SANTA CRUZ -- The body arrived in a cooler, packed on blue ice.
The sea otter had washed up on Pismo Beach the day before, with shark bites sunk deep into its hips and back legs -- and scratches on its bones.
Melissa Miller, a Department of Fish and Wildlife veterinarian and wildlife pathologist, knew what killed the animal just by looking at it: Bacteria had infected its wounds, so it drowned. But she has found that otters often keep secrets, hiding serious diseases beneath the surface. So a postmortem exam was in order.
Miller runs something similar to an otter CSI at the Marine Wildlife Veterinary Care and Research Center. She mounts thin slices of brains and livers onto slides and peers into the microscope, looking for signatures of various maladies. And having worked 15 years at UC Santa Cruz's Long Marine Laboratory, she has found plenty.
"Fifty percent of the animals that are found dead have died of disease," said Steve Shimek, director of the Otter Project, an environmental nonprofit based in Monterey.
A high death toll keeps otters from rebounding back to historic levels.
Between 15,000 and 18,000 otters swam off California's coast before 18th- and 19th-century fur traders hunted the animals almost to extinction. Today, their numbers are closer to 2,800.
"That's fewer otters than kids in a big high school," despite their listing as threatened under the federal Endangered Species Act in 1977, Shimek said.
Since then, their numbers have mysteriously bobbed up and down. Miller's work has shown that otters are dying from a wide range of things, including unexpected threats that come from land.
Toxins from algal blooms in lakes, as well as microscopic organisms living in the feces of animals like cats and opossums, have begun to stream into the ocean with stormwater, poisoning otters and breeding disease.
Miller's small team of biologists and technicians catalog every dead otter that surfaces on California's beaches. In 2011, Miller's team recorded 300 otter deaths. In 2012, that number jumped about 10 percent, according to Brian Hatfield, a biologist at the U.S. Geological Survey in Menlo Park.
Detailed postmortem exams that look for the cause of death -- called necropsies -- are reserved for otters older than a year, which are dying in the greatest numbers.
The team used to slice open every dead animal, but declines in state funding have limited exams, Miller said. Now, every teenage or adult otter is placed on the metal operating table, no matter how it died.
"If he comes in with a knife sticking out of him, we're still going to do a necropsy" because some hidden disease could be at the root of the animal's death, Miller said.
Even if they don't kill outright, diseases can make otters more vulnerable to collisions with boats or attacks by sharks or humans. "Picture a person who is walking around on the street drunk," said Miller, comparing it to illnesses that can impair an otter's ability to find food or defend itself. "Doesn't it make sense that their risk of getting into some kind of trouble and trauma might be a little bit higher?"
Each exam takes two to three hours. Miller snaps full-body X-rays and records the length and weight of the animal. She pulls out brains, lungs and kidneys, placing them in plastic containers full of preservatives. The organs hold important clues.
Binders labeled "Dead Otter Fact Sheets" fill the shelves of Miller's lab -- one for every year she's been collecting information.
The otter found on Pismo Beach was No. 6,631, another in a long string of otters that have been tracked by the California Department of Fish and Wildlife since 1968.
Three large metal freezers, set to 80 degrees below zero, hummed in a nearby room. Inside was Miller's "cryo-zoo," a frozen array of otter parts: vials containing bits of brain, plastic bags full of pieces of liver and slices of heart tissue.
Studying these samples, Miller discovered new threats pouring in from land.
In 2007, 12 bright yellow dead otters arrived at the lab. Miller opened them up and found their livers swollen and bleeding. "The liver would just fall apart in my hand," she said.
All the symptoms pointed to a toxin called microsystin, which poisons the liver, brain and kidneys.
The toxin found its way inside otters through food. Otters eat creatures like mussels and clams, which filter pollutants from the water and stockpile them in their meat. Otters need to eat a quarter of their body weight in food every day and can gobble up a lot of these dangerous meals.
But the toxin is released by algae found in freshwater lakes and streams. It shouldn't have been in the ocean, nor was it known to affect otters. Miller didn't know if she was on the right track.
"I went back to previous years before 2007 and said, 'Anyone who has liver in the diagnosis, we'll pull the liver, scrape up the money, and we'll test them for microsystin,'" Miller recalled.
Thirty-one otters tested positive -- a dramatic number given the few otters that remain.
"That's like having 35 million Americans die,'' said Robert Ketley, water quality program manager in Watsonville.
Algal blooms often explode in spring and fall at Watsonville's Pinto Lake, carpeting the lake with green scum. "It's like the snot you'd get out of the Incredible Hulk," Ketley said.
Wetlands and dense vegetation used to act as a natural filtration system between the land and sea, removing pollutants. But over time those natural areas have been bulldozed and wetlands filled in. Stormwater may be driving toxins straight to the ocean.
Many agencies are working to manage stormwater runoff and keep toxins like microsystin out of the ocean, said Karen Worcester of the Central Coast Regional Quality Water Control Board. But pollutants still make it to the ocean, breeding a collection of mysterious diseases in otters.
Back at the lab, Miller stared at the heart of otter No. 6,631 under a microscope. Speckled orange and white, it showed the beginnings of heart failure, possibly triggered by pollution. It's something Miller wouldn't expect to see in otters in the prime of their lives, but it's common.
Now if she could only figure out what's causing it.
Contact Ryder Diaz at 408-920-5064. Follow him at Twitter.com/ryderkdiaz.