41 Planning of Egg Stock Assessments According to Reproductive Characteristics of Japanese Anchovy Yoshinari TSURUTA Abstract In order to enhance the accuracy of the Egg Production Method applied for Japanese anchovy with a relatively long spawning season and short time interval between spawning episodes, the effect of daily change in developmental stage of ovary on gonosomatic index was discussed. Moreover, the effect of water temperature, food ration and population density on batch fecundity and spawning frequency was formulated definitely in rearedanchovy. As a result, the best sampling time ofadult female is about1800 hour just before the beginning of spawning. The number in a batch fecundity per gram body weight changed about 33 ind. per one centigrade and 38 ind. per one percent of food ration respectively. Population density also affected exponentially on the number in a batch fecundity. Therefore, it was necessary to carry out the investigation of food environment and school size of anchovy at the same time. Key words: Japanese anchovy, reproductive parameter, batch fecundity, spawning frequency, water temperature, food availability, population density, stock assessment 7 1992 1970 12cm 2 3 1990 1986 1997 1990 12cm 5 Funamoto and Aoki, 2002; 1997 2003 2006 1 6 Accepted on January 6, 2006 * 101-0047 2-2-1 National Abundantly Productive Sea Promote Association, Chiyoda, Tokyo 101-0047, Japan. Tel 81-3-5297-5631.Fax:81-3-5297-2653.Email:y.tsuruta@yutakanaumi.jp
42 1. 4 10 7 1.5 1992 Fig. 1 25 9 4 6 1 6,800 1 20 23 Aoki and Tsuruta, 1989Fig. 21 21 15 3 6 Fig. 2 6 104 9 Fig. 1. Develop ental stage of ovaries each sampling time. The developmental stage of ovary is represented by the histological maturity stage of the most advanced group of oocytes in the ovary. E: number of eggs spawned, S: number of spawning females estimated from the batch fecundity (6,800) in September.
43 Fig. 2. Seasonal change in gonosomatic index in anchovy collected during 1984 field survey. The incidence of individual with postovulatory follicles indicates as the females with postovulatory follicles divided by the total number of females. Each point represents the mean( SD) gonosomatic index. 1984 1986 3 1986 6 3 1 1992 15 2, 3 10 Funamoto and Aoki, 2002 1997 1997 24 1997 12.5 15 1992; Kawaguti et al., 1990 2. 15 30 1 1,5004 3 1 1 batch fecundity Fig. 3 1 g batch fecundity relative batch fecundity, RBF RBF B 32.77T 290.85 B RBF T 15 26 1 RBF 1 33 g 24 RBF
44 Fig. 3. Relationship between water temperature and two egg-production variables batch fecundity and egg size. 4 23 26 7 8 1 g 9 11 E 38.45F 16.61 23 26 2 E 1 g F 0.8 2.5 1 1 g 38 10 1992 Fig. 5 23 26 2 Ep 169.83 e 0.0274P 23 26 2 3 E p 1 g P 1 g 1 g 35 35 1 1 g 10 50 2 1992 Fig. 6 1992 3 E 108.33F 46.82 e 0.0274P 4
45 Fig. 4. Relationship between food rations and numbers of eggs spawned per gramme body weight. Fig. 5. Relationship between population density and numbers of eggs spawned per gramme body weight.
46 E F P 4 23 26 24.5 RBF 1 T 24.5 RBF 518.02 32.77T 290.85 518.02 5 E 32.77T 290.85 518.02 108.33F 46.82 e 0.0274P 6 E T F P 1 1 g E t t w 32.77T 290.85 /518.02 108.33F 46.82 e 0.0274P 7 E t tt w g T F P 1 g RBF I 32.77T 290.85 /518.02 108.33F 46.82 e 0.0274P 32.77T 290.85 518.02/ 108.33F 46.82 e 0.0274P 8 T F P 3. 1998; Alheit, 1993; Lasker, 1985 1 RBF 1 RBF batch fecundity Fig. 6. Relationship between population density and swimming speed of the reared anchovy.
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48 starvation. Bull Jpn. Soc. Fish. Oceanogr., 54, 364-372. Lasker R., 1985: An egg production method for estimating spawning biomass of pelagic fish: application to the northern anchovy, Engraulis mordax. NOAA Tech. Rep. NMFS., 36, 1-99. 1986 7 35-43 1992 13 129-168 1997 Engraulis japonicus 61 9-15,,,,,,,,, 2003: 2002.,, 69-70. 1997 2 3 63 665-761