ICES ASC2009/E:28, Not to be cited without prior reference to the authors

Effect of Siberian High on the catch fluctuation of Pacific cod, Gadus macrocephalus, in the Yellow Sea

Heeyong Kima, H.J. Hwangb, D.H. Kimc, M.H. Sohnd, J.B. Kime, K.H. Choib and I. Yeona H. Kim and I. Yeon: South Sea Fisheries Research Institute, 16 Dangmuri-gil Hwayan-myeon Yeosu, 556-823, Korea. H.J. Hwang and K.H. Choi: West Sea Fisheries Research Institute, 707 Eulwang-dog Jung-gu Incheon, 400-420, Korea. D.H. Kim:Korea Inter-university Institute of Ocean Science, 599-1 Daeyeon 3-dong Nam-gu Busan, Korea, 608-737, Korea. M.H. Sohn and J.B. Kim: East Sea Fisheries Research Institute, 30-6 Dongduk-ri Yeongok-myeon Gangneung, 210-861, Korea. Correspondence to H. Kim: tel: +82 61 690 8946; fax: +82 61 686 1588; e-mail:[email protected]

Abstract The catch of Pacific cod in the Yellow Sea accounts for more than 50% of the total Pacific cod catches in Korean waters when abundance started to increase. The fluctuation of Pacific cod catch in the Yellow Sea is influenced by changes in hydrographic conditions due to the Siberian High Pressure (SHP). The decadal pattern of the SHP corresponds to that of the Pacific cod catch, which indicates that the catches increase in strong period of the SHP in 1980s and 2000s and decrease in weak period in 1990s. The SHP dominates the cooling of sea surface waters in the Yellow Sea in the winter season. The cooled surface waters sink and then form the Yellow Sea Bottom Cold Water (YSBCW) that exists at the bottom of the Yellow Sea, even in summer. The main of the YSBCW temperature when Pacific cod catches are made in the Yellow Sea ranged 6 to 10 oC. The isotherms of 10 oC in 1990s were located at the northern area in the Yellow Sea relative to those in 1980s and 2000s. It suggests that Pacific cods in 1990s were restricted within the northern area of the Yellow Sea. The cooling period of sea surface waters corresponds to the main spawning season of Pacific cod in Korean waters. The effect of the SHP on water temperature is an important factor for hatching of the Pacific cod in the Korean waters. The change of the isotherm of 10 oC in December from 1981 to 2007 suggested that temperature condition act as a limiting factor for their hatching.

Keywords: Gadus macrocephalus, Siberian High Pressure, Yellow Sea Bottom Cold Water

Kim et al. page- 1 Introduction Pacific cod distribute in continental shelf and upper continental slope waters of the Northwest Pacific from off Port Arthur, China in the northern Yellow Sea, north around the North America coast to Santa Monica Bay, California (Hart, 1973; Bakkala et al., 1984; Allen and Smith, 1998; Love, 1991, Westrheim, 1996). They have been found more recently at depths ranging from 50 m to 300 m with a water temperature range between 5 oC to 12 oC (Allen and Smith, 1988; Love, 1991). The Pacific cod was divided into two populations, the Yellow Sea and the East Sea population in Korean waters by genetic information and spawning ecology (Gong et al., 1991). The Yellow Sea population is currently isolated from other Pacific cod populations by a high temperature barrier that exists in shallow waters around the southern tip of the Korean Peninsula (Zhang, 1984). The catch of Pacific cod in Korean waters reached to the peak of 4,462 tons and then continued to decrease to the lowest level of about 500 tons in 1990s. However, it increased to over 1500 tons in 2000 and until 2,641 tons in 2004 (Baik et al., 2005). The catch fluctuation of Pacific cod in Korean waters shows an intensive decadal variation. Main commercial fisheries for the Pacific cod in Korean waters are drift gill nets and bottom trawls in the Yellow Sea. Recently, the catches of the Pacific cod by drift gill nets has increased to about 70% of total catch of Pacific cod in the Yellow Sea while catches by bottom trawl decreased (Lee et al., 2006). Hydrographic conditions in the Yellow Sea are changed rapidly by external forces because of shallow depth, a maximum depth of 152 m and a mean depth of 45 m, and a strong tidal current. Particularly, a seasonal variation is distinct because monsoon regime prevails. Northwesterly generated by Siberian High Pressure (SHP) cools sea surface waters in the Yellow Sea in winter season and then the cooled surface waters sink to the bottom and then form the Yellow Sea Bottom Cold Water (YSBCW) maintaining less than 10 oC at the center of the Yellow Sea. Pacific cod spawns from December to January (Lee et al., 2005; Cha et al., 2007) at depths of from 40 to 265 m and their eggs are fertilized externally (Hart, 1973). Eggs are demersal and weekly adhesive (Hart, 1973; Palsson, 1990) and larvae and small juveniles are pelagic. These characteristics of early life ecology and hydrographic conditions are affected by the northwesterly due to the SHP from December to January, a main spawning season of Yellow Sea cod. Studies on the Pacific cod in the Korea waters are mainly about biological informations (Park, 1965; Chung and Kim, 1971; Gong et al., 1991; Lee et al., 2005) and the distribution change and the catch fluctuation of Pacific cod have not been researched. Therefore, to clarify the fluctuating factor of Pacific cod catches in the Yellow Sea, the present study is about to investigate the effect of the Siberian High that affects directly the water masses in the Yellow Sea during the spawning and the main fishing season of Pacific cod on the catch of the Pacific cod.

