Sea Animals That Are Going Extinct and Why

Dozens of marine species face extinction right now, driven by a web of human activities that ranges from fishing nets to rising ocean temperatures. While recorded marine extinctions have historically been rarer than on land, the gap is narrowing fast, and the number of ocean species classified as threatened keeps climbing. The threats are not mysterious: overfishing, climate change, pollution, and habitat destruction account for the vast majority of cases, though the way these pressures combine makes each species’ story distinct.

Why Marine Extinctions Seemed Rare Until Recently

For a long time, the ocean appeared more resilient to extinction than land. Fewer than two dozen confirmed marine extinctions had been documented out of more than 850 total recorded extinctions globally, a rate roughly nine times lower than for non-marine species.¹ But that number is misleading. The ocean is enormous and poorly surveyed. Only about 3% of known marine species have been formally assessed for extinction risk by the IUCN, compared with 4% of non-marine species. When researchers account for this assessment gap, the difference in extinction risk shrinks considerably.

There is another wrinkle: wide geographic ranges, which tend to protect land animals from extinction, do not seem to offer the same buffer in the sea. Studies of large marine species found that extinction risk among wide-ranging ocean animals is actually higher than for most groups on land, and that having a big range does little to reduce a marine species’ vulnerability.² One analysis showed virtually no relationship between range size and extinction risk for high-value marine megafauna, a stark contrast to the pattern seen on land.³ In other words, even ocean animals that roam vast stretches of water are not safe.

The Vaquita and the Gillnet Problem

The vaquita, a small porpoise found only in the upper Gulf of California, is probably the most critically endangered marine mammal alive. Fewer than a dozen individuals are thought to remain. The cause of its collapse is singular and well understood: drowning in gillnets set for totoaba, a large fish whose swim bladder commands high prices on the black market.⁴ Gillnet entanglement has already driven one cetacean to extinction, the baiji, a river dolphin from China’s Yangtze, and the same mechanism is responsible for the vaquita’s imminent disappearance.⁵

What makes the vaquita situation so frustrating is that the biology is not complicated. This is not a species struggling against warming temperatures or shifting ecosystems. It is being caught and killed in fishing gear, and decades of bans and enforcement attempts have failed because illegal totoaba fishing persists. The vaquita has become a symbol of how enforcement gaps can override even the clearest scientific warnings.

North Atlantic Right Whales

With an estimated population hovering around 350 animals, the North Atlantic right whale is among the most endangered large whales on the planet. Two threats dominate: entanglement in fishing gear and collisions with ships. A mass mortality event in Canadian waters in 2017 killed at least a dozen right whales in three months, driven by a combination of gear entanglement and vessel strikes, and galvanized emergency regulatory action.⁶

Ship strikes alone are a staggering problem. A risk model covering the U.S. East Coast estimated that ocean-going vessels account for roughly 16 whale mortalities per year, making up about 78% of total vessel-strike mortality risk. Smaller vessels add another few deaths annually.⁷ For a population this small, losing even a handful of reproductive-age females each year can push the trajectory toward extinction. Speed restrictions and modified shipping lanes help, but compliance remains uneven.

Sharks and Rays in Freefall

About one-third of all shark, ray, and chimera species are now threatened with extinction, and overfishing is the universal driver.⁸ Of the 391 species classified as threatened, overfishing is the sole threat for roughly two-thirds. For the rest, it combines with habitat loss, climate change, or pollution. Two-thirds of shark species showing up in a major global fin trade hub were themselves threatened with extinction, highlighting how commercial demand accelerates the problem.⁹

Pelagic sharks are especially vulnerable. Species like the silky shark, shortfin mako, oceanic whitetip, and bigeye thresher score high on ecological risk assessments for longline fisheries because they reproduce slowly and are frequently caught as bycatch.¹⁰ A shark that takes a decade to reach reproductive age and produces only a few offspring at a time simply cannot withstand heavy fishing pressure the way a fast-breeding fish might. Once populations decline past a certain point, recovery takes decades even if all fishing stops.

