WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2016 35 fingerlings from 2013 to 2015. In general, fry stocked in the summer attain an average of 2.5 kg in one year and 6 kg in two years. Feed conversion has averaged 2.5 and weight gain approximately 7.5 g/d. EOF’s pilot operation has invested significant time and resources in optimizing and automating offshore farm functions, such as controlling cage buoyancy/rotation, cleaning, feeding, monitoring, and harvesting. A comprehensive environmental monitoring program is in place to ensure water and ocean bottom sediment quality remains optimal. This totoaba farming model is very resource-efficient. Projecting data from the pilot-scale farm to a larger scale, it is theoretically possible to produce 2, 300 t — equivalent to totoaba landings at their peak in 1942 — with a 30-cage farm that occupies less than 30 ha. In practice, this would be done in a much larger area or in multiple locations to allow for buffer zones and for assimilation of waste nutrients by the ocean’s natural processes. Stock Enhancement The totoaba fishery collapsed, like others worldwide, from overexploitation of stocks and habitat degradation. This is not an isolated phenomenon but merely another example of a global trend. Almost one-third of worldwide commercial fish stocks are now fished at biologically unsustainable levels and many also suffer from the effects of habitat degradation (FAO 2016). Viable measures to restore these fisheries include regulation of fishing effort, protection or restoration of habitats, and stock enhancement programs. Rehabilitation of the totoaba resource may require all three approaches. When properly done, culture-based fisheries enhancement has the potential to generate many benefits. In biological terms, stock enhancement can increase the yield and productivity of fisheries, aid in conservation and restoration of endangered or overfished stocks, and mitigate the effects of habitat destruction. These can translate (CONTINUED ON PAGE 36) FIGURE 7. Totoaba eggs, and larvae. (A) Eggs at embryo stage prior to hatching, 950 µm diameter. (B) Newly hatched yolk-sac larva, 2.9 mm length. (C) 5 days post-hatch larva, 4.1 mm length. (D) 13 days post-hatch larva, 5.9 mm. (E) 19 days post-hatch fry, 7.4 mm length. EOF photos by Fernando Cavalin. FIGURE 8. Submersible, 1600-m3 Aquapod® cage with juvenile totoaba. Photo by Johnny Friday. 2.6 1.4 6.6 8.2 3.8 7.3 6.9 4.84 13.5 2.2 16.5 14.5 17.3 35.7 11.2 6.2 8.6 10.2 1.8 6.1 7.3 4.0 2.8 4.1 3.7 0 5 10 15 20 25 30 35 40 - 1,000 2,000 3,000 4,000 5,000 6,000 7,000 Weight gain (g/d) and Average Weight (g) Weight gain (g/d) Average weight (g) FIGURE 9. Growth of a batch of totoaba at Earth Ocean Farms during 2012-2014. Average daily weight gain bars and surface water temperatures on the right axis. A B C D E
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