Brodziak and Macy: Growth of Loligo pealei 



213 



(Dawe, 1988). Squid populations with protracted 

 spawning seasons, such as that of L. pealei (Sum- 

 mers, 1971; Macy, 19801, can be composed of numer- 

 ous broods or microcohorts that may experience dif- 

 ferent growth and survival rates (Caddy, 1991). As a 

 result, length-frequency samples may consist of sev- 

 eral microcohorts with differing growth rates. Mi- 

 gration of microcohorts with differing hatching dates 

 and growth rates to and from an area (e.g. II lex 

 illecebrosus, Dawe and Beck 1 ; Ille.x argentinus, 

 Arkhipkin, 1993a) may also substantially influence 

 the size composition of a local population, and may 

 bias growth estimates based on length-frequency 

 data (Hatfield and Rodhouse, 1994). Further, 

 postspawning mortality of squid may also influence 

 local size composition if the sampled area is a spawn- 

 ing ground. For these reasons, analysis of length- 

 frequency data may be inadequate in representing 

 the potentially complicated pattern of individual 

 growth within a squid population. Therefore, it is 

 highly desirable to have a method to age individual 

 squid directly. 



Statolith ageing techniques (Jereb et al., 1991) 

 have recently provided useful information on the age, 

 growth, and population structure of several squid 

 species (Rodhouse and Hatfield, 1990a; Jackson and 

 Choat, 1992; Arkhipkin, 1993, a and b; Arkhipkin 

 and Nekludova, 1993; Hatfield and Rodhouse, 1994 ). 

 Ageing of squid, based on counts of fine increments 

 presumed to have daily periodicity, was first devel- 

 oped for Ille.x illecebrosus ( Lipinski, 1978) and Loligo 

 opalescens (Spratt, 1979) in the late 1970s. Subse- 

 quently, studies of several species have indicated that 

 increments within statolith microstructure are 

 formed daily (Dawe et el., 1985; Hurley et al., 1985; 

 Lipinski, 1986; Jackson, 1990, a and b; Jackson et 

 al., 1993), although the mechanisms that regulate 

 increment formation have not yet been determined 

 (Jackson, 1994a). 



The application of statolith ageing techniques to 

 L. pealei suggests that this species has a life span of 

 less than one year and grows more rapidly than pre- 

 viously thought (Macy, 1995; Macy 2 ). In this study 

 we provide estimates of growth rate for L. pealei in 

 the northwest Atlantic based on a data set of 353 

 animals aged by counting putative daily increments 

 on statoliths. We examine empirical patterns in 



1 Dawe, E. G., and P. C. Beck. 1992. Population structure, 

 growth, and sexual maturation of short-finned squid at New- 

 foundland, Canada, based on statolith analysis. ICES Coun- 

 cil Meeting, Shellfish Committee/K, 33 p. 



2 Macy, W. K., III. 1992. Preliminary age determination of the 

 squid, Loligo pealei, using digital imaging. ICES, Shellfish Com- 

 mittee Council Meeting (mimeo), 9 p. 



length and weight at age and estimate parameters 

 of a general growth model proposed by Schnute ( 1981 ) 

 by squid sex and season of hatching. We discuss some 

 practical implications of our findings for the assess- 

 ment and management of the stock in the northwest 

 Atlantic. 



Materials and methods 



Sampling 



Data used in this growth study consisted of 353 squid 

 collected during 1991-93. Squid samples were ob- 

 tained from catches of a commercial fishing vessel 3 

 and from inshore research surveys in the northwest 

 Atlantic (Table 1; Fig. 1 ). Samples were flash frozen 

 and stored for subsequent analysis. Basic measure- 

 ments of mantle length (ML) (to the nearest mm), 

 wet weight (g), and morphometric characters needed 

 to assess maturity stage according to the scheme of 

 Macy ( 1982a) were taken. Statoliths were dissected 

 from all animals and stored dry in plastic 96-well 

 immunoassay microplates. Statoliths were randomly 

 selected from representative size categories of squid 

 on the basis of observed length-frequency distributions 

 for male, female, and squid of indeterminate sex. 



Statolith preparation 



Statoliths were prepared by mounting them in a ther- 

 moplastic medium (Crystal Bond, Aremco Products; 

 cf. Secor et al., 1991) and by grinding both anterior 

 and posterior surfaces in a manner similar to that 

 described by Jackson (1990a). Several steps were 

 required to prepare a statolith for ageing (Fig. 2). 

 First, a small piece of mounting medium was placed 

 on a petrographic slide ( 26 x 46 mm ) and melted with 

 a hot-air gun. The statolith was then placed in the 

 fluid medium with its concave anterior side down 

 and allowed to cool (Fig. 2B). Material was ground 

 from the exposed convex posterior surface (Fig. 2C) 

 with a graded sequence (12 um to 3 um) of water- 

 lubricated abrasive films (Imperial Brand lapping 

 film, 3M Co.) to reveal the nucleus. Progress was 

 monitored throughout the grinding procedure with 

 a stereoscopic dissecting microscope. When the 

 nucleus was clearly revealed, the exposed surface was 

 polished with 0.3-um aluminum oxide polish (Buehler 

 micropolish) in water on a felt lapidary pad, rinsed 

 with deionized water, and cleaned ultrasonically. 

 After the posterior face was ground, the mounted 



3 FV Huntress, Deep Sea Fish Co.. Point Judith, RI. 



