Analysis of Length and Weight Data 



On Three Species of Billfish 

 From the Western Atlantic Ocean 



WILLIAM H. LENARZ 1 and EUGENE L. NAKAMURA 2 



ABSTRACT 



Estimates of parameters of relations among weight, girth, total length, fork length, body length, trunk 

 length, and caudal spread were made for blue marlin, white marlin, and sailfish captured in the western 

 Atlantic. Some sexual differences were found. 



Estimates of relations between length and weight 

 of fish are important, because weight is often the 

 desired measure when only length measurements are 

 practical. For example, obtaining accurate weights 

 on vessels at sea is difficult, especially when speci- 

 mens may weigh hundreds of pounds, as is often the 

 case for billfish. Both sport and commercial fisher- 

 men are more interested in weight than in length, for 

 game fish records are listed by weight and commer- 

 cial fishermen are paid by the weight of their catch. 



Although length measurements of billfish have 

 been taken in numerous ways (Rivas, 1956; Royce, 

 1957), we chose eye-fork length as the most mean- 

 ingful, because it involves parts of the body that are 

 least apt to be damaged. 



In this study we estimated relations between eye- 

 fork length and weight for blue marlin (Makaira 

 nigricans), white marlin (Tetrapturus albidus), and 

 sailfish (Istiophorus platypterus) in the western At- 

 lantic Ocean. The relations between girth, eye-fork 

 length, and weight were also estimated, for weight 

 can be more accurately estimated from eye-fork 

 length and girth than from eye-fork length alone. The 

 relations between total length, fork length, body 

 length, caudal spread, and eye-fork length were es- 

 timated so that measurements of the first four types 

 could be converted to eye-fork length for compara- 

 tive purposes. We also examined sexual, spatial, and 

 temporal differences among some of the relations. 



'Southwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, La Jolla, CA 92037. 



2 PanamaCity Laboratory. National Marine Fisheries Service, 

 NOAA, Panama City, FL 32401. 



SOURCES OF DATA AND 

 TYPES OF MEASUREMENTS 



Most of the data were obtained by personnel of the 

 Panama City Laboratory, Gulf Coastal Fisheries 

 Center, National Marine Fisheries Service, from 

 sportfishermen's catches in the northeastern Gulf of 

 Mexico during 1971. Weights, lengths, girths, and 

 sex were determined for billfishes landed at Port 

 Eads, Louisiana, and at three ports in northwest 

 Florida: Pensacola, Destin, and Panama City. 



Data were also obtained from cooperative scien- 

 tists for catches made in various years off the coasts 

 of New Jersey, North Carolina, and Florida, 

 around the Bahama Islands, in the Caribbean Sea, 

 and off Rio de Janeiro. 



Most measurements were made in English units, a 

 few in metric units. All weights were recorded in 

 pounds. Lengths were recorded in inches or in cen- 

 timeters. Metric measurements were converted to 

 inches for the analyses, since sportsmen and com- 

 mercial fishermen use inches and pounds. Four 

 kinds of length measurements plus the girth and 

 caudal spread were made by personnel of the 

 Panama City Laboratory, except when conditions 

 did not permit (e.g. , broken bill or shark bites). Data 

 from the cooperating scientists consisted of one or 

 two kinds of length plus weight. 



Measurements and their criteria are listed below. 



Criteria for body length, girth, and caudal spread are 



the same as those of Rivas (1956). All, except girth, 



consisted of horizontal, straight-line measurements. 



(1) Total length: tip of bill to line joining tips of 



caudal lobes. 



121 