Kim et al. page- 2 Data and methods The catch fluctuation of Pacific cod in Korean waters was analyzed by using the landing data of statistical yearbook of agriculture forestry and fisheries of Korea from 1969 to 2008. Data deficiency by the commercial fisheries was made up by the results of bottom trawl survey conducted four times every year by the West Sea Fisheries Research Institute from 2003 to 2008. The survey data were used to estimate biological properties such as a spawning season and a group maturity, etc. The Pacific cod spawns between December and February. Oceanic conditions in winter season in the Far East Asia were dominated by the northwesterly originated from the SHP. Therefore, understanding the fluctuating characteristic of the SHP is necessary to investigate the fluctuating factors of Pacific cod catches that spawns in winter season. In order to investigate the fluctuation of the SHP, Daily and monthly NCEP/NCAR reanalysis data (http://www.cdc.noaa.gov/) with horizontal resolution of a 2.5˚ latitude-longitude square from 1948 to 2008 were used. The period from December of 2007 to February of 2008 was regarded as winter of 2007. At first the Siberian High Area (SHA) was defined as the area 40-60°N and 80-120°E where is the central area of the SH in winter. Next, the Siberian High Pressure (SHP) was defined as the regional mean Sea level pressure over the SHA. Definition and calculation of SHP were followed by Kim et al. (2005). The characteristics of water temperature change according to the change of the SHP were investigated by using the hydrographic data from the KODC (Korea Oceanographic Data Center) from 1981 to 2007. Annual fluctuation of water temperature was examined using two criteria of it, less than 10 oC that indicates the main fishing temperature range (Fig. 1) and less than 12 oC that indicates the critical temperature for hatching of cod eggs (Seo et al., 2007).

Results and Discussion Pacific cod catches in Korean waters was about 2,000 tons in 1970s and showed a peak of 4500 tons in 1980s (Fig. 2). However, that in 1990s decreased abruptly until about 500 tons. The catches started to increase from 2000 and came up to the maximum level of 7,500 tons in 2007. The decadal variation of Pacific cod catches in Korean waters was distinct in the Yellow Sea since the catches in the Yellow Sea occupy 50% of total catches in Korean waters. Eventually, the inter-decadal variation of the Pacific cod catches in Korean waters was dominated by the catch fluctuation in the Yellow Sea. For the comparison of Pacific cod catches to the climate change, the annual fluctuation of the SHP was firstly shown in Fig. 3. Linear trend for the SHP is -0.48hPa/decade and the trend is statistically significant as 99% confidence level. Mean SHP in each decade from 1970 to 2008 showed a low level of 1028.36 and 1029.01 in 1970s and 1990s, respectively but a high level of 1029.88 and 1029.95 in

