Diet

To examine survival processes in marbled sole Pseudopleuronectes yokohamae larvae, nutritional-transition-date distributions (NTDDs) were compared between larvae and large juveniles (LJs) in Hakodate Bay from 2001 to 2003. NTDDs were used instead of hatch-date distributions because the onset of increment formation coincides with the timing of the transition from endogenous to exogenous nutritional sources for marbled sole. LJs were defined as being large enough to be safe from predation by the sand shrimp Crangon uritai. In 2001 and 2002, the ranges of the NTDDs of LJs largely overlapped with those of the larvae. However, in 2003, the early cohort (those whose otolith rings formed before 17 March) disappeared from the NTDDs during and after April, and the NTDDs of LJs were heavily biased toward a later period than those of the larvae. In 2003, Oyashio Coastal Water (< 3 ℃ and 33.0 salinity) unexpectedly intruded into the bay in late March and lowered the water temperature from 6.3 ℃ on 6 March to 4.1 ℃ on 25 March. One possible cause of mortality in the early cohort of 2003 might be feeding failure caused by the extremely low water temperature.