A review of kuruma prawn Penaeus japonicus stock enhancement in Japan

We reviewed the stock enhancement programme for kuruma prawns Penaeus japonicus in Japan. The annual catches of kuruma prawns for the whole of Japan have fluctuated between ∼1300 and 3700 t since the mid-1960s. The kuruma prawn stock enhancement programme started at the Seto Inland Sea in western Japan in 1964. Since then, annual releases of juveniles increased to ∼300 million p.a. and then decreased to 140 million p.a. There has been a corresponding increase in size at release. Analysis of catch and release histories for the whole of Japan suggested that population sizes of kuruma prawns fluctuated depending on the condition of the coastal marine environment, particularly the tidal nursery habitats, and that hatchery releases have not succeeded in augmenting total production of this species. We examined 40 case studies from recent release experiments that used 2 methods to mark kuruma prawns: coded wire tags, and uropod clipping. Estimates of recapture rates for released prawns ranged from 0.0 to 22.1%, but exceeded 10% in only two cases. Higher recapture rates were obtained at a smaller release size in regions where there were more extensive tidal nursery grounds. Analysis of economic efficiency showed that stock enhancement of kuruma prawn was only profitable in 5 of 40 cases. The results of this synthesis highlight the importance of the quality and quantity of release habitats and the need for restoration of nursery habitats. They also show marked variation in the success of releases and emphasise the need for research to develop appropriate strategies to improve survival of cultured juveniles in those places where releases are predicted to provide benefits.