Harmful Algal Blooms Linked to Deaths of Northern Fur Seals in the Southeast Bering Sea

Testing confirmed widespread exposure of saxitoxin in marine mammals and other wildlife. In the study, researchers collected and analyzed data from 10 dead northern fur seals and hundreds of dead, mostly benthic, fish that washed ashore on a popular beachcombing beach on St. Paul Island in August 2024.

AI Comment from GPT 4.1:

The confirmed link between harmful algal blooms and northern fur seal deaths on St. Paul Island comes amid a broader context of unexplained or unusual marine mammal mortality events across the North Pacific and Arctic regions. Several related posts document mass seal deaths with various hypothesized causes—such as toxins, disease (including avian influenza and distemper), and environmental stressors linked to warming climates. For example, past die-off events in Alaska and Russia have sometimes been tied to algal blooms or toxic exposure (Death of Sea Life Off Russia Peninsula 'Caused By Algae'), but in other cases, viral infections or unknown causes were suspected (Bird flu confirmed in 2 ringed seals near Resolute Bay, Nunavut; Mystery mass death of seals on remote, uninhabited Siberian island under investigation). Research has also highlighted the vulnerability of marine mammals to rapid Arctic warming, with trends of declining seal health and shifting food webs in the Bering Sea (Study links Alaska seals' waning health to warming Arctic). Notably, previous increases in seal strandings and deaths in Alaska have been considered unusual mortality events, with some investigations considering harmful algal blooms as one of several possible factors (NOAA sees dramatic increase of ice seal deaths in Bering and Chukchi seas; Feds declare unusual mortality event for three ice seal species). However, the current report stands out by providing clear, direct evidence of widespread saxitoxin exposure throughout the food web, identifying the algal species responsible, and confirming a link between warming trends, harmful algal blooms, and marine mammal mortality in this region. Together with earlier observations, this post adds to a growing body of evidence that climate-driven ecosystem changes—including more frequent harmful algal blooms—are increasing the risks faced by northern fur seals and other marine wildlife in the Bering Sea and surrounding waters.