Prespawn Hooking Mortality

  • MN DNR Fisheries – Lake City
    Lake CIty, MN
    Posts: 158
    #1361120

    I got a question from an IDO member (Curgedgeon) this morning via e-mail about hooking mortality among pre- and post-spawn Walleyes caught in the Red Wing area on Pool 4. His question was this:

    “I was wondering what your opinion was about the fishing at Red Wing at this time of year. Specifically is there any data about the survival of female walleyes that are caught in the last couple of weeks before spawning? Mortality of the fish caught now vs post spawn?”

    He asked that I post my response to his question on the forum so that others could see the information.

    I typically link my posts to PDF documents that I have BK load for me, but I will do my best to get the response up here in several posts this afternoon, and if need be I will have him set up a PDF for the whole response.

    Nick

    Nick Schlesser
    Large Lake Specialist (Lake Pepin)
    Minnesota Department of Natural Resources
    1801 S. Oak Street
    Lake City, MN 55041
    651-345-3365 x235
    [email protected]

    MN DNR Fisheries – Lake City
    Lake CIty, MN
    Posts: 158
    #1395845

    Hey Curgedgeon,

    Thanks for the question.

    I think you are asking about the effects of hooking mortality on pre-spawn vs post-spawn Walleye. There are three major things that contribute to hooking mortality from the fishes side: 1) Water temperature (Warmer = higher hooking mortality), 2) Depth (Deeper = higher hooking mortality (especially if deeper than ~30 ft)), 3) Other stressors (this is kind of a catch all that would include parasites or diseases that were pre-existing or contracted due to angler handling disrupting the slime coat and could include increased stress from spawning activity).

    Additionally there are some factors from the angler side: bait choice, experience of the angler (hook setting and fish handling), desire of the angler for harvest (harvested fish experience 100% hooking mortality) etc.

    Back to the fish though. During this time of year the temperature is low enough that it probably contributes very little to increasing hooking mortality, and as long as you are fishing in less than 30 ft of water (20 if you want to be really safe) you are likely only going to be causing the normal amount of hooking mortality for these conditions. We (MN DNR) have evaluated hooking mortality in Walleye in various locations over the years to be able to better estimate the effect of hooking mortality on those fisheries. Currently we use the estimate developed for Mille Lacs on Pool 4 because both bodies of water are relatively shallow and therefore mortality is principally driven by temperature. I have included a table (see attached photo) with 2 columns of numbers representing another method used on Rainy Lake. Rainy is far to the north and rarely gets warm enough to represent a serious thermal threat to Walleye, but it is much deeper than Pool 4 on average. The large lake specialist there found that the depth the Walleye was caught at was the primary contributor to hooking mortality on Rainy, and the table below shows the estimate of percent mortality in 5 foot increments. During the cool months of the year on Pool 4 these numbers are probably a reasonable estimate for mortality rates, but during warmer months would likely be low for the same depth on Pool 4. (See attached Table)

    Next is a figure (see attached photo)representing the estimates for Walleye mortality on Pool 4/Lake Pepin during the 2012-2013 creel year (that runs Nov 1, 2012-October 31, 2013). Note that the early part of the year with cool water has very low estimates for mortality compared to the late summer months like July when mortality rates go up significantly especially for larger fish. (See attached Chart)

    Post spawn fish have already experienced the stress of spawning, and therefore likely have increased injury and disease rates because of the increased stress. There is likely a small increase in hooking mortality during this period due to these additional stressors, BUT if the water is still cool it would probably be difficult to detect even if we focused a study on hooking mortality during this specific period of time. Also as you look at the attached figure it is important to recognize that the highest angling pressure and harvest on Pool 4 occurs during late May and June so the dramatic increase in pounds of walleye mortality is partially driven by increasing temperatures and partially by a much larger number of fish being handled.

    Hopefully this has been helpful to you in explaining what is likely happening with our Walleye during this period of the year. Please feel free to give me a call or another e-mail if I missed something you wanted addressed or you would like more information.

    Good Fishing,

    Nick

    Nick Schlesser
    Large Lake Specialist (Lake Pepin)
    Minnesota Department of Natural Resources
    1801 S. Oak Street
    Lake City, MN 55041
    651-345-3365 x235
    [email protected]

    Everts Fishing Resort
    Inactive
    Hager City WI
    Posts: 254
    #1395847

    Thanks Nick!

    mbenson
    Minocqua, Wisconsin
    Posts: 3842
    #1395869

    Well done Nick!!! Love the responses from our state DNR’s regarding the vitality of the fish we seek to catch, release and keep to eat!!!

    Mark

    Trapper16
    Lakeville, MN
    Posts: 197
    #1395874

    Wait just a minute, you mean guys should not fish in the scour hole in front of the damn

    Thanks for the great read and intresting information.

    Mike W
    MN/Anoka/Ham lake
    Posts: 13294
    #1395883

    Interesting info. What I got out of it is that if people are concerned about fish dieing they should not keep them. That had the highest mortality factor of 100%. Always had a feeling that was true.

    basseyes
    Posts: 2513
    #1395907

    So in some ways, pre spawn fishing is less harmful than post spawn fishing. And it is not only a water temperature increase issue, but also one derived from the stress of the spawn.

    Interesting

    One could conclude that pre spawn fishing is less harmful than post spawn fishing. So that begs the question, does holding the fishing opener on inland lakes post spawn, really help fish out, because it is after the spawn. And within that, is all that focused fishing pressure of opener good for post spawn fish, which seem more susceptible to hooking mortality because of stress from the spawn and rising water tempratures?

    smalls
    Lake City, MN
    Posts: 25
    #1395945

    Quote:


    There is likely a small increase in hooking mortality during this period due to these additional stressors, BUT if the water is still cool it would probably be difficult to detect even if we focused a study on hooking mortality during this specific period of time. Also as you look at the attached figure it is important to recognize that the highest angling pressure and harvest on Pool 4 occurs during late May and June so the dramatic increase in pounds of walleye mortality is partially driven by increasing temperatures and partially by a much larger number of fish being handled.


    Seems like the emphasis is on SMALL, and there are many things besides dying from hooking mortality that could disrupt a successful spawn.

    shockers
    Rochester
    Posts: 1040
    #1395951

    I really appreciate that well-written response, supported by some solid research. Thanks for taking the time to respond, Nick.

    rvvrrat
    The Sand Prairie
    Posts: 1840
    #1396173

    Quote:


    I really appreciate that well-written response, supported by some solid research. Thanks for taking the time to respond, Nick.


    So do I. I appreciated such a well thought out and through reply. Nick!

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