DEVELOPMENT AND APPLICATION OF AN OBJECTIVE METHOD 



FOR CLASSIFYING LONG-FINNED SQUID, LOLIGO PEALEI, 



INTO SEXUAL MATURITY STAGES 



William K. Macy III 1 



ABSTRACT 



An objective method of classifying long-finned squid, Loligo pealei, by their sexual maturity was 

 developed using cluster and discriminant analysis techniques. The resulting system recognizes four 

 developmental stages and employs a maximum of only five easily measured morphometric parame- 

 ters. Such a system is easy to use and is suitable for large-scale field studies with relatively untrained 

 help. The value of determining clearly recognized reproductive stages is demonstrated by an appli- 

 cation of the method. 



Each summer schools of long-finned squid, Loli- 

 go pealei Lesueur, 1821, move into shallow coastal 

 waters from Delaware Bay to Cape Cod to spawn 

 (Verrill 1882; Haefner 1964; Summers 1968, 

 1971). During the colder months, however, the 

 squid are found only offshore, concentrated in 

 canyon mouths along the continental slope (Sum- 

 mers 1967, 1969; Vovk and Nigmatullin 1972; 

 Serchuk and Rathjen 1974). While the size/age 

 composition of the species has been relatively 

 well described by Verrill (1882), Summers 

 (1967, 1968, 1969, 1971), Tibbetts (1975, 1977), 

 and Mesnil (1977), many details of its reproduc- 

 tive cycle, particularly during the offshore peri- 

 od, remain unclear (see Summers 1969, 1971; 

 Vovk 1972; Arnold and Williams-Arnold 1977; 

 Mesnil 1977). From such studies it appears that 

 L. pealei lives only 12-18 mo on average, and that 

 like most squid it dies after spawning (Arnold 

 and Williams-Arnold 1977). Details of the repro- 

 ductive biology and population structure of such 

 a short-lived species, with only two year classes 

 at most, are especially important in the develop- 

 ment of prudent stock management programs. 

 Unfortunately, no single method for character- 

 izing the reproductive state of individuals of this 

 species has been employed to date. 



A number of classification methods have been 

 employed for a variety of squid species, which 

 reflect both interspecific differences and differ- 

 ing requirements of the investigators using them 

 (Tinbergen and Verwey 1945; Mangold-Wirz 

 1963; Fields 1965; Hayashi 1970; Vovk 1972; 



•Narragansett Mussel Co., 146 Main Street, North Kings- 

 town, RI 02852. 



Holme 1974; Ikehara et al. 1977; Durward et al. 

 1978; Juanico 1979; Hixon 1980). Many of these 

 methods are slow because of the large number of 

 variables required or the need for sample weigh- 

 ing or microscopic examination. Some methods 

 also rely mainly on subjective distinctions. 



From 1975 through 1978, ecological studies 

 concerning the population structure, movement 

 patterns, and feeding habits of L. pealei were 

 conducted (Macy 1980). During the first year of 

 the study, the Vovk (1972) method for classifying 

 squid into one of five stages of sexual maturity 

 was used with length-frequency data to charac- 

 terize changes in the population reproductive 

 structure over time. While the Vovk method was 

 useful, in practice squid were often encountered 

 which could not be readily classified. This report 

 concerns the development and application of a 

 new, faster, and more objective maturity classifi- 

 cation system. The method was then successfully 

 employed to classify large numbers of squid 

 throughout the remainder of the study referred 

 to above. 



METHODS 



From late April through November each year, 

 squid were collected on an approximately bi- 

 weekly basis throughout the inshore study area 

 located in the southern part of the West Passage 

 of Narragansett Bay, R.I. (inset Fig. 1). A bal- 

 loon-type otter trawl (Oviatt and Nixon 1973), 

 towed at ca. 4.6 km/h, was used. To insure ran- 

 domness and adequate size-class representation, 

 samples of at least 100 squid each were randomly 

 selected from the pooled catch of duplicate 20- 



Manuscript accepted January 1982. 

 FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 



449 



