Do Blue Whales Migrate? Mapping Their Epic Journeys

Yes, most blue whales migrate. They live in every ocean except the Arctic, and in most places they follow the seasons.1NOAA. Blue Whale Their year runs on a basic pattern: feeding in one part of the ocean, breeding in another, and making long journeys in between.2NOAA. Blue Whale The pattern isn’t fixed, though. Some groups seem to skip migration altogether, and the whales appear to time their trips by what they remember about the ocean, so the schedule shifts from year to year.

Where North Pacific Blue Whales Travel

Blue whales tagged off southern California mostly headed south in the fall, along the coast of Baja California, Mexico.3Marine Mammal Science. Movements of North Pacific blue whales during the feeding season off southern California and their southern fall migration One tagged whale went north to Cape Mendocino in northern California instead.4Marine Mammal Science. Movements of North Pacific blue whales during the feeding season off southern California and their southern fall migration Another whale that went south kept traveling another 2,959 km in about a month, to within 450 km of the Costa Rica Dome.5Marine Mammal Science. Movements of North Pacific blue whales during the feeding season off southern California and their southern fall migration

The dome is an area out in the open Pacific off Central America where cold, nutrient-rich water rises from the deep.6Marine Mammal Science. Movements of North Pacific blue whales during the feeding season off southern California and their southern fall migration It is thought to be a place where these whales breed and give birth.7Marine Mammal Science. Movements of North Pacific blue whales during the feeding season off southern California and their southern fall migration

Adult females are the most regular travelers. Each season they move between feeding grounds in cooler mid-latitude waters and breeding grounds in warmer subtropical waters.8Frontiers in Marine Science. Sex- and age-specific migratory strategies of blue whales in the northeast Pacific Ocean Some females skipped migration for a year, then returned to the same breeding area near the Costa Rica Dome, possibly to give birth.9Frontiers in Marine Science. Sex- and age-specific migratory strategies of blue whales in the northeast Pacific Ocean So a whale missing from its usual spot one year isn’t necessarily lost.

Why Blue Whales Migrate

Blue whales travel thousands of miles to feed on krill, small shrimp-like animals.10Scripps Institution of Oceanography. Research Highlight: Blue Whales Are Arriving in Southern California Earlier and Earlier Krill gather where cold, nutrient-rich water rises from the deep, a process called upwelling.11Science. Ship strikes threaten blue whale numbers That water fuels blooms of the tiny plants krill eat, and a swarm can grow dense enough for a whale to take in a huge mouthful in one lunge.

The swarms are huge but short-lived, so whales have to be in the right place at the right time.12Annual Review of Ecology, Evolution, and Systematics. How Whales Dive, Feast, and Fast: The Ecophysiological Drivers and Limits of Foraging in the Evolution of Cetaceans Their enormous size, filter feeding and ability to go long periods without eating make such long trips possible.13Annual Review of Ecology, Evolution, and Systematics. How Whales Dive, Feast, and Fast: The Ecophysiological Drivers and Limits of Foraging in the Evolution of Cetaceans

Births tie the trip together. Most blue whales appear to give birth shortly after leaving their summer feeding grounds.14Endangered Species Research. Timing hypothesis explains the mystery of the missing blue whale calves Mothers wean their calves about 7 months later, when they come back to feed.15Endangered Species Research. Timing hypothesis explains the mystery of the missing blue whale calves Pregnant females build up blubber at the feeding grounds before giving birth, and that store lets a mother produce milk carrying around 4,000 megajoules a day, roughly the energy in a million calories.16PubMed. Lactation in whales and dolphins: evidence of divergence between baleen- and toothed-species

This also explains the old puzzle of the “missing” calves. Births happen far offshore, right after the whales leave the coast, so whale watchers on the feeding grounds almost never see newborns. By the time calves arrive there, they are about 7 months old.

