NOAA Suspects Toxic Algal Bloom Causing Dolphin, Sea Lion Deaths

An aerial view of a large harmful algal bloom in Lake Erie. File photo: NOAA Great Lakes Environmental Research Laboratory.

NOAA Fisheries biologists say harmful algae growing rapidly along parts of the coast of Southern California is believed to be the culprit in the deaths of hundreds of sea lions and nearly 60 dolphins in early June.

Reports fielded by the Channel Islands Marine & Wildlife Institute show more than 1,000 incidents of sick and dead marine mammals from June 8-14, Ruth Dover, co-founder and managing director of the institute, said.

The institute, which serves Santa Barbara and Ventura counties is part of the West Coast Marine Mammal Stranding Network, which is coordinated by NOAA Fisheries and responds to live marine mammal strandings in both counties.

Dover said the institute had been receiving over 200 reports a day of marine mammals in distress and was doing its best to keep up with the intense pace.

Researchers explained that the rapid growth of the algae Pseudo-nitzschia causes production of a neurotoxin called domoic acid. As the toxin is transferred into the marine food, web animal strandings occur.

Seabirds and marine mammals, such as sea lions and dolphins, ingest the toxin when they eat affected prey.

While domoic acid only affects humans if they consume it in contaminated foods, it can cause seizures, brain damage and death in marine mammals.

Stranding responders said they believe domoic acid is the reason for marine mammals’ deaths, given the neurological symptoms exhibited in the animals. They have collected tissue samples for testing to confirm the connection between the domoic acid.

Forecasts provided by NOAA CoastWatch and the Southern California Coastal Ocean Observing System showed high concentrations of domoic acid from Orange County north to San Luis Obispo County, with concentrations especially high around Santa Barbara and Ventura counties.

Michelle Berman Kowalewski, founder and director of the Channel Islands Cetacean Research Unit, said in her 20 years of responding to strandings she had never seen anything this intense in terms of the number of animals affected.

The research unit, which is also part of the Marine Mammal Stranding Network, examines and collects samples from dead dolphins and whales in Ventura, Santa Barbara and San Luis Obispo counties. Several of the affected dolphins and many sea lions were pregnant females, Kowalewski said.

NOAA Fisheries notes that seasonal outbreaks of domoic acid poisoning are common along the California coastline, and that ocean conditions favoring algae sometimes lead to more widespread outbreaks, which can involve hundreds of animals.

Finfish, shellfish and crustaceans are regularly tested for domoic acid, which in people can cause Amnesic Shellfish Poisoning.

This year, the spread of domoic acid appears to have included more offshore areas. Dolphins reflect an even further offshore distribution, said Justin Viezbicke, California Stranding Coordinator in NOAA Fisheries’ West Coast Region, particularly since the nearshore sampling sites are not indicating blooms of Pseudo-nitzschia, according to the Southern California Coastal Ocean Observing System Harmful Algal Bloom Mapping and Alert Program.