Characteristics of the Sulukna River spawning population of inconnu, Yukon River drainage, Alaska

Abstract

Inconnu Stenodus leucichthys are large migratory whitefish harvested in subsistence and sport fisheries in Alaska. Research on the Sulukna River spawning population of inconnu was conducted in September and early October from 2007 to 2009. Samples were collected to verify maturity and spawning readiness, and to determine age distributions of mature males and females. Spawning abundance was estimated and post-spawning migration timing was identified. Otoliths were analyzed optically to determine age and chemically to determine amphidromy. Maturity sampling indicated that all sampled fish were in spawning condition or had recently spawned. Abundance estimates were 2,079 and 3,531 inconnu in 2008 and 2009, respectively. Post-spawning downstream migration timing was nearly identical between years, with the majority of fish moving downstream between September 30 and October 9. In both years, migrating inconnu displayed a nocturnal migration pattern, with 96% migrating between 10:00 pm and 9:00 am hours daily. Age estimates ranged between 6 and 26 years. Chemical analysis indicated that some Sulukna River inconnu were amphidromous, making migrations of over 1,300 km to the sea. This information indicates that the Sulukna River spawning population of inconnu has a large and variable abundance, in which amphidromy is facultative.