Article written by Kylie Marozsan.
On June 19, 2025 Monterey Bay National Marine Sanctuary’s research coordinator, Andrew DeVogelaere, spotted something strange in Moss Landing Harbor. There was a frenzy of brown pelicans and seagulls swarming above the water in the North Harbor area. Two days later there were thousands of dead anchovies along the shore in the harbor. This die-off is not likely from a harmful algal bloom or disease, because there were no signs of dead birds. Moreover, CeNCOOS data indicated toxic algae levels were low in the region. A more likely cause of the die off is one that has happened before: extremely high densities of anchovies in the confined harbor rapidly deplete the available oxygen in the north Moss Landing harbor waters, leading to suffocation for thousands of the anchovies.
Birds swarming water with dead anchovies. Photo: Andrew DeVogelaere, NOAA.
In the past, this kind of event has happened in both Santa Cruz Harbor in 2013 and Monterey Harbor in 2017 and 2024, but not recently at Moss Landing Harbor. In both Santa Cruz and Monterey harbors, aerators were placed in the water to replenish the levels of oxygen in the water to prevent die-offs. Anchovy die-offs in harbors were also recorded in 1964, 1974, 1980 and 1984, each causing the removal of up to 2,000 tons of fish. If anchovies escape the harbor, they are consumed by sea lions and birds, serving as a vital part of the food chain. It remains a mystery why the anchovies swim into the harbor in the first place. Some scientists suggest the anchovies made their way into the harbor by mistake, or were trying to escape predators.
Dead anchovies covering boat launch dock. Photo: Andrew DeVogelaere, NOAA.
With this many dead fish in one area, it is almost impossible to avoid the stench that comes along with it. For fishermen in the area, this die-off provides them with free bait to collect and use later. However for tourists, seen in the image below, the kayak businesses have to take a pause from launching in certain areas– many excursions for Elkhorn Slough begin nearby in Moss Landing. Although this is a sad and smelly sight to be around, this kind of die-off could mean that the Monterey Bay is healthy– giving humpback whales and sea lions plenty of food to feed on.
Thousands of dead anchovies blocking the kayak launch point. Photo: Andrew DeVogelaere, NOAA.
Click here to learn more about anchovies, or here, if you want to learn more about local anchovy harbor impact events.