Is El Niño Bringing Great White Sharks to California? A Marine Biologist Reacts

If you went swimming or surfing in Central California this summer, chances are you weren’t alone. Great white sharks are migrating up the California coast in record numbers. Sharks aren’t uncommon in Central California, but in these numbers, they are. Normally, white sharks don’t show up in these waters until spring, but this year, they were seen as early as February.

And this isn’t the first time. See those shadows? Those are great white sharks. This photo is from a study on the unprecedented number of juvenile great whites sighted in Central California from 2014 to 2016. The reason for this increase in great white sharks is a powerful weather phenomenon called a super El Niño.

I’m KP, [music] a marine biologist, and today we’re diving into the science behind El Niño. Why it’s driving apex predators north, and why this biological shift might not be the nightmare that you think [music] it is, or at least not in the way that you might think it is. Two important factors at play here are food and temperature.

 Most sharks are ectothermic, or cold-blooded, meaning their body temperature is the same as their environment. Lamnid sharks, like mako sharks and great white sharks, belong to a rare group of just 0.1% of all marine life that are mesothermic, or partially warm-blooded. They have a special network of blood vessels called the retia mirabilia.

This acts as a countercurrent heat exchanger. They basically trap and store the heat generated by their swimming muscles. Because mesothermic sharks can maintain their internal body temperature above that of the surrounding water, they can be more active predators in cooler waters compared to cold-blooded shark species.

 But, it also requires them to expend more than four times the energy of cold-blooded sharks of the same size. The energy expenditure increases as water temperatures rise. And as great white sharks grow and get bigger, their bodies generate heat faster than they can shed it. So, they tend to prefer colder waters. The opposite is true for juvenile white sharks because of their higher surface area to volume ratio.

 They lose body heat fast, making it tough to stay warm when the water gets cold. That makes water temperature a strict boundary line for young sharks. As a result, the thermal range of juvenile white sharks is likely a major driver of the habitats they occupy. And this appears to be sensitive to climatic shifts during El Niño events.

From 2001 to 2019, researchers tagged 14 juvenile white sharks. These tags took 22 million measurements of oceanic thermal temperatures. This information provided a detailed thermal habitat for juvenile white sharks and allowed scientists to map [music] the cold limit range of these juvenile sharks. Now, what they found was remarkably consistent with previous independent studies.

The northern edge of the cold limit range for juvenile great white sharks was Point Conception. This massive terrestrial headland marks a sharp marine biogeographic [music] boundary that separates the cold, turbulent currents of North Carol- Gosh, I was doing so well. I was on a roll. It was flying off the tongue.

This massive terrestrial headland marks a sharp marine biogeographic boundary that separates the cold, turbulent currents of northern California from the warmer, sheltered waters of the Southern California Bight. This biogeographic boundary shifts north of the Bight during El Niño years, and that shift is even more extreme during super El Niño.

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 Varies by plan. Code K Passionate FM at hellofresh.com. >> How was it? >> You’re going to like it. Speaking of food, I mentioned that the two factors that push great white sharks north of the bite are sea surface temperatures and food. El Niño can disrupt both. Let’s break it down using sea surface mapping from NASA’s Scientific Visualization Studio.

The key to understanding El Niño is the temperature of the ocean surface. Tropical waters are typically warmer than other waters in the world because they receive more solar radiation. But that’s not the only factor. Sea surface temperatures are continuously shaped by variations in trade winds, cloud cover, and deep ocean currents.

These variations are mostly irregular patterns, but they do appear to have cycles. Under normal conditions, the waters of the Americas remain significantly cooler than the warm pool in the western Pacific off the coast of Asia. But those oceanographic dynamics break down roughly every two to seven years. If we look below the surface, we can see what’s called a thermocline.

 A sharp transitional layer separating warm surface waters from the colder deep waters. In the western Pacific, the accumulation of warm water pushes this boundary downward creating a significantly deeper thermocline and a thicker layer of warm water. Every two to seven years that thermal balance shifts.

