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Episode 343: Gritty Grey Whales

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The gigantic and gentle Gray Whale (image from interpretivecenter.org)

The Gray Whale is arguably one of the biggest conservation success stories we’ve covered on this podcast. After years of intensive whaling, Gray Whales bounced back when strict controls were brought in to protect them. Long before the pressures of whaling, Gray Whales survived many cycles of global cooling and warming, largely due to the fact that they are dietary generalists and were able to swap their main feeding strategy. Usually, Gray Whales adopt a bottom feeding strategy. They prey on invertebrates, like tube worms, molluscs and amphipods (tiny shrimp like organisms), sucking in huge amounts of mud and water and using their giant baleen plates to filter out the food. The excess water and mud is then blown out back into the ocean. This feeding strategy is important for the health of the oceans, as it allows for the effective transfer of nutrients from the sea sediment into the water. Changing sea levels over their evolutionary history would have meant that Gray Whales would not have been able to maintain their bottom feeding strategy, as the waters on some of the continental shelves would have been too shallow for them. However, studies of their genetics don’t show any evidence of the genetic bottleneck that often occurs when populations numbers fall very low. This suggests that Gray Whales must have changed their feeding behaviour to survive these fluctuating sea levels, which could be a very positive sign for their survival in a changing world. During these genetic studies, scientists also found that their closest relatives are rorquals whales of the family Balaenopteridae like the humpback whale and fin whale.

Massive mammals with a massive migration

Gray whales are famous for their migration, one of the longest of any mammal. This well studied migration is a 12,000 mile round trip from their feeding grounds in the cold Arctic waters to the warmer climes of Baja, California, where they breed and calve. The migration is well understood and often followed by eco-tourism boats, as they prefer the shallower waters off the coast for bottom feeding.

The lengthy migratory routes of the Gray Whales (image from https://nc.mymcn.org)

In the summer months, the whales spend their time in the icy, nutrient rich waters of the Arctic, feeding on the small amphipods that are abundant in the ocean floor sediments. In September, the begin to leave these feeding grounds and head south along the coastline to the breeding grounds in the far warmer waters of Baja, California, covering as much as 75 miles a day. In December, adult males and females arrive in Californian waters, where the females can give birth in the sheltered warm waters. Through to February calves are born, and are known to be curious and friendly to boats, actively interacting with whale watchers. Recently in Baja, a whale was filmed approaching a whale watching boat and getting a staff member to remove whale lice from around his mouth! From February through to April, the whales will begin to travel back to the Arctic, with females and their calves leaving last to allow the vulnerable calves to grow and strengthen as much as possible. On their way back to the Arctic, females and their calves will stick close to the coast, avoiding predators like orcas. As many as 24,000 whales will migrate, and this phenomenon is viewed by thousands upon thousands of tourists eager to interact with these amazing whales.

A Gray Whale mother and calf beginning their migration back to the icy feeding waters of the North (image from www.oregoncoastmagazine.com)

A bloody history: threats yesterday and today

Like so many whale species we have covered, Gray Whales once suffered from intensive whaling, almost driven to extinction over a few hundred years. Throughout the 1700s and 1800s, Gray Whales were extensively hunted for their oil, meat and baleen. European and American whalers targeted them in the North Pacific and Japanese and Korean fleets hunted them in the Western Pacific. At any one time as many as 480 whales could be taken in one bloody day, as they tended to congregate in shallower lagoons to feed. These huge depletions would have massively impacted their ecosystems, as it is estimated that the numbers of whales back then would have resuspended as much as 700 million cubic metres of sediment, moving nutrients around and boosting the efficiency of oceanic food webs. Gray whales were particularly vulnerable to whaling, as they are slow swimmers and easily spotted off the coast. In 1946, as the demand for whale products fell away and society began to recognise the horrors of whaling, an international treaty was signed to provide oversight and management of whale hunting. By 1974, Gray Whales were placed on the Endangered Species Act, protecting them to enable their recovery.

Gray Whale populations have rebounded amazingly, making them a huge conservation success story. However, they are still facing threats that threaten these gains we’ve made in recovering the species. Entanglements in fishing gear is a common way for the whales to drown and their vast migration routes put them at particular risk of ship strikes. Western Gray Whale populations off the coast of Russia are particularly imperilled at the moment, with their key feeding grounds falling right in the middle of important oil and gas fields. It is speculated that more offshore oil development will begin in these areas, and the noise pollution from drilling and increased ships are a major concern. As with so many marine species and of particular relevance for Plastic Free July, Gray Whales are often at risk from plastic, with some whales found washed up with stomachs full of garbage ingested as they scoop up water and sediment to sieve for food.

Conservation optimism

Despite the threats to them today, Gray Whales remain a major success story in the conservation world. In the 1930s, their numbers had fallen into the 100s, but today their numbers sit around 24,000 -25,000. Off the coast of California, populations of the Western Gray Whale were falling, but recent surveys revealed hope for increasing numbers and whales in better conditions after an unknown mortality event that peaked in 2016.

The WWF have their blue corridors programme, which protects migratory pathways and aims to reduce noise pollution and mortalities from fisheries bycatch, not just for the Gray Whales, but all the amazing whale species globally. Learn more about this ambitious initiative at Protecting Blue Corridors Report 2022 — WWF Protecting Whales & Dolphins Initiative (wwfwhales.org) 

The WWF initiative called the Blue Corridors Programme, which aims to protect whale migratory pathways (image from WWF)

After concerns over whale populations off the coast of Sakhalin Island in Russia, seismic surveys for new gas and oil pipelines have been restricted, and a large oil drilling station was barred from being built in the middle of critically important whale feeding grounds. In California, the species is closely monitored to determine their population size and health, and returning Gray whales are surveyed, with marine biologists taking tissue samples and recording underwater communications. NOAA, the National Oceanic and Atmospheric Administration, have a specialised Gray Whale conservation strategy, where they aim to reduce deaths from entanglements in fishing gear by working closely with fishermen to find new strategies to reduce bycatch. They also respond to dead or injured gray whales, either to autopsy them to determine cause of death, or more hopefully to rescue and rehabilitate them. By recording whale appearances in shipping zones, scientists at NOAA aim to assist large vessels in reducing whale strikes. They have also worked to implement speed controls across important migratory paths. You can learn all about this work at Gray Whale | NOAA Fisheries , where you can find all of their documentation on Gray Whale conservation strategies.

Awesome Videos!


Alter, S.E. Rynes, E. and Palumbi, S.R. (2007) ‘DNA evidence for historic population size and past ecosystem impacts of gray whales.’ PNAS

Bradford, A.L. Weller, D.W. Ivaschenko, Y.V. Burdin, A.M. and Brownell Jr, R.L. (2009) ‘Anthropogenic scarring of western gray whales.’ Marine Mammal Science

Findley, T.L. and Vidal, O. (2002) ‘Gray whale at calving sites in the Gulf of California, Mexico.’ Journal of Cetacean Research

Pike, G.C. (1962) ‘Migration and feeding of the gray whale.’ Journal of the Fisheries Research Board of Canada

Pyenson, N.D. and Lindberg, D.R. (2011) ‘What happened to Gray Whales during the Pleistocene? The ecological impact of sea-level change on benthic feeding areas in the North Pacific Ocean.’ PLOS ONE

Weller, D. Budin, A. Wursig, B. Taylor, B. Brownell Jr, R.L. (2002) ‘The western gray whale: a review of past exploitation, current status and potential threats.’ Journal of Cetacean Research and Management


July 12, 2023
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