A BEAK KEY FOR EIGHT EASTERN TROPICAL PACIFIC CEPHALOPOD SPECIES WITH RELATIONSHIPS BETWEEN THEIR BEAK DIMENSIONS AND SIZE GARY A. WOLFF! ABSTRACT A method of identifying the beaks and estimating body weight and mantle length of eight common species of eastern tropical Pacific cephalopods is presented. Twenty specimens were selected from each of the following species: Symplectoteuthis oualaniensi.~. DosidicWl gigas. Ommastrephes bar­ tramii. Onychoteuthis banksii. Abraliopsi.~ a/finis. Pterygioteuthis giardi. Liocranchia reinhardti. and Loligo opalescens. Seven dimensions measured on the upper beak and five dimensior\s measured on the lower beak are converted to ratios ~nd compared individually among the species using an analysis of variance procedure and Tukey's w. Significant differences (0'~O.05) observed among the species' beak ratios means. in addition to structural characteristics. are used to construct artificial keys for the upper and lower beaks of the eightspecies. Upper and lower beak dimensions are used as independent variables in a linear regression model with mantle length and body weight (log trans­ formed). Two equations are given for estimating the length and weight for each species from the upper or lower beak. One uses the rostral length dimension because of its durability and the second uses a dimension derived from a stepwise regression procedure. The importance of cephalopods as prey is well expanded to include other species of cephalo­ documented for whales (Gaskin and Cawthorn pods. 1967; Clarke et al. 1976; Clarke 1977), seals(Aus­ This study presents a key based on structural tin and Wilki 1950; Laws 1960), seabirds (Ash­ and biometric differences among the beaks of mole and Ashmole 1967; Imber 1978), tunas eight species of cephalopods. The species ofceph­ (Pinkas et aI. 1971; Matthews et aI. 1977), tunas alopods examined were: Symplectoteuthis oua­ and porpoise (Perrin et aI. 1973), and sharks laniensis (Lesson), Dosidicus gigas (d'Orbigny), (Clarke and Stevens 1974; Tricas 1979). Due to Ommastrephes bartramii (Lesueur), Onychoteu­ the rapid digestion of the softer body parts, how­ this banksii(Leach), A braliopsis affinis(Pfeffer), ever, the cephalopod's beak is often the only iden­ Pterygioteuthis giardi Fischer, Liocranchin tifiable structure remaining in these predator's reinhardti (Steenstrup), and Loligo opalescens stomachs as evidence of feeding on cephalopods. Berry. Regression equations of body weight and Consequently, the accuracy of specific identifica­ mantle length from beak dimensions are also tions and estimates of cephalopod biomass con­ presented. sumed by these predators often suffers. Two methods have generally been used to ap­ MATERIALS AND METHODS proach the problem of characterizing cephalo­ pod beaks. A descriptive method was used most The cephalopods for this study were obtained notably by Clarke (1962, 1980), Mangold and from Southwest Fisheries Center, National Ma­ Fioroni (1966), and Pinkas et aI. (1971). Families, rine Fisheries Service, and Invertebrate Collec­ genera, and occasionally species were identified tion, Scripps Institution of Oceanography, La from structural characteristics of the beak. A Jolla, Calif. Twenty specimens of each species biometric method was used by Wolff (1977) and were selected in the maximum mantle length Wolff and Wormuth (1979) to separate two spe­ range available. Table 1 shows the ranges for cies of ommastrephid squid with beak dimen­ mantle length and body weight and collection sions. It was suggested that the method could be locations for the cephalopods. The buccal masses were removed, after the specimens were mea­ sured and weighed, and placed in a solution !Departmentof Oceanography. Texas A&M University. Col­ lege Station. TX 77843; present address: Environmental Engi­ saturated with sodium borate and trypsin (8 g neering. Texas A&M University. College Station, TX 77843. trypsin/l sodium borate solution) for 6 to 10 d. Manuscript accepted October 1981. 357 FISHERY BULLETIN: VOL. 80. NO.2. 1982. FISHERY BULLETIN: VOL. 80, NO.2 TABLE I.