Say goodbye to the big fish in the ocean, and say hello to the small fish.

Vancouver, British Columbia – Villy Christensen summed it up in a sentence: „Say goodbye to the big fish in the ocean, and say hello to the small fish.“

Christensen, a professor at the University of British Columbia and director of the new Nereus program that aims to predict the future of the world’s oceans, had good reason to give a warning so dire.

First, the good news. He says that there are still a lot of fish in the sea: There is about 2 billion tons of fish biomass in the ocean, which works out to about 661 pounds (300 kilograms) per person on the planet. Even better, the total biomass in the ocean is staying relatively consistent.

The bad news? The balance in the type of fish has shifted. Big fish in the ocean, like grouper and cod, have experienced a 55 percent decline in last 40 years. In their place are small, oily fish such as myctophids.

The fish that remain are fish humans aren’t so interested in catching or eating, Christensen explained here at the annual meeting of the American Association for the Advancement of Science. „Half the world’s fish are small, in the open oceans and not exploitable.“

For some fishermen in the northern seas, climate change seemed like a total win: as oceans warmed, fish moved northward, meaning a bigger catch. But this won’t continue to be the case, said William Cheung, a researcher at the fisheries center at the University of British Columbia.

Northern waters are able to absorb and hold more gases, particularly carbon dioxide, which is growing steadily in the Earth’s atmosphere. Increased carbon dioxide in ocean waters makes it more acidic, and so northern oceans are becoming acidic faster than other parts of the globe; and more acidic seawater means less oxygen available in the water, making it difficult for fish to grow to full size.

….Cheung developed a global model that includes more than 600 species of fishes and invertebrates, to investigate the combined impacts of multiple human stressors on marine fisheries potential catch. With warming alone, northern fishermen increase their catch potential by 30 percent. But with the addition of acidification, they end up losing more than they gain.

„Although it’s not a crystal ball, these models are a useful tool for developing scenarios,“ Cheung said.