Sampling to Investigate Klukshu Early/Late Population Structure

The purpose of this project is to improve information regarding the population structure and status of early and late run Klukshu River sockeye salmon.

The early and late runs together serve as an indicator stock for international management of Alsek River sockeye salmon, which is linked to Klukshu weir counts. Differences in timing, spawning locations, and life history between the two runs are not well understood, and previous work is inconclusive. Fillatre (2002) and Petkovich (2000) document differences between early and late components, but Eggers and Bernard (2011) developed biological escapement goals for total Klukshu sockeye, because (a) they considered the evidence for biologically distinct sub-populations insufficient, and (b) catch could not be separated into early and late components. DFO currently uses a cut-off date of August 15 to track weir counts for early and late components, but Fillatre (2002) showed that the timing of migration pulses varies substantially between years. Some years show two clear peaks with variable timing and different degrees of overlap (1977, 1991, 1992, 2002, 2006), but years with 3 peaks or 1 peak have also occurred. Any summary based on a fixed break-point can be highly misleading. As an illustration, consider that moving the break-point about 10 days earlier or later gives opposite abundance trends.

The current working hypothesis by the WG is that there are two distinct populations: (1) Early migrating river-spawners with unknown juvenile rearing behaviour, and (2) Late migrating lake spawners, which are true lake-type sockeye. However, the annual migration timing is strongly influenced by hydrology making it difficult to accurately assign samples (genetic baseline, scales) purely based on the timing curve.