Blue Whale Routes Around the World

Pygmy blue whales, a smaller type of blue whale, migrate from the southern coast of Australia north to Indonesia.17Global Ecology and Conservation. Pygmy blue whale movement, distribution and important areas in the Eastern Indian Ocean Whales tagged off Western Australia traveled consistently to the Banda and Molucca Seas, which suggests a regular rather than random journey.18Biological Conservation. Telemetry-based home range and habitat modelling reveals that the majority of areas important for pygmy blue whales are currently unprotected Much of this route passes through areas used for oil and gas production.19Global Ecology and Conservation. Pygmy blue whale movement, distribution and important areas in the Eastern Indian Ocean

Antarctic blue whales, the largest type, pass through central New Zealand mostly in winter and spring, which there runs from June to November.20Frontiers in Marine Science. Passive Acoustic Monitoring Reveals Spatio-Temporal Distributions of Antarctic and Pygmy Blue Whales Around Central New Zealand Southern Hemisphere seasons are reversed, so this “winter migration” happens during the northern summer. New Zealand’s South Taranaki Bight works as a corridor on their route.21Frontiers in Marine Science. Passive Acoustic Monitoring Reveals Spatio-Temporal Distributions of Antarctic and Pygmy Blue Whales Around Central New Zealand Pygmy blue whales gather in the same bight, especially from March to May.22Frontiers in Marine Science. Passive Acoustic Monitoring Reveals Spatio-Temporal Distributions of Antarctic and Pygmy Blue Whales Around Central New Zealand Antarctic blue whales are so hard to track that only two have ever been followed by satellite tag.23Biodiversity Data Journal. Satellite tag derived data from two Antarctic blue whales (Balaenoptera musculus intermedia) tagged in the east Antarctic sector of the Southern Ocean

The two types differ in other ways. Antarctic blue whales feed in polar waters, while pygmy blue whales live in warmer Indian Ocean and Pacific waters. Each type sings its own song, which lets listeners tell them apart. Their routes rarely overlap, though New Zealand hosts both.

In the North Atlantic, blue whales pause their spring migration in middle latitudes to feed, possibly building up energy for the rest of the trip.24PubMed Central. North Atlantic Blue and Fin Whales Suspend Their Spring Migration to Forage in Middle Latitudes: Building up Energy Reserves for the Journey? Whales are thought to find their way using a mix of senses and cues from the environment.25PubMed Central. North Atlantic Blue and Fin Whales Suspend Their Spring Migration to Forage in Middle Latitudes: Building up Energy Reserves for the Journey?

Blue Whales That Don’t Migrate

Some blue whales in certain areas may not migrate at all.26NOAA. Blue Whale Those in New Zealand’s South Taranaki Bight form their own separate population that stays put.27Smithsonian Magazine. OSU researchers discover new population of blue whales At least one Antarctic population may also stay in the Antarctic all year, following the edge of the sea ice as it grows and shrinks.28PubMed Central. Towards population-level conservation in the critically endangered Antarctic blue whale: the number and distribution of their populations The evidence is that Antarctic blue whale calls have been recorded year-round off the Antarctic Peninsula, eastern Antarctica and the Crozet Islands.29PubMed Central. Towards population-level conservation in the critically endangered Antarctic blue whale: the number and distribution of their populations Calls alone don’t say whether the same whales stay or different whales pass by in turn, so the idea is possible rather than proven.

Staying put requires food that is available year-round. The upwelling in the South Taranaki Bight helps keep krill there, which makes the bight a dependable place to see blue whales.

When Blue Whales Arrive and Leave

Whales use last year’s ocean as a forecast. Sea temperatures during one feeding season predict when whales arrive the following year.33PubMed Central. Timing is everything: Drivers of interannual variability in blue whale migration Cooler water draws more krill, so a cool year signals a good krill year ahead.34Scripps Institution of Oceanography. Research Highlight: Blue Whales Are Arriving in Southern California Earlier and Earlier The whales seem to remember past conditions and time their return to match.35Scripps Institution of Oceanography. Research Highlight: Blue Whales Are Arriving in Southern California Earlier and Earlier Antarctic blue whales likewise change their migration from year to year as ocean and climate conditions shift.36The Journal of the Acoustical Society of America. Examining environmental conditions that influence long-term Antarctic blue whale migration patterns in the Southern Hemisphere using an 18-year passive acoustic dataset

