594 



Fishery Bulletin 103(4) 



2.5 



2- 



=5 1 5 



05 



25 



75 10 125 15 



Standard length (mm) 



17.5 



20 



225 



Figure 5 



Relationship of the ratio of snout length to orbit diameter with standard length. Lines 

 represent 99% confidence intervals. 



Lower jaw pigment patterns 



Sailfish of all flexion stages with chromatophores on 

 one or both sides of the lower jaw rami and sometimes 

 in the middle of the gular membrane comprised single- 

 species clusters. Examination of all molecularly identi- 

 fied larvae showed that many sailfish had pigment on 

 the posterior % of the lower jaw, but a few marlins also 

 had stray pigments in that region. The minimum crite- 

 rion to identify sailfish by lower jaw pigment without 

 misidentifying other species was pigment in at least 

 three of lower jaw pigment grids 1, 2, 3, 7, 8, 9, and 

 11. The shape and number of chromatophores within 

 the grids was inconsequential. Not all sailfish larvae 

 possessed the putative sailfish pattern, but 61.8% of 

 molecularly identified sailfish (353 of 571 with intact 

 lower jaws) could be identified by their lower jaw pig- 

 ments alone. 



Preflexion and flexing blue marlin also formed single- 

 species clusters owing to the pattern of a single, pointate 

 chromatophore in each of lower jaw grid cells 4 and 6, but 

 without any other pigment (except occasionally in grid cell 

 12 or 13). However, not all small blue marlin exhibited 

 this pattern. Eight of the 20 (40%) preflexion, molecularly 

 identified blue marlin with intact lower jaws could be ac- 

 curately identified by lower jaw pigments. Although some 



postflexion white marlin had a similar pattern, no preflex- 

 ion or flexing larvae of other species were misidentified as 

 blue marlin by virtue of this pigment pattern. 



Linear regressions 



Residual plots showed no deviations from homogeneity 

 of variance. Snout length, snout to mid-eye, ratio of 

 snout length to eye diameter, and ratio of snout length 

 to orbit diameter were all linearly related to SL. Jaw 

 difference was linear and appeared to be helpful for dis- 

 criminating istiophorids >12 mm SL, but too few larvae 

 of this size were available for meaningful regressions. 

 The ratio of snout length to orbit diameter provided the 

 most separation between the species as indicated by the 

 full model CVA. The 99% upper limit of the regression 

 of this ratio against SL for white marlin was used to 

 separate sailfish from both marlin species at 10 mm SL. 

 If white marlin is ruled out as a possibility by month 

 of capture, sailfish can be separated from blue marlin 

 by the blue marlin upper 99% confidence limit for the 

 regression of the ratio of snout length to orbit diameter 

 at 8 mm SL. The lower 99% confidence limit for the 

 regression of the ratio of white marlin snout length 

 to orbit diameter separated them from blue marlin at 

 17 mm SL (Fig. 5, Table 2). 



