Researchers counting humpback whales from a shore station above Kawaihae Bay saw 60% fewer whales in 2016 than in 2015, and calves were 1.1% of the whales they counted that year. A 2024 population study puts the loss in Hawaiʻi at 34% between 2013 and 2021. The studies on this page tie the drop to a marine heatwave that cut the food supply on the whales’ North Pacific feeding grounds.
We chart the Ocean Count island averages alongside what the studies and NOAA reports measured. Full citations and summaries for every study are on our research page.
How many humpback whales Hawaiʻi lost, 2013–2021
The broadest estimate comes from “Bellwethers of change” (Cheeseman et al., 2024), which matched fluke photographs of individual whales from 46 organizations and 4,292 community contributors. Across the North Pacific, the estimate grew from 16,875 whales in 2002 to 33,488 in 2012, then fell about 20% to 26,662 by 2021.
The authors found the decline most evident among whales wintering in Hawaiʻi. The Hawaiʻi estimate peaked at 18,728 whales in 2013 and was 12,294 in 2021, down 34% and back to the level of 2006. Whales that winter off mainland Mexico showed no decline over the same years. The authors measured a fall of 4.3% a year in Hawaiʻi from 2014 to 2021.
These are estimates with error margins, built by matching whales photographed in Hawaiʻi in winter with whales photographed on the feeding grounds off northern British Columbia and Southeast Alaska. The paper’s Hawaiʻi table gives a standard error of 1,914 whales for 2013 and 492 for 2021.
What the Kohala shore scans showed, 2001–2019
The Hawaiʻi Marine Mammal Consortium (HMMC) scanned Kawaihae Bay from the same shore station every winter from 2001 through at least 2023, with the study’s authors as the observers. Frankel et al. (2022) analyzed 19 years of those scans. Counts rose from 2001, peaked in 2010 at an average of 34 whales per scan, and swung more widely from 2010 to 2015. After 2015 the average fell to 13.1 whales per scan for 2016–2019.
Calves dropped faster than the overall count. Calves made up 6.5% of the whales counted in an average year from 2001 to 2015, and 2.1% in 2016–2019. HMMC’s newsletters put the calf share at 7.6% in 2021, and report lower calf counts again in 2022 and 2023. Our research page lists each season’s whale and calf totals from the newsletters.
Other signs of the drop in Hawaiʻi waters
In November 2018, the sanctuary and NOAA Fisheries gathered whale researchers in Honolulu to compare data. Pacific Whale Foundation’s boat transects off Maui found 54.6% fewer whales in 2015–2016 than in 2012–2013. Underwater recorders at five sites around Maui measured monthly male song chorusing levels up to more than 6 decibels lower from the 2014–2015 season on, which points to fewer singing males. Cartwright et al. (2019), working from boats in Maui’s ʻAuʻau Channel, found mother and calf encounter rates down 76.5% between 2013 and 2018.
Volunteer counts fell too. The sanctuary compared Ocean Count sightings off Kauaʻi for the three seasons before and after 2016 and found 37.3% fewer. Maui’s Great Whale Count recorded 64.5% fewer whales and 37.4% fewer calves in 2018 than in 2015.
The northeast Pacific marine heatwave as the likely cause
From late 2013, the largest marine heatwave on record spread across the northeast Pacific. NOAA’s sanctuary office puts the warming at up to 7°F above average. Phytoplankton declined, and with it the zooplankton and forage fish that humpbacks feed on in summer. Researchers in Alaska reported thin whales and few calves, and HMMC saw more emaciated whales off Kohala in 2016.
Frankel et al. found that whale numbers off Kohala tracked the Pacific Decadal Oscillation, a North Pacific climate pattern, with a lag of about 18 months. Cool, productive summers on the feeding grounds were followed by more whales off Kohala. Their reading is that whales in poor condition skipped the migration, and that females did not have the reserves to carry a calf.
