96 



Fishery Bulletin 92(1). 1994 



deviant collections occurred in the northern Gulf 

 (east Texas and Alabama-Mississippi). The other 

 three (1988— *a*a phenotype on Atlantic coast; 1989- 

 *b*b, and 1990-*a*a phenotypes in northwest 

 Florida) are believed to have resulted from sampling 

 inadequacies (in 1988, only 9 *a*a were collected on 

 the Atlantic coast, and in 1989 northwest Florida 

 had 136 of the 275 *b*b in the <600-mm-FL cell, 

 which represented 167 of the 344 fish; and in 1990, 

 northwest Florida had 12 *a*a of the 17 *a*a in the 

 900, 1,000, and >1,100 mm cells). 



When allele distributions were compared by sex 

 at seven locations for each year in which sufficient 

 data were available, eight of the 23 allele compari- 

 sons deviated significantly (chi-square contingency 

 test, P<0.05). Six deviant collections occurred in the 

 northern Gulf (Texas-Mississippi 1985-1989) and 

 were from collections that did not conform to Hardy- 

 Weinberg expectations with regard to their pheno- 

 typic distributions. Two others occurred in Veracruz, 

 Mexico (1988 and 1990). The total allele-sex (1985- 

 90) comparisons for the seven locations did not de- 

 viate significantly, except for Veracruz, Mexico. 

 Veracruz collections were dominated by small fish 

 (<600 mm FL) of which sex determination was dif- 

 ficult, especially early in the year (Jan. -July) be- 

 cause of undeveloped gonads. Sex could only be de- 

 termined for 68% of the fish tested from this area. 



The geographic pattern of dipeptidase (PEPA-2*) 

 (1985-90) indicated that western Gulf differed from 

 eastern Gulf and Atlantic coast king mackerel. In 

 all years except 1985, comparison of allele counts 

 (Table 1) of the various geographic groupings of the 

 Gulf varied significantly (P<0.05) both within the 

 Gulf and between the Gulf and the Atlantic coast. 

 On the Atlantic coast (north of Florida vs. Florida), 

 the variation was found not significant (except in 

 1990). The trend in these comparisons was for ex- 

 cess *a allele in the western Gulf and for excess *b 

 allele in the eastern Gulf and the Atlantic coast. 



Discussion 



Comparisons of subdivisions (Table 2) show a con- 

 sistently higher level of PEPA-2*a in western Gulf 

 king mackerel and a deficit of this allele in king 

 mackerel in the eastern Gulf and along the Atlan- 

 tic coast. 



Electrophoretic data (ours and that of May ( 1983 ) 3 

 indicating high dipeptidase PEPA-2* a frequency in 

 the western Gulf and low *a frequency in the east- 

 ern Gulf and along the Atlantic coast supports a two 

 stock hypothesis for king mackerel in the Gulf. Sup- 



porting information can be obtained from other in- 

 vestigations: mark-recapture (Fable et al., 1990 4 ), 

 charterboat catches (Trent et al., 1987b) and spawn- 

 ing date analysis (Grimes et al., 1990). Fish move- 

 ments indicated by mark-recapture are consistent 

 with the two stock hypothesis. The charterboat in- 

 formation provides evidence of simultaneous north- 

 ward migration on both sides of the Gulf, while the 

 spawning date information offers evidence for repro- 

 ductive isolation. 



The king mackerel dipeptidase (PEPA-2") varia- 

 tion found in 1985-90 was similar to the variation 

 first reported by May (1983) 3 . His data showed 

 higher dipeptidase *a allele frequencies for Louisiana 

 (0.618) and Texas (0.736) than were found eastward. 



Temporal variations in the PEPA-2* allele frequen- 

 cies are difficult to interpret without taking into 

 consideration the migratory behavior. The variation 

 was extreme at some locations, giving the impres- 

 sion that the samples were collected from different 

 or mixed schools from different origins. For example, 

 in east Texas (Galveston-Freeport area) (1986), five 

 discrete collections (5 July-28 August) of 27 to 56 

 fish each (204 total) were sampled. The PEPA-2* a 

 frequencies were 0.933, 0.769, 0.202, 0.839, and 

 0.037 (in collection order). In other collection peri- 

 ods, variations in frequencies indicated that we had 

 sampled the same school of fish. For example, in 

 Louisiana (1987) three collections 7 days apart (21 

 Aug.^1 Sept.) were obtained. Their PEPA-2* a fre- 

 quencies were 0.590 (50 fish), 0.580 (50 fish), and 

 0.594 (48 fish). In view of the extreme variability of 

 PEPA-2* frequencies, numerous deviations from 

 Hardy- Weinberg expectations, and sampling difficul- 

 ties (one or more schools per collection), proper spa- 

 tial subdivision and grouping of collections for test- 

 ing specific hypotheses is arduous. The expanse of 

 the sampling area (Virginia to Yucatan) can be di- 

 vided into various subdivisions representing dis- 

 tance or physical features (Table 2). Examples of 

 subdivisions by distance are the following: Missis- 

 sippi westward vs. Alabama eastward, Alabama to 

 Florida Keys, Florida vs. Atlantic coast, and Florida 

 east vs. Georgia northward. Examples of physical 

 subdivisions are the following: Florida peninsula 

 (Florida east coast versus Florida west coast), east- 

 ern Gulf and Atlantic coast (Alabama to Florida 

 Keys versus Atlantic coast), and northern and west- 

 ern Gulf (Louisiana-Mississippi versus Texas versus 

 Mexican sector of the Gulf) (See also Collard and 

 Ogren, 1990). 



Caution should be applied to interpreting electro- 

 phoretic results in which variation has not been 

 proven to be of genetic origin by the use of breed- 

 ing analysis (i.e., crossing of phenotypes and analy- 