Kim et al. page- 3 1980s and 2000s. These decadal patterns of the SHP correspond to that of Pacific cod catches, which explains that the cod catch increase in strong period of the SHP and decrease in weak period. Monthly mean of Pacific cod catches was largest in December (Baik et al., 2005). To investigate the effect of the change of water masses on seasonal catch properties, the isotherms of 10 oC at 50 m depth in December from 1981 to 2008 were plotted in Fig. 4. The isotherms of 10 oC in 1990s were located at the northern area in the Yellow Sea relative to those in 1980s and 2000s. Therefore, Pacific cods in 1990s were restricted within the northern area in the Yellow Sea. The change of water temperature between December and January, the main spawning season, influences the success and failure of hatching directly. Furthermore, the critical temperature for hatching of Pacific cod in the East Sea is 12 oC and the hatching duration of Pacific cod shorten as water temperature increases (Seo et al., 2007). The results of trawl survey from 2002 to 2006 showed the appearance of individuals less than 10 cm TL in summer season (Fig. 5), which explain that the individuals were hatched in January of this year (Seo et al., 2007). The recruitment appearing in summer season was affected by temperature condition in winter season for their hatching. The change of the isotherm of 12 oC in February from 1981 to 2007 suggested that the temperature condition did not act as a limiting factor for their hatching because the whole area of the Yellow Sea was less than 12 oC. According to Yamamoto (1939), the range of water temperature for hatching was 5 to 9 oC, the optimal temperature range of 6 to 7 oC. He also reported that a malformation rate reached 75% more than 10 oC. It explains the difference between the Yellow Sea population and the East Sea population. The East Sea population distribute mainly in the coastal area different to in the offshore area in the Yellow Sea population. Moreover, the temperature range for hatching in the East Sea may be large since the change of water temperature is not intensive. If the isotherm of 10 oC in December as shown in Fig. 4 is considered as hatching condition of Pacific cod in the Yellow Sea, decadal trend for the recruitment of Pacific cod in the Yellow Sea may be able to be explained.

Kim et al. page- 4 References Allen, M.J. and G.B. Smith. 1988. Atlas and zoogeography of common fishes in the Bering Sea and north Pacific. NOAA Tech. Rep. NMFS-NWFSC 66, 151p. Baik C.I., Y.S. Kim, D.W. Lee, Y.M. Choi, D.H. An, Y.Y. Chon, K.H. Choi, J.B. Kim, K.S. Hwang, J.G. Kim, Y.H. Kim, J.B. Lee, J.H. Choi and H.K. Cha. 2005. Ecology and fishing grounds of main coastal and offshore fisheries resources. National Fisheries Research and Development Institute, Busan, 74-85. Bakkala, R.G. 1984. Pacific cod of the eastern Bering Sea. Int. North Pac. Fish. Comm. Bull., 42, 157-179. Cha, H.K., S.I. Lee, S.C. Yoon, Y.S. Kim, Y.Y. Chun, D.S. Chang and J. H. Yang. 2007. Maturation and spawning of the Pacific cod, Gadus macrocephalus TILESIUS in the East Sea of Korea. J. Kor. Soc. Fish. Tech., 43(4), 320-328. Chung, T.Y. and Y.U. Kim. 1971. Length-weight relationship of Gadus macrocephalus Tilesius of the Yellow Sea. Bull. Kor. Fish. Soc., 4, 103-104. Gong, Y., Y. C. Park, and S. S. Kim. 1991. Study of the management unit of fisheries resources by genetic method. 1. Genetic similarity of Pacific cod in the North Pacific. Bull. Nat. Fish. Res. Dev. Agency, 45, 47-61. Gong, Y., Y.C. Park and S.S. Kim. 1991. Study on the management unit of fisheries resources by genetic method. 1. Genetic similarity of Pacific cod in the North Pacific. Bull. Natl. Fish. Res. Dev. Inst., 45, 47-58. Hart, J.L. 1973. Pacific fishes of Canada. Bull. Fish. Res. Board of Canada 180, 730p. Kim, D.-W., H.-R. Byun and Y.-I. Lee. 2005. The long-term changes of Siberian High and winter climate over the Northern Hemisphere. J. Kor. Meteor. Soc., 41(2-1), 275-283. Kim, D.-W., H.-R. Byun and Y.-I. Lee. 2005. The long-term changes of Siberian High and winter climate over the northern hemisphere. J. Kor. Meteor. Soc., 41(2-1), 275-283. Lee, C.S., Y.H. Hur, J.Y. Lee, W.K. Kim, S.H. Hong, S.J. Hwang and S.H. Choi. 2005. Maturity and spawning of Pacific cod (Gadus macrocephalus) in the East Sea. J. Kor. Fish. Soc., 38, 245-250. Lee, C.S., Y.H. Hur, J.Y. Lee, W.K. Kim, S.H. Hong, S.J. Hwang and S.H. Choi. 2005. Maturity and spawning of Pacific cod (Gadus macrocephalus) in the East Sea. J. Kor. Fish. Soc., 38(4), 245-250. Lee, D.W., Y.H. Kim, J.K. Kim, J.H. Choi, S.T. Kim, D.S. Chang, J.T. Yoo, Y.M. Choi and S.G. Jeong. 2006. Year 2006 monitoring report of fisheries regulation for aquatic plants and animals species. Natl. Fish. Res. Dev. Inst., 1-164. Love, M.S. 1991. Probably more than you want to know about the fishes of the Pacific coast. Really

