Impacts to the Kluane Fall Chum Salmon Stock from a Major, Natural Hydrological Change

Between 10% and 15% of all Yukon River fall chum salmon (U.S.- and Canadian-origin) return to the Kluane River to spawn. About 25% of the fall chum salmon that come back to the Yukon River return to the Upper Yukon River in Canada (i.e., are Canadian-origin). Of these, nearly half (an average of 46 %) return to the White River (JTC, 2016) and the major spawning areas in this system are in the Kluane River and in Kluane Lake.

A major, natural hydrological change resulting from a glacial-shift in the St. Elias Mountians (headwater areas) has affected Kluane Lake and River with potentially significant consequences to the spawning habitat of this major population of Yukon River chum salmon.

With its source in the ice fields of the Saint Elias Mountains, the Kaskawulsh glacier sits on the drainage divide between the Alsek and Yukon drainage basins in south western Yukon (Figure 1). For the last 300 – 400 years, the Kaskawulsh glacier meltwater has drained into the Yukon River basin via the Slims River, to Kluane Lake, to Kluane River, and downstream to the White River (Figure 2). In the spring of 2016, meltwater from the Kaskawulsh glacier change from flowing primarily into the Slims River and the Yukon drainage to flowing primarily to the Kaskawulsh River in the Alsek drainage. Flow to the Slims River during 2016 has been minimal.

The Slims River is the major input to Kluane Lake and modern isotope hydrology confirmed that positive water balance is dependent on input from the Slims River (Brahney et al. 2010). This summer the lake level is one meter lower than in previous years.

The key chum salmon spawning areas potentially impacted are Kluane River from the Duke River fan approximately 20 km downstream (identified in yellow in Figure 2). Chum salmon spawn in Kluane River’s active stream channels and high densities of spawning adults have been observed at specific sites, in particular Swede Johnson slough – a significant spawning area first documented in the 1940s. This section of Kluane River will be referred to as Kluane River spawning grounds for the remainder of this proposal. There are also lake spawning chum salmon in Kluane Lake. The records of specific spawning locations are not well established.

Information on current habitat use, habitat requirements and suitability, and anticipating the changes to habitat and the chum salmon that rely on them will be key elements of understanding the impacts of the hydrological changes in the Kluane/White River system and will help managers to make informed decisions.