The annual migration cycle of the gray whale

There are two known populations of gray, or grey whale. One small population is in the Western Pacific, of which there is not much available information. A much larger one of about 22,000 individuals in the Eastern Pacific is much better known.

An incredible journey begins

One of the most incredible migrations of mammals on earth must possibly be the annual journey of the gray whale of the Eastern Pacific. The journey begins in their feeding grounds in the waters of the Arctic and takes them south to their breeding lagoons off the Pacific coast of Baja California. 

To get there they have to swim the length of the North American coastline. They then give birth to their young before making the return journey. All round an incredible total distance of about 12,400 mile (20,000 kilometers).

During the journey north the weather is usually good and they usually like to swim quite close to the coastline. The weather on the southward journey to their breeding lagoons is often rougher and they prefer to stay further from the shore though they tend to keep it in sight.

April to October – Summer feeding  

To prepare them for this arduous journey they spend the summer months from April to October feeding in the cold waters of the Arctic. Using their mouths like a vacuum cleaner they suck up sediment from the sea floor which is then filtered through their baleen plates trapping crustaceans and other creatures. They need to eat as much as they can so that they can store the fat and blubber that will give them the energy to last while they make their journey.

November to February – Heading south  

When the weather begins to deteriorate in early October the whales prepare to head south. This is a highly structured operation with pregnant females being the first to begin the journey south. They are followed by non-pregnant females, with mature males following them. Next go the immature females and lastly immature males finally embark on the journey south.

They all follow the ancient migratory route which takes them through a gap in the Aleutian Islands called the Unimak Pass. They will then head south following the North American shoreline. It’s a hard journey and they will seldom take a break as they average about 125 kilometers a day over a period of a couple of months.

December to April – Breeding

While a long line of migrating whales stretches along the North American coastline, the pregnant females are the first to arrive in the breeding lagoons off the Pacific coast of Baja California. In the shallow waters they give birth to their calves while many other whales are still making their way there.

The calves need to fatten up as quickly as possible and consume huge quantities of the mother’s rich milk. They have only a few months to grow big and strong enough to make the long journey north to the feeding grounds of the Arctic.

February to June – The return journey

On the return journey the gray whale takes a slower pace. The mothers with the calves tend to rest more. Sometimes they may rest for a few hours and sometimes for a few days, though they still average around 80 to 90 kilometers a day. As they cross Monterey Bay the calves are vulnerable to attack by Killer whales.

Eventually, they will all have returned through the Unimak Pass to spend the summer months feeding and gaining weight ready to begin the migratory cycle once again.