These 14 ocean species have already gone extinct. A dozen others will probably disappear in our lifetime.

According to environmental news site Mongabay, the 15 extinct species include various marine birds and mammals, sea snails, and the Christmas sandpiper pictured above.

There's urgency to protect wildlife. A 2017 study suggested the Earth is undergoing a process of "biological annihilation." As many as half of the total number of animal individuals that once shared the planet with us are already gone, it found.

The sea duck generally wasn't hunted for food, but it's possible that European settlers pushed the animal out of its natural habitat.

Far fewer ocean species have gone extinct over the past 500 years than those on land — just 15 marine animals have gone extinct, compared to 514 terrestrial animal species, a 2015 study from the  found. But that ratio could shift in the coming years.

Humans once hunted the bird and harvested its eggs extensively. The great auk was even eaten by Neanderthals 100,000 years ago.

Other extinct ocean birds include the Saint Helena petrel and Pallas's cormorant.

These graylings were amphidromous — meaning they spawned in freshwater streams then migrated, maturing in saltwater.

It lived and fed exclusively on one type of seagrass called eelgrass. But the population and distribution of eelgrass plummeted from disease in the 1930s, causing the limpet to die out.    

Another species of sea snail native to China, called Littoraria flammea, also disappeared in the last 100 years or so.

Monk seals were a target for hunters, who caught them easily while they were resting or nursing their pups.

In 2007, experts thought they had located some remaining Japanese sea lions, but the creatures turned out to be California sea lions, which look very similar. 

It was the largest type of mink, so hunters and fur traders pursued it with aplomb.

As its name suggests, this sea cow was an herbivore, feeding mainly on kelp. It was covered in blubber like today's walruses to keep warm in the Arctic waters.

The primary threats to the dugong are boat injuries, unintentional capture in fishing gear in East Africa, and poaching in New Caledonia, per an IUCN 2022 update. 

Pollution from agriculture or oil exploitation is also leading to seagrass to become too scarce in both locations, per the IUCN

There are now only 250 mature individuals in East Africa and under 900 in New Caledonia.

Oceans hit their warmest levels on record for the fourth consecutive year in 2022, according to a new report by two dozen scientists.

Higher water temperatures and acidification cause corals to expel the algae living in their tissues and turn white, a process known as coral bleaching. 

Almost 33% of reef-forming corals are threatened with extinction, according to the recent UN report.

Twenty of the world's 54 abalone species are now threatened with extinction, per the ICUN 2022 update. 

Increasingly frequent and severe marine heatwaves are a critical danger for abalones. A 2011 heatwave killed 99% of Roe abalone in Western Australia, and the increased marine temperatures are making diseases spread more easily. 

According to the IUCN's Red List, 72 marine animal species are critically endangered, meaning they face an extremely high risk of extinction.

According to Australian Geographic, the species resides only in the Ashmore Reef and Hibernia Reefs off the coast of northwestern Australia. 

The venomous snake prefers to munch on eels and fish and has been negatively impacted by warming ocean waters.

The snake had thought to have been extinct. But it was thankfully spotted once in 2021.

"The short-nosed sea snake was thought to be lost forever from Ashmore – so it truly is a remarkable find, the whole ship of researchers was squealing in excitement," said Karen Miller of the Australian Institute of Marine Science who made the discovery. 

Vaquita means "little cow" in Spanish, and despite conservationists' best efforts to save the species, less than 30 of the animals remain today, according to the Marine Mammal Center.

An adult Hawksbill can weigh up to 150 pounds, according to the World Wildlife Fund. Named for its pointed beak, the Hawksbill turtle enjoys eating sea anemones, sponges, and jellyfish found around coral reefs. But poor reef health limits the turtles' access to food.

Named for its distinct nose, this creature was the first marine fish to receive federal protection as an endangered species under the Endangered Species Act in 2003, according to NOAA.

These fish are predators and are found near southern Florida, the Florida Keys, Bermuda, the Yucatan, and the Caribbean. The groupers swallow fish, crabs, and shrimp whole using suction created by their protruding mouths.

Starry sturgeons can reach more than 7 feet in length and weigh 180 pounds. They, too, are threatened by overfishing. Fishermen harvest the species for its caviar.

These tuna swim in the open seas and only breed in one part the Indian Ocean, southeast of the island of Java. They can reach lengths of 8 feet and weigh up to 570 pounds.

In the Netherlands, eels are smoked and eaten with toast. Londoners eat jellied eels and enjoy eel stew. In Italy and Egypt, eels are often fried as a tasty treat.

In addition to overfishing, the construction of dams and decreasing water quality have caused declines in European eel populations, according to the European Commission.

Since 2010, it has been illegal to keep angelsharks caught in waters of the European Union.

In addition to all the species listed here, there are more than 60 other critically endangered marine animals in the oceans today, according to the IUCN. All of these creatures have been negatively impacted by dying coral reefs, rising ocean temperatures, and pollution. 

Two-thirds of the world's oceans are in international waters, and up to now, only 1% of those were protected. 

That means that most of the marine wildlife was at risk from climate change, fishing, and collisions with boats. 

The treaty aims to achieve the protection of 30% of the ocean by 2030. 

A previous version of this article was published on May 6, 2019 and was updated to reflect the High Seas Treaty agreement. Aylin Woodward contributed to the previous version of this article.