realized what we thought we knew about this species was completely wrong. I was hooked, and I've been researching great whites ever since."

Year after year, Domeier and Nasby Lucas returned to tag and identify the sharks there, leading to the creation of a database that now includes hundreds of great whites. From their research, we now know a huge amount about this population of sharks. Males return there on an annual basis, while females have a two year migration cycle when they are pregnant. "The more we learnt about the sharks, the more questions we had," Nasby Lucas said. The team discovered that these great whites spend an awful lot of time in the open ocean, sometimes making their way to Hawaii, almost 2,500 miles away. What they are doing out there and why is still a mystery. An app, Expedition White Shark, also allows users to track these sharks in real time. Updates are also published by Domeier on his Instagram account. Nasby Lucas said that on this year's expedition, which came to an end at the start of November, they saw 40 different sharks, including a female they had previously spotted in 2016. "It's really exciting when you get to [see] one of the big females." She said that over the 20 years, the number of sharks off Guadalupe Island has gone up. "It's just a really good sort of stable place for them," she said. While they continue to monitor the population, they have cut back on the tagging in Guadalupe Island and have shifted their attention to U.S. shores and a new, very big population of great whites off the coast of California. After returning from Guadalupe Island, Domeier and Nasby Lucas headed to Point Conception, a headland in southern California, about 130 miles north of Los Angeles. It is here that a huge population of great white sharks has been discovered. "Our new site off California is, in my opinion, the most important great white shark research site in the northeastern Pacific," Domeier said. "Why? It's quite simple: no one knew this site even existed just a few years ago. And there are a lot of sharks there." Domeier and Nasby Lucas are currently working on assessing the population and have started tagging the sharks in this area. "[We're] trying to understand [that] region because it's really poorly understood. It seems like it's another adult aggregation," Nasby Lucas said. "There are a lot of sharks there, I'll say that."

The tagged sharks should hopefully show the team where they are going and what regions they are utilizing. They hope to find out if these sharks move up and down the coasts, or visit other areas thousands of miles away, like Guadalupe, or closer locations, like central California. Their latest expedition to Point Conception has just come to an end. Nasby Lucas says they will now be putting together their findings so they can present them in scientific publications. Initial results appear to show the males going offshore for half of the year before returning. The females, she said, are "still a bit of a mystery." She said the numbers seem to suggest the population seems healthy and is increasing. This may be the result of protections put in place by California. "We have quite a bit more work to do before we will have our results," Domeier said. "What it immediately means is that there are many more great white sharks in California than previously believed. We are just now starting the hard work of assessing the number of sharks at this site, while also tagging and tracking them to see how they differ from sharks from the other known sites." This article has been updated to include more information on the Expedition White Shark app.