JOHNSON ET AL.: AGE, GROWTH. AND MORTALITY OF KING MACKEREL 



Table 13.— Summary of length-weight relations of U.S. king mackerel. W - weight 



Table 14.— Estimated annual mortality rate (A) by estimation technique, assuming 1:1 



and 1:2 male:female ratios. 



son and Chapman 1961). This was a result of the 

 age-length keys being developed for a different 

 fish sample than the one being analyzed for mor- 

 tality rates. The difficulties in applying Robson 

 and Chapman's technique resulted in an implica- 

 tion that king mackerel are not fully recruited 

 into the south Florida recreational fishery until 

 age 7, after which the annual mortality rate is 

 0.53. This mortality estimate is similar to Beau- 

 mariage's (A = 0.54), but the age at recruitment 

 was found by Beaumariage to be 2-3. His esti- 

 mate was based on a smaller age range (0-7) than 

 was ours. This difference probably influenced 

 the resulting mortality estimates. 



Many difficulties are also involved in the basic 

 concept of using catch-curve analysis to estimate 

 mortality in king mackerel. Rounsefell and Ever- 

 hart (1953) emphasized that catch-curve analy- 

 sis is based on false assumptions when applied to 

 most pelagic species, including mackerel. Rob- 

 son and Chapman (1961) reiterated this warning, 

 stating, "if year classes.. .vary in strength and 

 survival rates vary from year class to year class 

 and age to age, then the age-frequency distribu- 

 tion in the catch of a single season provides no 

 identifiable information whatsoever regarding 

 [mortality rates]...." These comments force us to 

 state our mortality findings with some wariness. 



ACKNOWLEDGMENTS 



We thank Michael Crow, Mark Farber, and 

 Dennis Lee of the National Marine Fisheries 

 Service, Miami Laboratory, Miami, Fla., for 

 their constructive reviews of this manuscript. 



ADDENDUM 



Fischer (1980) reported on the length-weight 

 relationship of king mackerel off Louisiana. His 

 length-weight values are similar to ours. 



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