Post‐release predation on hatchery‐reared Japanese flounder Paralichthys olivaceus in the coast of Fukushima, Japan

Abstract

To determine the predators of 100 mm total length hatchery-reared juvenile Japanese flounder Paralichthys olivaceus, fishes and crabs were collected using gillnets and a small trawl net off the coast of Fukushima Prefecture, Japan. Predation on juvenile P. olivaceus by older conspecifics, the snailfish Liparis tanakai, ocellate spot skate Okamejei kenojei and the swimming crab Ovalipes punctatus, was detected based on analogical observation and molecular techniques. These predators are nocturnal feeders except for P. olivaceus. Liparis tanakai with body sizes large enough to consume juveniles only appeared in winter, whereas the large O. punctatus was abundant in early summer and in late autumn. Such seasonal variation in predator abundance indicates that the release season can be optimized for reducing predation mortality.

Post‐release feeding and growth of hatchery‐reared Japanese flounder Paralichthys olivaceus: relevance to stocking effectiveness

“…Moreover, long off‐bottom feeding is observed in starved fish (Miyazaki et al , 2000) and in fish infected by the monogenean parasite Neoheterobothrium hirame (Shirakashi et al , 2009). Although starvation‐related predation might have occurred in this study, the effect of N. hirame infection can be disregarded because the predation mortality was detected only during the 15 days immediately after release (Tomiyama et al , 2009 a ). At the study sites, the adult N. hirame appeared in HR P. olivaceus from 20 DAR in 2000 (M. Watanabe, unpubl.…”

“…A million HR P. olivaceus have been released annually at nine sites of coastal sandy areas with depths of <10 m (Tomiyama et al , 2008 a ). Three sites for release [site A 37° 46′ N; 141° 00′ E: site B 37° 28′ N; 141° 03′ E: site E 36° 53′ N; 140° 49′ E (Tomiyama et al , 2009 a )] were selected for post‐release surveys. Approximately 100 000 HR individuals have been released every year at each of the sites B and E. The number released at site A was c. 150 000 individuals because of the larger area of nurseries for P. olivaceus .…”

“…Release sites are shallow sandy areas inhabited by wild P. olivaceus . Fish are released during the summer, a time with abundant prey (Watanabe et al , 2001) and few predators (Tomiyama et al , 2009 a ). The size at release is c. 100 mm total length, L T .…”

Effect of decreased fishing effort off Fukushima on abundance of Japanese flounder (Paralichthys olivaceus) using an age‐structured population model incorporating seasonal coastal‐offshore migrations

“…To evaluate validity of the estimated and predicted abundance from the model, yearly CPUE of Japanese flounder (I T , ton km À2 ) by otter trawl net (7.5 m mouth opening, 13 m long, 10 mm mesh size) from the research vessel (R/V) 'Takusui' (30 tons) during 2003-2014 was used. A scientific bottom trawl survey was conducted by the R/V Takusui at a speed of 2.5 knots for 30 min at fixed research points (10, 20, 30, and 50 m depth) off Fukushima almost once a month from June 2003 (Tomiyama et al, 2009). Because all of the research points have been set in the shallow coastal area, we assumed that the trend of I T reflected that of abundance in the coastal area.…”

A Method to Train Groups of Predator‐Naive Fish to Recognize and Respond to Predators When Released into the Natural Environment

“…Suboski and Templeton (1989) and Olla and Davis (1989) were among the first to anticipate that this form of learning could be used as a potential management tool to prepare predator-naive 78 OLSON ET AL. animals reared in captivity for release into the wild. Fisheries management practices have long used hatchery populations to augment fisheries, but a major limitation of stocking programs is high mortality of stocked fish, particularly in the first days and weeks of introduction into natural water bodies (for recent examples see Berejikian et al 1999;Karam et al 2008;Kekäläinen et al 2008;Sudo et al 2008;Tomiyama et al 2009;Christensen and Moore 2010;Ochiwada-Doyle et al 2010;Thorstad et al 2011).…”