492 



Fishery Bulletin 100(3) 



the winter months along the southeast coast of Florida. 

 For purposes of stock assessment and resource allocation 

 (Sutter et al, 1991; GMFMC^), the boundary between the 

 two stocks was specified as the Volusia/Flagler county line 

 (east coast of Florida) in winter (1 November-31 March) 

 and the Monroe/Collier county line (west coast of Florida) 

 in summer (1 April-31 October). Pragmatically, this 

 means that king mackerel caught south of the Volusia/ 

 Flagler county line (including the Florida Keys) between 1 

 November and 31 March belong to Gulf stock, whereas fish 

 caught south of the Monroe/Collier county line between 1 

 April and 31 October belong to Atlantic stock. 



Data from additional mark-capture (Fable et al., 1987; 

 Sutter et al., 1991; Schaefer and Fable, 1994; Fable«), 

 growth rate (DeVries and Grimes, 1997), otolith shape 

 (DeVries et al., 2002), and temporal-geographic sampling 

 studies (Collins and Stender, 1987; Trent et al., 1983; 

 Grimes et al., 1990) are consistent with the hypothesis that 

 king mackerel in the Atlantic differ from those in the Gulf 

 In addition, on the basis of allozyme evidence (Johnson et 

 al., 1993) and studies of early life history (Grimes et al., 

 1990; Grimes et al."), DeVries and Grimes ( 1997) suggested 

 that there might be two distinct stocks of king mackerel 

 in the northern Gulf Johnson et al. (1993) found a high 

 frequency of the PEPA-2a allele of the nuclear-encoded 

 dipeptidase (PEPA-2) locus among king mackerel from the 

 western and northwestern Gulf whereas a high frequency 

 of the PEPA-2b allele occurred among king mackerel from 

 the Atlantic and northeastern Gulf Johnson et al. (1993) 

 hypothesized that the two (putative) Gulf stocks mixed to 

 varying degrees in the northern Gulf Considering all the 

 data acquired to date, DeVries and Grimes (1997) sug- 

 gested there may be three stocks of king mackerel in U.S. 

 waters: one in the Atlantic, one in the eastern Gulf and one 

 in the western Gulf 



The allozyme data of Johnson et al. (1993) did not distin- 

 guish king mackerel in the eastern Gulf from those in the 

 Atlantic, and to that extent, argued against the hypothesis 

 that king mackerel in the Atlantic and Gulf represented two 

 distinct stocks. Gold et al. ( 1997), however, assayed variation 

 in restriction sites of mitochondrial (mt)DNA among king 

 mackerel collected from 13 localities along the U.S. Atlantic 



■5 GMFMC (Gulf of Mexico Fishery Management Council). 1984. 

 Final amendment 1, fishery management plan and environ- 

 mental impact statement for coastal migratory pelagic re- 

 sources (mackerels I in the Gulf of Mexico and South Atlantic 

 region. Gulf of Mexico Fishery Management Council, 3018 U.S. 

 Hwy, 301 North, Suite 1000, Tampa, FL 33619-2266. 



'' Fable, W. A., Jr 1988. Stock identification of king mackerel 

 based on mark-recapture. Unpubl. manuscript from meeting 

 on stock identification of king mackerel in the Gulf of Mexico. 

 Southeast Fish. Sci. Center Contribution Report 2-18-88, 24 

 p. Southeast Fisheries Science Center, 3500 Delwood Beach 

 Road, Panama City, FL 32408. 



' Grimes, C. B, J. H. Finucane, and L. A. Collins. 1988. Distri- 

 bution and occurrence of young king mackerel, Scomberomorus 

 cavalla, in the Gulf of Mexico. Unpubl. manuscript from meet- 

 ing on stock identification of king mackerel in the Gulf of 

 Mexico. Panama City Lab. Contribution Report 2-18-88, 31 p. 

 NMFS SE Fish. Cntr, 3.500 Delwood Beach Road Panama City, 

 FL 32408. 



coast and northern Gulf and found significant (but weak) 

 heterogeneity only in comparisons of pooled mtDNA hap- 

 lotypes from Atlantic localities with pooled haplotypes from 

 Gulf localities. Thus, the mtDNA data did not support the 

 hypothesis that two genetically identifiable stocks of king 

 mackerel occur in the northern Gulf but rather were consis- 

 tent with the hypothesis that separate stocks of king mack- 

 erel may exist in the Atlantic and in the Gulf Estimates 

 of Fgj,, a measure of population subdivision, between king 

 mackerel in the Atlantic and Gulf were small, indicating that 

 mixing between Atlantic and Gulf king mackerel occurs. 



Gold et al. (1997) also examined spatial variation in fre- 

 quencies of the two alleles at PEPA-2. Results were essen- 

 tially the same as those reported by Johnson et al. ( 1993): 

 high frequency of the PEPA-2a allele among king mackerel 

 in the western Gulf and high frequency of the PEPA-2b 

 allele in the eastern Gulf and Atlantic. Tests of indepen- 

 dence of PEPA-2 genotypes with age and sex of individual 

 fish, however, revealed significant nonrandom associations 

 among Gulf fish of PEPA-2a homozygous genotypes with 

 males and of PEPA-2h homozygous genotypes with females. 

 Moreover, among fish sampled from the Atlantic, there was 

 a highly significant decrease in the frequency of PEPA-2b 

 alleles with increasing fish age. The same trend was found 

 among fish sampled from the Gulf but to a lesser extent. 

 Tests of independence of sex versus age, and of mtDNA 

 variation versus sex or age, were nonsignificant. These find- 

 ings strongly indicated that the use of PEPA-2 genotypes 

 to distinguish stocks of king mackerel is compromised and 

 that the hypothesis of eastern and western stocks of king 

 mackerel in the Gulf needs to be re-evaluated. 



Finally, Broughton et al. (2002) surveyed allelic variation 

 at five nuclear-encoded microsatellites among a subset of 

 the samples of king mackerel studied by Gold et al. ( 1997). 

 Tests of homogeneity in allele distribution at the five micro- 

 satellites indicated that samples from Port Aransas, Texas 

 (western Gulf), and Gulfport, Mississippi (central Gulf), dif- 

 fered from each other and from the remaining samples (in- 

 cluding two samples from the Atlantic, one from the Florida 

 Keys, one from the eastern Gulf one from the western Gulf 

 and one from Veracruz, Mexico). No significant differences 

 in allele frequencies at any microsatellite were found be- 

 tween samples representing geographic extremes, and no 

 significant geographic patterns were found when samples 

 were combined into regional groupings reflecting current 

 hypotheses of king mackerel stock structure in U.S. waters. 



Of concern to management of the king mackerel resource 

 in U.S. waters is the degree of mixing between the pre- 

 sumed stocks in the Atlantic and Gulf Analysis of mark- 

 and-recapture data collected from 1985 to 1993 (MSAPM 

 indicated that roughly 3.0% of fish tagged in the Atlantic 

 were recaptured in the Gulf whereas 6.4% tagged in the 

 Gulf were recovered in the Atlantic. More liberal estimates 

 (SFC**) of recaptures (generated when utilizing summer 



^ SFC(SoutheasternFisheriesCenter). 1992. Preliminary anal- 

 ysis of southeastern US. king mackerel mark-recapture data: 

 1985-1993. Contribution report MlA-93/94-36, 19 p. South- 

 east Fisheries Science Center, National Marine Fisheries Ser- 

 vice, 75 Virginia Beach Dr, Miami, FL 33149. 



