Dead Zones, Part 5

In yesterday’s blog, we began a general discussion of how our food choices affect the environmental health of our oceans. With catches of wild fish declining worldwide, people have increasingly been raising food species of fish by “aquaculture”—more commonly known as fish farms. These facilities have grown so rapidly over the last few decades that almost half the fish eaten worldwide (46 percent) are now raised via aquaculture. At first glance, aquaculture seems like a reasonable way to continue feeding the ever-growing worldwide demand for fish while taking pressure off our depleted fisheries.

Unfortunately, aquaculture seems to pose as many environmental problems as it solves. One of these problems is that it produces the same conditions caused by the runoff of chemical fertilizers in farming, creating waters rich in phosphates, nitrates, and organic nutrients that promote the rapid and large-scale growth of plant life, especially algae. This, in turn, leads to the leaching of oxygen from the waters and the formation of the same dead zones caused by chemical fertilizer runoff.

Another environmental problem produced by aquaculture is that many of the fish raised by this method are carnivorous (species such as salmon, for instance). These fish need to be fed with fishmeal made from other, smaller fish (also called forage fish) of the kind eaten by the carnivorous fish in the wild. So while the aquaculture operations have served to take some of the pressure off the fisheries for the larger, carnivorous species, it has only redoubled the pressure on the global stocks of forage fish, such as sardines, anchovies and herring. And since these fish serve as food for a huge variety of animals, their overfishing doesn’t just threaten the survival of the forage fish species; it also imperils other top-predator fish, not to mention marine mammals and seabirds.

To be continued …

Photo courtesy of Pixabay.