Since the release of offspring from the Warm Springs Fish Hatchery at Lake Sonoma back in 2004, their survival and subsequent lack of in-stream spawning by returning adults was becoming a concern. Hatchery biologists and geneticists determined that these low numbers of founding individuals in the Russian River meant that there was low genetic diversity among the source population. To counter this, during the winter of 2008-2009, the Warm Springs team began outbreeding the Russian River coho broodstock with fish from a neighboring stream population to increase the genetic diversity. The neighboring coho came from Olema Creek - part of the Lagunitas Watershed in Marin County (about 100 miles south of the Russian River).
Hatchery staff at Warm Springs use a spawning matrix as a script for matching pairs up. Provided by NOAA Fisheries geneticists, the goal of the matrix is to preserve the integrity of the Russian River genetics while introducing desired diversity from the Olema Creek population.
Other operating rules applied to the spawning matrix: Males are ranked for each female. No half-siblings are spawned. The 4 top ranked males are spawned with each female. Each male gets spawned up to 5 times and then he's retired.
Once a male has been choosen, his sperm motility (how active are the little guys) is checked by taking a small sample and viewing under a microscope. If you look into the scope and see a bunch of tiny black lines wiggling like crazy, then his sperm is ready for fertilization.
Since 2008, 25% of all mating pairs included one Olema Creek parent and one Russian River parent. Those pairings have shown increased survival in both the Warm Springs hatchery and Russian River watershed. Given this outcome, the Warm Springs hatchery plans to continue outbreeding Russian River coho with Olema Creek coho through 2010/11 and possibly beyond.
Next entry - Mix Eggs & Milt. Wait. Then Just Add Water.