After surfers photographed Tuesday morning, lifeguards contacted the Shark Research Committee to confirm the fin belonged to a shark and estimate its size.
Ralph Collier, the committee’s founder and president, determined it was a 16- to 18-foot-long great white shark that could weigh up to 5,000 pounds.
“That shark could be off Long Beach or it could have went south to Baja, or it could be in the same place,” he said. “When you’re that big, you can go wherever you want to go.”
The research committee documents attacks, sightings and other incidents.
Since 2007, there have been nine incidents in Imperial Beach, from dead mammals who washed ashore with shark bites to a surfers or swimmers who had encounters.
The last time there was a shark attack in Imperial Beach was in the 1950s.
Last week, Collier met with San Diego lifeguards, representatives from federal agencies, advocacy groups like Surfline and academics to enroll them in an effort to help increase reports of shark sightings and incidents.
It can be difficult tracking the movement of an animal that moves constantly, but with the public’s help, research may be able to make it safer to coexist with great white sharks, who accounted for nearly 90 percent of attacks along North America’s Pacific coast in the 20th century.
Pictures are most effective. To report an incident, visit the Shark Research Committee website.
If signs of a shark’s presence are found over the course of a few days, the committee can deploy a team to try and find and tag the shark.
Once a shark’s movements are tracked with GPS tags, he said, collected data may be help accurately define migratory patterns and better predict when sharks will be in an area.
In 2008, David Martin of Solana Beach was killed by a great white shark. A day later Collier said he received three reports of dead seals in the area. Had he received reports of dead seals earlier, that information could have been passed on to local lifeguards or warn the public to be on alert.
Shark Encounter Tips
Overall, Collier said sharks aren’t all that interested in people. Along the Pacific coast of North America in the 20th century, 108 unprovoked shark attacks were reported.
In California last year, eight shark attacks were reported, none of them fatal.
“Except for one person who was bitten on the arm and neck, most of them walked away with no injuries at all,” he said.
But it goes without saying that great white sharks can be dangerous.
Collier remembers the humbling experience of coming close to a 17-foot great white in the water:
“You realize that if this thing wants to eat me, there is absolutely nothing I can do to stop it,” he said. “That really puts you in your place in the environment as far as the food chain goes.”
To avoid being attacked by a great white shark, he recommends:
Tip 1: Stay calm
Keep the shark in your eyesight, and slowly move to a safe area.
“If you keep calm, nine times out of 10 nothing will ever happen,” Collier said.
Tip 2: Don't panic
Sharks can hear, sense pressures waves in the water and have eyes like humans.
“Usually the reason they’re coming in is investigation. They don’t know what the hell you are and they want to see.
“Do not start thrashing and screaming because you could replicate an injured animal to a shark that might not know who you are,” he said.
Tip 3: Avoid low-visibility water
In cloudy, unclear water a shark can mistake you for something else.
In clear water a shark can typically discern distinct shapes.
“That a shark would mistake a diver for a seal is highly unlikely,” he said.
Tip 4: Be aware of your surroundings
Be cautious and make intelligent decisions. Before the shark was spotted off the shore in Imperial Beach, witnesses reported that gray whales and dolphins in the area quickly scattered.
“When a big school of fish jump out of the water, you should be alert to the fact that something is chasing them,” he said. They may be trying to avoid a predator.
Some other useful information based on attacks that occurred in the 20th century:
- Attacks most often occur between 9 a.m. and 6 p.m.
- Surfers and divers are most likely attacked, as opposed to kayakers or swimmers.
- Attacks most often occur in August, September and October.
Top of the food chain
The other purpose of the committee’s work to track sharks is to identify areas where conservation efforts can be concentrated in the future.
Collier said humans need to ensure populations of great white predators stay healthy in order to avoid an imbalance in the food chain and breakdown of the ecosystem “like a set of dominoes.”
Shark populations are in decline.
When Collier began his research in the 1960s, he helped conduct an experiment on Catalina Island. Two hundred baited hooks were put out for four hours and 194 sharks were caught.
When the same experiment was done again 1997 over the span of 24 hours, six sharks were caught.
According to the Pew Charitable Trusts, 73 million sharks are killed every year.
“You can’t take that many sharks out of the ocean and not have an effect on it,” Collier said. “And if we aren’t careful, it can be extremely detrimental to us as a species.”