Permalink : http://hdl.handle.net/2115/68164

JaLCDOI : 10.14943/mem.fish.59.1-2.19

KEYWORDS : Decadal observation;Walleye pollock;Early life history;Funka Bay;Food availability;Year class strength

Funka Bay is the main nursery ground of the Japanese Pacific population of walleye pollock Gadus chalcogrammus. To better understand how hydrographic and biological conditions are related to the survival of this population during the early life stages, hydrographic observations and field samplings have been conducted in Funka Bay since 1991 aboard the T/S Usio-Maru, Faculty of Fisheries, Hokkkaido University. Data have been collected on hydrographic conditions and the distributions of larval pollock and copepod nauplii(larval prey). The year class strength estimated by tuning VPA calculation has fluctuated annually and strong year classes occurred in 1991,1994,1995, 2005, and 2007. In these years, the Tsugaru Warm Water(TWW,>6℃, salinity>33.6) distributed in late January in Funka Bay and the Oyashio Cold Water(OCW,<3.0℃, salinity 33.0-33.3)entered the bay after mid February. In contrast, the recruitment failure was found in 2010,when cold water prevailed in early February in the bay due to early intrusion of OCW. From 1991 to 2013, walleye pollock larvae were mostly collected in late January. A positive relationship was found between the temperatures at 15 m depth in late January and the year class strength of the population(r=0.56, p=0.017). While no significant relationship was found between the density of copepod nauplii in late January and the year class strength(r=0.32, p=0.259). Previous studies have shown the feeding success of larval pollock is higher in TWW than in OCW. These results suggest that higher feeding success during the warmer years in late January in Funka Bay might have resulted in the strong year classes.