A recent influx of stranded, dead dolphins and whales along Central and Southern California beaches has prompted the National Oceanic & Atmospheric Administration to officially declare an “Unusual Mortality Event” in the region.

Over the past four weeks, at least 21 dolphins and whales have washed up onto the beaches between San Luis Obispo and Los Angeles. In order to garner both attention and resources for the investigation of the situation, the NOAA Fisheries’ Office of Protected Resources officially deemed the situation a UME last week, which is defined under the Marine Mammal Protection Act as “a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.”

Michelle Berman, Assistant Curator of Vertebrate Zoology at the Santa Barbara Museum of Natural History, said the UME designation should open up funding for more comprehensive analysis of tissue samples from the beached mammals, which will help researchers determine the cause of the recent whale and dolphin deaths.

Local scientists first noticed the unusually high levels of cetacean stranding early this spring. April brought the highest concentrations of marine mammal fatalities in one month – including the occurrence of a dead sperm whale washing up on a Del Playa beach. It was during this period that Berman initiated the movement for official recognition of the situation.

“We were finding almost one [dead or stranded] dolphin or whale every day, which is unusually high for this area, though the numbers have since tapered off,” she said.

Although Berman said the cause of the high levels of stranding is not yet known, she and her colleagues said they have theories about possible contributing factors.

One potential culprit is an increase in the levels of domoic acid in the affected regions, Berman said. The toxin, which is excreted by certain fish and shellfish that feed on phytoplankton, has been shown to cause seizures and tremors in marine mammals, according to Berman.

Berman said it is essential for researchers to examine all possible conclusions to avoid overlooking other possible causes.

“It is important that we understand unusual marine mammal mortality events because they can serve a barometer of ocean health, and marine mammals can serves as sentinels of human health,” Berman said in a recent press release.

According to the NOAA records, the last UMEs in this region were declared in 2002 and 1998, and were both later attributed to local biotoxins.