FISHERY BULLETIN: VOL. 86, NO. 3 



9 months old. It was still faster than Novikov's 

 growth rate of the corresponding age period (0.83 

 mm/d), which was the highest rate of all the previous 

 reports. The fish would become 316 mm in one year 

 according to our model. 



Support for the fast growth rate of Pacific saury 

 presented in this paper in the western Pacific can 

 be found in rearing experiments. Hotta (1958) 

 reared young sauries caught by a set net. He reared 

 them in a crawl and fed them minced anchovy and 

 mackerel twice a day. Young sauries 116 mm in 

 mean length became 172 mm in the rearing period 

 after 72 days. The growth rate was 0.78 mm/d. The 

 sauries fed three times a day grew 130-143% faster 

 than the group fed twice a day. Thus growth rates 

 of young sauries may be higher than 1.1 mm/d (0.78 

 X 1.4 mm/d) when food is readily available. Our 

 growth rate of sauries in this size range was approx- 

 imately 1.5 mm/d in the western Pacific. For Atlan- 

 tic saury, Scomberesox saurus scombroides, reared 

 by Brownell (1983), the average growth rate of the 

 larvae was 0.62 mm/d from hatching (7.5 mm SL) 

 to 47-day old (36.8 mm SL). The growth rates of 

 Cololabis saira in a corresponding period were 0.48 

 mm/d in the eastern Pacific and 1.0 mm/d in the 

 western Pacific. 



Our results indicate that the growth rate of Pacific 

 saury in the western Pacific is much higher than in 

 the eastern Pacific. This could be due to a differ- 

 ence in food availability between the two areas. 

 However, mean zooplankton standing stock in 

 1951-66 was 34.8 g/m^ in the California Current 

 region in June (Smith and Eppley 1982), whereas 

 that of Kuroshio water off southern Japan was 4.7 

 g/m^ and of Oyashio area off northern Japan was 

 25.7 g/m2 in May to July (Odate 1986). Thus, differ- 

 ences in zooplankton standing stock do not explain 

 the difference in growth rates. 



On the other hand, there seems to be a reasonable 

 explanation for the reacceleration of growth rate at 

 around 100 mm in the western Pacific saury. The 

 western sauries hatch out mainly in offshore water 

 of the Kuroshio Current (lat. 31-33°N) off Japan 

 in winter. They migrate north to the Oyashio area 

 (up to 46-50 °N) where copepods are highly avail- 

 able. Young and adult sauries feed actively and gain 

 fat. They are in the northward migration stage in 

 early summer when they are about 100 mm, and are 

 moving from poor Kuroshio water to rich Oyashio 

 water (Fukushima 1979). High zooplankton stand- 

 ing stock in the Oyashio water and its derivatives 

 might be responsible for the reacceleration of 

 growth rate in fish older than 100 days. 



The growth rates of Pacific saury in the western 



Pacific may differ from year-to-year due to environ- 

 mental factors and may result in changes in size 

 composition of the fish. Between 1968 and 1972, 

 mean knob length of exploited sauries in the west- 

 ern Pacific was 170-250 mm, whereas in the 1980's 

 the major mode in the size composition was 290-310 

 mm (S. Kosaka''). This increase could have been 

 due to an acceleration of growth rate or a shift of 

 spawning season to early months or both in recent 

 years. The high growth rate of western Pacific saury 

 presented in this paper has come from specimens 

 collected in 1984 and 1985. The growth rate in the 

 late 1960's and early 1970's may have been lower 

 than that presented in this paper. Investigation of 

 the interannual variation in growth rates using daily 

 increments would distinguish between these two 

 hypotheses. 



We used three different gears to collect Pacific 

 saury samples in the western Pacific. Knob lengths 

 of sauries collected were from 8.3 to 125 mm by ring 

 net, 145 to 282 mm by gill net, and 300 to 330 mm 

 by stick-held dip net. Sauries of 125-145 mm might 

 not be available either to the ring net or to the gill 

 net. Further, the ring net may select small juveniles 

 of a cohort in the size range over 100 mm, and this 

 may have produced the two growth curves. This 

 problem needs to be examined further with data on 

 gear selectivity. 



We do not know how long Pacific sauries survive 

 after becoming adult. The oldest specimen in our 

 sample was about 14 months old after hatching (418 

 increments). The largest saury aged (330 mm), 

 which had 328 growth rings, is close to the max- 

 imum size. Although the maximum known length 

 of the Pacific saury was reported to be about 400 

 mm (Hubbs and Wisner 1980), the largest fish ex- 

 ploited in Japan is about 340 mm. Therefore, the 

 lifespan of the Pacific saury is about one year in the 

 western Pacific. Our results are more consistent 

 with those of Kosaka (1979) who found two age 

 groups (0 and 1 year) than those (Sablin 1979) who 

 found three age groups (0, 1, and 2 years). 



In Japan, fishing efforts of the Pacific saury is 

 regulated by fishing season as well as by the num- 

 ber of fishing boats. The fishing season starts in mid- 

 August. Pacific sauries hatched in the main spawn- 

 ing season are about 250 days old at this time of year 

 (approximately 270 mm) and are grovdng at the rate 

 of 0.8 mm/d. Thus a 2-wk postponement at the 

 beginning of fishing season would result in an 11 

 mm (10-15 g body weight) increase of average fish 



*S. Kosaka, Tohoku Regional Fisheries Research Laboratory, 

 Fisheries Agency, Shiogama, Miyagi 985, Japan, pers. commun. 



496 



