Distribution and Biological Characters of Pink (Oncorhynchus gorbuscha) and Masu Salmon (0. masou) in the Sea of Japan

Transcription

1 Bulletin of the National Salmon Resources Center, No. 3: - December 2 Distribution and Biological Characters of Pink (Oncorhynchus gorbuscha) and asu Salmon (. masou) in the Sea of Japan Kazumasa Ohkuma*', Yukimasa Ishida*2, Oleg A. Rassadnikov"', and Viktor G. arkovtse~"~ * 'Research Division, National Salmon Resources Center, Fisheries Agency of Japan, 2-2 Nukanoshima, Toyohira-ku, Sapporo 62-9, Japan (ohkuma~salmon.aff~-c.ro.jp) *2Hokkaido National Institute of Fisheries, Fisheries Agency of Japun, I6 Katsurakoi, Kushiro, Hokkaido 85-82, Japan *3Pac~ic Research Fisheries Centre (TINRO Centre), 4 Shevchenko Alley, Vladivostok, 696 Russia Abstract. - Distribution and biological characters of pink (Oncorhynchus gohischa) and masu salmon (. masou) in the Sea of Japan in spring were summarized based on the data obtained from the research cruises carried out from 993 to 999. Though pink salmon showed higher CPUEs within the 8-3'C SSTrange, they were caught even in lower temperature around 5'C. In contrast, masu salmon were caught only in 8-4'C SST range waters. The body size of pink salmon excluding the result in 997 were larger in the odd years and smaller in the even years. Though the sex ratio of pink salmon were almost even, about 7% of total catch were female in masu salmon. From the results of age determination, 64% of masu salmon were identified as age.i fish and 36% were age 2.. Key words: pink salmon, maw salmon, distribution, Sea of Japan Introduction Pink (Oncorhynchus gorhuscha) and masu salmon (. masou) are the dominant salmon species in the Sea of Japan. Both species spend one winter in the ocean after their seaward migration. After wintering, masu salmon return to their natal river from spring to summer (Tanaka 965, achidori and Kato 984), and pink salmon return from summer to autumn. Pink salmon are distributed not only in the Sea of Japan, but also over a broad area of the North Pacific Ocean and Bering Sea, and they are more abundant than other Pacific salmon species. On the other hand, maw salmon are distributed only in the western North Pacific Ocean, where their abundance low compared to pink salmon (Kato 97 ; Kaeriyama 985). In the Sea of Japan, pink and maw salmon are important fishery and biological resources. The Sea of Japan is not very wide, but complex oceanographic structures formed by Tsushima warm current from southwest and Liman cold current from northeast Contribution A No. 6 from the National Salmon Resources Center. 2 National Salmon Resources Center affect distribution and ecology of salmon in this region (Shimomura et al. 962). We use data obtained from Japan-Russia cooperative research in to clarify the recent distribution and biological characteristics of pink and masu salmon in the Sea of Japan. aterials and ethods The dates of the research cruises, the number of gill net operations, and the total number of tans of gillnet gear used are summarized in Table I. The locations of experimental fishing operations are shown in Figure I. Research was conducted from mid to late April, except in 997 and 998. Research was conducted in mid February in 997 and from late April to early ay in 998. There were only three gillnet operations in 997 due to severe ocean conditions, and because of the long cruise period there were 5 operations in 998. In other years, there were 8- gillnet operations. The total amount of gillnet gear (SO m/tan) used varied in proportion to the number of operations, from 765 tans in 998 to 48 tans in 997 (Table ). Gillnets were usually 49 tans in total length, including 3 tans of research net ( different

