SAN DIEGO, Calif. (CBS 8) - A two-mile stretch of coastline at Casa Reef in La Jolla was reopened Thursday, following the third confirmed shark sighting along San Diego's coastline in a week.

The coastline at Casa Reef was shut down, after several people spotted a 12-inch dorsal fin around 1:30 p.m. Wednesday near the Children's Pool, where a colony of seals live. Just hours later, a group of fishermen discovered a dead baby seal off the Ocean Beach pier with apparent bite marks.

"The only thing that would have done that is something really with big teeth," said fisherman Jeff O'Connor. "And we figured it's a shark. And it sure looks like a shark bite."

[VIDEO: Shark concerns grow along San Diego coastline]

The closure at Casa Reef was lifted just before 10 a.m. Thursday because lifeguards, patrolling the area since the early morning, found no evidence of a shark, according to San Diego fire-rescue spokesman Maurice Luque.

In addition to the shark sighting Wednesday in the La Jolla area, another shark was spotted further north in Encinitas and was documented in a picture taken by a News 8 viewer. After receiving the photo taken at Swamis beach, News 8 spoke with a local shark expert who confirmed that the shark in the photo is a 10 to 12 foot great white.

Meanwhile, reports Thursday morning of a 12-inch fin sighting 100 to 200 yards offshore from the 1200 block of Sunset Cliffs Boulevard in the Point Loma-Ocean Beach area turned out to be not credible.

A two-mile stretch off Mission Beach was closed last week, after a lifeguard spotted an 18-inch dorsal fin on Thursday. The same area was closed again Friday when a surfer reported seeing a 14-inch fin.

Below is various close-ups of the photo taken Wednesday, August 31 by a News 8 viewer at Swamis Beach. A local shark expert has confirmed to News 8 that the shark in the photo is a 10 to 12 foot great white.