I do not claim to know all about Blackmouth, but some of what is here is True and Flase.
As I understand Blackmouth are held in thier fresh water hatcheries for an extra year. This way they grow to be as large as 5 fish/pound, This throws off there timing as far as going to the ocean and returning in time to spawn. Blackmouth generally stay in the Sound for 3 years and return as four year olds to the hatchery they were raised in. They ARE sexually mature and when they return are not much different then normal Fall Chinook that spent there time in the ocean. The reason that we catch them as 5-10 pounders more often is still not completly understood, they just bite alot better as 3 year olds then they do as fours. My personal thought on this is similar to Fall Kings they tend to feed more when they are in the ocean growing and not as well once they are returning in the sound.
I still am not totally sure what is going on in the Canal. I think that some test showed that alot of the Chinook fry were staying in the area instead of going to Sea like the rest of Puget Sound Chinook. Could HC Chinook be a different race or is it because the last few years have had less then 1000 returning WILD Chinook in HC. The largest factor though regarding less time in the HC for Blackmouth is that the agency is allowed to give out so much time fishing for Blackmouth, and number of fish caught. Area 10 got an extra 2 weeks of Blackmouth fishing and 2 weeks of CnR season, therefore the HC got closed down.
In regards to 60 pounders in Alaska it is possible because a Blackmouth is just a immature Chinook, if a 7 year old 100 pound Kenai King is caught when he is 60 pounds and only 5 years old he is a Blackmouth.I hope this sheds some light on the subject. One thing I know for sure is the one I got on Sunday was oh so good.
NEN