Kim et al. page- 5 Big Press, Santa Barbara, Cal. 215p. Palsson, W.A. 1990. Pacific cod (Gadus macrocephalus) in Puget Sound and adjacent water: biology and stock assessment. Was. Dept. Fish. Tech. Rep. 112, 137p. Park, B.H. 1965. On the race of cods (Gadus macrocephalus Linnaeus) between the Yellow Sea and Chinhae Bay of Korea. Fisheries Resources Report of the Fish. Res. Dev. Agency, 6, 107-115. Seo, Y.S., M.E. Park, J.G. Kim and S.U. Lee. 2007. Egg development and juvenile growth of the Pacific cod Gadus macrocephalus (Korean East Sea population). J. Kor. Fish. Soc., 40(6), 380-386. Westrheim, S.J. 1996. On the Pacific cod (Gadus macrocephalus) in British Columbia waters, and a comparison with elsewhere, and Atlantic cod (G. morhua). Can. Tech. Rep. Fish. Aquat. Sci., 2092, 390 p. Yamamoto, K. 1939. Effects of water temperature on the rate of embryonal development of eggs of the Korean codfish, Gadus macrocephalus Tilesius (Translated from Japanese by Fish Res. Board Can. Transl. Ser. 554, 1965). Bot. Zool. Tokyo, 7, 1377-1383. Zhang, C.I. 1984. Pacific Cod of South Korean Waters. Bull. Int. North Pacif. Fish. Comm., No. 42, 116–129.

Kim et al. page- 6 34.0

33.5

33.0 t y (psu) i n i l

a 32.5 S

32.0

31.5 2 4 6 8 10 12 14 Temperature (oC)

Fig. 1. Temperature- Salinity diagram for the abundance of Pacific cod catches by bottom trawl survey in the Yellow 8,000 100 West Sea Korea total West Sea/Korean total

80

6,000 Rate of catches (%)

60

4,000

40 Catches (M/T)

2,000 20

0 0 0 5 0 5 0 5 0 5 8 7 7 8 8 9 9 0 0 0 9 9 9 9 9 9 0 0 0 1 1 1 1 1 1 2 2 2 Year

Fig. 2. Annual fluctuation of Pacific cod catches in Korean waters from 1969 to 2008. 1038 1036 Siberian High 1034 1032 1030 Decadal mean 1028 1026

Sea Level Pressure (hPa) 1024

1948 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 Year

Fig. 3. Long term variation of the winter mean Siberian High Pressure from 1949 to 2008. 38° 38°

1983 1987 37° 37° 1982 1986 yellow.kodc_Dec._10deg 1993 1996 yellow.kodc_Dec._10deg

1995 1994 36° 36°

1984 1998

1988 1984 1983 35° 35°

1985 1981

34° 34°

33° 33°

0 50 km 0 50 km

32° 32° 123° 124° 125° 126° 127° 128° 129° 123° 124° 125° 126° 127° 128° 129° 38°

2000 2007 2004 37° Fig. 4. Distribution of isotherms of 10 oC at

2007 50 m depth in December in 1980s (a), 1990s (b) and 2000s (c). 36°

2001

2006

2005 2002 2003 35° 2004 2000

34°

33°

0 50 km

32° 123° 124° 125° 126° 127° 128° 129° 60 Summer 2002 Summer 2004 N=277 N=84 40 20 0 60 Autumn 2002 Autumn 2004 N=98 N=292 40 20 0 60 Winter 2003 Winter 2005 N=15 N=38 40 20 0 60 Spring 2003 Spring 2005 N=14 N=57 40 20 0 60 Summer 2003 Summer 2005 N=324 N=49 40 Frequency (%) 20 0 60 Autumn 2003 Autumn 2005 N=192 N=134 40 20 0 60 Winter 2004 Winter 2006 N=43 N=35 40 20 0 60 Spring 2004 Spring 2006 N=39 N=537 40 20 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 TL (cm)

Fig. 5. Size frequency of Pacific cod collected by bottom trawl survey in the Yellow Sea from 2002 to 2006