An Incubation System Using Re-Circulating Water to Imprint Artificially Cultured Kokanee to Natal Stream Odors

Distinct populations of kokanee, the freshwater resident form of sockeye, may occur in lakes indicating a high fidelity to natal spawning areas. The U.S. Fish & Wildlife Service, King County (Washington State) and the Washington State Department of Fish and Wildlife recently implemented a program to supplement kokanee in Lake Sammamish, a highly urbanized lake located in western Washington. Currently, Lake Sammamish kokanee spawn in three tributaries, Laughing Jacobs, Ebright, and Lewis Creeks. Initially remote incubation and rearing sites were to be established on each of these streams to facilitate early survival and homing. However, the urbanized setting and dynamic nature of the streams placed the eggs and fry at unacceptable risk. To imprint kokanee to their natal streams, we designed and built a re-circulating water incubation system. It was installed at the Issaquah Creek Fish Hatchery, a facility located within the Lake Sammamish watershed. Water from each natal stream was brought to the hatchery where it was pumped through 100, 25, and 1 micron filters to remove silt. After being filtered the water passed through a UV sterilization filter and was then delivered to one of five upwelling, 19 L-capacity incubation barrels. Three sets of incubation barrels and UV filters were assembled, one for each stream. After one week of use, the water in each incubation system was replenished with fresh stream water.  Each barrel had a perforated pressure plate that forced water to uniformly up-well through the barrel. Submersible pumps re-cycled the water continuously through the UV filter and incubation barrels. The pump and UV filter heated the incubation water so a heat exchange system and small portable water chiller were added to each system to keep the re-circulating water at ambient stream temperatures. Incubation substrate consisted of plastic saddles that filled 90% of the barrel. Eyed eggs are buried close to the bottom of the barrel. At hatching, alevins remained in the saddles until yolk absorption. They then migrated out of their barrel into a net-lined collection bucket where they were retrieved for short-term rearing before being released into Lake Sammamish. All eggs used were thermally marked making it possible to evaluate whether exposure to natal stream water from hatching to yolk absorption would enhance their homing ability. If this method of exposing newly hatched salmonid alevins to natural stream odors enhances homing it may have wide application in other salmon supplementation efforts.