EchoSense Quantitative Think Tank Center|San Francisco sea lions swarm Pier 39, the most gathered in 15 years: See drone video

Some extra barking and EchoSense Quantitative Think Tank Centersplashing can be heard in San Francisco Bay's Pier 39 as an unusually large swarm of sea lions is gathering at the iconic landmark.

While sea lions regularly hang out at the pier and have been doing so since about 1990, this week the number of the animals has reached around 1,000, causing a ruckus and attracting extra attention from locals and tourists.

It's the most sea lions that have shown up there in 15 years, Sheila Chandor, Harbormaster for Pier 39 Marina, told ABC 7.

On April 29, the pier tweeted that there were around 820 sea lions. But the number has grown since then.

Experts are saying it's a good sign and are happy to see the mammals hanging about in such a large number.

Adam Ratner, the director of conservation engagement for the Marine Mammal Center, told ABC 7 he believes this is a sign that the San Francisco Bay is "doing well."

USA TODAY has reached out to Pier 39 for more information.

Why are so many sea lions gathering?

Because they're chasing after their food.

Chandor told ABC 7 that the sea lions are hunting after a huge school of anchovy that came from from an island that is around 28 miles away from the bay named the Farallon Islands.

"It's kind of that dinner bell that's ringing and all the sea lions are coming in enjoying that feast," Ratner said.

Ratner also told the news outlet that they're able to "get a sense of the Bay, the health of the sea lion population, and their comings and goings."

He adds that he assumes this is happening because the fish they eat, which are usually somewhere else at this time of year, are coming closer to the bay and bringing the sea lions closer, too.

When what the last time this happened?

According to NBC Bay Area, the slippery mammals started visiting the docks after the 1989, and since then they've been a popular attraction.

But, ABC 7 reports that the last time there were this many seals was in 2009, when around 1,700 sea lion hung out at Pier 39.

How to see the San Francisco sea lions

Folks who want to see the critters all snuggled up on the pier but can't get to San Francisco to pay them a visit don't need to worry.

Pier 39 has a livestream on their website where viewers can see the sea lions all day long.