FISHERY BULLETIN: VOL. 81. NO. 1 



NORTH 

 CAROLINA 



SOUTH CAROLINA 



CAPE CANAVERAL 



Figure 1. — Location of king mackerel, Scomberomorus cavalla, sampling sites. 



fleeted light, while the interspaces were hyaline 

 (dark). 



Otoliths were classified into age groups accord- 

 ing to the number of opaque nonmarginal marks 

 (following the method of Beaumariage 1973). 

 Each otolith was examined by two readers. If the 

 readers did not agree on the age of a fish, data for 

 that fish were not used. 



We determined the time of mark formation by 

 comparing frequency per month of otoliths with 

 opaque margins. A high percentage of opaque 

 margins indicated recent mark formation. 



Comparison of age estimations was made, 

 based on surface (whole) and internal (sectional) 

 examination of 133 otoliths. Three to 10 otoliths 

 from each age (0+ through 14+) were used for 

 the comparison. Three to six sections, each 0.15 

 mm thick, were made through the focus of each 

 otolith, using a Norton 3 diamond blade (SD519- 

 N50m-l/8) rotating at about 285 rpm on an Iso- 

 met low-speed saw. The otolith was mounted in 

 thermoplastic (quartz) cement (No. 70C Lake- 

 side) and cooled with mineral spirits during sec- 

 tioning. Later the cement was dissolved by soak- 

 ing in 50% isopropanol. The free sections were 

 then mounted on glass slides using Piccolyte ce- 



'Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



ment and examined with a binocular dissecting 

 microscope. 



The relationship of the size of the aging struc- 

 ture (OR) to the size of the fish (FL) was deter- 

 mined by using least-square regressions with 

 both linear and power curves. Once the relation- 

 ship was established, fork lengths at earlier ages 

 were back-calculated from surface otolith mea- 

 surements, using methods adopted from Tesch 

 (1971), Ricker (1975), and Everhart et al. (1975). 



Otolith measurements were analyzed for im- 

 plications of compensatory growth. A frequency 

 distribution of otolith lengths from the focus to 

 the proximal edge of the first opaque mark was 

 developed. Both slow- and fast-growing fish 

 were separated from those that grow at inter- 

 mediate rates, and lengths at earlier ages were 

 back-calculated for both the slow and fast grow- 

 ers. 



A computer program by Abramson (1971) was 

 used to fit von Bertalanffy theoretical growth 

 curves. Each age was given equal weight, and 

 mean back-calculated lengths were used in the 

 computations. 



Length-weight equations were developed for 

 the entire king mackerel collection, and for 

 males and females separately, by a computer 

 program following Ricker's (1975) suggestions. 

 Nonlogarithmic length intervals (50 mm) and 



98 



