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



pelagic trawl "Suketodara" with horizontal opening 

 of 75 m, vertical opening of 20 m, and a 70-mm mesh 

 size at the codend. The duration of each trawl was 

 about one hour and the average speed of each trawl 

 was 6.5-7.8 km-rr 1 . 



Length-frequency sampling 



A total of 23,765 squids were analyzed during the 

 expeditions, including 3,533 juveniles. A random 

 sample of one hundred specimens was taken from 

 each catch. If the number of squid in a given catch 

 was less than 100, the entire squid catch was exam- 

 ined. Dorsal mantle length (ML) was measured to 

 the nearest 1 mm and total body weight (BW) 

 weighed to the nearest 1 g (during periods of calm 

 sea only). Sex and maturity stage were identified 

 according to the maturity scale for Illex argentinus 

 (Nigmatullin, 1989). Evidence of mating and indices 

 of stomach contents (fullness) were examined accord- 

 ing to the methods of Zuev et al. ( 1985). The sex ra- 

 tio was also determined. Because sex can be deter- 

 mined by eye only in squid >120 mm ML, all indi- 

 viduals <120 mm ML were considered juveniles and 

 analyzed separately from males and females. Be- 

 cause juveniles were taken from the mesh of the trawl 

 wings, we could not precisely estimate their abun- 

 dance and occurrence. 



For each sample, four length-frequency curves for 

 each sex were constructed for the following ontoge- 

 netic periods: immature (maturity stages 1-2), ma- 

 turing (maturity stages 3-4), mature (maturity stage 

 5), and spent (maturity stage 6). After preliminary 

 analysis of the samples, length frequencies of all the 

 catches taken within a given month were pooled to- 

 gether for each maturity period and for the three 

 regions: Olyutorsky Bay, and both Navarin-Olyu- 

 torsky and Navarin-St. Matthew regions (Fig. 1). 



Age sampling 



Every month from June to October, statoliths were 

 removed from one hundred randomly sampled indi- 

 viduals ofB. magister from one successful catch (> 100 

 kg). In addition, statoliths were dissected from 50 

 juveniles and from specimens of uncommon sizes and 

 maturity stages (i.e. large-size males and females and 

 spent animals) that were not found in the sample 

 but occasionally occurred in other catches within each 

 month. Statoliths were sampled and analyzed sepa- 

 rately in two regions: Olyutorsky Bay and the cen- 

 tral part of the Navarin-Olyutorsky region. In June 

 and October, statoliths were taken from two samples 

 from the first and second halves of each month. A 

 total of 1,453 statoliths were collected, washed in 



distilled water, and stored in oil-paper envelopes in 

 96% ethanol. 



In June and July, 87 gladii and pairs of statoliths 

 were dissected from the same specimens for a com- 

 parison of the number of growth increments between 

 ageing structures. 



Statolith ageing analysis 



From a total of 1,453 statoliths, 740 were processed 

 and read by two of the authors (AIAand VAB) aboard 

 the Tenyu-Maru N 57; the rest were analyzed in the 

 Laboratory of Commercial Invertebrates of AtlantNIRO 

 by ALA From the entire sample, 1,381 (95.1%) sta- 

 toliths were successfully read. Statolith processing 

 was rather time consuming because sizes (especially 

 in adults ) were unusually large: total statolith length 

 (STL) ranged from 2.5 to 3.2 mm. Statolith terminol- 

 ogy followed Clarke ( 1978) and Lipinski et al. ( 1991). 



Statoliths were processed according to standard 

 techniques (Arkhipkin and Murzov, 1985) with mi- 

 nor modifications. They were ground (on 600 grit) 

 and polished (on 1,000 grit) wet waterproof sandpa- 

 per. Because the direction of the maximum growth 

 within statoliths changed during ontogenesis, it was 

 necessary to grind the convex side of the same sta- 

 tolith in two planes: one plane running through the 

 lateral and dorsal domes and spur, and the other 

 plane running through the spur and along the cen- 

 tral axis of the rostrum. This method of grinding 

 exposes the growth increments lying immediately 

 below the wing. The ground statolith was not flat and 

 thin as in Natsukari et al. ( 1993) but thickened in the 

 region of the lower part of the lateral dome and the 

 proximal part of the rostrum. This feature allowed 

 all increments from the nucleus to the most distal 

 part of the rostrum to be unambiguously resolved. 



Ground statoliths were embedded in glycerin and 

 covered with glass for immediate reading. Statoliths 

 were read under a Biolam R14 light microscope with 

 450-500x magnification. Growth increments were 

 counted from the nucleus to the distal part of the 

 rostrum and from farther within the rostrum as de- 

 scribed by Natsukari et al. ( 1993) by using the eye- 

 piece (as described in Dawe and Natsukari, 1991). 

 To avoid possible counting errors, each statolith was 

 counted at least twice by two observers, and if the 

 difference between readings was less than 5%, squid 

 age was taken as the mean of these counts. Read- 

 ings were made only after achievement of the maxi- 

 mum resolution of growth increments with fine-ad- 

 justment focusing. Because the periodicity of differ- 

 ent types of growth increments was unknown for the 

 northern populations of B. magister, their number 

 was calculated separately for each type. 



