Rescue centers are struggling to cope with a mystery surge in the numbers of starving sea lion pups which have washed up on Californian shores since January. More than 1,100 starving and sick pups have been rescued from California's beaches, as well as public bathrooms, behind buildings and along railroad tracks since the beginning of the year. The number is almost five times higher than the 250 pups which would usually be expected in the key monitoring period between January and April - and no one knows why. Scroll down for video . Crisis: More than 1,100 sick or starving sea lion pups have washed up on Californian shores this year . Surge: Rescuers usually only expect to see about 250 in the same period, and so volunteers like BrennanSlavik (pictured) have been helping save the pups, like this one on Laguna Beach . Rescue: At SeaWorld, in San Diego, the sea lion show has been suspended and two temporary pools have been dedicated to housing pups like this one, in the hope they can be saved . It's not unusual to have some sea lions wash up each spring as the pups leave their mothers, but Keith A. Matassa, executive director at the Pacific Marine Mammal Center, said they started getting calls in December. His center, in Laguna Beach, is currently rehabilitating 115 sea lion pups. On a recent day, over the course of two hours, five suffering animals came in. One was brought in by a police officer, three more came in with an animal control team and the fifth was called in by a couple walking along beach. The last pup, at almost a year old, weighed just 23 pounds - a third of what it should have. It was so ill, staff had no choice but to put it down. Matassa explained pups that should be gaining 20 to 40 pounds in a two-month period have put on just two pounds. 'These animals are coming in really desperate. They're at the end of life. They're in a crisis ... and not all animals are going to make it,' he said. Feeding: Once rescued, pups who are healthy enough to be saved are fed formula to help them put on weight . Volunteer: Brennan Slavik carries a just-rescued sea lion pup into a holding pen after feeding it . Surgery: Dr Todd Schmitt, center, and veterinarian technician Jen Rego, right, prepare an injured sea lion for eye surgery at SeaWorld's Animal Rescue Center, in San Diego . An hour down the coast, the situation is so bad that SeaWorld, in San Diego, suspended its sea lion show so it can focus on rescue efforts. The theme park has treated 400 pups - more than twice the number it would care for in a typical year - and constructed two temporary pools to house them. Scientists aren't sure what's causing the crisis, but suspect that warmer waters from this winter's mild El Nino weather pattern are impacting the sea lion birthing grounds along the Channel Islands off the Southern California coast. The warm water is likely pushing prime sea lion foods - market squid, sardines and anchovies - further north, forcing the mothers to abandon their pups for up to eight days at a time in search of sustenance. Dying: A starving pup, weighing a third of what it should have done, looks out from a playpen at the Pacific Mammal Center. It later had to be put down, so weak it could not be saved . Stronger: Once pups get stronger, they graduate from formula to whole fish, and are playfully called 'feeders' while those that can once more compete for fish tossed into a pool are called 'fighters.' Washed up: Pups have been found in public washrooms, behind buildings and on railway tracks . The pups, scientists believe, are weaning themselves early out of desperation and setting out on their own despite being underweight and ill-prepared to hunt. 'They're leaving with a very low tank of gas and when they get over here, they're showing up on the beach basically ... starving to death,' said Justin Viezbicke, a coordinator with the National Oceanic and Atmospheric Administration's California Stranding Network. For rescue centers like Pacific Marine Mammal, that translates into round-the-clock, back-breaking work for dozens of volunteers who've arrived from all over the U.S. to help. The center in one of Southern California's premiere beach communities has rescued more than 213 pups since the beginning of the year and has treated ones that weighed as little as 14 pounds at eight-months-old. Volunteers have been arriving from all over the U.S. to help with the escalating crisis. Crates holding animals awaiting assessment are crammed into every corner, including the laundry room, as those already housed in communal pens barked and bleated in a deafening racket as mealtime approached. Warming: The surge could be down to rising sea temperatures, pushing the sea lion's normal food north . Listed: The names of the rescued sea lion pups at the Pacific Marine Mammal Center . Overwhelmed: The Pacific Marine Mammal Center currently has 115 sea lion pups - far more than usual . Release: They hope to get them healthy enough to set free, tracking some to monitor their progress . Each incoming pup has its temperature taken and is weighed, measured and given a blood sugar test before the team decides if they can save it. Most of them are so weak they barely resist. Those that make the cut are tube-fed a gruel of pureed herring, Pedialyte, vitamins and milk three or four times a day after starting out with a simple broth of hydrating fluids and dextrose. Those that graduate to whole fish are playfully called 'feeders' and those that can once more compete for fish tossed into a pool are called 'fighters.' The goal is to get the pups strong enough to swim free again - but the volunteers who nurse them back to health may never know if they make it in the wild. Only a handful will be fitted with expensive tracking devices. The rest are tagged with a number and fall off the radar unless they are rescued again. 'The tricky part is we're putting them back into the same environment that they just came from. And that's going to be a challenge for them,' Viezbicke said.
More than 1,100 starving or sick sea lion pups rescued  since January . Rescue centers would usually expect to only see about 250 in the period . Situation so dire California's SeaWorld has suspended its sea lion show . Famous attraction treating 400 pups in two specially constructed pools . Rising sea temperatures could be one cause of the surge in numbers .