COLLINS ET AL.: AGE AND GROWTH OF KING MACKEREL 



Table 2.— Mean fork lengths (mm) at capture and mean back-calculated fork lengths at ages from sectioned otoliths of male king mackerel. 



sistently greater than from sections, except for age 

 1 females (Fig. 6). The von Bertalanffy growth con- 

 stants (K) from whole and sectioned otoliths are 

 greater for males (Table 8), while females attain 

 greater maximum length. Estimates of asymptotic 

 length (L„) from both otolith preparations are con- 

 servative for both sexes. 



The distribution of monthly percentages of sec- 

 tioned otoliths with zero marginal increment was 

 unimodal and reasonably normal, indicating annual 

 ring formation that peaks in August- September 

 (Fig. 7). Few section margins were opaque during 

 October-May, though sample sizes were smaller 

 then. Similar treatment of marginal increment data 

 from whole sagittae produced completely different 

 results: opaque margins seem to occur irregularly 

 from March through November. This suggests 

 either that readings of whole otoliths were often in 

 error despite agreement between observers, or that 

 rings were not true annuli. 



DISCUSSION 



The daily nature of rings on lapilli of larval and 

 YOY king mackerel was not validated, although cor- 

 relations between otolith radius and fish length were 

 very strong. If the marks are daily, they imply a 

 moderately high average growth rate for early lar- 

 vae followed by very rapid growth (2.9 mm/d) for 

 fish 1-3 months of age. Future studies should con- 

 centrate on validation, possibly by chemical (tetra- 



cycline, calcein) labeling of otoliths or by describ- 

 ing diel variations in marginal increments. 



Readability (percentage legible enough for ob- 

 servers to agree on age) of sectioned otoliths was 

 greater than that of whole otoliths, especially among 

 fish >850 mm FL. The two techniques agreed only 

 47% of the time, primarily for smaller individuals. 

 Why Johnson et al. (1983) and Manooch et al. (1987) 

 found much higher agreement (96% and 87%, re- 

 spectively) between whole and sectioned otoliths is 

 not clear. The opacity and appearance of sagittae 

 may differ between Gulf of Mexico and Atlantic king 

 mackerel (pers. commun., S. P. Naughton'), and 

 could account for differences in agreement. Beamish 

 (1979) noted that readability and reliability of whole 

 otoliths differed between stocks of Pacific hake, 

 Merluccius productus, supporting this hypothesis. 

 He reported a 47% agreement between whole and 

 sectioned otolith ages and concluded that ages from 

 sections were more reliable, especially in older age 

 groups and for certain geographic areas. He also 

 found even greater deviations that we found be- 

 tween ages from whole and sectioned otoliths, but 

 utilized all readings. If our procedures were liberal- 

 ized in a like fashion, or if readings from a single 

 observer were used, we feel that the deviations 

 reported here would be much greater. 



'S. p. Naughton. Southeast Fisheries Center Panama City Lab- 

 oratory. National Marine Fisheries Service. NOAA, Panama City. 

 FL 32407, pers. commun. 



55 



