Fish Stocks Are Declining Worldwide, And Climate Change Is On The Hook

December 14, 2015,, Claire Leschin-Hoar

A fisherman shovels grey sole, a type of flounder, out of the hold of a ship at the Portland Fish Pier in Maine, September 2015. New research finds the ability of fish populations to reproduce and replenish themselves is declining across the globe. The worst news comes from the North Atlantic, where most species are declining.For anyone paying attention, it’s no secret there’s a lot of weird stuff going on in the oceans right now. We’ve got a monster El Nino looming in the Pacific. Ocean acidification is prompting hand wringing among oyster lovers. Migrating fish populations have caused tensions between countries over fishing rights. And fishermen say they’re seeing unusual patterns in fish stocks they haven’t seen before.

Researchers now have more grim news to add to the mix. An analysis published Monday in the Proceedings of the National Academy of Sciences finds that the ability of fish populations to reproduce and replenish themselves is declining across the globe.

“This, as far as we know, is the first global-scale study that documents the actual productivity of fish stocks is in decline,” says lead author Gregory L. Britten, a doctoral student at the University of California, Irvine.

Britten and some fellow researchers looked at data from a global database of 262 commercial fish stocks in dozens of large marine ecosystems across the globe. They say they’ve identified a pattern of decline in juvenile fish (young fish that have not yet reached reproductive age) that is closely tied to a decline in the amount of phytoplankton, or microalgae, in the water.

“We think it is a lack of food availability for these small fish,” says Britten. “When fish are young, their primary food is phytoplankton and microscopic animals. If they don’t find food in a matter of days, they can die.”

The worst news comes from the North Atlantic, where the vast majority of species, including Atlantic cod, European and American plaice, and sole are declining. In this case, Britten says historically heavy fishing may also play a role. Large fish, able to produce the biggest, most robust eggs, are harvested from the water. At the same time, documented declines of phytoplankton made it much more difficult for those fish stocks to bounce back when they did reproduce, despite aggressive fishery management efforts, says Britten.

When the researchers looked at plankton and fish reproduction declines in individual ecosystems, the results varied. In the North Pacific — for example, the Gulf of Alaska — there were no significant declines. But in other regions of the world, like Australia and South America, it was clear that the lack of phytoplankton was the strongest driver in diminishing fish populations.

“When you averaged globally, there was a decline,” says Britten. “Decline in phytoplankton was a factor in all species. It was a consistent variable.”

And it’s directly linked to climate change: Change in ocean temperature affects the phytoplankton population, which is impacting fish stocks, he says.

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New Ocean Acidification Study to Launch in Prince William Sound, By Darcy Dugan, April 29th, 2014

Beginning this week, two surface wave gliders, resembling yellow surfboards, will be cruising around Prince William Sound as part of a five-month monitoring program to measure ocean acidification. Simultaneously, state-of-the-art instrumentation installed on a glacier tour boat will monitor glacial runoff while an underwater autonomous glider will patrol beneath the surface looking for plumes of water that could be harmful to some species.

A remote-controlled glider, similar to the one shown here, will measure ocean acidification in Prince William Sound from May to September. Photo credit: Richard Feely, NOAA/PMEL

A remote-controlled glider, similar to the one shown here, will measure ocean acidification in Prince William Sound from May to September. Photo credit: Richard Feely, NOAA/PMEL

The project, funded mostly by the National Oceanic and Atmospheric Administration’s Ocean Acidification Program, is led by Dr. Jeremy Mathis of the Pacific Marine Environmental Laboratory and Dr. Wiley Evans from the University of Alaska Fairbanks (UAF) Ocean Acidification Research Center in partnership with the Alaska Ocean Observing System (AOOS).

Scientists estimate that the ocean is 25% more acidic today than it was 300 years ago, largely due to increasing levels of atmospheric carbon dioxide (CO2) from burning fossil fuels and changes in land use. Almost half of the CO2 emitted remains in the atmosphere, with the land and ocean absorbing the rest. When the ocean absorbs CO2, its pH balance changes through a process called ocean acidification. Because cold water can absorb more CO2 than warm water, acidification can disproportionately impact coastal regions around Alaska.

Recent publications by Dr. Mathis and Dr. Evans have shown that the process of ocean acidification may be worsened around tidewater glaciers due to the freshwater melt plumes that occur is summer and fall. “The glacier melt plumes have some really unique chemistry that can exacerbate ocean acidification and impact the environment in Prince William Sound and out into the Gulf of Alaska,” Mathis said. “Our goal is to use the latest technology to find out what’s happening so we can communicate that to Alaska residents and stakeholders.”

According to AOOS Executive Director Molly McCammon, the research effort builds upon the partnership developed with the OA Research Center at UAF to support statewide OA monitoring. The consortium supports five buoys around the State, as well as twice a year sampling in the Gulf of Alaska, and development of a Gulf of Alaska OA forecast model. Data from the monitoring efforts will be available on both the AOOS website and the UAF’s OA Research Center website. “With this new effort, we’re increasing our ability to view and understand Alaska’s oceans in four dimensions – two dimension space, depth and time.”

When completed in early September, the study will have provided the longest continuous observations of ocean acidification in Alaska to date. “We are very proud to have the opportunity to partner with AOOS and be the leaders in glider technology in Alaska,” said Mathis. “This work could be a game-changer in our understanding of how ocean acidification will impact our state.”