The difference between a dolphin and a shark is fairly significant when either could be sharing a shoreline with San Diego beachgoers.
When Claire Entrup from Kentucky arrived to the Mission Beach last week on their vacation to see a dark black fin with an ominous wave protruding from its sides, she decided to change her plans.
“Well we were going to go to the beach today, so I don't know about that anymore,” Entrup said. "We’re definitely a little hesitant about going to the beach.”
Lifeguards and fire officials last week closed portions of Mission Beach twice after they believed they saw a shark. On Wednesday, lifeguards closed the Children’s Pool in La Jolla after they saw a similar dorsal fin.
An hour after a tourist reported seeing a shark off Point Loma Thursday morning, lifeguards said they did not consider the report to be a confirmed shark sighting.
Experienced surfer Tom Lochtefeld was certain he saw a shark and not a dolphin on Friday in Mission Beach. He said he’s seen both – and this was definitely a shark.
A tourist’s pictures of a fin off the shore of Mission Beach last week leave room for question, though.
Shark expert Pete Klimley said the pictures are most likely of a dolphin, not a shark.
“If it were a white shark, the tail fin would stick out of the water, just as the dorsal fin did,” Klimley said in an email. “Furthermore, the shark would swim in a sinuous manner as it moves its tail back and forth.”
A dolphin’s flukes would be underwater – which is what the tourist’s picture showed.
However, Klimley said the outline of the body underwater is unusually long for a dolphin.
Other experts agree that it’s often difficult to tell just from seeing the dorsal fin.
“To an untrained eye it’s very easy to confuse the dorsal fin (the back fin) of a dolphin with that of a shark," said Andy Nosal, a PHD Student at Scripps Institution of Oceanography.
“Just the fact we're seeing more sharks in the water doesn't mean you should be changing your behavior, however it would still be a good idea to follow the lifeguard’s suggestions. If they close a beach, follow their instructions and don't go in the water there."