596 



Fishery Bulletin 103(4) 



Table 3 



Key for ethanol-preserved larvae and postlarval specimens of Istiophoridae caught in the Straits of Florida and the Bahamas. 



Part I: for larvae <10 mm standard length (SL) 



la Preflexion or flexing: a single, pointate chromatophore in each of lower jaw pigment grids 4 and 6: 



with or without a single pigment in either grid 12 or 13; no other lower jaw pigments Makaira nigricans 



lb Not as above 2 



2a Any flexion stage; chromatophores of any number or shape in 3 or more of lower jaw pigment 



grids 1, 2, 3, 7, 8, 9, 11 Istiophorus platypterus 



2b Not as above 3 



3a Larva caught in March, April, or May either Istiophorus platypterus or Tetrapturus albidus 



3b Larva caught in June or later 4 



4a Larva caught in June either Istiophorus platypterus, Tetrapturus albidus, or Makaira nigricans 



4b Larva caught in July, August, September, or October 5 



5a Standard length a8 mm 6 



5b Standard length <8 mm either Istiophorus platypterus or Makaira nigricans 



6a Snout length / orbit diameter >0.030SL + 0.551 Istiophorus platypterus 



6b Snout length /orbit diameter s0.030SL + 0.551 Makaira nigricans 



Part II: for larvae >10 mm SL 



la Chromatophores of any number or shape in 3 or more of lower jaw pigment 



grids 1, 2, 3, 7, 8, 9, 11 Istiophorus platypterus 



lb Without the above lower jaw pigment pattern 2 



2a Snout length / orbit diameter >0.057SL + 0.427 Istiophorus platypterus 



2b Snout length / orbit diameter s0.057SL + 0.427 3 



3a Larva caught in March, April, or May Tetrapturus albidus 



3b Larva caught in June or later 4 



4a Larva caught in July, August, September, or October Makaira nigricans 



4b Larva caught in June 5 



5a Standard length >17 mm 6 



5b Standard length <17 mm either Makaira nigricans or Tetrapturus albidus 



6a Snout length / orbit diameter >0.047SL + 0.319 Tetrapturus albidus 



6b Snout length / orbit diameter <0.047SL + 0.319 Makaira nigricans 



a measurement was missing. Thus, when the key and 

 CVA analyses were combined, 92.4% of the tested larvae 

 were correctly identified. 



One of the two naive observers found that one larva 

 out of the test set of 50 was too damaged to be evalu- 

 ated. He correctly identified 35 larvae and found 14 to 

 be unidentifiable with the key. Overall, his success rate 

 was 71.4%. The other observer correctly identified 30 

 larvae, misidentified one (the larva not evaluated by 

 the other observer and the same larva misidentified by 

 the authors), and found 19 to be unidentifiable by the 

 key. His overall success rate was 60%. The difference in 

 the number of larvae that could not be identified with 

 the key was the result of differences in interpretation 

 of the lower jaw pigment position for larvae less than 

 10 mm SL. 



Discussion 



Because adults of four istiophorid species are found in 

 the Straits of Florida and Bahamian waters, a reliable 

 larval identification technique for these species is neces- 

 sary (Voss, 1953). Incorrect species identifications can 

 have serious ramifications on other areas of istiophorid 

 early life history research. For example, studies on early 

 growth would suffer if a larval blue marlin, which is 

 thought to reach 174 cm lower jaw fork length (LJFL) 

 by age one (Prince et al., 1991), were to be confused 

 with a larval sailfish, which reportedly grows to only 

 108.9 cm LJFL (Hedgepeth and Jolley, 1983; Prager et 

 al., 1995) by age one. 



Few characters are available to separate the spe- 

 cies of larval istiophorids (Richards, 1974). Although 



