A Permafrost Thaw Slump and Its Effect on Selawik River Inconnu Recruitment in Northwest Alaska

In 2004, a major permafrost thaw slump blocked the Selawik River in northwest Alaska. The yearly erosion and re-deposition of material from this thermokarst feature threatened sedimentation of the spawning area of a population of Inconnu Stenodus leucichthys, one of two that share rearing and overwintering habitat in a large lake and estuarine system. The second population in the Kobuk River was not affected by sediment making these systems ideal as a control and affected pair. A study to explore the effects of the slump using otolith aging was begun in 2011 and has collected approximately 200 samples from each river yearly through 2014. Minimum age of recruitment to these spawning populations appears to be age-9 and both populations were dominated by individuals greater than 15 years with minimal evidence of recruitment. The observed age distributions indicate periodic recruitment failures affecting both populations, perhaps driven by cannibalism. The significant strength of young age classes in the 2014 Kobuk River collection indicates the beginning of a recruitment event, but it was not observed in the 2014 Selawik River collection. Evidence of affected recruitment year classes due to sedimentation will become clear in the next few years.