(a) Sampling map displaying the location of two hybrid zones. (b) Heat map of the Bay of Biscay and English Channel with sampling sites of this study (black dots) and of Becquet et al. (2012) (white dots). SST are monthly averages for July, for 1982, 1992, 2002, and 2012; high resolution SST data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA (Reynolds et al., 2007). (c) Mitochondrial haplotype frequencies at cox1 (data from Becquet et al., 2012, site locations on panel b) and allele frequencies at the nuclear atp5c1 (this study). For panels (b) and (c), the sites that are within the putative Finistère hybrid zone (Becquet et al., 2012 and unpublished data) are identified with bolder outer circles.