Apparently, a winter vacation in the warm water off Baja was more enticing than another winter in the chilly ocean off Southern California.
For the first time in years, juvenile great whites sharks are resuming what has long been considered their normal migration pattern, traveling away from cool winter water that’s typical off the local coast in favor of something warmer, shark expert Chris Lowe said this week.
“When the temperatures drop, they start their southern migration,” said Lowe, who runs the Shark Lab at Cal State Long Beach.
That hasn’t been true in recent years, as El Niño conditions have boosted water temperatures off Southern California.
Lowe spent much of the past few years tagging juvenile great white sharks as they showed up in unprecedented numbers off the Southern California coastline. The local population boom, while scary for surfers and others, reflected a rebound for the ocean predator that experts said came after decades of protections for sharks and their food sources, including sea lions. What’s more, as sharks have hung out locally, there’s been a surge in a second food source — sting rays — that’s provided a close-to-shore buffet for shark pups.
During the El Nino period, from 2014 through 2016, juvenile sharks that typically leave the region during winter months stuck it out in Southern California, rotating between hot spots in the South Bay, Sunset and Surfside beaches, Long Beach, Dana Point and San Clemente.
“This year, so far, they are acting more like they did prior to El Niño,” Lowe said.
In addition to spooking surfers and other ocean enthusiasts, the shark sightings prompted lifeguards to post regular warnings and advisories, along with many beach closures. In some cases, the notices were the first shark-related closures of local beaches in decades.
Though Lowe and other experts have noted that young sharks have little interest in humans, the presence of so many great whites hasn’t been without incident.
In April, an estimated 10-foot shark nearly killed a woman swimming in the water off San Onofre State Beach while her boyfriend surfed. And in 2016 a woman who was training for a triathlon near the mouth of Newport Harbor was nearly killed following a shark encounter.
In recent weeks, Lowe and his graduate students have been downloading shark-related information from receivers that dot the waters off Southern California. The data suggests that many of the sharks they’ve tagged in the past two winters left the area, starting in October.
The tracking devices ping data into an estimated 120 receivers, sending ID numbers, times and dates. That data is how researchers learned that sharks were congregating at one beach for 40 to 50 days before venturing on to the next hot spot, sometimes making the trip in just a few hours.
The data indicated there were 16 sharks off Dana Point and San Clemente last summer. But as of a few weeks ago only four of those animals remained in the area.
Six sharks stayed in the water off Long Beach for much of the summer, and researchers tracked four of them as they visited Dana Point. Two eventually returned to Long Beach, while one left the area immediately and the other hung around until October before also disappearing, Lowe said. Of the six sharks tagged off Santa Barbara, only two remain.
There are 12 receivers off shore from Palos Verdes to Malibu that have yet to be analyzed.
Researchers won’t know for sure if the sharks that have vacated Southern California are all headed for Baja, their normal migration, until data is pulled from receivers in La Jolla. Those receivers are run by the Scripps Institute of Oceanography. A team in Mexico also will collect data from their receivers to see if the Southern California sharks made their way to that area.
“We’ll find out if any of the babies made it down there,” Lowe said. “We last detected those in October. That would be plenty of time for them to make it down there. Usually they don’t meander.”
Lowe said there is much basic information to learn about great whites. For example, it’s still not known where they typically give birth, though experts believe it’s usually in deeper waters. What is known is that pups are abandoned by their mothers and head to warm water, near coasts, to feed on sting rays.
The ocean off Baja is favorable for baby white sharks because the winter water temperature there typically runs about the same as the summer water temperature off Southern California. From what marine biologists understand, baby white sharks don’t like temperatures that get below 60 degrees. These young sharks also don’t like it too warm, leaving an area or moving to deeper, cooler water if the water gets higher than 84 degrees.
Another unknown it this: Whether or not bigger, juvenile sharks will leave Southern California or stick around.
Two animals in the 9- to 10-foot range tagged in South Bay five years ago have made four annual migrations to Baja and back. But as adult great whites they can withstand much cooler water and might opt to hang out in Southern California this winter, even if the El Niño condition abates and the winter water temperatures return to normal.
“Technically, they don’t have to leave,” Lowe said of the adult great whites. “Why they still do that, maybe it’s just a migratory pattern. It’s not that they have to, it’s that they want to. Maybe they are going to Baja because the winter feeding is better.”
Those same two sharks, when they reached about 3 years of age, traveled north to the Channel Islands and south to the Guadalupe Islands, according to their trackers.
Even as the migration starts to resume, some younger sharks seem to be remaining in Southern California. Lowe heard of a reported sighting just two days ago. And he wasn’t surprised to see video of an angler catching a shark off San Clemente Pier last week, noting that the shark looked to be between 1 and 2 years old.
“There are a few of them around,” Lowe said of the young-but-no-longer-pup-sized stragglers.
“It kind of makes sense, the bigger sharks can hold out a little longer.”
source: daily news