Fish without footprints

Kona Blue is a leader in innovative mariculture, having pioneered an open ocean fish farm operation off Kona, Hawaii, that has produced up to 500 tons/yr of sashimi-grade Kona Kampachi^® (Seriola rivoliana), with no measureable environmental impact beyond the immediate area of the net pens. However, expansion of such operations in nearshore waters is subject to various constraints, such as conflict with other ocean and shoreline users; exposure of farmed stocks to pathogens from wild fish; and difficulty in procuring further ocean leases for additional farm sites. This last constraint is of prime significance as it severely limits the ability to allow farm sites to lie fallow between harvest and stocking: a practice proven to be most beneficial for maintaining fish stock health. The solution to these problems lies over the horizon, in expanding mariculture operations into deeper waters, further offshore. Unanchored net pens (so-called "drifter cages") have been proposed as a means of expanding mariculture in a scalable, environmentally sound manner. These drifting net pens not limited to a single lease site - would essentially be "perpetually fallow", yielding improved fish health and growth performance. Fish in these pens would also have essentially no environmental footprint, with no discernible impact on water quality or benthos, and no means of transmitting pests or parasites between reef fish reservoirs and farm stock or vice versa. Any escapees would simply be prey for larger pelagic fish. Scale-up of such an emerging open ocean industry would not conflict with other user groups and would reduce regulatory issues, as it would require no leases or other tenure over defined areas of ocean space. As the farm would drift with ocean currents, farm husbandry tasks would also be facilitated by the absence of any apparent current on the cages, gear, divers and tender vessels. Trans-ocean drifters are still considered to be the stuff of science-ficti- n, because of biosecurity and logistics concerns (feed delivery, return of net pens, etc). However, unanchored net pens that are retained within regional ocean eddies would not face these same constraints. Kona Blue has therefore been developing the technology for regional unanchored open ocean drifter pens, under "The Velella Project" (named for a genus of pelagic hydrozoan). The goal of the Velella Project is to test the feasibility of a drifting mariculture operation entrained in regional ocean-current eddies in the lee of the Big Island of Hawaii. An extended current drogue tracking study, conducted using GPS-tracked drifter buoys, suggests that these eddies are stable and persistent. It appears that little energy expenditure will be required to maintain a cage array\´s position within the eddies in the desired operating area. The keys are to now: develop technologies for predicting net pen motion using satellite sea-surface data; to explore passive, sustainable propulsion technologies such as sails and sea anchors to reduce diesel costs; and to reduce labor costs offshore by automating or controlling via satellite link the essential husbandry functions of an open ocean fish farm. Initial sea trials with a two-cage, axle-bridle array were informative. A Velella beta-test voyage is currently in progress, using a single 132 cubic meter brass-meshed Aquapod® net pen tended by a 65 ft steel-hulled schooner, S.V. Machias, with a single tow-line umbilical, and multiple bridle attachment points. This array can be towed at speeds over 1.25 kts (65 cm.s^-1), with minimal diesel consumption (around 4 gal.hr^-1, or 161.hr^-1). Critical commercial criteria are being evaluated, to assess costs (the amount of diesel required for course corrections in the eddies; logistical costs for remote pen operation far offshore) and benefits (economies of scale; improvements in fish growth performance, and reduced cage capital and operating costs).