14 



Fishery Bulletin 92(1), 1994 



have been obtained from a variety of neritic squid 

 species (see review by Rodhouse and Hatfield, 1990a). 

 The objectives of this study were to 1) estimate 

 the age and growth of O. borealijaponica from sta- 

 tolith microstructural analysis, 2) determine the 

 periodicity of increment formation, 3) statistically 

 compare appropriate growth models fit to the age- 

 ing data, 4) determine the distribution of back-cal- 

 culated hatching dates of O. borealijaponica and 

 draw inferences about spawning locations, and 5) 

 determine the relationship between age and matu- 

 rity stages. 



Materials and methods 



Taxonomic clarifications 



At least five onychoteuthid species are found in the 

 North Pacific: O. borealijaponica from subarctic 

 waters; an undescribed species occupying the North 

 Pacific transition zone (-29— 40"N, Bigelow, unpubl. 

 data); and three subtropical species of the O. banksii 

 complex (Young and Harman, 1987). Juvenile, sub- 

 adult, and adult O. borealijaponica (69-343 mm ML) 

 were separated from other onychoteuthid species 

 based on the number of tentacular hooks (n =25-29) 

 on each club. Identification of O. borealijaponica 

 paralarvae (11.5 to 35 mm ML) was based on mantle 

 chromatophore patterns (Bigelow, unpubl. data). 



Data collection 



Subadults, adults During July-September 1990, 

 O. borealijaponica specimens were collected on vari- 

 ous research cruises in the North Pacific. Most squid 

 specimens were captured by research drift net ( mesh 

 size=48-220 mm stretch mesh) in the western and 

 central North Pacific, but squid jigs were also used 

 to capture specimens from the central and eastern 

 North Pacific (Fig. 1, Table 1). Squid samples were 

 frozen (-20°C) upon capture and returned to the 

 laboratory for analysis. 



Paralarvae, juveniles From 5 to 24 August 1991, 

 39 tows with a modified Cobb trawl were made 

 along meridian 179°30'W between 36°56'N and 

 46°00'N, and along meridian 174°30'W between 

 39°00'N and 45°00'N. The trawl was dual warp, with 

 a mouth area of approximately 140 m 2 when fish- 

 ing and a cod-end liner constructed of 3.2 mm 

 knotless nylon delta mesh ( Wyllie Echeverria et al., 

 1990; Lenarz et al., 1991). Thirty-one oblique night 

 tows (0-150 m) and eight oblique day tows (0-750 

 m> were conducted. O. borealijaponica specimens 

 from eight tows (Fig. 1, Table 1) were sorted on 



board and immediately frozen (-20°C, juveniles) or 

 fixed in 95% ethyl alcohol (paralarvae). 



Laboratory analysis 



Dorsal mantle length measurements were made to 

 the nearest millimeter (mm) on thawed specimens. 

 Squids less than 0.5 g were blotted dry and weighed 

 to the nearest 0.001 g, whereas larger specimens 

 were weighed to the nearest 0.1 g. No correction was 

 made for shrinkage of paralarvae from fixation in 

 ethanol, because the species possesses a strong 

 gladius and exhibited minimal shrinkage (<2%). 

 Specimens were sexed and assigned a maturity 

 stage (I: juvenile; II: immature; III: preparatory; 

 IV: maturing; V: mature) based on the appearance 

 and relative size of the gonads and accessory repro- 

 ductive organs (Lipinski, 1979). Statoliths were dis- 

 sected from the specimens and stored in 95% ethyl 

 alcohol. 



Statolith preparation and microstructural 

 analysis One statolith of the pair was mounted on 

 a microscope slide in Eukitt resin (Calibrated In- 

 struments Inc. 200 Saw Mill Rd., Hawthorne, NY 

 10532) with the concave side (anterior) facing up. 

 The transparency of paralarval statoliths allowed 

 their examination without further preparation (Fig. 

 2). The thickening of statoliths from larger squid 

 (>35 mm ML) required that they be ground with 

 fine-grained (1200-grade) carborundum paper and 

 polished with 0.3-|am alumina-silica powder prior to 

 microstructural examination. 



Increments were counted beginning at the first 

 visible increment outside the nucleus (Fig. 3A), and 

 continued to the margin of the dorsal dome (Fig. 3B). 

 The diameter of the circular nucleus averaged 28.0 

 urn (SD=2.4 |im, n-37). The precision of increment 

 counts was assessed by using the coefficient of varia- 

 tion (Chang, 1982). Two nonconsecutive blind incre- 

 ment counts were made on each statolith with trans- 

 mitted light at a magnification of 1500x. The mean 

 of the two increment counts was accepted if the co- 

 efficient of variation was <7.0%, otherwise a third 

 count was conducted. With this criteria, two incre- 

 ment counts were acceptable for 115 statoliths, 

 whereas three increment counts were required for 

 11 statoliths. Hatching dates were computed by 

 subtracting the mean increment count from the date 

 of capture and were pooled into monthly periods. 

 Increment counts were assumed to represent the 

 individuals' age in days, based on the following re- 

 sults (periodicity of increment deposition) which 

 provided support for the hypothesis that one incre- 

 ment is deposited per day. 



