Yukon River Bering Cisco: A Biological Analysis of the Spawning Population

Abstract

Bering cisco Coregonus laurettae is an anadromous coregonine endemic to three rivers in Alaska: the Yukon River and the Kuskokwim River, which flow to the Bering Sea, and the Susitna River that flows to Cook Inlet. Recent research on Bering cisco was initiated in response to a commercial fishery that began in 2005 at the mouth of the Yukon River and operated for 15 years. Biological data were collected across their range in the Yukon River, but no comprehensive analyses have been published. Here we use these data to conduct basic analytical procedures to gain a better understanding of the biology of the species. Specifically, we identify migration timing, reproductive details, age and growth patterns, and survival. The spawning migration passed a test fish wheel located 1176 km from the sea was present throughout the summer but was strongest from mid-July to mid-August. Spawning took place in October in a braided main-stem reach between 1600 km and 1700 km from the sea. Ovaries of pre-spawning females grew over the summer to as much as 40% of whole-body weight at spawning time. Minimum age at maturity was age three, and few individuals attained an age of 10 years or more. Bering cisco did not feed during the spawning migration. The species grew rapidly for four to six years and exhibited minimal growth after that. Annual survival was estimated to be 61%. Those that survived spawning migrated back to sea to feed and prepare for another spawning event. The data we present here offer new insights into the biology of this extraordinary species, which is truly unique among Alaska coregonines.