we are not even One month into “super” Niño, the Pacific’s natural weather pattern characterized by warmer-than-average sea surface temperatures, and fisheries around the world are already turbulent.

In Peru, government officials have effectively canceled the anchovy fishing season, one of the country’s most important exports and a leading source of fish oil and animal feed globally. The Indian government is preparing for a smaller, less plentiful Indian mackerel season. Meanwhile, in Southern California, recreational and commercial fishermen have reported some of the most successful months of tuna fishing they have ever seen.

The divergent scenarios show how El Niño can create winners and losers throughout the fishing industry, decimating some species and making others easier to catch. For fishermen, the result is instability, and many are forced to consider seasonal diversification. And consumers can expect fluctuations in the price of key seafood products.

“People are worried,” said Juan Carlos Sueiro, economist and fisheries director for the nonprofit Oceana Perú. As climate change is expected to make El Niño more frequent and stronger, “our vulnerability is increasing.”

El Niño is a weather phenomenon that occurs every two to seven years in the tropical Pacific Ocean. It was named for Peruvian fishermen who, hundreds of years ago, noticed periodic fluctuations in their catch, with large declines every few years around Christmas. They called him El Niño, in honor of the baby Jesus.

The reason it has such disparate impacts on different fisheries has to do with the way it moves through ocean water.

Under normal conditions, trade winds blowing westward along the equator move warm water from South America toward Asia. This causes cold, nutrient-rich water to rise from the depths, a process known as “upwelling” that encourages the growth of small algae near the ocean’s surface. However, during an El Niño event, weakening trade winds slow or even stop this upwelling. Less algae on the surface means that species that depend on them, such as anchovies, are forced to search for food in deeper waters. This not only makes fish more difficult to catch, but can also stress and reduce their populations.

At the same time, these ocean dynamics can boost other fisheries. El Niño often sees warm-water species like skipjack tuna drifting toward the coastal waters of the Americas, where temperatures would normally be too cold for them. Closer to the coast, these species are easier to catch.

Both dynamics affect Peru, where El Niño of the past ended the life of the country. anchovy fishery (the largest single-species fishery in the world) and increased the availability of shrimp, scallops, dorado and tuna. This spring and summer, El Niño coastal conditions have already affected the country’s anchovies, prompting the government to issue an indefinite ban on their fishing during the April to July season so that their populations do not decline further. Humberto Speziani, a Peruvian industrial fishing advisor and former director of the International Marine Ingredients Organization, said vessels equipped with sonar technology have been locating anchovies more than 100 meters below the sea surface. Even if commercial fishermen tried to catch those anchovies, they probably couldn’t do it: that’s twice the depth that can be reached with normal purse seines.

Seafood prices may also change due to the milder impacts of El Niño outside the Pacific Ocean. Wild salmon, for example, can become so thin due to lack of food during El Niño that they are called “snakes”; Their decline in North American coastal waters can lead to higher boat prices (which fishermen receive at the dock) that are then passed on to retail and restaurant customers. And in local Peruvian markets, prices for horse mackerel and croaker have already doubled, prompting families to buy more chicken. Sueiro said the opposite may happen with species like shrimp, whose populations increased during the past El Niño.