FISHERY BULLETIN: VOL. 81, NO. 1 



Table 11.— Annual fork length in- 

 crements (mm) computed from back- 

 calculations on fast- and slow-grow- 

 ing male and female king mackerel 

 (from all areas combined). 



probably the result of an extended spawning sea- 

 son. Long spawning seasons and multiple spawns 

 are discussed by Beaumariage (1973) and would 

 result in great size variation in young-of-the- 

 year king mackerel. Some of that size variation 

 would be decreased as the smaller fish continue 

 to grow at a higher rate in their second year than 

 do larger fish in their second year. Although the 

 slow-growing fish make up some difference in 

 size during year 2, they remain smaller than the 

 fast growers throughout their lives. 



Theoretical Growth 



The von Bertalanffy theoretical growth param- 

 eters computed from back-calculated fork 

 lengths are shown in Table 12, along with those 

 reported by other authors. The von Bertalanffy 

 (1938, 1957) growth equation is the following: 



1* = L„(l 



-*<< 



to)\ 



where 1; = length at age t, 



Loo = asymptotic length, 

 k = growth coefficient, and 



Table 12.— von Bertalanffy growth parameters for king 



mackerel. 



to = time when length would theoreti- 

 cally be zero. 



Our theoretical growth parameters are be- 

 tween those calculated by Beaumariage (1973) 

 and Nomura and Rodrigues (1967). Beaumar- 

 iage 's theoretical growth parameters were calcu- 

 lated by employing observed sizes offish at each 

 age, while Nomura and Rodrigues apparently 

 combined both back-calculated lengths and em- 

 pirical lengths in their calculations. We employed 

 mean back-calculated lengths at age in our com- 

 putations, which may account for some of the dif- 

 ferences between our values and those of the 

 other investigators. 



Length-Weight Relationship 



The length-weight values for king mackerel 

 computed for the equation W = a L b , where W 

 is weight in grams and L is fork length in milli- 

 meters, are presented in Table 13. Male length- 

 weight values from our study were within the 

 confidence intervals set by Beaumariage (1973), 

 but for both our female and combined sexes, 

 length-weight values were below his lower con- 

 fidence intervals. 



Mortality 



Mortality estimates are presented in Table 14. 

 The mean annual mortality rate (A = 0.37) is low- 

 er than Beaumariage's (1973) estimate (A = 

 0.54). We feel that our results are more concor- 

 dant with generally accepted techniques of catch- 

 curve analysis, in that our catch-curves were de- 

 veloped from age-frequency data, as opposed to 

 the length-frequency catch-curve used by Beau- 

 mariage. We also feel that our results are less in- 

 fluenced by the effects of gear selectivity than 

 Beaumariage's results, since Trent et al. (1981) 

 stated that commercial hook-and-line gear ex- 

 cludes small and large king mackerel to a great- 

 er extent than does recreational hook-and-line 

 gear. Nevertheless, there are many difficulties 

 in using catch-curve analysis in our study. Spe- 

 cific problems are related to the Beverton and 

 Holt ( 1957 ) and Robson and Chapman ( 1961 ) tech- 

 niques. The first technique involves using sev- 

 eral consecutive years of data, which were un- 

 available in our study. With the second technique, 

 we used age-length keys as the basis for our 

 catch-curves but were unable to make correc- 

 tions for the bias when such keys were used ( Rob- 



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