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]