 The thermocline flattens as warm water surges eastward toward the Americas. This phenomenon is what’s known as El Niño Southern Oscillation or ENSO and it can cause extreme weather across the entire globe including heat waves, drought, [music] and torrential rain. It also disrupts ecosystems. During El Niño, the influx of warmer water suppresses the upwelling of cold nutrient-rich deep water.

The result is a severe ecological cascade. Without those nutrients, biological productivity drops. Zooplankton starves, which decreases the abundance of schooling fish. This leads to hunger all the way up the food web. These warmer oceans with fewer nutrients can cause mass migrations with cold water species moving further north, which is what happened during the unprecedented 2015 to 2016 super El Niño.

Researchers documented a dramatic poleward range shift of juvenile great white sharks along the California coast. Historically, temperature-sensitive juveniles remained confined in the warmer waters of the Southern California Bight. However, during this extreme warming anomaly, the Southern Oh my goodness. However, during the extreme warming anomaly, the thermal cold edge of their preferred habitat jumped significantly north from its historical average of 34° north to 38.

5° north, causing a sudden, multi-year influx of juvenile sharks into Monterey Bay, and creating new ecological dynamics in the region. Researchers and experts expect that the same thing is going to happen this year. The juvenile white sharks of the California Bight will move into central California. The white shark nurseries off the Baja Peninsula will likely move north into the Southern California Bight.

Essentially, an entire generation of apex predators are going to be pushed hundreds of miles north into waters that used to be too cold for them. Honestly, this is a much bigger problem for the great white sharks and the marine ecosystems than it is for people. Shark attacks on humans are incredibly rare.

 There have been just 201 verified shark bites in California waters between 1950 and 2021, with 107 causing injury and 15 resulting in fatalities. Although significant to those people and everyone involved, that is an incredibly small fraction of the people who surf, swim, and dive off the coast of California. It’s estimated that between 150,000 to 300,000 people swim in California waters on any given day.

Tourists alone visit California beaches 150 million times a year, according to the California State Water Resources Board. And that’s not counting locals who swim in those waters regularly. And science has shown these people were swimming near sharks, and the sharks [music] didn’t care. Some of our most recent data in California shows that white sharks [music] are around people all the time.

 People just don’t know that they’re there. Using drone footage, we see sharks swimming right by people and not even changing their path. They’re completely [music] ignoring people. The bigger threat is to the sharks themselves. For the most part, great white sharks are apex predators throughout most of their range, but there are a few exceptions.

Specifically, when the great whites run into certain ecotypes of killer whales. The Central California region is a key area where white sharks and killer whales interact. And last year, rising sea temperatures likely drove juvenile white sharks into the Gulf of California, where they ran into a group of orcas known as Montezuma’s pod.

This pod of orcas had previously been documented preying on bull and whale sharks, but this was the first time they had been seen preying on great whites. Ecologically speaking, predation by orcas is a natural, localized pressure. Humans, on the other hand, represent a bigger threat. As these juvenile and neonate great whites migrate north, they’re running into commercial and recreational fisheries.

On July 3rd, California wildlife officials enacted emergency fishing regulations to help protect both the species and the beachgoers. The use of large hooks or hooks greater than an inch and a half in inside measurement, as well as wire and metal leaders and lines, is prohibited for recreational shore fishing, including from piers, as well as within 1,000 ft of shore.

Also, I think it’s important to remember that whenever you are entering the ocean, you’re entering their home. We can respect their home by swimming in groups, only swimming during the day and not at dusk and dawn when they’re more active, and avoiding murky waters, active fishing areas, and areas with seals and sea lions.

And give these animals the respect they deserve. And if you want to learn more about biogeographic barriers and lines in the ocean that animals can’t cross, you can check out one of my most popular videos right here. It’s always bothered me that we pronounce it February. Shouldn’t it be February? You said it would be very hard to say.