Green Sturgeon Carcass.
Photo Credit: @deantroi on iNaturalist
Quantifying the white and green sturgeon die-off resulting from the 2022 San Francisco Bay Area harmful algal bloom (HAB) event.​
​
864 sturgeon carcasses resulting from the historic 2022 HABs event of the Bay Area were identified using aggregated data from citizen scientist, agency and consultant sources. This number represents a minimum, since there are sections of coastline that could not be surveyed and carcasses may sink/decompose before reaching the shoreline.
Background
This is the largest HABs event that has affected the Bay Area to this degree in recorded history. Low flow from the estuary, warming water and nutrient loading prime the system for HABs, so we can expect more HAB events in the future with climate change playing a role. Learn more about what caused the sturgeon die-off below.
Photo Credit: Encyclopedia of Life (EOL)
Heterosigma akashiwo
What killed the fish was likely a combination of the toxicity of the algae, Heterosigma akashiwo, and the lower dissolved oxygen levels (DO).
​
We know the toxicity of the algae was a contributing factor, because the DO levels in the North Bay and Central Bay were not low enough to cause a sturgeon die-off on their own.
Lower O2 levels in South Bay and eutrophication
Over the summer water temperatures rise, which leads to less dissolved oxygen. Warm waters and low water flow also promote the growth of algae, such as Heterosigma akashiwo. Algae has a high turn-over rate and gets decomposed by bacteria when it dies. This decomposition absorbs oxygen from the water. The combined effects are deadly for aquatic life.