212 



Abstract. ^The application of sta- 

 tolith ageing techniques to long-finned 

 squid, Loligo pealei, suggests that this 

 species has a life span of less than one 

 year and grows more rapidly than pre- 

 viously thought. In this study we pro- 

 vide direct estimates of growth for long- 

 finned squid in the northwest Atlantic 

 based on a data set of 353 animals aged 

 by counting putative daily statolith in- 

 crements. We examine empirical pat- 

 terns in length and weight at age and 

 estimate parameters of a general 

 growth model. The results indicate that 

 growth rate increases rapidly as squid 

 age and that growth in length and 

 weight is exponential. Although there 

 is substantial heterogeneity in L. pealei 

 size at age, sexual dimorphism is evi- 

 dent: males grow more rapidly than do 

 females and achieve larger sizes. Back- 

 calculated hatching dates show that L 

 pealei spawning is not restricted to 

 spring through late-autumn, as previ- 

 ously supposed, but occurs during win- 

 ter months as well. Differences between 

 growth rates of squid hatched during 

 June-October and November-May are 

 suggested and lend support to the hy- 

 pothesis that growth can be influenced 

 by seasonal environmental conditions. 

 We discuss the practical implications 

 of our findings for the assessment and 

 management of the long-finned squid 

 stock in the northwest Atlantic. 



Growth of long-finned squid, 

 Loligo pealei, in the 

 northwest Atlantic 



Jon K. T. Brodziak 



Northeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



Woods Hole, Massachusetts 02543-1097 



Present address Northwest Fisheries Science Center at 



Hatfield Marine Science Center, Newport, Oregon 97365 



William K. Macy III 



Graduate School of Oceanography 

 University of Rhode Island 

 Narragansett, Rhode Island 02882 



Manuscript accepted 25 October 1995 

 Fishery Bulletin 94:212-236 1 19961. 



The long-finned squid, Loligo pealei 

 (also known as the longfin inshore 

 squid (FAO, 1984), is a pelagic 

 schooling loliginid distributed in 

 continental shelf and slope waters 

 from Newfoundland, Canada ( Dawe 

 et al., 1990), to the Gulf of Venezu- 

 ela ( Summers, 1983 ). A substantial 

 commercial fishery exists in the 

 northwest Atlantic where annual 

 landings averaged 17,300 metric 

 tons (t) during 1963-92, and to- 

 talled 22,300 t in 1993 for an ex- 

 vessel value of approximately $30 

 million (NEFSC, 1995). Recent ad- 

 vances in the use of statolith incre- 

 ments to age squid directly and re- 

 cent increases in fishing effort in the 

 northwest Atlantic have led to a re- 

 newed interest in the life history of 

 this species, and, in particular, its 

 growth rate. 



Several estimates of the growth 

 rate of L. pealei have been made by 

 comparing modes of length-fre- 

 quency distributions (Verrill, 1881; 

 Summers, 1968, 1971; Cohen, 1976; 

 Mesnil, 1977; Whitaker, 1978; 

 Lange, 1980; Lange and Sissen- 

 wine, 1980; Macy, 1980; Hixon et al., 

 1981 ). These studies generally have 

 suggested that growth rate, mea- 

 sured by change in dorsal mantle 

 length (ML), ranged from 10 to 24 



mm per month, and that growth 

 rate was dependent upon sex, 

 hatching date, and season ( Hixon et 

 al., 1981). Sexual dimorphism was 

 evident; males attained larger sizes 

 than did females ( Summers, 1971). 

 Seasonal effects on growth were 

 also suggested; higher growth rates 

 occurred during summer months 

 and lower rates during winter 

 months (Mesnil, 1977). Latitudinal 

 differences in age structure and 

 mean size of L. pealei have also been 

 proposed (Summers, 1971), namely 

 that mean size has been suggested 

 to be greater at higher latitudes. 

 These studies, combined with the 

 observed maximum size of approxi- 

 mately 46.5 cm mantle length ( Sum- 

 mers, 1968), were consistent with a 

 maximum life span of roughly three 

 years in the northwest Atlantic, a 

 value that was assumed for stock 

 assessment (NEFSC, 1988). 



The inferred growth rates of L. 

 pealei, based on length-frequency 

 analyses, should be viewed cau- 

 tiously because they have not been 

 supported by direct ageing data 

 (Caddy, 1991). In general, growth 

 rates of squid might be expected to 

 vary with prey availability (O'Dor 

 et al., 1980), temperature (Forsythe, 

 1993), and population density 



