A disturbingly high number of sea lion pups are becoming stranded along the Californian coast this year, worrying experts who can only speculate as to why these animals are not with their mothers during what is normally a safe and essential nursing period.

According to the San Francisco Chronicle, one of the first to break the story, rescuers from San Diego to San Francisco have already rescued a stunning 250 emaciated pups.

Most of these animals are only seven months old and would normally be nursing with their mothers in the Channel Islands, along the Mexican coastline, or on a number of small eastern Pacific islands. Instead, they are winding up along the US West Coast, and no one knows why.

Experts at the Marine Mammal Center (MMC) in Sausalito, within the Golden Gate National Parks, recently reported that this is the third year in a row where they are seeing an unusual number of sea lion strandings.

Normally, some pups wind up along western shores simply because curiosity got the better of them. Other times, their mothers never returned with food. Desperate and hungry, these inexperienced swimmers will slip into the ocean only to be pulled along by north-bound Pacific currents.

Volunteers and experts alike would rescue these animals and nurse them back to help, but starting in 2013, things took a surprising turn. Starving and dehydrated pups started showing up on Californian beaches en masse, with 542 of the animals seen in Los Angeles alone over the course of the year. That's compared to the year before, which only saw 156 wayward pups. The NOAA quickly declared it an "unusual mortality event," which persisted into 2014.

Now, according to Bay City News, the MMC has already rescued 120 pups in the first five or six weeks of 2015. Last year the center didn't treat 100 pups until April.

Still, it's important to note that despite these die-offs, the NOAA estimates that Pacific sea lions boast a population hovering around 300,000.

Justin Viezbicke, the stranding network coordinator for NOAA Fisheries in California, suggested to the Chronicle that the mysterious cause of these stranding may simply be that the animals have hit a natural ceiling. The harsh reality may be that there just isn't enough food or habitat left to support so many pups.

"These animals are a puzzle piece for us," Viezbicke said.

He added that his agency won't rule out that the die-offs could be tied to a potential sustainability problem, but it could also just be nature taking its course.

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