Otolith trace element chemistry as an indicator of anadromy in Yukon River drainage coregonine fishes

Eight coregonine species have been documented in the Yukon River drainage. They include inconnu Stenodus leucichthys, broad whitefish Coregonus nasus, humpback whitefish C. pidschian, Alaska whitefish C. nelsonii, least cisco C. sardinella, Bering Cisco C. laurettae, round whitefish Prosopium cylindracium, and pygmy whitefish P. coulterii. Personal use, sport, and commercial fisheries within the drainage target several of these species. Some species are capable of anadromous life histories, as evidenced by their presence in estuaries, yet few studies have investigated the upstream migrations of anadromous components of these populations. Only inconnu migrations have been previously examined in the Yukon River drainage. We investigated the distribution of anadromous coregonine fish in the Yukon River drainage in Alaska using sampling and otolith chemistry procedures. Six species were identified in sample collections from eight regions of the drainage between 1,200 and 2,000 km upstream from the Bering Sea. Gonadosomatic indices indicated that most sampled fish of all species were mature and preparing to spawn. Anadromous inconnu, broad whitefish, and humpback whitefish were distributed in the Yukon River and its tributaries to a maximum distance of 1,700 km from the sea. Anadromous least cisco were distributed in the Yukon River and its tributaries up to 1,600 km from the sea, whereas anadromous Bering cisco were present in the Yukon River main stem as far upstream as 2,000 km. No anadromous round whitefish were detected. Few coregonine spawning areas have been identified, so the actual migration distances of anadromous species may be greater than presented here.