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PREVIOUSLY: 

• Dead Humpback Whale Found on Mad River Beach
• Another Dead Humpback Whale Found on Humboldt Beach

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Staff with Cal Poly Humboldt’s Marine Mammal Research and Education Program are still investigating the deaths of two humpback whales that washed ashore on two local beaches over the past two weeks. 

While the cause of death for each whale has yet to be determined, external and internal examinations revealed that both — a subadult male found on Mad River Beach on July 3 and an adult female found on Centerville Beach on July 11 — were in “advanced stages of decomposition” when they were evaluated by university and North Coast Marine Mammal Center staff.

“Both whales … were resting on their backs, limiting our ability to determine the cause of death through external examination,” Allison Lui, stranding coordinator for the university’s Marine Mammal Stranding Program, told the Outpost via email. “An internal examination of the female whale also confirmed advanced decomposition of the internal tissues, further limiting our ability to identify a cause of death.”

“Whale strandings can result from a variety of natural and human-related factors, and it is often not possible to determine a definitive cause of death, particularly when animals are in advanced stages of decomposition,” she added. “While samples are collected for testing, decomposition may reduce their diagnostic value.”

Lui acknowledged that it is “somewhat unusual” for two humpback whales to wash ashore in such a short timeframe but said local researchers typically respond to “one to two” humpback whale strandings each year. 

“Although every stranding is important and evaluated when possible, humpback whale strandings do occur periodically along the California coast,” she said. “Seasonally, we typically see more humpback whales along the North Coast during the summer and fall as they return to productive coastal feeding grounds.” 

This most recent whale stranding marks the fourth humpback whale death on the California coast since the beginning of June. Scientists with the UC Santa Cruz Marine Mammal Stranding Network conducted necropsies on two whales found on the central coast last month and identified domoic acid, a marine biotoxin associated with harmful algal blooms, in both samples. 

One whale, located near Sunset Beach in Santa Cruz County, had “particularly high levels” of domoic acid, indicating the toxin played a “significant role in its death.” The other whale, local to the Pacific Grove area of Monterey County, had lower levels of domoic acid, but scientists believe the toxin still contributed to its death. 

Cal Poly Humboldt scientists are still awaiting test results for two whales found on the North Coast. 

As a reminder, if you find a dead or stranded marine mammal on a local beach, contact Cal Poly Humboldt’s Marine Mammal Stranding Program at (707) 826-3650 or marinemammals@humboldt.edu. Researchers encourage residents to photograph and document animals, but please remember to keep a safe distance.

Injured or sick stranded marine mammals can also be reported to the North Coast Marine Mammal Center at (707) 951-4722.