38 



Fishery Bulletin 94(1), 1996 



Sample 



Table 7 



G ST values for pairwise comparisons of samples of European anchovy, Engraulis encrasicolus. 



Coefficient of between-sample variation G ST 



Trieste 



Ancona 



Vieste 



Ionian 



Sicily 



Tyrrhenian 



0.1945 



main anchovy mtDNA phylads (groups of related 

 haplotypes) in the Mediterranean: phylad A domi- 

 nated the Black and Aegean seas, and phylad B was 

 more numerous in western waters. More extensive 

 sampling in the Aegean and Black seas would allow 

 us to test whether the same groupings are supported 

 by analysis of the ND5/6 genes only. 



The effective number of female migrants between 

 populations, N e M, may be estimated from mtDNA 

 data by using the term N e M = ( l/G sr -l)/2 (Nei, 1973; 

 Ward and Grewe, 1994). On the basis of our data 

 from pairwise comparisons, between 2 and 20 mi- 

 grant females per generation could account for ob- 

 served levels of interpopulation diversity. The former 

 figure was calculated for the comparison between 

 Aegean Sea and Tyrrhenian Sea fish, the two most 

 spatially isolated samples. Such data should always 

 be interpreted with caution, however (Ferguson, 

 1994), because small (and nonsignificant) values of 

 G S7 ,will still generate estimates of numbers of effec- 

 tive migrants that will appear low relative to esti- 



mates of stock size for pelagic species. For example, 

 the higher figure of 20 quoted above was derived 

 from a G ST value of 0.0261, although Monte Carlo x 2 

 analysis had not demonstrated significant heteroge- 

 neity between the samples. 



All Monte Carlo comparisons of haplotype distri- 

 bution that omitted the Aegean Sea sample were 

 nonsignificant, although, after pooling the three 

 Adriatic samples, a comparison of restriction pattern 

 distribution was significant for one enzyme (Sau 961). 

 There was thus some indication of genetic differen- 

 tiation between fish from the Adriatic Sea and adja- 

 cent waters, as has already been suggested by 

 allozyme analysis (Carvalho 5 ). The discreteness of 

 the Adriatic stock has also been demonstrated with 

 more traditional methods, and meristic studies have 

 shown that these anchovies are highly distinct from 

 those found in the neighboring Ionian Sea (Car- 

 valho 5 ). The large number of unique, composite hap- 

 lotypes found in the ND5/6 genes undoubtedly con- 

 founded analysis, and further work on E. encrasicolus 



