Length-Weight Relationships for Six Species 

 of Billfishes in the Central Pacific Ocean 



ROBERT A. SKILLMAN and MARIAN Y.Y. YONG 1 



ABSTRACT 



Weight-length relationships for six species of billfishes in the central Pacific Ocean were developed by 

 analyzing 20 yr of data. Log-linear and nonlinear statistical models were fitted to the data by regression 

 analysis, and residuals from the models were tested. Blue marlin, Makaira nigricans Lacepede, (50-135 cm 

 FL), male blue marlin (^135 cm FL) and sailfish, Istiophorus platypterus (Shaw and Nodder), apparently 

 have coefficients of allometry less than 3.0. Black marlin, M. indica (Cuvier) and female blue marlin (&135 

 cm FL) apparently have coefficients equal to 3.0. Shortbill spearfish, Tetrapturus angustirostris Tanaka, 

 striped marlin, T. audax (Philippi). and swordfish, Xiphias gladius Linnaeus, apparently have coefficients 

 greater than 3.0. 



As with most studies on the length-weight rela- 

 tionship, this study is not an end in itself. It was 

 initiated to provide length-weight conversion rela- 

 tionships (Equation 1) for use in a growth paper on 

 blue and striped marlins (Skillman and Yong 2 ), as 

 well as to provide conversion charts for the sport 

 fishermen at the Hawaiian International Billfish 

 Tournament. There are few published papers on the 

 weight-length relationship of billfishes 3 (de Sylva, 

 1957; Royce, 1957; Kume and Joseph, 1969); hence, 

 we decided to calculate this relationship for all six 

 species of billfishes on which data had been collected 

 by the Honolulu Laboratory of the Southwest 

 Fisheries Center, National Marine Fisheries Ser- 

 vice. These six species were the black marlin. 

 Makaira indica (Cuvier), blue marlin, M. nigricans 

 Lacepede, sailfish, Istiophorus platypterus (Shaw 

 and Nodder), shortbill spearfish, Tetrapturus an- 

 gustirostris Tanaka, striped marlin, T. audax 

 (Philippi), and swordfish, Xiphias gladius Linnaeus. 



Although all of the length-weight data collected on 

 billfishes from 1950 to 1971 by the Honolulu 

 Laboratory were used, this study should not be con- 

 sidered exhaustive or definitive. Even in the best 

 represented species, there were too few data to sepa- 



1 Southwest Fisheries Center, Honolulu Laboratory, National 

 Marine Fisheries Service. NOAA. Honolulu. HI 96812. 



2 Skillman, R.A., and M.Y.Y. Yong. Growth of blue marlin, 

 Makaira nigricans Lacepede. and striped marlin, Tetrapturus 

 audax (Philippi) in the north central Pacific Ocean by the progres- 

 sion of modes method. Manuscript. National Marine Fisheries 

 Service, Southwest Fisheries Center. Honolulu. HI 96812. 



3 The term billfishes. as used in this paper, includes swordfish. 



rate the data according to sex, maturity, and season 

 as suggested by Le Cren (1951) and Tesch (1968). 

 Thus, it was impossible to perform a detailed 

 analysis of covariance similar to that performed re- 

 cently by Brown and Hennemuth (1971) on haddock, 

 Melanogrammus aeglefinus (Linnaeus). Some 

 species were so poorly represented that the length- 

 weight relationships should be considered as tenta- 

 tive relationships. 



In general, fishery biologists have accepted the 

 appropriateness of the allometric growth equation 

 (Huxley and Teissier. 1936) or its mathematical 

 equivalent, the power function, as a descriptor of 

 growth in weight to growth in length. We accepted 

 the general form of the relationship (Equation 1) and 

 applied both the log-linear and the nonlinear statisti- 

 cal 



Wj = b x Li a > 



(1) 



models of the relationship. Each model is discussed, 

 and statistical procedures for evaluating the good- 

 ness of fit are presented. Papers by Glass (1969), 

 Pienaar and Thomson (1969), and Hafley (1969) are 

 particularly relevant to this discussion. 



MATERIALS AND METHODS 



Collection of Data 



The data used in this report came from three 

 sources. In nearly all of them fork length (FL) mea- 

 surements were taken to the nearest centimeter 



126 



