Effects of Multiple Variables on Sockeye Salmon Prespawn Mortality

Every year, Fraser River sockeye salmon (Oncorhynchus nerka) migrate up the Fraser River to the spawning grounds where they reproduce and then die. However, a variable number these female sockeye die after completing the migration, but before depositing all of their eggs. This phenomenon, known as prespawn mortality, is likely caused by a number of different stress or habitat variables encountered during the return migration. I use statistical techniques such as regression trees and random forests to further understanding of the cumulative and synergistic impacts of these variables on Fraser River, sockeye salmon, prespawn mortality. Furthermore, I will show that these techniques could also be used as a tool to predict future levels of sockeye salmon prespawn mortality. Preliminary results suggest that elevated temperature and discharge encountered during return migration, as well as spawning ground temperatures during the peakspawn period may be the most important factors influencing prespawn mortality. Furthermore, these results suggest that random forests techniques could provide accurate predictions of sockeye salmon prespawn mortality.