Sea Turtles and the Warming Sand Problem

Sea turtles face a distinctive climate threat that stems from their biology: the sex of their hatchlings is determined by the temperature of the nest during incubation. Warmer sand produces more females. As global temperatures rise, turtle populations are becoming increasingly female-skewed, raising fears that a shortage of males could eventually threaten reproduction. A study of green sea turtles at the northern Great Barrier Reef found that nearly all juveniles were female, prompting warnings about long-term population viability.¹¹

The picture is more complex than the headline suggests, though. A global analysis of 64 nesting sites found female-skewed sex ratios at 57 of them, with skews exceeding 90% female at 17 sites. But the researchers found no correlation between the degree of recent warming and the degree of sex-ratio skew, suggesting that female-heavy ratios have likely persisted at some sites for many decades and that factors like sand color, nest depth, shade, and rainfall also play important roles.¹² Meanwhile, a study of the Cape Verde Islands, one of the world’s largest turtle rookeries, projected that while sex ratios are becoming more female-heavy, complete feminization of that population is not imminent. Rising temperatures actually increased the number of breeding females and hence the natural rate of population growth in the near term.¹³ So the threat is real but not uniform, and it plays out on different timelines at different beaches.

Plastic ingestion adds another layer of risk. A quantitative study of sea turtle deaths found a 50% probability of mortality once an animal had 14 pieces of plastic in its gut.¹⁴ Turtles that died of causes unrelated to plastic had consistently less plastic in their digestive tracts than those that died of indeterminate causes, suggesting that even sub-lethal plastic loads contribute to mortality in ways that are not always obvious during necropsy.¹⁵

Coral Reefs Are Collapsing, Not Just Bleaching

Coral bleaching gets a lot of attention, but what is happening now goes beyond bleaching into outright death. Marine heatwaves are increasingly killing corals directly, dissolving their skeletons and destroying the three-dimensional reef structure that thousands of other species depend on.¹⁶ The 2016 heatwave on the Great Barrier Reef drove catastrophic die-offs of fast-growing staghorn and tabular corals, transforming the ecological structure of 29% of the reef system’s nearly 3,900 individual reefs.¹⁷

The fourth global bleaching event, which unfolded in 2023-2024, pushed things further. In the Tropical Eastern Pacific, sea surface temperature anomalies peaked at over 2°C above normal, with accumulated heat stress reaching record levels far beyond established mortality thresholds. Regional coral mortality exceeded 76%, and some reefs lost every living coral.¹⁸ When corals die on this scale, the reef stops producing the calcium carbonate skeleton that gives it structure. Without that framework, the entire ecosystem of fish, invertebrates, and algae that depends on the reef unravels.

Acidification, Oxygen Loss, and the Creatures Nobody Sees

Two slower-moving consequences of carbon emissions are reshaping ocean habitats in ways that threaten species most people have never heard of. Ocean acidification, caused by seawater absorbing excess atmospheric CO₂, is already dissolving the shells of pteropods, tiny swimming snails that form a critical base of marine food webs. Along the U.S. West Coast, surveys found that more than half of nearshore pteropods showed severe shell dissolution damage. The extent of corrosive waters in the upper ocean had increased more than sixfold compared to pre-industrial conditions, and researchers estimated that severe shell dissolution had already doubled and was on track to triple by 2050.¹⁹ Similar dissolution was documented in live pteropods pulled from the Southern Ocean, where upwelling deep water mixed with surface water containing human-produced CO₂.²⁰

Pteropods may seem insignificant, but they are a primary food source for salmon, herring, and many other commercially important fish. Their decline ripples upward through the food chain. And while shell dissolution does not immediately kill the animals, lab experiments confirmed that it worsens as water becomes more corrosive and is likely affecting pteropod populations well before outright mortality is observed.²¹

Meanwhile, warming oceans hold less dissolved oxygen, and expanding low-oxygen zones are squeezing the habitable space for large pelagic fish like marlins and tunas. In the tropical northeast Atlantic, the upper oxygen-rich layer shrank at a rate of about a meter per year between 1960 and 2010, resulting in an estimated 15% habitat loss over that period. Electronic tagging of blue marlin confirmed that these fish are being compressed into shallower water, which makes them more vulnerable to surface fishing gear.²² The pattern is expected to worsen: as oxygen minimum zones keep expanding, both fish diversity and demersal fisheries face increasing pressure.²³

Deep-Sea Species and Bottom Trawling

The deep ocean was once assumed to be beyond human reach, but bottom trawling now operates along most continental margins worldwide. Trawling over hard seabed, particularly on seamounts, routinely strips away most of the living organisms attached to the bottom, including ancient deep-sea corals and sponges that can be centuries old. Because these animals grow extremely slowly and reproduce infrequently, recovery after trawling is predicted to take decades to centuries.²⁴ A study of chronically trawled deep-sea slopes confirmed that this represents a major threat to deep seafloor ecosystems at a global scale.²⁵ Many of these species have not even been formally described by science, meaning some may be lost before they are discovered.

