NOTE Hattori et al ; Hatching date, nursery grounds, and early growth of juvenile Theiagia cholcogramma 



471 



2000 



2001 



140°E 141 142 143 140 141 142 143 140 141 142 143 



Figure 2 



Distribution of catch per unit of effort (CPUE) (fish/hourl for walleye pollock 

 {Theragra chalcogramma) caught with a midwater trawl net in May 1999-2001 

 off the Pacific coast of northern Japan. 



where L., and L, 



body length at time /,, and t^ 

 respectively. 



In this study, we defined L, = 4.6 mm at hatching (t^=0) 

 according to Nishimura and Yamada (1988) and L.,= 

 TL of fish at the number of otolith increments it.^). All 

 tests were evaluated for significance at the P=0.05 

 level. 



Results and discussion 



Distribution of juveniles 



In 1999, juvenile pollock were collected only from Funka 

 Bay to northern Tohoku, but no fish were sampled in 

 southern Tohoku (Fig. 2). In 2000, juvenile pollock were 

 caught in abundance at almost all sampling stations: 

 highest catch per unit of effort (CPUE) was recorded at 

 a station in Funka Bay (973 fish/h) and many juveniles 

 were found in northern and southern Tohoku (max: 227 

 and 184 fish/h, respectively). In 2001, the juvenile dis- 

 tribution was similar to that in the previous year, but 

 few juveniles were caught in southern Tohoku. These 

 results show interannual variability in the distribution 

 of juvenile walleye pollock between 1999 and 2001. 



Inada and Murakami (1993) suggested that the pol- 

 lock catch and distribution in the Tohoku area are 

 strongly affected by the coastal branch of the Oyashio 

 Current but little information is available on the rela- 

 tionship between oceanographic conditions and juvenile 

 distribution and abundance in this area. The southern 



limit of the coastal branch characterized by the position 

 of 5°C at 100 m depth has been regarded as an index to 

 show the strength of the current (Ogawa, 1989). Thus 

 we examined annual changes in the position of southern 

 limit of the coastal branch based on water tempera- 

 ture data (TNFRP). In April, the coastal branch of the 

 Oyashio Current mostly stagnated in northern Tohoku 

 in 1999 and 2001 but there were some annual varia- 

 tions, but it went far south to southern Tohoku in 2000 

 (Fig. 3A). It is likely that the juvenile distribution in 

 May of the three years from 1999 to 2001 is associated 

 with the southern limit position of the coastal branch of 

 the Oyashio Current in April. Kitagawa et al.'- reported 

 the recruitment index of age-0 pollock based on bottom 

 trawl surveys in the Tohoku area. We compared the 

 recruitment index {X, xlO'^ fish) given by Kitagawa et 

 al.- with the latitude of the southern limit of the coastal 

 branch of the Oyashio Current (Y) and, as a result, a 

 significant relationship was observed in the 1995-2001 

 data (F=46.653X-«oi3_ r2 = 0.960, Fig. 3B). This result 

 may indicate that abundant recruitment is brought by 



TNFRI (Tohoku National Fisheries Research Institute). 

 1997-2002. Tohoku Block Suisan Kaiyo Renraku Kaihou, 

 vols. 26-32. TNFRI, Fisheries Oceanography Division, 3- 

 27-5 Shinhama-cho, Shiogama, Miyagi 985-0001, Japan. 

 [In Japanese.] 



Kitagawa, D., T. Hattori, and Y. Narimatsu. 2002. Moni- 

 toring on the demersal fish resources in the Tohoku area. In 

 Kaiyo Monthly 34, p.793-798. Seikai Nat. Fish. Res. Inst., 

 1551-8 Taira-machi, Nagasaki, Nagasaki 851-2213, Japan. [In 

 Japanese, the title was translated by the authors.] 



