Deep dive…into Grey whales

Grey whales (Eschrichtius robustus) make one of the longest annual migrations of any mammal, travelling between 15,000 to 20,000 kilometres.  

The baleen whales were once commonly found through the Northern Hemisphere but are now only regularly found in the North Pacific Ocean. There are two populations in this region: the Eastern Pacific grey whale and the Western Pacific grey whale.  

The species can weigh up to 40 tonnes (equal to the combined weight of 20 cars) and grow to 15 metres long, making it one of the bigger whales in our ocean. It has a mottled grey appearance with a relatively small narrow head, a robust body and small paddle-shaped flippers.  

Instead of a dorsal fin, grey whales have six to twelve knuckles between their hump and flukes, with these knuckles forming a low hump. They’ve small eyes located just above the corners of the mouth.  

On first glance and due to their similar size, some people mix up grey whales and humpback whales but there are a few distinctive aspects to the grey whale. These include its heart-shaped blow. And, interestingly, the grey whale has two blow holes whereas other whales, including humpbacks, only have one blow hole. 

The whale’s mottled grey appearance (think crusty skin) is due to the large amounts of whale lice and barnacles that attach themselves to the cetacean’s head and body. Parasites attach and later detach in cold feeding grounds, leaving behind scars and patches that are used by scientists to identify individual whales.  

A grey whale’s lifespan is generally 50 to 70 years though there is research indicating they may live up to and beyond 75 to 80 years.  

Grey whales aren’t highly social as a group and tend to come together during the breeding season and parts of their annual migration. 

However, the species has been observed showing curiosity towards boats and approaching them to check out occupants. It’s no surprise then that when whale watching first began in the U.S. in the 1950s, grey whales were amongst the first species that companies focused attention on.   

Grey whales predominantly live in the North Pacific Ocean amongst two population groups. The first population lives along the Pacific coast of North America (usually called Eastern Pacific grey whales or North American grey whales) and the second population group, which is smaller in size, lives in the western part of the Pacific Ocean (around Korea, China and Japan). They’re called Western Pacific grey whales or Asian population grey whales.  

The Eastern Pacific grey whale feeds during the summer in the Bering and Chukchi Seas between Alaska and Russia. A small group of “summer resident” whales don’t migrate as far as Alaska to feed during the summer – instead, they do their feeding further down the coast (they’re found off British Columbia, Canada, down to northern California).

In the autumn, these grey whales migrate south along the west coast of the U.S. to the Baja Peninsula in Mexico and the south eastern Gulf of California. In the warm waters, they breed and give birth to calves.  

On the other side of the Ocean, the Western Pacific grey whale feeds in the summer in the Sea of Okhotsk (near the northeastern coast of Sakhalin Island in Russia) and also in an area of the Bering Sea (around the Kamchatka Peninsula). In the autumn, the species migrates down to the South China Sea where it breeds. 

Research since 2004 has detected some members of the Western Pacific grey whale population migrating to the Pacific coast of North America to visit feeding and wintering grounds used by their Eastern Pacific grey whale counterparts.  

Grey whales have been spotted in other areas around the world, prompting scientists to question if they are increasing their geographic spread and/or reverting back to habitats that they lived in prior to their population drop caused by commercial whaling.   

A fascinating 2022 EU funded research project Demise of the Atlantic Grey Whale investigated whether the species might eventually return to European waters.  

This was also explored by Rebecca Giggs in her book Fathoms: The World in the Whale. She writes, “Grey whales, too, are altering the choreography of their long transportations. Grey whales are leaving the North Pacific and crossing over the top of the globe through the ice-free Northwest Passage to appear in the Atlantic. Grey whales surface now off Israel, Spain, and Namibia, where they have never been recorded before.” 

In the summer of 2021, a grey whale was spotted off the coast of Morocco and was seen also off the coast of France and Italy.  

More is known about the Eastern Pacific grey whale than the Western species but they share the same broad migratory pattern of going from warm to colder waters and back again. They usually migrate for about two to three months annually in large groups and they pace themselves, swimming up to 8 kilometres per hour.  

