What do whales eat for dinner?
Whales are always on the move, so they have to eat a lot to keep them going. Fortunately, the ocean offers a range of dining options.
All whales are divided into two suborders: Odontoceti (those that have teeth) and Mysticeti (which have baleen plates instead). A whale's diet depends on its suborder.
But not all whales within each group eat exactly the same thing. Each species has a favourite food.
And no matter where they are or what they eat, whales are almost always on the hunt for a tasty meal.
Blue whale diets
Blue whales are the largest animals ever to have lived. These colossal cetaceans often reach 30 metres in length and can weigh up to 180 tonnes - so they need to eat a lot to keep them swimming.
But despite their enormous size, blue whales feed almost exclusively on krill - small, shrimp-like crustaceans that grow to about six centimetres. These tiny animals are found in all of Earth's oceans, swimming in massive swarms, sometimes of more than 30,000 individuals.
The blue whale has one of the largest appetites of any animal, eating up to four tonnes of krill every day.
Blue whales, which have baleen plates, feed by taking huge mouthfuls of water and food. They then push the water back out using their baleen plates as a strainer, keeping the food in their mouths.
Right, minke, fin and sei whales also have baleen plates. All of them feed on krill, but sometimes include other sea creatures in their diets, such as copepod crustaceans and small fish.
Humpback and Bryde's whales also actively hunt for small schooling fish such as herring and anchovies.
Which whales have teeth?
Odontocete whales have traditional teeth. This means their feeding techniques and preferred foods are different from the Mysticeti.
There are over 80 species of odontocete, from the huge sperm whale to tiny, dog-sized porpoises. Dolphins, pilot whales and beaked whales are also odontocetes.
These whales catch their food, such as squid and fish, by either sucking them into their mouths or by grabbing and biting.
If their prey is too big to be swallowed whole, they will grip it in their teeth and shake it apart into smaller pieces.
For scientists, the only way to work out what a toothed whale eats is to either observe it hunting and eating, or look at the stomach contents of dead whales.
The deep ocean is so dark that it is difficult for whales to locate prey by sight, so toothed whales use echolocation to find their prey. The whale emits a call, which bounces off the prey. The echoes help the whale navigate towards its food.
What do killer whales eat?
Killer whales, the largest dolphin species, also have teeth, but their diet is different to other odontocetes.
Killer whales are apex predators, meaning they are at the top of their food chain.
They feed on fish and squid like other toothed whale species, but will also target seals, sea birds and even other whale species - even if they are far bigger than themselves. Killer whales are also the only known predator of great white sharks.
These whales are highly social and spend the vast majority of their lives swimming in large pods of family members, led by a female.
Hunting techniques are passed down through generations, so their diets depend on the region they inhabit and the pod's approach to hunting.
These highly intelligent whales have been documented creating large waves to wash seals off ice floes, and even intentionally beaching themselves to catch prey on the shore.
For scientists, one way to learn what their diet was like is by looking at the shape of an individual whale's teeth.
If the teeth have remained sharp, they are likely to have hunted seals and other large mammals. But if the teeth are noticeably worn down, it is because they spent their lives sucking up small fish.
An ocean of plastic
Plastic in the oceans poses an enormous threat as whales can become entangled in it or mistakenly swallow it.
Unlike foods in their day-to-day diets, plastic is indigestible. The material becomes lodged in their stomachs and intestines, causing blockages and severe pain.
Swallowing plastic can be fatal for whales and other sea creatures, even if they are otherwise completely healthy.
In February 2017, a stranded Cuvier's beaked whale in Norway was found to have ingested around 30 plastic bags.
It is estimated that more than eight million tonnes of plastic ends up in Earth's oceans every year. Experts are warning that by 2050, there could be more plastic in the water than fish.
This man-made material is now found on the sea floor, at the surface, on coastlines and even embedded in Arctic sea ice.