With the near exponential growth of the human population, the global demand for fish protein is the highest it has ever been. This leads to increased fishing pressure on wild fisheries, which when coupled with anthropogenic pollution and habitat destruction, results in the collapse of these fisheries. Yet the global demand is relentless: if we can no longer obtain wild fish from our oceans, the market demands that we obtain fish from some other source.
The ONLY answer to this growing crisis is aquaculture, or fish farming as it is commonly known. Just as agriculture is concerned with growing plants and animals on land, aquaculture is the practice of farming species in the water. Virtually every commercially-valuable species is farmed, from salmon and tilapia to urchins, mussels, and even seaweeds. These farms also take many forms, such as sea cages in the open ocean, earthen ponds near the shore, and recirculating systems in-land.
While all of the commercial aquaculture practices and systems used today are lucrative and economically-successful, most of them create a substantial environmental impact. From a commercial perspective the entire industry is relative young and the long-term environmental effects of these systems are still unclear. However, most academics agree that many fish farms in use today are detrimental to the surrounding environment to some degree.
The secret here is sustainability. While most current farming practices are economically-sustainable, they are FAR from environmentally-sustainable. In order to protect our planet for future generations, an immediate and drastic change needs to made in aquaculture policy and practice.
That change is manifested in two ways: recirculation and polyculture. One of the main environmental impacts of a fish farm is the effluent discharge from the system, which is loaded with nutrients stemming from excess feed and feces. Recirculating systems are essentially zero-discharge: the water is filtered and sterilized before being pumped back into the start of the system. In this way, a farm could run with a set amount of water almost indefinitely (a major bonus when examining the current shortage of usable water on the planet).
The other solution is polyculture: growing many different species in the same environment. For example, effluent from salmon cages could be pumped into ponds containing sea cucumbers, a scavenging species that would reduce particulate organic matter levels. The water could then be pumped past mussel beds, which would further filter the water of particulates. Finally, the water could be passed through ponds containing algae, which would help to filter the water of any remaining dissolved nutrients. The water can then be passed through a series of biological filters, which helps to ensure that the effluent released from a farm does not contaminate the surrounding environment. Plus, if all the species used are economically-valuable, the farm is able to turn a greater profit.
Only through the utilization of one or both of these solutions can aquaculture become truly sustainable, both economically and environmentally.
