The Lake Billy Chinook kokanee population varies in abundance from year to year. Knowing trends in kokanee population abundance can help with fisheries management decisions. Every year from August through October, fisheries department personnel from the Confederated Tribes of Warm Springs, the Oregon Department of Fish and Wildlife and Portland General Electric work together to estimate the number of Lake Billy Chinook kokanee that spawn in the Metolius River and it’s tributaries. To do so, a mark-recapture study is conducted. Such studies are commonly used in ecology to estimate the number of individuals in a given animal population. Every August 3,000 kokanee are captured in a seine net from Lake Billy Chinook and marked with two orange tags (see photographs) and released immediately back into the lake. During September tagged and untagged kokanee will swim from the lake into the Metolius River and spawn during the month of October. At that time, fisheries department personnel walk the riverbanks and count spawning kokanee with tags (marked) and without tags (unmarked). The ratio of marked fish to unmarked fish during October counts should be proportional to the ratio of fish marked in August (3,000) to fish in the whole population. The table below shows Metolius River kokanee population estimates from 2009 to 2014. Each year’s estimate was determined using the mark-recapture study method.
|Metolius River Kokanee Spawner Population Estimate