To examine predation on larval and juvenile Pleuronectes yokohamaeby Crangon uritai, the spatial distribution and feeding habits of C. uritai were studied.C. uritai fed on various prey, including P. yokohamae. Density-dependent predation on juvenile Crangon spp., larval and juvenile gobiid fish Chaenogobius heptacanthus, mysids, and gammarids was observed. The abundance of alternative prey might therefore play an important role in reducing the pressure of predation on P.yokohamae. In each year, C. uritai migrated from depths of 10m in March to depths of 3m in May. There was a significant negative correlation between the weighted mean depth (WMD) of C. uritai and the weighted mean bottom water temperature (WMBWT). The migration was therefore delayed in the cold spring, during which C. uritai occupied depths of approximately 10m. In contrast, no significant correlation was found between the WMD of P. yokohamae and WMBWT.Settlement of P. yokohamae began at depths of 15m, mainly during early April.The spatial distributions of these two organisms show greater overlap during the cold spring, resulting in increased opportunities for predation.
To examine survival processes in marbled sole Pseudopleuronectes yokohamae larvae, nutritional-transition-date distributions (NTDDs) were compared between larvae and large juveniles (LJs) in
Flatfishes drastically change their habitat, body form, and feeding during metamorphosis; thus, the early juvenile and larval stages are viewed as being critical for early survival. However, to the best of our knowledge, no studies have tested the growth-mortality hypothesis for both larval and juvenile stages of flatfishes. Therefore, we investigated the relationship between growth rate and environmental factors and tested the hypothesis for both larval and juvenile stages of marbled sole Pseudopleuronectes yokohamae in Hakodate Bay, Japan from 2001 to 2003. For both larval and juvenile stages, otolith growth correlated with water temperature. Eye-migrating larvae were defined as survivors of planktonic life (SV pelagic). Large juveniles captured in late June and July were defined as survivors of shrimp predation (SVjuvenile). To test the growth-mortality hypothesis, otolith growth was compared between the SV and the original population. During the pelagic larval stage, growth-selective survival was not detected in any of the 3 yr. During the early juvenile stage, fast-growing individuals survived selectively in 2002 but not in 2003. In 2002, population growth of juveniles was slow because water temperatures were low. Thus, juveniles in 2002 required time to exceed the size spectrum that is vulnerable to shrimp predation; consequently, the individuals that grew more rapidly were able to survive selectively. Our results show the importance of the early juvenile stage for the survival of flatfishes
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