On a partly cloudy day in late July, a drone takes off from the sand at Marina State Beach and buzzes out over the dark water. Flying the drone is Dylan Moran, a lab technician in the Ocean Predator Ecology Lab at Cal State Monterey Bay. For the last two years, he’s surveyed parts of the coast off Marina and Aptos by drone to keep tabs on the number of juvenile white sharks in the area.
Historically, the range of juvenile white sharks didn’t reach Northern California. But over the last 10 years, they have been spotted in droves in certain pockets of Monterey Bay, including near Aptos and Marina.
Moran and his colleagues start patrolling the shores in the spring, when the water becomes warm enough for the young sharks.
“What we believe they're looking for is going to be these micro habitats that are going to be warm pockets of water,” Moran said. “And we think they're targeting those for the fact that the surrounding bay is too cold for them. They want to find areas that are thermally suitable.”
Moran said he almost always sees at least one shark during his spring and summer drone surveys. But on this particular July day, the drone didn’t pick up anything.
“My prediction is the water is also a little bit cooler, which tends to drive the sharks away,” Moran said.
But that bucks the overall trend. Oceans are warming due to climate change, including in Monterey Bay. That’s why there are so many juvenile white sharks here these days. It’s a recent phenomenon though.
“The nursery area for white sharks really has been in Southern California and northern Baja. But this all changed in 2014, when we really began to experience a lot of warming in the ocean,” said Salvador Jorgensen, who leads the Ocean Predator Ecology Lab.
Jorgensen has studied juvenile sharks in Monterey Bay for the past decade. Since 2014, many species, including white sharks, have been leaving their traditional ranges and pushing away from the equator to find cooler temperatures. Monterey Bay was previously too cold for juvenile white sharks, but not anymore.
“If you bring in a whole bunch of new predators to an area, you're likely to see some changes in the ecosystem that maybe you didn't expect,” Jorgensen said.
For example, the southern sea otter — an endangered species whose population has been slowly recovering — has seen its recovery stalled in recent years. That’s due to one key factor, according to Jorgensen.
“What's stalling the population from growing is shark bites,” he said.
Until the early 2000s, shark bites accounted for a very small percentage of southern sea otter deaths, according to Mike Harris, senior environmental scientist at the California Department of Fish and Wildlife. Today, in cases where trauma is involved, shark bites account for over half of all otter deaths.
The consensus among otter and shark researchers alike is that it’s a case of mistaken identity.
“All of these interactions, whether it's juvenile, subadult or adult white shark that are biting otters, it's an investigative bite,” Harris said. “We have zero evidence of consumption of any case we've ever recovered.”
In other words, these sharks don’t even want to bite otters. What happens is they think the otters are blubbery seals, take one bite, are met with a mouth full of fur and swim off.
Jorgensen thinks juvenile sharks could be responsible for many of these bites, because they are at an age where their prey is changing from animals like fishes and rays to marine mammals.
“During that transition, they're a little bit naive to what their prey should look like. And so every year you have a new crop of maturing sharks, and it's possible that these are the ones that are making the mistakes over and over,” Jorgensen said.
For endangered sea otters, the mistakes are costly. Yet, because it seems like the sharks are here to stay, otter researchers like Harris are focusing their attention elsewhere.
“There's nothing we're going to do about it,” Harris said. “So let's focus our efforts on those sources of mortality that we know we can have some impact on.”