The Cheeseman team attributes the decline to a decrease in carrying capacity, the number of whales the food supply can support, triggered by rapid climate change. Researchers at the 2018 meeting also listed other explanations to test: whales shifting to other breeding areas, human impacts such as entanglement and noise, and natural swings in the population.
The decline and the 2016 delisting
In September 2016, while the decline was under way, NOAA Fisheries took the Hawaiʻi population off the endangered species list, citing an estimate of 11,398 whales growing 5.5 to 6% a year. The rule took effect October 11, 2016. All humpbacks stay protected under the Marine Mammal Protection Act, and the 100-yard approach limits in sanctuary and state waters are separate rules.
Delisting required NOAA Fisheries to monitor the population for at least five years. NOAA Fisheries’ 2022 interim monitoring report reviewed the Kohala scans and the 2018 meeting. Because sightings in Hawaiʻi had since increased, it found the trends “not conclusive enough” to reach a response trigger, the plan’s threshold for further action, and said NOAA Fisheries, the sanctuary and research partners would keep monitoring closely.
Ocean Count island averages and the Cheeseman estimates, 2002–2026
| Year | Estimate | s.e. | Number of island averages | Median island average | Range |
|---|---|---|---|---|---|
| 2002 | 10,631 | 2,650 | – | – | – |
| 2003 | 10,309 | 996 | – | – | – |
| 2004 | 9,853 | 534 | – | – | – |
| 2005 | 10,625 | 697 | – | – | – |
| 2006 | 11,927 | 706 | – | – | – |
| 2007 | 14,314 | 1,127 | – | – | – |
| 2008 | 14,312 | 1,479 | – | – | – |
| 2009 | 16,275 | 1,338 | – | – | – |
| 2010 | 13,309 | 1,703 | – | – | – |
| 2011 | 14,888 | 2,291 | – | – | – |
| 2012 | 18,275 | 2,572 | – | – | – |
| 2013 | 18,728 | 1,914 | 9 | 4 | 2–7 |
| 2014 | 16,597 | 1,872 | 9 | 4 | 2–6 |
| 2015 | 14,395 | 1,203 | 6 | 3.5 | 2–8 |
| 2016 | 13,327 | 986 | 9 | 3 | 0.45–6 |
| 2017 | 12,647 | 1,070 | 9 | 3 | 1–4 |
| 2018 | 12,167 | 730 | 9 | 2 | 0.03–4 |
| 2019 | 12,094 | 588 | 9 | 2 | 0.5–6 |
| 2020 | 12,999 | 566 | 6 | 2.3 | 2–3.9 |
| 2021 | 12,294 | 492 | 9 | 2 | 0.17–3.8 |
| 2022 | – | – | 9 | 3 | 0.06–6.4 |
| 2023 | – | – | 9 | 1.8 | 1–5 |
| 2024 | – | – | 12 | 3 | 1–6 |
| 2025 | – | – | 12 | 4 | 0–6 |
| 2026 | – | – | 11 | 3 | 0–5 |
Volunteers scan from dozens of sites from 8:00 am to 12:15 pm on the last Saturday of January, February and March. Each results sheet is titled “Sanctuary Ocean Count Preliminary Data”. The official results give an average number of whales per 15-minute count period for each island. A single morning’s count depends on the weather: the sanctuary tied the low March 2026 count partly to Kona Low storms and poor visibility from shore.
The sanctuary also notes that its totals can include the same whale seen by different observers or at different times. To compare the Ocean Count with the population estimates, use the island averages across several years.
Hawaiʻi humpback numbers since 2019
The Cheeseman estimates for Hawaiʻi held near 12,000 to 13,000 from 2018 to 2021, and the authors write that the decline “may be temporary” if feeding-ground conditions return to the long-term average. HMMC counted 24 calves in 2021 (7.6% of the whales seen), then 11 in 2022 and 14 in 2023. NOAA’s sanctuary office wrote in March 2026 that the population has partly recovered but has not returned to pre-heatwave levels.
The next Ocean Counts are on January 30, February 27 and March 27, 2027, from 8:00 am to 12:15 pm. Registration opens in early January at oceancount.org.