Generally speaking, grey whales stay close to the shore (they rarely venture more than 20 to 30 kilometres offshore) and feed in shallow water.  

The grey whale was extensively hunted during the peak years of commercial whaling, almost to the point of extinction. The species was once known as “devil-fish” because they fought back aggressively when attacked by whalers.   

It looked like the species was on the right track to recovery having come under the protection of the International Whale Commission ban on commercial whaling in 1986.  

In 2016, NOAA Fisheries in the U.S. estimated the size of the Eastern Pacific grey whale population to be nearly 27,000, an increase from previous figures.  

However, a new assessment by NOAA released in October 2022 shows that the numbers have decreased in the past six years. The count put the population at 16,650, down 38% since 2016. The whales in the assessment also produced the fewest calves since scientists began counting their births in 1994.   

But the Eastern Pacific grey whale population size is still considerably more than the Western population, which has one of the smallest whale populations in the world and is listed on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species as critically endangered.  

Some estimates state there are around 250 – 300 whales in this population whilst other more conservative estimates put it at 100 individuals remaining.  

Grey whales are bottom feeders, which means they trawl the soft muddy part of the seabed in shallow areas. They use their baleen to sieve out water, leaving the food behind in their mouths.  

They consume mostly small invertebrates (plankton, amphipods) along with crab larvae,  and are also known to feed on herring eggs and larvae in eelgrass beds. They eat around one tonnes of food each day.  

Interestingly, most grey whales turn on their right side when they bottom feed and this means the baleen on the right side is usually shorter and more worn than the baleen on the left side.

Like other whales, grey whales can become entangled in different types of fishing gear. This can cause injury, fatigue, compromised feeding and even death.  

Climate change and pollution can lead to loss of habitat as waters become warmer. Plastics and micro plastics in the ocean pose a threat to whales, along with all other marine mammals and fish. Chemical pollutants entering into the water ecosystem are also a serious threat to all creatures in our ocean.  

The grey whale’s summer feeding habitats around Sakhalin Island and the Bering and Chukchi Seas are increasingly being targeted for offshore oil and gas development. These developments disturb whales in terms of underwater noise being generated, water pollution and negative impacts on their feeding behaviour.  

In 2019, NOAA Fisheries in the U.S. declared an “Unusual Mortality Event” or UME for grey whales. This was due to a significant increase in the number of whales washing up on beaches on the country’s Pacific coast (384 cases).  

The reasons for these deaths is not fully clear but researchers say factors could have included climate change, its effect on sea ice as well as availability of prey. It was reported that many – but not all – of the dead whales that washed up appeared malnourished or emaciated, prompting questions as to whether their food sources are being reduced.  

A 2021 study into the UME examined food scarcity as a potential cause for the rise in skinny whales and said, “[It] could also be due to a decline in prey on their feeding grounds. Benthic amphipods are of great importance to grey whales…comprising 90% of their food intake.” 

It’s thought that with less amphipods, grey whales may be turning to krill as a food source and unfortunately it’s not as nutritionally rich for their needs.  

A number of these UME cases were found to be caused by vessel strikes.  

Large ships operating in the North Pacific Ocean pose a threat to grey whales due to vessel strikes. A study published in 2021 showed that large ships operating in the Bering Sea, Gulf of Alaska and along the west coast of North America (where there is a huge amount of commercial shipping routes) all posed a high risk to the species.  

It also identified areas in the Russian Far east where vessel strikes pose a significant threat to the whale species. 

During northward migrations, grey whale mothers and calves stay close to the shore (usually within 200 metres). This is thought to be an evasive measure to avoid attacks from orcas. 

Attacks on grey whales by orcas are not always fatal, in which case the grey whale bears the signs of survival (usually tooth rake scars and disfigurements on their tail flukes). 

Humpback whales have been observed coming to the aid of grey whales under attack from orcas. Check out the video below filmed for BBC’s Planet Earth.