Disease Outbreaks Amplified by Warm Water

Warming oceans are also fueling disease outbreaks. The sunflower sea star, once one of the largest and most common predators on the Pacific seafloor, collapsed across its entire range in just a few years after a wasting disease swept through during a marine heat wave. The decline was continental in scale and so rapid that researchers described it as a threat to the species’ persistence.²⁶ A decade of follow-up research confirmed that elevated sea surface temperature was one of the strongest factors associated with the outbreak.²⁷ The loss of sunflower sea stars triggered a cascade: without this keystone predator, sea urchin populations exploded and devoured kelp forests along much of the West Coast, creating barren underwater landscapes.

Noise, Chemicals, and Less Visible Threats

Not every threat to marine life is as visible as a fishing net or a bleached reef. Underwater noise pollution, particularly from military sonar, has been repeatedly linked to mass strandings of beaked whales. Stranding events associated with naval sonar exercises have now been documented in the Bahamas, Canary Islands, Mediterranean, and the Mariana Islands, where sonar events between 2011 and 2019 coincided with the stranding of multiple beaked whale species.²⁸ Research on northern bottlenose whales showed strong behavioral responses to both close and distant sonar signals, supporting the hypothesis that noise-driven behavioral disruption is the pivotal link between sonar and strandings.²⁹

Chemical contamination adds yet another pressure. Endocrine-disrupting compounds have been found in top predators across the Mediterranean, raising flags about potential reproductive harm in species that are already under stress from other threats.³⁰ For long-lived species that accumulate contaminants over their lifetimes, even low-level chemical exposure can compound other sources of decline in ways that are hard to measure directly.

When Populations Get Too Small

Once a marine population drops below a certain size, genetic problems start to compound the external threats. The Southern Resident killer whales of the Pacific Northwest illustrate this dynamic. Genetic analysis found that just two adult males sired 52% of all sampled offspring born since 1990, and at least four cases of inbreeding were documented, including matings between parents and their own offspring and between half-siblings.³¹ So far, researchers have not detected reduced survival or fertility in the inbred individuals, but the population’s tiny size means the genetic risks will only grow over time. Giant clams face a similar bottleneck problem: overharvesting has reduced wild densities to the point where rampant illegal fisheries continue to erode populations despite legal protections.³²

What Actually Helps

The evidence on marine protected areas is remarkably clear. No-take marine reserves, where all fishing is prohibited, show fish biomass averaging roughly 670% greater than in unprotected waters and about 340% greater than in partially protected areas that still allow some extraction.³³ All major fish groups, from top predators to herbivores, had higher biomass in effective no-take reserves, with gains between 40% and 200% compared to fished areas.³⁴ Partially protected areas, by contrast, often showed no meaningful difference from open waters. The implication is uncomfortable but straightforward: half measures do not work very well.

For coral reefs, an emerging approach involves selective breeding of heat-tolerant corals. Recent experiments showed that choosing parent colonies with high heat tolerance increased the survival of adult offspring under simulated marine heatwaves, with the genetic basis of heat tolerance estimated to be substantial enough that selective breeding could theoretically boost tolerance by roughly 1°C-week of additional heat exposure within a single generation.³⁵ Forecasting models have identified hundreds of reefs, about 7.5% of the Great Barrier Reef, that may harbor naturally heat-tolerant corals suitable for breeding programs or transplantation to degraded areas.³⁶ The researchers themselves caution, however, that the moderate levels of enhancement they found mean selective breeding cannot substitute for aggressive climate action.

The Economics of Keeping Animals Alive

One of the more pragmatic arguments for marine conservation comes from ecotourism. On Boa Vista Island in Cabo Verde, the estimated annual economic value of sea turtles rose from roughly €300,000 to nearly €2 million between 2008 and 2019, driven by conservation investment and the growth of turtle-watching tourism, while the consumptive value from poaching declined. The shift gave local communities a financial stake in keeping turtles alive.³⁷ Similar dynamics play out with shark ecotourism: even communities that have historically depended on shark fishing may shift toward conservation when the long-term revenue from shark-watching tourism exceeds what fishing provides.³⁸

Indigenous and local ecological knowledge is also proving valuable for understanding marine decline. In Baja California, fishers’ memories of abalone catches over the past 60 years correlated strongly with official landings data, demonstrating that local knowledge provides a reliable, long-term signal for tracking species collapse.³⁹ For species like yelloweye rockfish, Indigenous knowledge has helped extend historical population baselines further back in time than scientific records alone could reach, filling gaps that are critical for understanding how much a population has actually declined.⁴⁰ This kind of information matters because conservation targets based only on recent scientific data risk normalizing already-depleted populations as a baseline, underestimating how much recovery is actually needed.