Overfishing is concentrated in several well-documented regions, with the worst hotspots in the Mediterranean Sea, Southeast Asia, West Africa, and the Indian Ocean. Globally, 35.5 percent of assessed fish stocks are classified as overfished, according to the FAO’s most detailed marine assessment to date. That means roughly one in three fish populations is being harvested faster than it can reproduce. The remaining 64.5 percent are fished within biologically sustainable levels, but the picture varies dramatically by region.
The Mediterranean and Black Seas
The Mediterranean is one of the most overfished bodies of water on the planet. Even after a decade of gradual improvement, 52 percent of assessed stocks in the Mediterranean and Black Seas remain overfished. That’s better than it used to be, but it still means more than half the fish populations scientists have evaluated are being depleted. The semi-enclosed geography of the Mediterranean makes this especially dangerous: fish populations have fewer escape routes and less mixing with healthier stocks from open ocean waters.
Southeast Asia and the South China Sea
Southeast Asia has experienced some of the most dramatic fishery collapses ever recorded. In the Gulf of Thailand, total harvestable fish biomass has dropped to roughly 7.5 percent of what existed before industrial fishing expanded in the region. The Bohai Sea in China shows nearly identical depletion, with both areas retaining less than 8 percent of their original fish biomass. That’s a 95 percent decline.
What makes these collapses unusual is that catches have remained relatively high even as populations cratered. Fish communities shifted toward smaller, faster-reproducing species that partially replaced the larger fish that were wiped out. This masks the severity of the problem: boats keep coming back with fish, but the ecosystem underneath has fundamentally changed. Similar patterns of severe biomass decline have been documented in the Philippines and Malaysia, making the broader South China Sea and Coral Triangle among the most stressed marine regions in the world.
West Africa’s Coastal Waters
The waters off West Africa are hit by a combination of overfishing and large-scale illegal fishing. Across just six countries in northwest Africa (Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, and Sierra Leone), illegal fishing is estimated to be worth $2.3 billion. That figure represents up to 20 percent of the total global losses from illegal, unreported, and unregulated fishing, all concentrated in one relatively small stretch of coastline.
For communities along this coast, the consequences are direct. Small-scale fishers who depend on nearshore catches for food and income find themselves competing with industrial foreign fleets, many operating illegally or under minimal oversight. Fish populations that once sustained millions of people are shrinking, and the economic scale of illegal extraction makes enforcement extraordinarily difficult.
The Indian Ocean
Yellowfin tuna in the Indian Ocean are in critical condition. Multiple independent assessments confirm the population is both overfished (the stock is too small) and subject to ongoing overfishing (too many fish are still being taken each year). This is significant because yellowfin tuna is one of the most commercially valuable species in the ocean, caught by industrial longline and purse seine fleets from dozens of nations.
By contrast, yellowfin tuna in the Eastern Pacific show the lowest levels of exploitation among the major ocean basins, illustrating how the same species can be healthy in one region and collapsing in another depending on how fishing pressure is managed.
The High Seas and Deep Ocean
International waters, where no single country has jurisdiction, present their own set of problems. Satellite tracking has identified high-seas hotspots where fishing vessels transfer their catch to refrigerated cargo ships at sea, a practice called transshipment. These transfers are concentrated in the south Indian Ocean and equatorial Pacific, and they often involve longline vessels targeting tuna, sharks, and billfish. Transshipment makes it harder to track how much fish is actually being caught and where it ends up, creating gaps in the data that regulators rely on.
Deep-sea bottom trawling is another pressure point. Most high-seas bottom trawling takes place in four areas: the Northwest Atlantic (particularly the Grand Banks and Flemish Cap), the Northeast Atlantic, the Southwest Indian Ocean, and the Southwest Pacific around New Zealand. These fisheries target slow-growing species like orange roughy, which can live over 100 years and reproduce slowly. That life history makes them extremely vulnerable to overfishing, and the pattern has been one of serial depletion: fleets find a new population, fish it down rapidly, then move on to the next one.
The Central Arctic Ocean
One region where overfishing is not yet happening is the Central Arctic Ocean, and an international agreement is working to keep it that way. A legally binding moratorium entered into force in June 2021, preventing commercial fishing in Arctic high seas before it begins. There are currently no commercial fisheries in the region, with most of the area still covered by ice year-round. But as summer ice coverage shrinks, commercially viable fishing could become possible. The agreement is the first of its kind to take a precautionary approach, protecting waters before they’re exploited rather than trying to recover stocks after they’ve collapsed.
Why Some Regions Are Worse Than Others
The global average of 35.5 percent overfished stocks obscures enormous regional variation. When weighted by production volume, 77.2 percent of global fish landings come from biologically sustainable stocks. This sounds reassuring, but it reflects the fact that a handful of well-managed fisheries (often in wealthier nations with strong enforcement) produce huge volumes, while smaller, poorly monitored fisheries in developing regions are collapsing with less statistical visibility.
The pattern is consistent: overfishing is worst where governance is weakest, where illegal fishing is most profitable, and where growing coastal populations depend heavily on fish for protein. Southeast Asia, West Africa, and parts of the Indian Ocean check all three boxes. The Mediterranean is an outlier as a relatively wealthy region with persistent overfishing, driven largely by the sheer number of nations sharing the same enclosed sea and the difficulty of coordinating management across them.