Run With the Whales

Welcome to Alaska in the North Pacific. You'll be travelling from here to Hawaii alongside a humpback whale as she completes her seasonal migration. She's pregnant for the first time this year. The water has warmed during summer and is rich with plankton, which humpback whales eat by filtering water through baleen. They can eat up to 3,000 pounds of food a day. Our whale has put on weight in blubber for the challenging journey ahead, since she won't be able to feed for many months. She'll travel 5,000 miles to Hawaii to welcome her baby into the world.

Our whale begins her journey near Juneau, Alaska's capital, where she's been delighting tourists who've come to see the rare phenomenon of "bubble net feeding", which only occurs in Alaska. A group of humpback whales work together to drive fish into a net of bubbles and trap them. Winter is coming though, and with temperatures plummeting, the whales' food source is drying up. While adults have thick layers of blubber to keep them warm, newborns lack this insulation, so our whale must travel to warmer waters.

Alaska is about 1,500km behind our whale now as she swims through the Pacific Ocean. She's roughly in line with Seattle, although over 1000km out to sea. The journey from Alaska to Hawaii takes four to six weeks. Around 10,000 humpback whales make the journey each year, with thousands more migrating on other routes. Some whales swimming from Antarctica to Central America can cover around 8,000km one-way! Our whale dives, and you can see the markings on her body – totally unique to each whale, allowing scientists to identify each individual.

Juneau is now 3,000km behind our whale, as she passes California and enters the Tropic of Cancer. The waters have warmed and there are coral reefs and dolphins in the area. Humpback whales' main food source isn't present here, but the warm, sheltered waters offer protection as baby whales gain the strength and skills to survive. Our whale can hold her breath for five to ten minutes and when she surfaces, she exhales a mixture of breath, mucus, and seawater through her blowhole. This can be collected by drones so scientists can learn more about the species without disturbing them. After nearly 5,000km our whale has reached Hawaii, and it's nearly time for her to give birth.

It's winter in Hawaii, and our whale has given birth to a female calf. The calf is 15 to 20 feet long and weighs around one ton. Mother and baby won't be apart for the next year, and often touch flippers as a gesture of affection. Whales rest one side of their brain at a time while the other side remains conscious so they can breathe while resting and keep a watch for danger. Our whale feeds her calf on milk with a fat content of between 45 and 60 percent, which will help the calf grow strong enough to travel. The calf drinks around 600 litres per day and will double in length by her first birthday. The mother, on the other hand, loses up to 40 percent of her body mass. Now though, it's time to begin the long journey back to Alaska.

They're about halfway back to Alaska and this gives the mother time to teach her calf the route. It's believed humpbacks travel to the same feeding and breeding grounds each year. Humpbacks were nearly hunted to extinction by the 1970s for their oil – used to make motor oils, candles, and cosmetics. An international ban on commercial whaling and global conservation efforts mean there are now over 80,000 mature humpback whales, and populations are on the rise. After a long journey, whale and calf reach Juneau, where the summer has filled the Alaskan waters with food. While there are many threats, hopefully the calf will live a long life, and may even reach around 80 years old.