North Pacific humpback whales are getting smaller — and scientists are alarmed
Researchers have documented a troubling trend: mature humpback whales in the North Pacific are, on average, about one to two feet shorter than their mid-20th-century counterparts. A recent study also found roughly an 80% drop in birth rates between 2013 and 2018 and observed shorter migrations between Alaska and Hawai'i.
What the scientists say
Lead author Martin Van Aswegen, a postdoctoral researcher at The Marine Mammal Research Program, described these findings as illustrating "the cost of being a humpback whale in the North Pacific: the cost of growth." Put simply, researchers believe these large animals are using more energy just to survive, leaving less available for growth and reproduction.
"The data suggest increased energetic stress on whales — likely a combination of environmental change and human pressures — is affecting their size and reproductive success." — Martin Van Aswegen
Likely causes
Scientists have not identified a single cause but point to multiple, interacting pressures, including:
- Increased ship noise and vessel traffic that disrupt feeding and communication
- Changing ocean conditions that alter prey distribution and abundance
- Direct and indirect human impacts on habitat and food webs
Broader impacts
The consequences extend beyond the whales themselves. Coastal economies that depend on whale-watching—from Maui to Alaska—may suffer if fewer or smaller whales appear or if breeding seasons are skipped. Ecologically, humpbacks help circulate nutrients across the ocean during migration; declines in their size or numbers can ripple through marine food webs.
Response and solutions
Researchers are expanding monitoring programs to better understand how these stressors affect humpbacks and to inform policy. Some management actions already show promise: reducing ship noise, rerouting heavy vessel traffic away from key breeding areas, and establishing protected marine zones. Conservation groups are pushing for stronger ocean protections and restoration efforts, building on policy gains such as California’s Marine Life Protection Act and federal initiatives to increase ocean biodiversity.
How the public can help
Everyday choices matter. Scientists and advocates encourage actions like choosing seafood from sustainable fisheries, cutting single-use plastic, supporting marine-protection laws, and backing policies that reduce vessel disturbance in critical habitats.
Conclusion: The observed shrinkage and lower reproduction rates among North Pacific humpbacks are a warning sign. Continued research, policy action, and public engagement are needed to address the multiple pressures that threaten these iconic marine mammals and the coastal communities and ecosystems that rely on them.
