Is tuna farming so bad? It depends on the situation including mortality in the cage.
Date: Wed, 16 Aug 2017 17:00:55 +0900
1. Catch of less than 3 years old is growth overfishing.
2. Under the current fishing mortarity, % SPR was less than 10%, implying heavy overfishing.
3. Catch of less than 5 years old or catch during spawning season is probably recruitment overfishing if we seek 40% SPR as sustainability constraint, the price during spawning season is much cheaper than during the winter, and assuming M=0.25/yr. I used the method by Matsuda et al. (1999).
4. Under the optimal age- and season-specific fishing, YPR under sustainable fisheries is nearly the same as the current YPR under current overfishing. We also expect a big stock recovery under the optimal fishery.


1) We can incorporate the effect of cultivated tuna. The impact on stock depends on the age caught, but as cultured tuna grows. It will rise in price. Tuna far,omg is not bad unless the mortality rate in the cage and the cost of cultivation are not too high.
2) However, a small part of immature tunas caught in purse seine are used for tuna farming (but we do not know the published data). Perhaps 3)It also depends on the cost of feeding and mortality in the cage (unpublished). In addition, now Japanese tuna farming is probably excessive and a large part of cultured tunas is not sold on the market. This implies an economic failure of tuna farming industry.
4) But reproductive values (ecological sense) during spawning season is only ca.10% larger than that during non-spawning season. Therefore, tuna farming is reasonable unless most of cultured fish are discarded on the market, the cost of cultivation or the mortality rate in the cage is not too high, or and these data are not published.

Matsuda H, Yamauchi A, Matsumiya Y and Yamakawa T (1999) Reproductive value, harvest value, impact multiplier as indicators for maximum sustainable fisheries. Environmental Economics and Policy Studies 2:129-146.
See also my Japanese blog.