Much scientific research has been conducted and reported on tuna fisheries assessment and management, physiology, nutrition, trophic and foraging ecology, and data monitoring and modeling throughout all life stages of a number of tuna species. These were discussed, presented and reported during the 70th Annual Tuna Conference in May 20-23, 2019 in California, US. Conversely, recent progress in tuna aquaculture has not been as fast and productive as anticipated. Whilst tuna fattening and farming activities continue to expand in the last decades, progress towards large scale fully farmed tuna bred from eggs spawned in captivity and raised to market size remains limited. With the exception of Kinki University and affiliated Japanese companies that continue to steadily yet slowly expand close-cycle tuna farming since first reported in 2002 - most tuna farming activities today are ranching or fattening, still relying on the capture of juveniles at sea and fattening them in pens fed on small pelagics such as sardines, pilchards, mackerel, and other low value species considered "trash fish".
The tuna fishery industry and management had to adapt to significant reductions in their fishery stocks worldwide as well as to the fact that over 50% of all juveniles and subadults are now caught for fattening and ranching purposes. Indeed, for these reasons, tuna fattening and ranching blur the line between fisheries and aquaculture and are intertwined to the point that it is difficult to analyze them separately.
Tuna ranching and fattening continue to improve efficiency. Despite criticisms, these activities can be considered value-added tuna fisheries from both ecological and economical perspectives. These activities are highly profitable, and improvements in farming practices have been driven by enforced TOCs limiting captures. Better management results in decreasing mortalities during capture, towing, transferring, and feeding in the cages. Tuna close-cycle aquaculture still faces important challenges. Closing their life cycle and the development of ecologically and economically efficient feeds that meet the specific nutritional requirements of tuna at the various developmental stages are required to ensure the future of tuna production and the conservation of tuna species.
Aquaculture and fisheries scientists continue to combine efforts and expertise to rely on science-based criteria and decisions to ensure the future of tuna fishery stocks and aquaculture production. Whilst much progress has been achieved at the experimental and research levels, technological feasibility and commercial viability of mass production of juveniles in hatcheries and the large scale production of practical diets for the ingrowing stages of farmed tuna remain largely elusive.