448 



Fishery Bulletin 89(3). 1991 



MAW 



V t»«i 



Figure 3 



Composite photomicrograph of reader interpretation (E .B. Brothers) of primary increments along the entire counting path of a whole 

 ground sagittae from a 23cm LJFL Atlantic blue marlin Makaira nigricans. Location of core, direction of growth, and margin are 

 shown for A (counts 1-18) and B (counts 18-38). Because of problems inherent in sectioning increments on a counting path whose 

 axis of growth is continually changing, mid-increments (20-30) appear in better focus than increments closer to the core and margin. 

 A few increments near the core are not visible in the photograph and thus the total (38) does not match the mean count of three replicate 

 counts (40). Black bar = 10/jm. 



An optically dense region (primordium) about 5^m 

 in diameter comprises the center of blue marlin sagit- 

 tae and is usually encircled by one or two diffuse, op- 

 tically dense layers. Well-defined growth increments 

 surround this region. We refer to the area circum- 

 scribed by the first clear growth increment as the core 

 (Fig. 1C). 



Subunits (optically light and dar.k rings) of primary 

 increments are of about equal thickness for the first 



two or three increments. Thereafter the optically 

 translucent subunit becomes progressively wider rela- 

 tive to the denser subunit (Fig. 3). As in other species 

 (Figs. 4A-D), increments on larval blue marlin otoliths 

 appear visibly distinct in nature for most specimens and 

 are structurally analogous to the daily growth incre- 

 ments seen in many other species, including some 

 tropical pelagic species (Brothers 1979, Pannella 1980). 

 Subdaily increments were also observed in blue marlin 



