Recent paleolimnology of three lakes in the Fraser River Basin (BC,Canada): no response to the collapse of sockeye salmon stocks following the Hells Gate landslides

The use of paleolimnology to reconstruct the collapse of the Fraser River sockeye salmon (Oncorhynchus nerka) populations following the landslides at the Hells Gate section of the Fraser canyon (British Columbia, Canada) is explicitly tested. Construction of the Canadian Pacific Railway caused a series of landslides in 1913–1914, partially blocking the Fraser River, preventing spawning salmon migration, and causing a near-complete collapse of upstream salmon stocks. We selected three sockeye nursery lakes upstream of Hells Gate, which varied in spawner density, migration length, and lake catchment characteristics. In each of the lakes, geochemical (stable nitrogen isotopes and C:N) and biological (diatoms) proxies failed to register the impact of a dramatic decrease in marine-derived nutrients (MDN). Additional variations in sockeye abundance, documented by the onset of commercial fishing and modern escapement records, were also not imprinted on the sediment record. Changes in diatom assemblages are coincident with 20th century climate warming and local catchment disturbances and are not attributable to variability in MDN subsidies. These results suggest that MDN do not remain within lakes in the Fraser River drainage long enough to become faithfully archived in the sediment record or that the lakes do not receive sufficient MDN to produce a recognizable sedimentary signature.