BROTHERS ET AL.: DAILY GROWTH INCREMENTS IN OTOUTHS 



Table 2. — Chronological age and number of growth increments 

 in the otoliths of the California grunion. 



species to species and must be independently 

 determined for each one. 



Young striped bass, Morone saxatilis, were col- 

 lected on 2 July 1974 in the Sacramento River 

 delta (Tracy Pumping Station), Calif. These five 

 fish measured 29 to 37 mm SL (standard length) 

 and their otoliths had 62 to 120 observable incre- 

 ments; i.e., a sample of striped bass which should 

 have been 2 to 4 mo old according to their known 

 spawning season (Scofield 1931) were 2 to 4 mo old 



according to the presence of growth layers found 

 in their otoliths. The spread in the age calculated 

 from daily increments probably corresponds to a 

 considerable spread in the dates when the fish 

 examined were hatched. 



Otoliths from two striped bass 135 and 142 mm 

 SL were also examined. Published information on 

 the growth rate of this species (Scofield 1931) 

 indicates that striped bass of this size taken in 

 July should be 14 to 16 mo old. The ages obtained 

 by counting the presumed daily growth marks 

 were 419 and 445 days respectively, i.e., 14 to 15 

 mo old. 



Figure 4 shows the daily marks in an otolith of 

 striped bass. Daily increments were fairly thick 

 near the center, thinner in an intermediate area 

 corresponding to the hyaline zone, and wider 

 again near the edge. In one specimen the central 



f» 



FIGURE 3. — Daily growth rings in an otolith of a 

 California grunion larva. The larva was approxi- 

 mately 26 days old. 



^ 



Jf 



Figure 4. — ^Daily growth rings in a striped 

 bass otolith. This fish was approximately 15 

 mo old. Differential growth can be seen in 

 rings grown in adjacent seasons. F = 

 fall; W = winter. 



