Effective size of an Atlantic salmon (Salmo salar L.) metapopulation in Northern Spain

The genetic diversity of metapopulations is influenced not only by the effective sizes (N(e)) of individual subpopulations, but also by the total effective size of the metapopulation (meta-N(e)). We estimated meta-N(e) of four neighbouring Atlantic salmon populations connected by gene flow using genetic estimates of subpopulation N(e)s and migration rates derived from capture-recapture data. The meta-(N) over cap (e) was lower than the sum of (N) over cap (e)s of the subpopulations, suggesting that genetic diversity harboured by the four river salmon metapopulation is lower than what would have been expected by viewing individual subpopulations separately. In addition, meta-(N) over cap (e) was found to be sensitive to changes in (N) over cap (e) of the subpopulation from which net emigration rate was largest, so as that the genetic diversity of the metapopulation would be best preserved by avoiding any reductions in N(e) of this subpopulation. Yet, this subpopulation is the one that has historically-and still is-experiencing the highest exploitation rate in the metapopulation system.