Oceans Acidification Could Starve Deep Sea Tuna - Research Urgently Neededff

By Atuna

The acidification of the world's oceans is a subject which increasingly starts to worry fisheries scientists and is getting more attention within the fisheries industry. The tuna industry, on the other hand, hasn't put a lot of effort in studying the impacts of this issue yet. The partnerships manager for Sustainable Fish in North America and consultant for many governmental institutions, Mr. Brad Warren, explains the possible implications of this environmental phenomenon on tuna fisheries.

Ocean acidification happens as a result of excessive Carbon Dioxide (CO2) in the atmosphere caused by pollution. The acid produced by CO2 in seawater thins the naturally rich soup of carbonate in seawater. That's the soup from which many organisms build their shells and bodies. They harvest the carbonate from the seawater around them and turn it into various forms of calcium carbonate. Once acidification worsens, it causes the soup to become so thin and acid that some small, young shellfish and some plankton species could start to dissolve.

According to the National Oceanic Atmospheric Administration (NOAA) in the United

States, since the industrial revolution human activities have resulted in atmospheric CO2 concentrations that have increased from approximately 280 to 385 parts per million (ppm). Environmental organizations, such as Oceana, claim that levels need to be kept below 350 ppm and that the tipping point would be 450ppm "at which point reefs as we know them would be extremely rare, if not non-existent".

NOAA claims that the oceans have absorbed approximately 525 billion tons of carbon dioxide from the atmosphere, or about one third of the anthropogenic carbon emissions released. Intergovernmental Panel on Climate Change (IPCC) suggests that by the middle of this century atmospheric carbon dioxide levels could reach more than 500 ppm, and near the end of the century they could be over 800 ppm.

"Will tuna see depletion of their food webs? It seems likely, but no one can predict exactly how it will play out. When they're young, most fish eat plankton, and tuna follow the same pattern. Once they grow a bit bigger, tuna become fish eaters, but they're still eating plankton-grazers like sardines", Mr. Warren explains and further alerts: "It's harder to predict impacts on tuna with any certainty, because there's very little research on the vulnerability of these species to CO2-driven changes in seawater chemistry. With that in mind, the tuna industry ought to consider pushing for research funding to understand potential impacts on tuna. The pollock industry has taken this concern so seriously that they've chipped in to fund some research on how acidification might affect the fish they catch in Alaska".

Studies show that so far acidification effects are more severe at depth than near the surface. This suggests that deeper-dwelling tuna might show an impact before those that prefer shallow waters. For example, bluefin might find a reduced prey base in their usual deepwater habitat: "However, what happens next is still speculation. Do they starve? Or do they move to shallower waters, or maybe less acidified waters? No clue. This is one area that merits further research", Brad Warren added.

At high concentrations of CO2, fish suffer all sorts of physiological problems: heart failure, respiratory trouble, and on and on. Larval forms show greatest vulnerability, and some studies show very high mortality when they're exposed to low-pH waters.

Therefore, Mr. Warren advises tuna fishermen to look seriously at two main mechanisms of harm that concern a lot of people in other fisheries:

1)     reduced forage supplies, and 2) potential direct impacts from CO2-altered seawater chemistry, especially on eggs, larvae and survival of juvenile fish.

"If tuna producers want more answers, they might want to think about getting in touch with the research community, joining research advisory boards to help steer the work toward relevant questions, and applying some muscle to the political process in support of programs that they view as priority research matters".

He added that supporting policies for deep reductions in CO2 emissions and reducing emission in fisheries as well are important steps to convert the problem and save money in energy spending.