Rare Abalone Die-off in Sonoma County

September 1, 2011

Question: I was diving in Sonoma County last weekend (Aug 28) in Fisk Mill Cove. The water was dirty as if there was a plankton bloom and visibility was only four to five feet. On my very first dive to about 12 feet I looked into a cave in the rocks with my light and saw something I’ve never seen before in 50 years of diving for abalone. There was an abalone laying upside down and clinging to a piece of kelp rather than clinging to a rock like usual. My dive partner told me he picked up two similar abalone on one dive. They were also in a rock cave just laying upside down on the rocks. Later we met two other divers who had been diving at Timber Cove the day before and they too came across a couple of abalone laying upside down on their shells among the rocks.

Have you heard or seen this before? Are these abalone dying? Is the plankton bloom doing something to the abs? Are the abs suffocating from the plankton bloom? Are the abalone ok to eat? (T. Yamashita)

Answer: What you observed last weekend in Sonoma County is a rare die off event and your observations are similar to many reports we’ve received from other abalone divers in the area. All of the reports mention abalone observed lying upside down on the bottom and the water a dark brown color with visibility less than a foot. Reports have come from Fort Ross State Park, Russian Gulch, Timber Cove and Salt Point State Park where the abalone are dying.

According to DFG Senior Marine Biologist Ian Taniguchi, these abalone deaths coincided with local phytoplankton blooms (red tide), accumulations of drift kelp and calm ocean conditions. Similar invertebrate die-offs have occurred along the North Coast in the past, typically inside protected coves and under similar ocean conditions. The abalone deaths may be due in part to the large phytoplankton bloom, but the investigation is still ongoing. While we don’t know exactly what’s causing the die-offs, we do know they are not due to Withering Foot Syndrome – a fatal disease found in some Southern California abalone.  Withering Foot Syndrome is specific to abalone (in this case, sea stars appear to be dying as well) and causes the abalone’s body to shrink (also not the case in this instance).

Large phytoplankton blooms can make some filter-feeding shellfish like mussels and clams toxic to humans and cause paralytic shellfish poisoning. Abalone are not filter-feeders though – they eat kelp and other seaweeds. At this time, the abalone season is still open and all harvest regulations remain in effect

The California Department Public Health (CDPH) is collecting samples of shellfish for analysis from the affected area and advises recreational consumers to be cautious and not consume seafood that may have been affected by the bloom. CDPH will post their analysis results as soon as they are available at http://www.cdph.ca.gov/programs/Pages/DDWEM.aspx.

I remember the smells of dead abs as u drove high way one. Even when fishing you could see dead abs getting swept by. 

Limpets and other snail relatives too... Dead critters all over the surf zone... Red tide sucks! Hope this passes soon. Last time it was horrible...