When fish farmers first decided to rear their fish in coastal waters, they didn't stop to think about where the fish waste and uneaten feeds would go. “After all,” they must’ve felt, “the ocean is huge, and already full of fish waste anyway!” Both assumptions are true, but don’t have much weight considering the magnitude of fish farming today. Every year, a single sea cage in Norway can grow ten times the entire biomass of the wild Norwegian salmon population. Multiply that amount to that which a whole farm can grow, times the number of farms along the coastline of the entire country, and you get an unimaginable amount of fish poop!
Scientists have only begun to unearth the horrors underneath the open sea cages. In many cases, the seafloor can look like a dead zone or a dirty rug composed of a single species of opportunistic polychaete, and this can extend to several meters beyond the jurisdiction of the farms. Even seabeds situated close to 100 m underneath an open cage can be compromised. This is especially true in the beautiful fjords of Norway, which sure can look pristine above water but can look like scenes straight out of a Lovecraft novel meters beneath the surface.
But there’s no need to fret and feel like salmon aquaculture is doomed to destroy the planet. Some of the biggest stockholder companies for salmon farming are beginning to test their prototypes of closed sea farms with mechanized water input and output valves. These farms can be equipped with sludge and waste collectors so that the extruded water is free of fish waste and uneaten feeds. And instead of dumping the collected waste into the ocean, it can be transported onto land and used to produce fertilizer. Indeed, that’s several steps towards keeping our oceans clean and keeping the economy green. Sensitive benthic species can rest assured that their genes will survive tomorrow!