Predation by the swimming crab Charybdis japonica and piscivorous fishes: A major mortality factor in hatchery-reared juvenile Japanese flounder Paralichthys olivaceus released in Mano Bay, Sado Island, Japan

A New PCR-Based Method Shows That Blue Crabs (Callinectes sapidus (Rathbun)) Consume Winter Flounder (Pseudopleuronectes americanus (Walbaum))

“…Our overall values, in the range of 20 to 30% WF208-positive crabs, are similar to the prevalence (14% and 33% in two years of study) of Japanese flounder ( Paralichthys olivaceus ) DNA found in Asian paddle crab ( Charybdis japonica ) in the days following a large release of vulnerable hatchery-reared juvenile flounder [9]. Sudo et al [9] found no P. olivaceus DNA in C. japonica before the hatchery flounder were released, so it is not clear whether C. japonica consume wild P. olivaceus . Our overall values are also similar to the 18% prevalence of “finfish” in blue crab gut contents reported by Ropes [23] but lower than the 60% reported by Fitz and Wiegert [27].…”

“…Although Paul [30] argued that portunid crabs are unlikely to be effective hunters of finfish, a variety of later studies have reported predation by portunid crabs on finfish, particularly juvenile flatfish, both in the lab and in the field [8], [9], [12], [13], [22], [23], [24], [26], [27], [28], [39]. The lower contribution of flatfish to the diets of Crangon spp.…”

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

“…The predation mortality possibly, however, is less serious in Fukushima than in other localities. Mortality rates of released P. olivaceus were higher in the coast of Tottori Prefecture [released at 42–93 mm, 4% survival 7 days after release (Furuta et al , 1997)], in Shijiki Bay [released at 82 mm, 45% of daily mortality during the first week after release (Sudo et al , 1992)] and in Mano Bay [released at 61 mm, 15–22% daily mortality during the first week after release (Sudo et al , 2008)] than in the present study (10–16% survival 40–50 days after release and 5% daily mortality). High recapture rates (7–31%) of released P. olivaceus in the coast of Fukushima (Fujita et al , 1993; Tomiyama et al , 2008) support high survival of juveniles.…”

“…Stomach contents of crabs were observed under the microscope and preserved in 99% ethanol when vertebrae, otoliths or any fish tissues were detected. Because it was mostly impossible to identify fish species from these tissues without molecular techniques, a species‐specific mitochondrial DNA (mtDNA) technique was used to detect P. olivaceus , following Sudo et al (2008): mtDNA detection by the polymerase chain reaction (PCR) was applied to fish tissues remaining in crab stomachs. The vertebrae from crab stomachs were homogenized with pestles and treated with proteinase K to digest protein and remove contamination from preparations of nucleic acid.…”

“…Predators of juvenile P. olivaceus that have been identified in some localities include age 1+ years P. olivaceus , (Sudo et al , 1992, 2008; Yamashita et al , 1993; Furuta, 1996), bartailed flathead Platycephalus sp. 2 [formerly Platycephalus indicus (L.)] (Furuta, 1996; Furuta et al , 1998; Sudo et al , 2008), and the swimming crab Charybdis japonica (Sudo et al , 2008). The complete predator profile is not known yet since these animals are predators for juveniles mostly ≤80 mm total length ( L T ), while average sizes of released fish can range to 110 mm L T .…”