Bellwethers of Change: What We Can Learn from Humpback Whales in Hawaiʻi
March 19, 2026
The idiom “canary in a coal mine” comes from an old mining practice, where canaries served as early warning signs of danger long before people could sense anything was wrong. Today, the expression is used more broadly to describe species that signal shifts in their environment. Marine mammals such as humpback whales are often referred to as “sentinel species” and serve a similar role in the ocean. Their health, behavior, and abundance can offer early clues about changing conditions in ocean environments, helping scientists understand when something is out of balance.
Whale Presence in Hawaiʻi
For more than 20 years, NOAA staff have studied humpback whales—known in Hawaiʻi as koholā—across the Hawaiian Islands. Using vessel surveys, shoreline sightings, fluke identification, and acoustic monitoring, NOAA staff have catalogued changes in koholā presence in Hawaiʻi and contributed to collaborative efforts assessing population trends across the North Pacific Ocean. Following the end of commercial whaling in 1986, Hawaiʻi’s humpback whale populations entered a prolonged period of recovery, growing rapidly over 35 years. Over the past decade, however, the population has declined from a peak of approximately 33,000 whales in 2012 to an estimated 26,000 in 2021.
While no one knows exactly what happened to the approximately 6,700 koholā unaccounted for in the Hawaiʻi population in 2019, scientists believe this precipitous drop in numbers may be linked to a major marine heatwave between 2014 and 2018, when ocean temperatures in the North Pacific rose by as much as 7 degrees Fahrenheit above average.
Nicknamed “The Blob,” this major warm water anomaly disrupted the marine ecosystem with devastating effects. Researchers saw a significant decline in phytoplankton—microscopic organisms that serve as the base of the food web. That, in turn, reduced food availability and affected the predators that depend on them. The widespread impacts ranged from reduced juvenile salmon survival and lower adult salmon returns, to altered migration and spawning patterns across many fish species. The disruption also contributed to the largest seabird mortality event in modern history, with an estimated 4 million common murres dying, primarily due to a collapse in the marine food web. While the impacts on humpback whales were not as straightforward, many scientists suspect whales were similarly affected by reduced prey availability. The lack of adequate food resources may have led to mortality and reduced energy reserves, preventing some whales from completing their full migration or migrating at all during those years. In turn, this may have reduced some whales' ability to reproduce over multiple seasons.
Additional impacts from the 2014-2018 marine heatwave included a significant reduction in calf presence, more sightings of “skinny” or otherwise unhealthy whales, increased stranding events, the use of different habitats and novel food resources, and the absence of individuals that previously showed strong fidelity to specific feeding grounds. NOAA’s Hawaiian Islands Humpback Whale National Marine Sanctuary scientists recorded significantly fewer koholā between 2016 and 2018 within breeding grounds for the Hawaiʻi population. While there has been some recovery since then, the Hawaiʻi population has not returned to pre-heatwave levels. Looking forward, marine heatwaves are expected to increase in size and frequency. Scientists are concerned that this may reduce the resilience of whale populations and limit their ability to fully recover between disturbances, potentially leading to a long-term decline in humpback whale abundance.
Our challenge as managers of this marine protected area established to safeguard koholā and their habitat, is understanding and reducing pressures on humpback whales to support their long-term recovery and resilience in the face of an uncertain future.
Collaborative Conservation
Hawaiian Islands Humpback Whale National Marine Sanctuary plays a vital role in marine conservation through its focus on koholā and their habitat. This approach involves research and monitoring that deepen understanding of the species’ ecological, economic, and cultural importance in Hawai‘i. The sanctuary also serves as a central coordinating force, building and sustaining a collaborative network of partners dedicated to the whales’ survival.
The sanctuary relies on the on-water community and NOAA line offices, such as the National Marine Fisheries Service, to help monitor koholā and their habitat, identify whales in distress, and report them for emergency response. NOAA Fisheries conducts marine mammal assessments and analyzes population trends to help inform and evaluate conservation measures in and around the sanctuary. The Large Whale Entanglement Response Network is a collaboration that includes researchers, tour operations, fishers, and even the general public that support monitoring animals in their natural habitat.
Working together, we use a number of coordinated survey methods to estimate how the Hawaiʻi population of koholā are changing over time.
Vessel Surveys and Shoreline Sightings
Researchers and citizen scientists contribute to population assessments by counting and noting whale presence and behavior. Each year, NOAA conducts several vessel surveys to record humpback whale sightings throughout the Hawaiian Archipelago. These surveys help NOAA provide estimates of whale abundance across multiple years. In addition, locals and visitors participate in the annual Sanctuary Ocean Count and Pacific Whale Foundation’s Great Whale Count to monitor koholā from coastlines across the islands and provide a snapshot of shoreline sightings.
Fluke Identification
Scientists and whale watchers can submit their photos of whale flukes to HappyWhale.com, which utilizes scientific expertise and artificial intelligence-based automated image recognition to identify individual humpback whales, helping researchers monitor the animals over time and space. The algorithm uses the shape, pattern, and other features of a whale’s tail to identify matches and recurring sightings, helping scientists understand movement and habitat use, survivorship, and even population estimates.
Acoustic Monitoring
NOAA’s Office of National Marine Sanctuaries maintains a nationally-coordinated underwater sound monitoring network across the National Marine Sanctuary System. In Hawai‘i, acoustic monitoring is used to record the structured singing activity of whales to identify trends in their migration patterns and population abundance. By combining sound data with other observations, scientists can better understand population trends over time.
The sanctuary's commitment to working with partners fosters a conservation model that blends academic research, community science, Traditional Ecological Knowledge, and local community engagement to identify and validate ecological trends while building support for effective ocean management. The sanctuary could not fulfill its mission without all of its partners who are working to understand and protect koholā during this unprecedented era of change.
A Shared Future: Sanctuaries and Beyond
Humpback whales face a growing number of external pressures, including vessel strikes, entanglement in marine debris, noise pollution, limited food resources, and changing environmental conditions around the world. Despite these challenges, they still migrate thousands of miles each year, connecting distant feeding and breeding habitats. This oceanic interconnectedness means we must work together to safeguard humpback whales not only within sanctuary boundaries, but throughout their migratory range—from Alaska to the Hawaiian Archipelago—to ensure they have adequate food and safe places to rest and reproduce.
A thriving humpback whale population is essential to a healthy ocean. Their migrations and presence contribute to the productivity of marine ecosystems and support the livelihoods, cultures, and well-being of countless communities across the Pacific. The recent decline in Hawaiʻi’s humpback whale numbers is a powerful reminder that the fate of these incredible creatures is inextricably linked to our own. It will take all of us working together across the ocean to ensure these majestic animals survive for future generations of koholā and people.
Catherine Takata-Tonini is a policy and planning specialist with the Office of National Marine Sanctuaries Pacific Islands Region
Rachel Plunkett is the content manager and senior writer/editor for NOAA’s Office of National Marine Sanctuaries