588 



Abstract — The identification of larval 

 istiophorid billfishes from the western 

 North Atlantic Ocean has long been 

 problematic. In the present study, a 

 molecular technique was used to posi- 

 tively identify 27 larval white marlin 

 (Tetrapturus albidus), 96 larval blue 

 marlin (Makaira nigricans), and 591 

 larval sailfish (Istiophorus platyp- 

 terus) from the Straits of Florida 

 and the Bahamas. Nine morphometric 

 measurements were taken for a subset 

 of larvae (species known), and lower 

 jaw pigment patterns were recorded 

 on a grid. Canonical variates analysis 

 (CVA) was used to reveal the extent 

 to which the combination of morpho- 

 metric, pigment pattern, and month 

 of capture information was diagnos- 

 tic to species level. Linear regression 

 revealed species-specific relationships 

 between the ratio of snout length to 

 eye orbit diameter and standard 

 length (SL). Confidence limits about 

 these relationships served as defining 

 characters for sailfish >10 mm SL and 

 for blue and white marlin >17 mm SL. 

 Pigment pattern analysis indicated 

 that 40% of the preflexion blue marlin 

 examined possessed a characteristic 

 lower jaw pigment pattern and that 

 62% of sailfish larvae were identi- 

 fiable by lower jaw pigments alone. 

 An identification key was constructed 

 based on pigment patterns, month of 

 capture, and relationships between 

 SL and the ratio of snout length to 

 eye orbit diameter. The key yielded 

 identifications for 69.4% of 304 (blind 

 sample) larvae used to test it; only 

 one of these identifications was incor- 

 rect. Of the 93 larvae that could not 

 be identified by the key, 71 (76.3%) 

 were correctly identified with CVA. 

 Although identification of certain 

 larval specimens may always require 

 molecular techniques, it is encour- 

 aging that the majority (92.4%) of 

 istiophorid larvae examined were 

 ultimately identifiable from external 

 characteristics alone. 



Toward identification of larval sailfish 

 (Istiophorus platypterus), white marlin 

 (Tetrapturus albidus), and blue marlin 

 (Makaira nigricans) in the western 

 North Atlantic Ocean* 



Stacy A. Luthy 



Robert K. Covwen 



Rosenstiel School of Marine and Atmospheric Science 



University of Miami 



4600 Rickenbacker Causeway 



Miami, Florida 33149 



Present address (for S. A. Luthy): Baruch Marine Field Laboratory 



PO. Box 1630 



Georgetown, South Carolina 29442 

 Email address (for S A. Luthy). stacy@belle.banjch.se edu 



Joseph E. Serafy 



National Marine Fisheries Service 

 Southeast Fisheries Science Center 

 75 Virginia Beach Drive 

 Miami, Florida 33149 



Jan R. McDowell 



The Virginia Institute of Marine Science 



School of Marine Science 



College of William and Mary 



PO Box 1346 



Gloucester Point, Virginia 23062 



Manuscript submitted 14 July 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 6 April 2005 by the Scientific Editor. 



Fish. Bull. 103:588-600 (2005). 



Research on the early life history of 

 exploited fishes benefits management 

 efforts by elucidating the temporal 

 and spatial distribution of spawning, 

 cohort strength, and biological and 

 physical factors affecting recruitment 

 (Lasker, 1987). The ability to confi- 

 dently identify specimens to species 

 is necessary in any early life history 

 study (Collette and Vecchione, 1995). 

 This has not yet been achieved for 

 larval billfishes of the family Istio- 

 phoridae from the Atlantic Ocean: 

 sailfish (Istiophorus platypterus), 

 blue marlin (Makaira nigricans), 

 white marlin (Tetrapturus albidus), 

 and longbill spearfish (Tetrapturus 

 pfluegeri). 



Larval istiophorids are easily dis- 

 tinguished from larval swordfish 

 (Xiphias gladius, family Xiphiidae). 

 However, larval istiophorids are dif- 



ficult to identify below the family lev- 

 el. Full fin-ray complements are not 

 present until a larva reaches 20 mm 

 in length, and even then, meristic 

 counts are of limited use for identifi- 

 cation because of significant overlap 

 in counts among species. At best, spe- 

 cies possibilities can be eliminated 

 only for specimens with counts in the 

 extremes of their ranges (Richards, 

 1974). The only definitively diagnos- 

 tic count is the vertebral formula for 

 Makaira (11 precaudal and 13 caudal) 

 versus that of the other istiophorids 

 (12 precaudal and 12 caudal) (Rich- 

 ards, 1974). Larger blue marlin lar- 



* Contribution SFD-2003-0010 from NOAA 

 Fisheries Sustainable Fisheries Division, 

 Southeast Fisheries Science Center, 75 

 Virginia Beach Drive, Miami, Florida 

 33149. 



