Johnson et al.: Evidence for distinct stocks of Scomberomorus cavalla 



97 



sis of offspring). Deviation from 

 Hardy- Weinberg expectations 

 can result from stock mixing, 

 natural selection, or drift in 

 small populations (Smith, 

 1990). While we favor the inter- 

 pretation that these king mack- 

 erel data suggest stock mixing, 

 consideration should be given 

 to natural selection as the ul- 

 timate maintenance factor of 

 PEPA-2* frequencies as sug- 

 gested for dipeptidase (PEPA- 

 LT*) and other variations found 

 in Menidia beryllina (Johnson, 

 1974). 



Electrophoretic data suggest 

 that two stocks of king mack- 

 erel occur in the Gulf, a west- 

 ern stock with high frequency 

 of the *a allele and an eastern 

 stock with a low frequency of 

 the *a allele. The northern Gulf 

 appears to be a zone of mixing 

 of these two stocks during the 

 summer. Our electrophoretic 

 information does not distin- 

 guish the eastern Gulf fish 

 from those along the Atlantic 

 coast. 



Historical tagging data 

 showed migration between 

 south Florida and the north 

 and northwest Gulf. Williams 

 and Godcharles (1984) 2 (and 

 Sutter et al.'s later analysis 

 (1991) of Williams and 

 Godcharles' data) can be exam- 

 ined in light of the two stock 

 hypothesis. Williams and 

 Godcharles tagged approxi- 

 mately 12,000 king mackerel 

 off south and southeast 

 Florida, primarily in winter 

 months. Forty-nine tags were 

 recovered in the northeast Gulf 

 and another 49 tags were re- 

 turned from the northwest 

 Gulf. Almost all tagged fish 

 were recaptured in the warmer 

 months of the year, supporting 

 the hypothesis of migration 

 from wintering grounds in 

 southeast Florida waters to 

 northern Gulf of Mexico waters 



