Arkhipkin et al : Distribution, stock structure, and growth of Berryteuthis magister 



27 



but two seasonal spawning groups: summer-spawn- 

 ing and fall-winter spawning, the latter with two 

 spawning peaks, during fall and winter. It is inter- 

 esting that Natsukari et al. (1993) found the same 

 two spawning peaks (summer and fall-winter), al- 

 though of different intensity, for B. magister occur- 

 ring in the Rebun Bank (Sea of Japan) and Kitami- 

 yamato Bank (Sea of Okhotsk). 



Age, growth, maturation, and possible life 

 cycle 



Until now, investigations of squid life cycles by any 

 direct method have shown that tropical species are 

 characterized mainly by a half-year life cycle (small- 

 and medium-size loliginids [Jackson and Choat, 

 1992]) and a one-year life cycle (medium-size and 

 large ommastrephids [Arkhipkin and Bizikov, 1991; 

 Arkhipkin and Mikheev, 1992]), whereas subtropi- 

 cal and temperate species generally have a one-year 

 life cycle (Natsukari et al., 1988; Arkhipkin, 1990; 

 Natsukari and Komine, 1992). The maximum age of 

 cold-water subarctic, Arctic, and Antarctic species has 

 not been determined directly yet. However, studies of 

 length-composition dynamics through various years as 

 well as growth data obtained from the hard structures 

 of squid have suggested that cold-water species may 

 live two years or more (i.e. B. magister [Fedorets, 

 1986a]; Kondakovia longimana [Bizikov, 1991; Jarre 

 et al., 1991]; Martialia hyadesi [Rodhouse, 1991]). 

 Natsukari et al. ( 1993 ) suggested that B. magister live 

 four years, but we have produced different estimates 

 which reflect different criteria for increment counting. 



According to our data, B. magister in waters of the 

 western Bering Sea live more than one year, with 

 the oldest specimens about 16 months old, and the 

 bulk of fall-hatched squid 13-14 months old and far 

 from being in a spent condition. However, summer- 

 hatched squid matured earlier, with the majority of 

 spent animals being 12-14 months old. 



Berryteuthis magister is a nektonic species resem- 

 bling active oceanic ommastrephids in body shape 

 and muscle strength (Nesis, 1985). It showed the 

 same growth and maturation features as many 

 middle- and large-size ommastrephids, namely 1) an 

 earlier decrease in growth rates for males, which re- 

 sults in smaller sizes at maturation for males in 

 comparison with females of the same age; 2 ) maximum 

 daily growth rates in the middle of ontogenesis with a 

 gradual decrease by the end of life; 3 ) a constant reduc- 

 tion of instantaneous growth rates from maximum val- 

 ues in early juveniles to minimum values in mature 

 specimens; 4) the achievement of maximum DGR in 

 body weight at older ages than those attained for maxi- 

 mum DGR in ML; 5) a wide length-weight range for 



squid of the same age; and 6) the presence of early and 

 late-maturing animals within the same seasonal group 

 of females. As expected, cold-water B. magister grew 

 and matured slower than large species of omma- 

 strephids, had a smaller body size, and lived longer. 



Growth curves of seasonal groups of squid would 

 probably differ, as has been shown before for omma- 

 strephid (Arkhipkin, 1990; Uozumi and Ohara, 1993) 

 and loliginid squid (Natsukari et al., 1988; Jackson 

 and Choat, 1992). This was confirmed indirectly for 

 B. magister in comparing the smaller sizes of mature 

 summer-hatched females (250-260 mm ML) with ma- 

 ture fall-hatched females (270-280 mm ML). 



Taking into account our data with those of several 

 previous studies (Fedorets, 1986a; Okiyama, 1993), 

 we were able to suggest an approximate scheme for 

 the life cycle of B. magister in the Bering sea for the 

 most fully investigated, abundant fall-hatched group. 

 The direction of ontogenetic migrations of B. magis- 

 ter is expected to coincide with the general scheme 

 of water circulation in the Bering Sea (Hughes et 

 al., 1974; Favorite et al., 1976; Shuntov et al., 1993). 

 In the deepwater southern part of the Bering Sea 

 there are three main counterclockwise circulations: 

 that which lies westward from Shirshov Ridge, that 

 between Shirshov and Bowers Ridges, and that be- 

 tween Bowers Ridge and the shelf of Bristol Bay. 

 There are many lesser circulations (Shuntov et al., 

 1993). Immature fall-hatched squid (180-200 mm 

 ML) in early summer appeared in the Navarin-St. 

 Matthew region and began migrating southwestward 

 along the continental slope of the Navarin- 

 Olyutorsky region. During summer, these squid fed 

 actively over the slope and grew quickly. In August- 

 September, maturing females attained 260-270 mm 

 ML. In October, the majority of them were mature 

 and, by the end of the month, had mated. In Novem- 

 ber they vanished, first from the Navarin-Olyutorsky 

 region and later from Olyutorsky Bay. One group of 

 these squid spawns and dies in the two regions just 

 mentioned. Another group of these squid, however, 

 may migrate actively in a southwest direction onto 

 the slope of the Commander Islands. There are two 

 possible migration routes from the main feeding 

 grounds in the Navarin-Olyutorsky region to the 

 area around the Commander Islands: 1) along the 

 slopes of Olyutorsky Bay and North Kamchatka (to- 

 tal distance about 1,800 km); and 2) south of Cape 

 Olyutorsky along the Shirshov Ridge (ca. 1,000 km). 

 Both routes include sections with great depths 

 (> 1,500 m); the first route having an approximately 

 100-km section and the second route an approxi- 

 mately 500-km section. It is known that not only 

 immature squid but even mature males and matur- 

 ing females of B. magister may occur in pelagic wa- 



