By Daniel de la Calle
Researchers believe we should prepare ourselves for a world with more anchovies and less tuna:
Various recent studies indicate a constant decrease in the number of marine predators; from sharks to tuna, our “lions and tigers of the seas” are becoming less and less abundant. If certain key elements do not change soon, urgently, those large fish-eating-fish might become a thing of the past. Villy Christensen, Reg Watson and their colleagues at the University of British Columbia have conducted a study of historic records and noticed the steady loss of around 10% of top predator fish in the decades between 1910 and 1970. It was in the last forty years though, once more advanced fishing gear and techniques were used, that numbers really plummeted to the point that the seas are now home to a mere third of the fish population of 1910.
Fishing activities, our global catch, escalated throughout the 20th Century:
from roughly some 16 million (metric) tons per year in the 1950s to 80 million tons in the 1990s. In these past twenty years numbers simply stagnated. During 2006, for example, the catch was 76 million tons, or around 7 trillion fish. If such a trend continues top predators could become in fact become rare by 2050. This obviously does not mean that the oceans will be empty, there has actually been an increase in the abundance of small pray fish like anchovies, but neither are these the fish that people prefer to eat nor the sort and size of predator that can cap the number of small fish with the potential of damaging ecosystems. In more plain words, we are breaking the natural balance and opening the door to an uncertain future.
Throw a changing climate into this strained scenario and the consequences will be dire: if, as expected, more rain falls in the tropics, we could witness a freshening of the upper seas and a stratification of ocean layers that would make harder for nutrients to reach the surface. Jorge Sarmiento of Princeton University recently showed at an American Association for the Advancement of Science meeting projections made by five different computer programs about plankton concentration in such a future scenario. While the global nutrient drop might average 1 to 2 percent, there are areas where numbers could go down as much as 16 percent, which would obviously have a direct impact on the size of fish. William Cheung of the University of East Anglia fed some of this information into another simulation program and initial results indicated a 10 percent decrease in fish sizes. But it was once he included Ocean Acidification into his calculations that things got much more serious: 30 and even 40 percent growth drops were predicted.
A warmer, more acidic ocean that makes fish move more for food and therefore need more oxygen will also see fish migrating to cooler areas, as I already mentioned on a previous post. William Cheung believes half of the world’s stocks will travel up to 40 kilometers per decade, possibly displacing fisheries from one country’s waters to another’s.
Snappers fly above you at the Natural History Museum, NYC.
After all these bleak views I really want to finish the post with some hopefulness, though. I recently read online that Eric Schwaab, administrator of the National Marine Fisheries Service, delivered at the Boston Seafood show last March the extraordinary message that we might be witnessing the end of overfishing in US waters. Strict annual catch limits were imposed in 2010 on fisheries experiencing overfishing and this year all remaining fisheries will undergo the same restrictions and caps (thanks to the Magnuson-Stevens Fishery Conservation and Management Act from 2007). As mentioned above, some species remain dangerously over-fished, but the current general picture in US waters could be one of positive change, where even some beneficial results for fishermen are already visible: the National Marine Fisheries Service will increase catch limits for species with growing populations (cod, haddock and flounder to name a few) in the New England groundfisheries for the new fishing year that begins this Sunday, May 1st.