The number of Arctic grayling Thymallus arcticus over 336 mm in FL was estimated at 424 fish (SE = 63) in a 12 km index section of the lower Pilgrim River. In the middle 25 km section upstream from the Nome - Taylor Highway bridge, 233 Arctic grayling (SE = 66) greater than 412 mm in FL were estimated to be present. An abundance estimate was not obtained for the upper Pilgrim River. Arctic grayling captured from the Pilgrim River ranged from 191 to 496 mm in FL and in scale age from 2 to 15 years. Arctic grayling captured from the Eldorado River ranged in FL from 301 to 500 mm, and in scale age from 4 to 12 years. Of 75 Arctic grayling captured from the Eldorado River, 11 had been marked with OTC and were collected in order to validate aging techniques.