There's a fishery out in Hawaii that aims to do something about this. Kona Blue is working to provide a sustainable source of sushi-grade yellowtail tuna. It's farm-raised but uses new techniques to avoid the environmental pitfalls of other attempts at tuna farming.
Much of tuna 'farming' in the world's oceans is actually a process of transferring immature wild tuna to pens in order to fatten them to the proper size and weight for consumption. In contrast, Kona Blue controls the entire life-cycle of the tuna, hatching spawn at a land-based facility and then transferring them to larger pens as they grow.
These ocean pens are 3,000-cubic-meters in volume and are situated in deep ocean water off the Kona Coast on the Big Island. The company website explains that strong currents flow through these pens, which do double duty keeping this area of the ocean clean and also better simulating the tuna's natural environment.
Kona Blue feeds their tuna a mix of "approximately 30% fish meal and fish oil from Peruvian anchovies (a sustainably managed fishery for the past 30 years) and trimmings from fish processed for human consumption, and 70% sustainable agricultural proteins and oils." No hormones hormones or antibiotics are used, and frequent lab tests indicate no detectable mercury in the fish.
Kona Blue continually stresses a commitment to sustainable farming for both the tuna and the ocean environment and keep their environmental monitoring logs and operation permits open to the public. If successful, Kona Blue and companies that follow similar models could ease the pressure off of deep-sea fishing and help refresh the population of wild tuna.
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(Image Credit: Kona Blue)