The 2015–2021 humpback whale decline in Hawaiʻi
Researchers counting humpback whales from a shore station above Kawaihae Bay saw 60% fewer whales per scan in 2016 than in 2015, and calves were 1.1% of the whales they counted that year. A 2024 study’s relative abundance estimates put the loss in Hawaiʻi at 34% between 2013 and 2021. The researchers’ likely explanation is a marine heatwave that cut the food supply on the whales’ North Pacific feeding grounds.
This page sets out what each study and NOAA report measured, and charts the Ocean Count island averages beside the Cheeseman estimates and a 2026 study’s non-calf estimates. 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 relative abundance estimate peaked at 18,728 whales in 2013 and was 12,294 in 2021, down 34% and back to the level of 2006, and the authors measured a fall of 4.3% a year from 2014 to 2021. Whales that winter off mainland Mexico showed no decline over the same years.
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 authors of the later Frankel et al. paper 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 up and down through 2015. The 2016–2019 average was 13.1 whales per scan.
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 season totals since 2019 are on our research page.
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 chorusing levels of male song more than 6 decibels lower in some months from the 2014–2015 season on, a sign of 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 the Kohala counts 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.
NOAA Fisheries’ stock assessment report for the Hawaiʻi stock (2024 edition, posted April 2026) gives a later estimate from a different method: 11,278 whales in 2020 (CV 0.56, 95% interval 4,049 to 31,412), from a model of ship survey sightings covering whales of all ages in US waters around the islands at the winter peak. Its Hawaiʻi stock is the population the 2016 rule delisted, and the report says it is unknown whether the population is currently increasing.
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 two population estimates, 2002–2026
Show the numbers as a table
| Year | Relative abundance estimate | s.e. | Number of island averages | Median island average | Range | Breeding season | Non-calf estimate | Non-calf s.e. |
|---|---|---|---|---|---|---|---|---|
| 2002 | 10,631 | 2,650 | – | – | – | – | – | – |
| 2003 | 10,309 | 996 | – | – | – | 2002/03 | 4,700 (excluded by the authors) | 511 |
| 2004 | 9,853 | 534 | – | – | – | 2003/04 | 9,578 | 924 |
| 2005 | 10,625 | 697 | – | – | – | 2004/05 | 9,711 | 533 |
| 2006 | 11,927 | 706 | – | – | – | 2005/06 | 10,728 | 446 |
| 2007 | 14,314 | 1,127 | – | – | – | 2006/07 | 11,398 | 471 |
| 2008 | 14,312 | 1,479 | – | – | – | 2007/08 | 11,840 | 500 |
| 2009 | 16,275 | 1,338 | – | – | – | 2008/09 | 15,067 | 1,239 |
| 2010 | 13,309 | 1,703 | – | – | – | 2009/10 | 13,443 | 715 |
| 2011 | 14,888 | 2,291 | – | – | – | 2010/11 | 14,109 | 935 |
| 2012 | 18,275 | 2,572 | – | – | – | 2011/12 | 12,904 | 847 |
| 2013 | 18,728 | 1,914 | 9 | 4 | 2–7 | 2012/13 | 12,678 | 626 |
| 2014 | 16,597 | 1,872 | 9 | 4 | 2–6 | 2013/14 | 14,714 | 878 |
| 2015 | 14,395 | 1,203 | 6 | 3.5 | 2–8 | 2014/15 | 14,736 | 736 |
| 2016 | 13,327 | 986 | 9 | 3 | 0.45–6 | 2015/16 | 11,537 | 761 |
| 2017 | 12,647 | 1,070 | 9 | 3 | 1–4 | 2016/17 | 11,088 | 596 |
| 2018 | 12,167 | 730 | 9 | 2 | 0.03–4 | 2017/18 | 10,116 | 421 |
| 2019 | 12,094 | 588 | 9 | 2 | 0.5–6 | 2018/19 | 10,441 | 374 |
| 2020 | 12,999 | 566 | 6 | 2.3 | 2–3.9 | 2019/20 | 9,554 | 318 |
| 2021 | 12,294 | 492 | 9 | 2 | 0.17–3.8 | 2020/21 | 9,457 | 318 |
| 2022 | – | – | 9 | 3 | 0.06–6.4 | 2021/22 | 9,311 | 306 |
| 2023 | – | – | 9 | 1.8 | 1–5 | 2022/23 | 9,921 | 325 |
| 2024 | – | – | 12 | 3 | 1–6 | – | – | – |
| 2025 | – | – | 12 | 4 | 0–6 | – | – | – |
| 2026 | – | – | 11 | 3 | 0–5 | – | – | – |
Volunteers at dozens of sites scan from 8 a.m. to 12:15 p.m. on the last Saturday of January, February and March. 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.
A 2026 study (Barber-Meyer et al.) estimates a different quantity through the 2022/23 season: non-calf abundance, the number of whales other than calves using the main Hawaiian Islands in each November to May breeding season. It draws on the same Happywhale photo-ID collection as the Cheeseman study. Its 2021/22 estimate, 9,311, was 37% below its 2014/15 estimate of 14,736. The 2022/23 estimate was 9,921 (standard error 325), which the authors read as a possible slight increase.
The study’s apparent survival, which cannot tell whales that died from whales that left the region for good, fell in one interval only: from 0.987 before 2014/15 to 0.684 between the 2014/15 and 2015/16 seasons, and it was 0.956 after that.
The 20 non-calf estimates from 2003/04 to 2022/23 averaged 11,617 (SD 1,914). The authors leave out the 2002/03 estimate, which they judge likely underestimated by about half.
The authors write that abundance has not yet recovered to the levels before 2015/16, and 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 a.m. to 12:15 p.m. Registration for the January count opens in early January at oceancount.org.