Long term egg thiamine monitoring in salmonid populations in California; 2020-2023

Monitoring of egg thiamine levels was initiated in California salmon and steelhead hatcheries in 2020 after thiamine deficiency complex (an insufficiency of vitamin B1) was first documented in this system resulting in widespread mortality of juvenile salmonids. Unfertilized eggs (~10g) from mature adult females were collected from populations of Chinook salmon ( Oncorhynchus tshawytscha
), steelhead ( Oncorhynchus mykiss
), and coho salmon ( Oncorhynchus kisutch
) across California to assess thiamine concentrations. Concurrent fork length, weight, as well as coded wire tag recovery information for Central Valley samples was recorded alongside egg thiamine concentration levels. Additionally, laboratory investigations have been undertaken to uncover the relationship between Chinook salmon egg thiamine concentration and the survival of offspring. From these findings we have understood the potential population-level impacts of thiamine-dependent Chinook salmon fry mortalities based on egg surveillance data. The annual monitoring of eggs from salmonid species in both Central Valley and coastal populations serves as a critical component in comprehending the prevalence, magnitude, and trends of this deficiency among California salmonids. This dataset is focused on supporting research and providing annual data to inform the public and resource managers responding to this emerging threat. Given the value of this information to managing salmonid resources and treatments, we expect this monitoring to continue into the future as funding allows.