Dave do you know if some systems have a higher % of Jills than others? I understand this is true for jacks. I never saw a jill coho in over 20 years of killing & cleaning jacks until I fished a small stream up the valley. This was over 30 years ago for those who might get excited in an angry way. Jacks that turned out to be jills were relatively common in that stream as I recall.
Cultus sockeye have a relatively high % of females, high enough they are considered a normal occurrence and are used, as are the jacks, in the hatchery program for these fish. Over the years I have caught and seen a few Jill coho on the Vedder but can't speak for other species or watersheds.
Interesting side note, back in the 70's, Cultus sockeye jacks (and jills) were routinely killed at the upstream fence on Sweltzer Creek, before they entered Cultus Lake. The science at the time suggested jacks were not an acceptable gene source and would produce 3 year old sockeye, a fish not really acceptable to the commercial salmon industry.
Amazing how sound science, and time, changes fishing and resource management decisions.