Live-trapping and radiotracking of American mink (Mustela vison) on 24 km of the River Thames, United Kingdom, revealed range sizes (male: 6.8 km, female: 2.7 km), numbers of other mink found in the range of each male (0.98 males, 1.95 females) and each female (1.18 males, 0.32 females), and range overlaps between dyads of males (88.2%), a male and a female (male: 32.6%, female: 69.1%), and females (66.3%). We used these data to estimate the potential energetic burden of conspecifics on each other. As a monthly average, cohabiting males and other females take an estimated 30% and 9%, respectively, of the total energy consumption by mink within the range of each female. Similarly, cohabiting males and females consume an estimated 21% and 40%, respectively, of the energy in each male's range. Intraspecific resource depression may force both sexes, especially males, to maintain larger ranges. We suggest that, in the case of American mink, intraspecific prey-resource competition affects the range sizes of both sexes.