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nerka questions

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  • nerka questions

    Got some questions about Kenai-Kasilof O. nerka. I'm sure nerka will be able to answer this for us.

    Obviously we have the sonar counters to estimate in-river passage, but when ADFG calculates how big the total run-size is in-season, how do they apportion the commercial catch as to river of origin?

    Are there distinct phenotypic features that allow biologists to distiguish Kenai fish from Kasilof fish on sight? Or is there some sort of DNA sampling of the landings that is then extrapolated for the entire commercial catch?

    Thanks, Ken.
    "Let every angler who loves to fish think what it would mean to him to find the fish were gone." Zane Grey
    The KeenEye MD

  • #2
    Question forwarded...

    Doctor, your question has been forwarded to ADF&G area and regional sport and commercial fisheries biologists. Their replies will be posted.


    • #3
      Apportionment. . .

      In-season apportionment of the commercial catch as to river of origin is accomplished by fishing area. The commercial gill-net catch of a particular river is total run minus Board of Fisheries-mandated escapement and minus projected sport/commercial sport/personal use (if any) catch.


      • #4

        From an ADF&G biologist:

        "We have an age comp model and now genetics to tell . . . how many of each are caught by day in the commercial fishery."

        Also, Kenai sockeye are phenotypically larger (five pounds plus) and blue-ish while Kasilof sockeye are smaller (about five pounds) and green-ish

        Hope that helps. . .


        • #5
          further clarification

          The total run is estimated from a program called "Offshore Test Fish" which uses the commercial harvest, the escapement numbers, and an estimate of the residual fish in the district to forecast the total return in-season. There is no daily allocation of the total return to river of origin in season. However, the age composition of the escapements and catch can give an impression of run strength for use with some of the management plans. The precision of these estimates are not as good as after the season analysis but they serve a purpose. Second, timing of the return with age composition can be used. For example, Kasilof sockeye 5 year old fish come in at a different time than the 4 year old fish.

          There are no reliable physical characteristics that can separate a Kasilof fish from a Kenai fish from a Susitna fish. Scale patterns were once thought of as a separation technique but this was proven not to be valid. If you line up sockeye that are similar in age you will not be able to tell the difference. You might guess that the larger fish are Kenai but there are large sockeye that go to other river systems in UCI. People want to make the smaller fish Kasilof (when the 4 year old are in) and the larger fish Kenai (5 year old) and this makes the public think they know the difference since Kenai usually has a small 4 year old component. However, if one mixes in Susitna fish and other stocks things go bad quickly.

          Hope this answers your questions.


          • #6
            Phenotypic differences...

            Originally posted by Nerka
            There are no reliable physical characteristics that can separate a Kasilof fish from a Kenai fish from a Susitna fish.... If you line up sockeye that are similar in age you will not be able to tell the difference.
            Nerka, I hate to gainsay your seeming expertise, but I've seen with my own eyes the phenotypic differences between Kasilof reds and Kenai reds. The Kenai fish are blue-ish in color and often are six-to-eight pounds, even bigger. Kasilof reds are smaller, maybe five pounds apiece and kind of green in color. How do you explain this?


            • #7
              not sure what to say

              Marcus, you may have more experience than I do. I just read lots of ADF&G reports that state what I posted. If you want to read these reports ask your biologist friends for a copy of the scale pattern analysis report by Waltemyer, Tarbox, and Bue. Also, talk to Paul Ruesch if he is still around about telling the differences. Also, the present research biologist Mark Willette can explain how age composition works.

              Good luck.


              • #8
                Good stuff guys. Keep up the positive posts!


                • #9
                  You're right. . .

                  Nerka, turns out a good friend of mine knows one of the authors, a now-retired ADF&G biologist, of the report mentioned above. We ran the question by him last evening, and you are correct it's age, not river-of-origin that makes folks think they can tell the difference between Kenai and Kasilof reds. So much for folk wisdom. . . thanks. . .


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