What are the main threats affecting baleen whales?

You have probably seen it at least once on the news. There are a lot of accidents happening with baleen whales. Worldwide reports of ship strikes (when a boat runs into a whale) and entanglement increase every year. It makes me sad because baleen whales are still recovering from the intensive industrial whaling that went on for centuries and decimated their populations. Baleen whales are the largest mammals on earth. The largest member of the 14 species of baleen whales is the blue whale (Balaenoptera musculus). Its length can reach 30m. Baleen whales are so-called because of their baleen plates (instead of teeth). Baleens act as filters to trap the krill and small fish inside the whales’ gigantic mouths. 
These baleen whales face many threats.

Photo by EcoHealth Alliance, NOAA Permit #932-1905

Climate change-induced prey-reduction

Many baleen whale species migrate from the tropics to the poles to feed. Whales eat krill (small shrimp), and krill feed on phytoplankton. Juvenile krill needs a constant source of algae growing on sea ice to survive. As a result, climate change could impact krill populations. These changes, combined with humans harvesting a lot of krill, could result in food shortages for the whales.


Reports of entanglements have increased in recent years. Entanglement means ” when a whale becomes caught in a range of equipment”. Whales can get caught in a lot of floating debris including:

  • ropes from crab/lobster pots and other fishing lines extending to the surface
  • gill and drift nets
  • aquaculture equipment (pearl oyster farms, mussel farms, fish farms)
  • discarded or lost fishing gear, ghost nets, or other marine debris

Short-term impacts of entanglement include minor inconvenience, behavioral change, and minor injuries.

Long-term impacts of entanglement include chronic injuries, the potential for infection, reduced mobility (which may affect the ability to migrate, feed, breed, or care for their calves), increased potential for predation, and ultimately the death of the animal or the death of the calf.

Ship Strikes

Collision with ships is one of the main causes of mortality in baleen whales worldwide. Ship strikes usually occur along commercial tracks. Speed limits have been established in some areas. However, the limits are usually not enforced, and many boats decide to go faster to save some time. A recent Montreal visitor, a beautiful young female humpback died after she was hit by a boat in the Saint Lawrence River.


We, as human beings, are responsible for a lot of noise in our oceans. The main sources of human-made noise include seismic exploration, shipping noise, military sonar systems, noise associated with coastal developments, etc. Noise is bad for whales. Some whales can change their dive time/dive profile; change their respiration rate, or change their direction of travel. These changes can impact their long-term survival. Additionally, some whales do not hesitate to leave an area with a lot of noise and relocate somewhere quieter. We have a post on the effect of military exercises on beaked whales here.

“Scientific” Whaling

Since 1986, Iceland and Japan have issued scientific research permits on several whale species. They agree to catch a certain number of whales and must report annually to the International Whaling Commission (IWC). Japan had quotas that included catches of minke whales, humpback whales, and fin whales in the Southern Ocean (under the JARPA II program for example). Under strong international pressure, Japan terminated the JARPA II program.

In 2018, Japan decided to leave the IWC. This is good news and bad news for our beloved whales. The good news is that, with Japan out of the way, the IWC can finally focus on marine protected areas for the protection of marine mammals. The bad news is that Japan is going to resume whaling in its own waters. You can find more information here.


Chemical pollution is not the biggest threat to baleen whales. Unlike for toothed-whales, the concentrations of industrial pollutants, pesticides, and heavy metals are low in baleen whales. Most of these pollutants increase in concentration at each step of the food chain and baleen whales feed on low-level prey like krill or small fish. However, pollutant levels are still measurable in baleen whales. 

Microplastics can reach a high density and turn the water into plastic soup — Credit: Anaïs Remili

Microplastics are a concerning threat for baleen whales. They enter their body when the whales filter water to feed. They can cause accumulate and block the digestive tract. Other effects of microplastics in baleen whales are poorly known at the moment. However, scientists around the world are trying to solve this question.

Now let us know:

Have you witnessed an entanglement somewhere in the world? Or a ship strike? What do you think we could do to reduce the threats to baleen whales? Let us know in the comments.

Anaïs is the founder of Whale Scientists. She is a PhD student at McGill University working on killer whale ecology and pollution. You can read more about her here.

1 thought on “What are the main threats affecting baleen whales?”

  1. I’m an X member of Greenpeace. I have witnessed Russia’s slaughter of whales. The kill is so unnecessary. I’m 60 years old now. I was 20 something when aboard the Rainbow Warrior. I find it so disheartening to know these wonderful creatures are still threatened by man. We are intelligent but some of us are not smart enough to save this fabulous species. I have no answer to mans ignorance.

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