Genetics 147 3 1249 1258

Effective population size (Ne) of a natural fish population was estimated from temporal changes in allele frequencies at 7 microsatellite loci. Analysis of an historical collection of fish scales increased the precision of estimates by increasing the time interval between samples and applying the results to an equation developed for discrete generations without correcting for demographic parameters. Estimates of Ne for the time intervals 1961-77 and 1977-93 were 35 and 72 respectively. For the entire interval, 1961-1993, the estimate of Ne was 48 based on a weighted mean derived from the above 2 estimates or 125 when calculated from 1961 and 1993 samples only. Corresponding ratios of effective size to adult census size ranged from 0.03 to 0.14. An Ne of 48 over a 32-year period would imply that this population lost as much as 8% of its heterozygosity in that time. Results suggest the potential for using genetic methods based on microsatellite loci data to compare historical trends in Ne with population dynamic parameters. Such comparisons will help to evaluate the relationship between genetic diversity and long-term persistence of natural populations.