OBSERVATIONS ON THE DEVELOPMENT OF THE ATLANTIC SAILFISH 

 ISTIOPHORUS AMERIC AN US (CITVIER), WITH NOTES ON AN UNIDEN- 

 TIFIED SPECIES OF ISTIOPHORID 



Bv Jack W. Gehringer, Fishery Research Biologist 



The South Atlantic Fishery Investigations, con- 

 ducted by the U. S. Fish and Wildhfe Service in 

 cooperation with the U. S. Navy Hydrographic 

 Office, the Office of Naval Research, the Georgia 

 State Game and Fish Commission, and the Florida 

 State Board of Conservation (through the Marine 

 Laboratory, University of Miami), has engaged 

 since July 1952 in a biological, chemical, and phy- 

 sical oceanographic study of the waters between 

 Cape Hatteras and the Florida Straits from the 

 coast to considerably bej'ond the axis of the Gulf 

 Stream. 



Field operations are conducted with the research 

 vessel Theodore A\ Gill. Biological specimens are 

 collected with standard half-meter silk nets, high- 

 speed metal nets (Arnold and Gehrhiger, 1952), a 

 continuous plankton sampler, 18-inch diameter 

 dip nets equipped with 10-foot bamboo handles 

 and lined with )^-inch nylon mesh, and trolling 

 and hand lines. 



During hydrographic observations, at which 

 time the vessel is drifting, dip-net operations are 

 carried out, aided at night by flood and spotlights. 

 Dip-netting sometimes produces relatively rare 

 fish larvae and juveniles. Such was the case on 

 July 29, 1953, between 1700 and 1900 hours dur- 

 ing the occupation of regular station 30 (approxi- 

 mately 90 miles east of Brunswick, Ga.) on 

 Theodore N. Gill cruise 3, when several small 

 istiophorids were captured. Dip-netting and sur- 

 face tows on that station and on subsequent sta- 

 tions produced a total of 26 specimens ranging 

 in standard length from 3.4 to 38.8 mm. 



Since little has been pubUshed on the early life 

 history of the sailfish and other istiophorids, in- 

 formation that could be obtained from the speci- 

 mens is of considerable value. There was a 

 dearth of material in the 3.8-9.4 mm. range in 

 our collections, however. The United States Na- 

 tional Museum kindly loaned their small istio- 

 phorid specimens, most of which were in the 3.8- 

 9.4 mm. range, including some from the Gulf of 



Mexico. I decided to include in the study all 

 available material both from the waters off the 

 South Atlantic Coast of the United States and 

 from the Gulf of Mexico. Additional specimens 

 were loaned by the Gulf Fishery Investigations 

 (Arnold 1955) and various other organizations. 

 Subsequent Theodore N. Gill cruises produced sev- 

 eral more specimens; one was removed from the 

 stomach of a small swordfish, Xiphias gladius 

 (Arata 1954), and one was taken from the stomach 

 of another small istiophorid. Three mounted 

 specimens of Atlantic sailfish, Istiophorus ameri- 

 canus (Cuvier), 374 to 625 mm. in standard length, 

 were photographed and measured. In total, 168 

 specimens were examined. 



During my examination of the material I found 

 two groups of fishes to be involved. Those below 

 approximately 10 mm. in standard length did not 

 separate into two groups on any character or group 

 of characters examined, or location or time of cap- 

 ture. The specimens exceeding approximately 10 

 mm. in standard length separated on some mor- 

 phometric measurements into two distinct groups 

 which converged at approximately 10 mm. The 

 converging of the two groups at 10 mm. precludes 

 the positive identification, by species, of speci- 

 mens below 10 mm., so far as my observations are 

 concerned. Beyond 10 mm. one group traces 

 through development to the Atlantic sailfish, 

 Istiophorus americanus (Cuvier). The other 

 group, with a maximum size of 45.0 mm. stand- 

 ard length, has not been identified. Lack of 

 specimens exceeding 45 mm. makes positive iden- 

 tification impossible. For these specimens I pre- 

 sent selected measurements, counts, and figures, 

 and discuss them with reference to Atlantic sail- 

 fish specimens of similar sizes. The unidentified 

 species is represented by 15 specimens exceeding 

 10 mm. Several specimens below 10 mm., which 

 were taken at the same time as these, possibly 

 belong to the same group. 



Though the taxonomy of the istiophorids is in 



139 



