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[96XJ]

Sorry Johnny Canuck I don't have a pic of my coho Jill  , If I knew this post was going to be started I would have taken a pic , just not part of the generation who takes pics of everything they do    , probably would have dropped my phone in the river

[RalphH]

Just a few thoughts that have come to mind:

the fish in the photo is a spring and it's a female. If you want to call it a 'jill' then call it a jill.

The topic was about a 'Jack Chinook Doe' but there was discussion about most every other salmon species yet there is considerable variability between species in terms of life cycle. Best I know pinks and coho have the most uniform life histories while there is considerable variability among sockeye, chum and chinook.

Take sockeye which may live 3 to 5 years or more and rear in freshwater anywhere from 3 or 4 years to all but zero heading downstream in a matter of weeks, like chum and pink. More commonly they spend about 2 years rearing in a lake.

Among sockeye, (chum and chinook for that matter) fish that spend one year in saltwater don't seem unusual. This is also common among steelhead and Atlantic salmon. Whatever we call those fish they are true adults. With Atlantics such fish are called grilse while among sockeye etc they seem to get called jacks and jills.

Coho generally go to sea in the spring and return in the late summer or fall of the following year - about a year and a half. Coho jacks spend just 1 summer - a half year or less and return with a mature length of 11 inches to 16 or 17 inches at a weight of less than a pound to maybe 2 or 2.5 . In  my experience most chinook jacks are similarly sized relative to their longer lived brothers and sisters though are somewhat larger than coho jacks - running more in the 16 to 18 inch range with some larger. Some stocks of steelhead also have similar sized fish usually under 20 inches and weigh 2 or 3 lbs. These are fish that likely have not spent a full year at sea.

I haven't found a lot of studies of jacks but I did find this one by HT Bilton from 1978

"Returns of Adult Coho Salmon in Relation to Mean Size and Time at Release of Juveniles"

This study look at close to 5,000 coho at Rosewall Creek and studies over 1500 coho jacks and reported:

A total of 1,569 jacks was recovered.... As had been expected, there were no jills (precocious females).

My experience is the same - I've killed hundreds of jacks in over 50 years and 2 were females - both caught the same year in a small unnamed creek north east of Mission one measured 15 inches the other 17 inches. Never saw a coho over 20 inches in that creek. Were they jills with only 1/2 a year of sea feeding? I don't know.