-Mantle length (ML) ranges, body weight ranges, and collection locations for the species (nla = specimens collected in the Pacific but spe- cific location not available). ML Weight Number range range of Species (mm) (g) specimens Lat. Long. Symplectoteuthis 130-290 79-927 1 00°33' S 111°14'W oualaniensis 2 03°25' S 110°31' W 2 06°49' S 86°14' W 1 05°12' S 91°49' W 1 08°09' S 100°31' W 1 05°46' S 102°31' W 1 00°26' S 109°28' W 1 01°15' S 112°51' W 2 02°40' S 116°11'W 1 00°01' S 118°03' W 2 00°46' S 105°35' W 1 02°52' S 97°21' W 3 07°19' S 94°24' W 1 05°14' S 83°32' W Dosidicus 196-321 191-842 2 00°33' S 111"14' W gigas 3 02°52' S 97°21' W 3 07°49' S 81°38' W 3 05°14' S 83°32' W 1 01°46' S 108°58' W 2 00°26' S 109°28' W 1 06°49' S 86°14' W 1 11°38' S 87°13' W 1 06°00' S 96°16' W 1 04°30' S 89°16' W 1 11°30' S 93°18' W 1 05°02' S 91°49' W 1 02°52' S 97°21' W 1 11°44' S 83°56' W Ommastrephes 85-165 11-118 4 30°03' N 156°11' W bartramii 2 30°08' N 135°02' W 5 24°18' N 155°00' W 9 28°11' N 155°17' W Onychateuthis 40-130 3-67 2 13°00' N 132°00' W banksii 1 nla 1 25°10' N 121°22' W 10 13°49' N 118°59' W 3 18°00' N 113°00' W 3 00°28' N 105°53' W Abraliopsis 19-26 0.5-4.3 5 24°06' N 109°37' W affinis 6 nla 7 11°31' N 131°08'W 2 05°42' N 86°53' W Pterygiateuthis 16-30 0.3-1.4 1 05°02' S 91°49' W giardi 2 11°44' S 83°56' W 2 10°24' N 107°46' W 2 06°30' N 139°00' W 2 00°04' N 127°47' W 2 00°20' N 120°21' W 9 01°21' N 130°47' W Liocranchia 23-125 1-24 1 00°30' N 96°50' W reinhardti 3 18°32' N 119°s1'E 1 32°34' N 117°29' W 1 12°40' N 112°46' W 14 13°49' N 118°59' W Loligo 80-153 12-49 7 34°00' N 120°10' W opalescens 6 26°30' N 114°50' W 7 33°29' N 117°47' W The beaks were then removed from the buccal sured on the lower beakof each specimen: rostral masses and placed in 40% isopropyl alcohol. tip to inner posterior corner of lateral wall (RC), Beak dimensions were measured with vernier rostral tip to inner margin of wing (RW), length calipers or an occular micrometer. Seven dimen­ of the rostrum (RL), length of the wing(WL), and sions were measured on the upper beak of each jaw angle width (JW) (Fig. 1). These dimensions specimen: length of the rostrum (RL), rostral tip were transformed to ratios to remove the dimen­ to inner margin of wing (RW), length of hood sionality. Comparisons among species' beak (HL), width of the wing (WW), wing to crest ratios were made with a one-way classification length (WCL), jaw angle width (JW) and length analysis of variance procedure (ANOVA). The of the crest (CL). Five dimensions were mea- ratios were normally distributed and the ratio 358 WOLFF: BEAK KEY FOR EIGHT CEPHALOPOD SPECIES side view top view LOWER UPPER FIGURE I.-Dimensions measured on the upper and lower beak. transformation met the criteria for validity as ric portion of the beak key. Combinations of de­ described by Anderson and Lydic (1977). Tukey's scriptive characteristics and significant beak w procedure was used to test for significant dif­ ratios are used to identify the eight species of ferences (aSO.05) among 21 ratio means from cephalopods. Separate keys are provided for the the upper beak and 10 ratio means from the upper and lower beak. lower beak for each species. This procedure in­ The ratio values presented in the key are mid­ volves the computation of a confidence interval points between species' means and often greatly from the formula: w = qa (p, n2) SiX, where w is a exceed the stated significance level (aSO.05) as range for the treatment means with a given indicated by the confidence interval for the spe­ probability level (aSO.05), q is the studentized cies' means which follows in parentheses. Addi­ range, p is the number of treatments, n2 is the tional descriptive characteristics and alternate error degrees of freedom and SiX is the standard beak ratios are given to corroborate the initial error of the treatment means (Steel and Torrie identification. Figures 3-10 show upper and 1960). Simple linear regressions were calculated lower beaks for each of the species. A few of the to express the relationship between a beak alternate ratios in the upper and lower beak key dimension and the mantle length and log trans­ have species' means which are not significantly formed body weight. An AMDAHL 470 V/6 different. These ratios can be considered reliable computer2 performed the majority of computa­ since Hartley (1955) suggested that the experi­ tions. mentwise error rate could be relaxed consider­ ably below the standard aSO.05 level due to the RESULTS conservative nature of Tukey's w procedure. Additional alternate ratio values can be deter­ The results of the ANOVA procedure are sum­ mined from Table 2 to distinguish species if the marized in Tables 2 and 3.