Tributaries of Lake Pend Oreille (LPO) form an integral component of the Pend Oreille Basin Bull Trout metapopulation. Tributaries such as Lightning Creek, Trestle Creek, Gold Creek, Granite Creek, Grouse Creek, and Hellroaring Creek function as the foremost spawning habitats for the adult lacustrine, adfluvial Bull Trout population residing within LPO. This population presents an opportunity for reintroducing Bull Trout to other habitats within the Pend Orielle Basin. IDFG has expressed interest to work in cooperation with the Washington State Department of Fish and Wildlife (WDFW), Kalispel Tribe Natural Resources Department (KNRD), and United States Fish and Wildlife Service (USFWS) to extract Bull Trout from selected tributaries of LPO for future introduction elsewhere.

An implementation working group from previously mentioned agencies have recommended that the extraction of Bull Trout from LPO tributaries is best accomplished through egg/embryo extraction from wild redds. Ease of collection in large quantities, high genetic diversity, and increased survivability through size at release are favorable qualities of egg collection versus juvenile, subadult, or adult collection methods. A protocol for salmonid egg collection with demonstrated success is hydraulic egg extraction, previously utilized by Berejikian (et at 2011). However, hydraulic egg collection requires eggs to reach the “eyed” stage of development before collection takes place, where “eyed” refers to embryos developing eyespots. When collection occurs before the formation of eyespots the viability of collected eggs is largely compromised. Therefore, establishing the maturation timing of eyespots is exceptionally important before collection can occur.

The timing of salmonid egg maturation is highly correlated with water temperature, with higher temperatures producing faster maturation rates. One metric for measuring water temperature over time is accumulated thermal units (ATU), in which 1° C water for 1 day (24 hours) = 1 ATU. Using this metric Berejikian correlated salmonid egg maturation to the “eyed” stage of development, finding that Chinook Salmon averaged 280 ATU and Steelhead 160 ATU before eyespots formed. Following similar methods, Bull Trout egg maturation could be correlated with ATU to guide collection timing to minimize loss of viability.