2 2 3 If. d T%?%giF+ 2 9' -;6Kf$ Bull. Natl. Salmon Resources Center, No. 3, 2 stretched-mesh sizes from 47 to 57 mm, 3 tans each) connected to and 9 tans of 93-mm mesh commercial net at each end of the net. However, a 5-tan net set (3 tans of research gillnet and tans of commercial gillnet at each end) was used in 993, and two kinds of small mesh gillnet (26 mm and 35 mm, one tan each) were added to the 49-tan gillnet in 998. A longline was also used during the survey. Because the number of fish caught by longline was small, only gillnet data were used for pink salmon analyses. Results were expressed as catch per unit effort (CPUE), calculated with following formula: CPUE (fish/tan) = number of fish caught in the each operation/number of all gillnets, expressed in tan, used in the operation. Details of experimental gillnet fishing are shown in Appendix. After each fishing operation, fork length (FL in mm), body weight (BW in g), and gonad weight (GW) of fish were measured, sex was recorded, and scales collected V 996. *: 997 A: 998. f. 999 Y 45" q Fig.. ap showing the locations of gillnet sampling in from defined area (INPFC 963, p. 5) were examined for age determination of masu salmon. To increase sample number of masu salmon for analysis of length, weight, and sex ratio, seven specimens caught by longline (3 fish in 993,4 fish in 996) were added. Condition factor (CF) and gonad somatic index (GSI) were calculated with following formulae: CF = (BW/FL3) x lo9, GSI = (GW/BW) x. Sea surface temperature (SST) was recorded before each fishing operation. In addition, 8 and 2 C isothermal curves of SST during each research cruise were obtained from "Gyokaikyo sokuho" supplied by the Japan Fisheries Information Service Center (Ikenohata, Tokyo -8). Results Salmon distribution and ocean conditions Pink salmon were caught at almost all stations in , although there were no or few pink salmon caught in northern waters with SSTs colder than 8 C (Fig. 2). Operations were conducted only south of 39% in 996, and the density of pink salmon was relatively high. High CPUEs of pink salmon were also recorded in 999, even though operations were limited to the area between 39-4%. Although pink salmon were distributed at lower SSTs in a wide area of 8-2? SST water in 996, many fish were caught in a narrow area of 8-2 C SST water in 998 and 999. As previously mentioned, ocean conditions in mid February 997 were severe, and the distribution of pink salmon could not be clearly determined. Some pink salmon, however, were distributed in waters around 8 C SST in the central Sea of Japan in February 997. Generally, masu salmon were caught in smaller numbers than pink salmon, and showed large annual fluctuation: fish in 998, four in 995, and only one in 997 (Table 2). Excluding the data in 995 and 997, when few masu salmon were caught, maw salmon Table. Outline of spring salmon research cruises in the Sea of Japan from 993 to 999 Year Y8 999 Total Name of RIV Hokuho Hokuho Wakatake WuLutuke Kanki,3R Wakatake Wa kutake Period of cruise Number of gillnet from to operation total (tan) Apr. 4 Apr Apr. 4 Apr Apr. 9 Apr Apr. 6 Apr Feb. 9 Feh Apr. 8 ay Apr. 5 Apr

3 Ohkuma et al. - Pink and maw salmon in the Sea of Japan 3 6.N 55 5,<5.6.< <O.I Nofish I Fig. 2. CPUE (number of fish per tan of gillnets) distribution of pink salmon in the springs of

4 4 3 if d %@d%%f+ j 5-4RffPG Bull. Natl. Salmon Resources Center, No. 3, 2 35 x O.ls,<l ( Nofish Fig. 3. CPUE (number offish per tan of gillnets) distribution of maw salmon in the springs of