The season is also getting longer. Over 10 years, arrival off Southern California moved 42 days earlier, from June to April.37PubMed Central. Timing is everything: Drivers of interannual variability in blue whale migration The date the whales leave didn’t change.38PubMed Central. Timing is everything: Drivers of interannual variability in blue whale migration Warming linked to climate change has lengthened the time whales spend there.39PubMed Central. Timing is everything: Drivers of interannual variability in blue whale migration

Timing can shift over days and weeks too. Off New Zealand, strong winds bring up cold water, and whale activity peaks about 3 weeks later.40PubMed Central. Temporal and spatial lags between wind, coastal upwelling, and blue whale occurrence

For a trip, aim for the middle of the season rather than its edges. Off California, summer is the most dependable time. Arrival dates can shift by weeks, so ask operators what they’ve been seeing recently.

Scientists know when whales come and go because underwater microphones record blue whale songs around the clock. The recordings show when whales are in an area, even when they can’t be seen from the surface.

Dangers Along the Way

Feeding areas off Santa Barbara and San Francisco are crossed by major shipping lanes.41Science. Ship strikes threaten blue whale numbers At least three blue whales were killed by ships within two weeks in 2007.42Science. Ship strikes threaten blue whale numbers When a ship approaches, whales often dive only shallowly and don’t move out of its way.43Endangered Species Research. Simultaneous tracking of blue whales and large ships demonstrates limited behavioral responses for avoiding collision Off southern Sri Lanka, blue whales are densest right in one of the world’s busiest shipping lanes.44Regional Studies in Marine Science. Distribution patterns of blue whale (Balaenoptera musculus) and shipping off southern Sri Lanka Slower ship speeds and moved shipping lanes are common fixes.

A collision with a large ship can kill a whale outright or injure it so badly that it dies later. Many dead whales sink or drift away and are never found, so the number of known deaths is likely lower than the true number.

Protection has gaps too. Much of the pygmy blue whale migration corridor, especially in international waters and Indonesian seas, has no protection.45Biological Conservation. Telemetry-based home range and habitat modelling reveals that the majority of areas important for pygmy blue whales are currently unprotected Protecting a migrating whale takes cooperation between several countries. Whale watchers can help by choosing tour operators that follow distance and speed guidelines, reporting sightings to local whale-tracking programs, and backing efforts to slow ships in areas whales use.

How Their Journeys Are Mapped

Satellite tags revealed the Australia-to-Indonesia route by following eleven whales.46PubMed Central. Migratory Movements of Pygmy Blue Whales (Balaenoptera musculus brevicauda) between Australia and Indonesia as Revealed by Satellite Telemetry A tag is attached to the whale’s back and sends its location to satellites when the whale reaches the surface. Because it only reports at the surface, the track is a series of points rather than a continuous line. Tags eventually fall off or run out of battery, so they cover weeks or months rather than years.

Underwater listening stations can record years of whale songs over huge areas.47Frontiers in Remote Sensing. Widespread passive acoustic monitoring reveals spatio-temporal patterns of blue and fin whale song vocalizations in the Northeast Pacific Ocean They show who is present over many years, though not which individual. Individual whales can also be identified from photos of their color patterns and dorsal fins, which confirms that the same whale returns year after year.48Research in Computing Science. Multi-spatial Classifier for Blue Whale Images using Photo-identification Method Matching photos by hand is slow and error-prone, and computer programs are now being built to help.49Research in Computing Science. Multi-spatial Classifier for Blue Whale Images using Photo-identification Method For humpback whales, AI photo matching has combined dozens of photo collections, including photos taken by the public.50Mammalian Biology / Scientific Reports / Royal Society Open Science. Humpback Whale Abundance and Migratory Patterns in the North Pacific Ocean Assessed by means of Automated Photo-identification

Visitors can contribute too. Many research groups accept photos from the public, and a photo of a whale’s flank can help identify it. Note the date and location when you take it.