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Thread: Chinook Size Declies

  1. #1
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    Default Chinook Size Declies

    Here is a story in AJOC about declines in Chinook size and age. http://www.alaskajournal.com/Alaska-...ize-statewide/

    "Lewis said larger salmon are being slowly culled from the gene pool by size-selective harvest methods, as fishermen target and keep the heavier fish."

    No direct cause is indicated.

  2. #2

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    Thanks for the link Tee Jay. Been slow on this part of the forums lately - I'm sure everyone is busy enjoying life, family and the outdoors... no better way to spark some conversation than posting links to informative articles such as this. Sure is better than just logging on to talk trash... Personally, I think that there are a number of reasons for the decline in chinook size - culling definitely being one of them. I've looked at the 50 year historical chinook catch data from my families' fishing operation, and it shows a pretty steady decline in the average size of harvest over the last few decades - to the tune of about 25% if I remember correctly, but it's been a few years. Everyone who catches these fish can shoulder some blame, but there are also a lot of factors which are out of our control. I'm less of a size queen per se, I'm just happy to have Kings in my boat - whatever boat that may be

    Found this article the other day. Loosely related - thought the part on kings interesting. Mr. Jones, I'd love to buy you a beer sometime.

    http://www.alaskajournal.com/Alaska-...out-for-board/

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    Simply put, salmon come back into the rivers either small, medium or large, then spawn or are caught. They are small, medium or large due to their genes. Obviously, selective harvest by those wanting trophy size fish will affect the gene pool. Who doesn't get this?

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    Quote Originally Posted by sayak View Post
    Simply put, salmon come back into the rivers either small, medium or large, then spawn or are caught. They are small, medium or large due to their genes. Obviously, selective harvest by those wanting trophy size fish will affect the gene pool. Who doesn't get this?
    While that is all true, it's not nearly that simple. Some of the smaller fish and jacks that have been returning early the last few years are likely still carrying those monster genes - size at and age of return is partly heritable, but also affected by environmental conditions.

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    I posted something similar on a different website, in response to the same article:

    I agree that the causes of the decline in body size are not readily apparent. However, high ocean harvest can explain much of it.

    If the ocean harvest is high, the only fish that return to spawn are those that spend as little time out there as possible. That is, fish that mature at a smaller body size are the fish that are spawning. So not only is the spawning stock smaller, they also pass on those genetic traits to the next generation. In my view, this explains the data from Alaska.

    Conversely, those stocks of salmon that are genetically programmed to spend more time in the ocean, and grow to a larger body size, wonít survive long enough to spawn, due to ocean harvest. Nobody throws back a 50lb Chinook hoping it will grow to 80lbs (which it might if it's not bonked). So not only do larger fish not return to the rivers and the spawning grounds (where they can be counted), they donít contribute to future generations. Again, a double whammy.

    I would add that size selectivity in freshwater (terminal areas) is far less obvious because those fish have already reached their maximum size. So eliminating freshwater harvest wonít help much. However, if ocean harvest was greatly reduced or eliminated, this problem would vanish, along with a host of other problems.

    By "ocean harvest", I mean harvesting salmon while they are still in their feeding stage. By the time they reach UCI, they're already at their terminal size. So a 50lb Chinook caught in UCI is likely going to be a 50lb spawner. But if that 50lber is caught in the GoA, the terminal size remains unknown since it is still in the feeding/growing stage.


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    Quote Originally Posted by Cohoangler View Post
    I posted something similar on a different website, in response to the same article:

    I agree that the causes of the decline in body size are not readily apparent. However, high ocean harvest can explain much of it.

    If the ocean harvest is high, the only fish that return to spawn are those that spend as little time out there as possible. That is, fish that mature at a smaller body size are the fish that are spawning. So not only is the spawning stock smaller, they also pass on those genetic traits to the next generation. In my view, this explains the data from Alaska.

    Conversely, those stocks of salmon that are genetically programmed to spend more time in the ocean, and grow to a larger body size, wonít survive long enough to spawn, due to ocean harvest. Nobody throws back a 50lb Chinook hoping it will grow to 80lbs (which it might if it's not bonked). So not only do larger fish not return to the rivers and the spawning grounds (where they can be counted), they donít contribute to future generations. Again, a double whammy.

    I would add that size selectivity in freshwater (terminal areas) is far less obvious because those fish have already reached their maximum size. So eliminating freshwater harvest wonít help much. However, if ocean harvest was greatly reduced or eliminated, this problem would vanish, along with a host of other problems.

    By "ocean harvest", I mean harvesting salmon while they are still in their feeding stage. By the time they reach UCI, they're already at their terminal size. So a 50lb Chinook caught in UCI is likely going to be a 50lb spawner. But if that 50lber is caught in the GoA, the terminal size remains unknown since it is still in the feeding/growing stage.


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    Great explanation along with smithtb's response.

    How does diet play into size? Can't a 4 year king have a 20lb swing based on what it's been eating for 4 years?

    My own observations this year (far from a trend) is that halibut, kings, reds, and silvers are smaller than average. Heck, even the sardines sold as bait have been tiny. Less food, smaller fish?

  7. #7

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    Warmer water temps also play into smaller size. Fish are cold blooded, so warmer water means they metabolize faster, but there is not necessarily more food to eat. It is also thought that warmer water temps can lead to later returns as fish stay out longer trying to pack on weight. I was told once by a bio that Kings can gain up to a pound a day towards the end of their life, but have never been able to verify that. Pretty crazy.

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    Cohoangler:

    Got any data points or sources for the ocean catch? I wonder if Chinook don't travel as far as Kamchatca or even Japan, but have no evidence one way or the other. All the effort seems to be focused on waters close (relatively) to Alaska.

    Also, the catch disparity between Alaska and the PNW seems related to PDO, but is there evidence that the PDo changes the feeding areas and thus the high seas catch areas?

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