5 Ohkuma et al. - Pink and masu salmon in the Sea of Japan 5 Table 2. Number and CPUE of fish obtained in the Sea of Japan by drift gillnets. Year Total Number of fish CPUE (catch/tan) PinWmasu pink masu chum pink masu chum ratio I , , were caught at higher water temperature locations. In 998 and 999 masu salmon were not caught at stations north of 4x, although pink salmon were distributed at these stations. Density of masu salmon was high at stations south of 4"N (Fig. 3). asu salmon are caught only at relatively high temperatures (8.5-4"C), and are not caught at SSTs under 8S"C (Fig. 4). Similar to maw salmon, CPUEs of pink salmon were higher at 8-3"C SSTs, but CPUEs of more than 2 fish per tan were recorded at lower SSTs (4-7T). High CPUEs (more than 5 fish per tan) were recorded three times, and occurred at SSTs of 2-3 C. Thus, masu salmon were distributed in relatively warm waters, and pink salmon were distributed not only in these warm waters but also in colder waters. Biological characters of pink and masu salmon In 997, the number of pink salmon caught was small, and their body size was small because of the early (mid February) sampling period (Table 3). Body size in odd years was large (average FL over 4 mm, BW range g, and CF around 2), except for the fish caught in 997. In even years, body size was small (average FL mm, BW range 5-7 g, and CF around ). The sex ratio was almost even (5.2% female, 48.8% male). Female masu salmon were the dominant (7.3%, Table 4). There was no clear correlation between FL and CF for either sex (Fig.5). GSIs of males were consistently lower than % over the entire range of BWs. Large females over 2, g had GSIs of 3-4%, and GSIs of smaller females ranged from % to 5%. For male fish there was no clear correlation between CF and GSI, but there was a clear positive correlation for female fish (Fig. 5). Among 5 from total of 2 masu salmon (including 7 fish caught by longline, and excluding 7 fish with regenerated scales), 37 out of 8 females and 7 2,? $ 8 \ -w ? l \ -.8 W PINK SALON 993 t Surface temperature ("C) ASU SALON A X Surface temperature ("C) Fig. 4. Relations between sea surface temperature (SST) and CPUE (number of fish per tan of gillnets) of pink and masu salmon. out of 43 males were age 2. fish (35.8% of the total) (Table 5). Discussion In the Japan Sea pink and masu salmon were distributed over a wide range of SSTs ( "C for pink salmon, "C for masu salmon). The abundances of masu salmon, however, were higher at warmer temperatures (28 C). This differed from previous informa-

6 ~ T$%;EgET-k % Bull. Natl. Salmon Resources Center, No. 3,2 Table 3. Average fork length (FL), body weight (BW). condition factor (CF), and gonad somatic index (GSI) of pink salmon caught in the sea of Japan. N, number of samples; F, female;, male. Year Sex N FL (mm) BW(g) CF GSI (%) 993 F F F F I997 F x F F x Table 4. Average fork length (FL), body weight (BW), condition factor (CF), gonad somatic index (GSI) and sex ratio of masu salmon caught in the sea of Japan. N, number of samples; F, female;, male. Year Sex N FL (mm) SW(P) CF GSI (7) Sex ratio (7) 993 F X F 448, , F 3 45, , F , F F , , F 6 45, , tion that pink salmon were distributed at higher temperatures and in more southern waters than masu salmon (Shimomura et al. 962). Takagi et al. (982), however, reported that the SST distribution of pink salmon ranged from 3 C to IS?, and that the most favorable temperature range was 4- I "C. achidori and Kato (984) suggested that masu salmon were distributed at SSTs higher than 74 C in the Sea of Japan. These historical data support our results. Azuma (Abstracts for the 994 Annual eeting of the Japanese Society of Fisheries Science, p. 6) concluded that in the Sea of Japan pink salmon distribution depends on prey distribution, and masu salmon distribution depends more on salinity and water temperature than on prey distribution. Thus, distributions of pink and masu salmon may be affected not only by water tem-

