Why humpback whales skip migration comes down to one thing: food. For years, underwater microphones in the Southern Ocean picked up humpbacks singing season after season, even when scientists expected them to have left for the tropics. Then came 2015 and 2016, two of the strongest El Niño years on record, and the humpbacks were nearly absent. In this episode of Ocean Decoded, marine biologist Andrew Lewin explains why, and what it means with another strong El Niño building in the Pacific right now.
Humpbacks split their lives between cold, krill-rich feeding grounds near the poles and warm tropical breeding grounds where they barely eat. Their schedule is regular enough that scientists notice when it changes. A team from Germany's Alfred Wegener Institute found that sea ice and the El Niño index best explained when humpbacks stayed in the Southern Ocean. Off Ecuador, 15 years of shore-based counts show El Niño can make the calf rate look higher, because some whales never arrive, then make the population jump the following year when they return. Off Costa Rica, researchers saw fewer humpbacks after warming events and propose that stronger warming leaves fewer whales with the energy to migrate, carry a pregnancy and raise a calf. One humpback was even recorded on breeding grounds in two different ocean basins, a rare move researchers linked to El Niño.
Closer to North America, 25 years of sightings from the Farallon Islands off San Francisco show El Niño shifts when humpback, blue and gray whales arrive off central California. During the 2014 to 2016 marine heatwave, offshore krill grew sparse, humpbacks fed closer to shore, and entanglements in crab gear jumped from about 10 a year to more than 50. NOAA expects a strong to very strong El Niño through early 2027. Andrew closes with what to watch this winter and how to report a whale in trouble.
Chapters:
00:00 - The year the humpback recordings went silent
02:13 - Seven breeding populations and the whales that break the pattern
04:20 - The year after, the count jumps
06:34 - What to watch for this winter
08:07 - Next: how El Niño starves the food web
Takeaways:
Humpbacks follow their food, so when El Niño moves the krill, whales change course.
In the El Niño years of 2015 and 2016, humpbacks were nearly absent from Southern Ocean recordings.
El Niño can distort whale counts: calf rates look high in El Niño years and populations appear to jump the year after.
Some whales skip the trip, some arrive early, and a few turn up in a different ocean.
Early arrivals off California overlap with crab and trap gear, raising entanglement risk.
Humpback entanglements off the US West Coast rose from about 10 a year before 2014 to 53 in 2015 and 55 in 2016.
NOAA expects a strong to very strong El Niño through early 2027.
When you see a "missing whales" headline, ask what happened to their food.
If you see an entangled or injured whale, report it to your local marine mammal response network. Don't try to free it yourself.
#OceanConservation #MarineBiology #SaveOurOceans #ProtectTheOcean #OceanAwareness #BluePlanet #ConservationMatters #ScienceForChange #SustainableOceans
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