7 Ohkuma et al. - Pink and maw salmon in the Sea of Japan 7 perature, but also by prey density, salinity, and other factors (achidori and Kato 984). In addition, long term fluctuations have been observed in SST anomalies in the Sea of Japan. Hirai ( 995) reported that SSTs decreased in the first half of 96Os, and that low temperatures continued until the 98s. In the 99s Sea of Japan waters shifted again to relatively high temperatures. In , the position of 8 C water along 35'E was located around 4"N; however, the position a? 4 5 ** 533 O2, 2, 3, 4, BW g 4 ae 533 ( CF LL r-- - I female 2 male FL mm Fig. 5. Relationships between body weight (BW) and gonad somatic index (GSI). condition factor (CF) and GSI. and fork length (FL) and CF, of maw salmon. Table 5. Age compositions of masu salmon caught in the Sea of Japan in Aee. 2. Total Female 7 (65.7)* 37 (34.3) 8 () ale 26 (6.5) 7 (3Y.S) 43 () Total 97 (64 2) 54(35.8) 5 () *Number (%) of 8 C water moved northward in 998, resulting in warmer conditions in 998. To clarify the mechanisms affecting salmon distribution and abundance of pink and masu salmon in the Sea of Japan, water temperature, salinity, prey abundance, and other phenomena influenced by changes in oceanographic structure should be investigated. Pink salmon were not caught during the mid-winter research cruise in February 997, although previous surveys showed a high abundance of pink salmon in southern waters of the Sea of Japan in February (Hiyama and arkovtsev 993). Only three fishing operations were conducted in 997, but our results indicated that pink salmon might migrate to waters south of our fishing stations at 38-4'N. Body size of pink salmon was negatively correlated with stock abundance (Takagi et al. 982). The abundance of maturing pink salmon stocks in the Sea of Japan changed from an even- to an odd-year dominance cycle in 962, and recently the even-year stock has become abundant again. Except for 999, we observed higher CPUEs and smaller body sizes in even years (Tables 2 and 3). In addition, data from arch- ay surveys in showed a negative correlation between CF and stock abundance (Hiyama et al. 998). Pink salmon CFs in our study ranged from.5 to 2.5, which were within the range shown by Hiyama et al. (998). This correlation may be useful for stock assessment in the future, if stock abundance could be estimated from the condition factor. The average body sizes of maw salmon (443 mm in FL,,36 g in BW) were slightly larger and the sex ratio was almost the same as in an earlier survey from mid to late April ( mm in FL,,93-,7 gin BW, 66.3% female / 33.7% male; achidori and Kato 984). Acknowledgements We thank to all research staffs and crew of R/Vs who participated the research cruises and obtained precious data. We would like to express our appreciation to Dr. Katherine W. yers of University of Washington, School of Aquatic and Fishery Science, for her valuable advice and suggestion on the manuscript. References Hiyama, Y., S. Hasegawa, and F. Kato 998. Density dependent effects on body weight of the pink salmon in the Japan Sea. Bull. Japan Sea Natl. Fish. Res. Inst., 48: 7-. Hiyama, Y., and V. G. arkovtsev 993. Pink salmon, Oncorkynchus gnrbuscka, in the southern open water

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9 ~ ~ ~ Ohkuma et al. - Pink and masu salmon in the Sea of Japan 9 Appendix. Data of experimental gillnet fishing in the Sea of Japan from 993 to 999. Location SST Year onth Date N E "C "OO' 4"OO' 4O"OO' 4'' 4 ' 39OOO' 38OOO' 39"' 38"lI' 36O.55' 42"OO' 4'' 4 ' 4"' 4O"OO' 39"oo' 38"OO' 39"OO' 38"OO' 36'55' 38OOO' 39"' 4'' 39"OO' 4"OO' 4 l"' 42"OO' 4 "' 4 '' 38'' 39"OO' 38"OO' 37"OO' 36"OO' 37"OO' 35"SY' 35"OO' 34'2' 35"5' 38"' 39"OO' 38"OO' 37 ' 36"OO' 37"OO' 36OOO' 3S"OO' 34 ' 35O5' 36"OO' 35"OO' 36"OO' 37'' 38"OO' 37'' 38'' 39"OO' 37"OO' "OO' 36"OO'.2 38"OO' 34"OO' "45' 35"45' '' 37"OO' "3' 36'3' '' 35'' "3' 34"3' "3' 35"3' OOOO' 36"6' '' 36"OO' OOO' 36"OO' 9.3 No. of gill Catch number CPUE net (tan', Dink masu Dink masu SO oO o.ixo

10 2 If. 3 $@$,$??@-k 2 5' -fif% Bull. Natl. Salmon Resources Center, No. 3, 2 Appendix. (continued) Location SST No. of gill Catch number CPUE Year onth Date N E OC net (tan) pink masu pink masu / 4O2' 37'' O' 37'' "3' 37"' 8. 4"' 37" ' "3' 37"OO' "' 37"OO' '7' 37'' '3' 37O3' ' ' 38 2 ' "OO' 38"' '' 37O' "' 37"OO'.7 39"' 36"OO' O3' 37"3' O3' 38'3' "' 35OOI' "' 35O' "OO' 35"' "' 36"' "' 36'' '' 36'' "3' 36"3' "OO' 37'' '' 37"OO' "' 38'' ' ' 3 X"' Total 3,275 3,