I contacted the DNR to get their take on the declining size thing…… Here is what Ron Benjamin had to say. Nothing to startling, alot of this has been touched on already. Don’t be afraid to contact these depts. guys…..squeaky wheel grease thing
We are getting these questions commonly. You are correct that the factors affecting year class strength vary widely. There are many pieces to the puzzle that relate to large bluegill abundance. Bluegill year class abundance has and is historically been variable on many of our waters. Our sampling, showed many fewer large (greater than 7.5 inch bluegill) in the population. This is attributed to a number of factors in this complex puzzle. The year class that represents the fish you speak of has never be abundant. Think about the last few years when good size gill’s seemed to be plentiful, there were fewer small ones in the population that gives the illusion of more larger fish. Another factor that is a piece of the puzzle is we had a hard winter last year and documented winterkill in many areas. This is also beginning to happen again this year. On a brighter note there are a good number of 4 to 6 inch fish out there that if everything works out will grow into nice size fish in a year or so.
We (Wisconsin, Iowa and Minnesota DNR’s) sample Centrarchids (the family of bass and panfish) extensively each fall as we do walleye and sauger. We see year class strength fluctuations commonly. In fact it’s uncommon for it not to fluctuate.
In this short piece I can’t describe all of the puzzle pieces in depth.
Here are some leads to much more data.
Jeff Janvrin, my habitat specialist is just completing a publication for the American Fisheries Society on the importance of Winter habitat to year class strength and abundance.
Bartels, A., J. Janvrin, and S. Giblin. Indirect Evidence of Fish Migration to Upper Mississippi River Backwaters in Late Fall. U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, October 2008. Long Term Resource Monitoring Program Completion Report 2006B8 submitted to the US Army Corps of Engineers, Rock Island, Illinois. 24 pp.
Knights, B. 2007. Identifying Potential Controls on the Abundance and Size Structure of Centrarchids and Diversity of Fishes in Off-Channel Areas in the Upper Mississippi River System: Aquatic Vegetation and Physical Features. U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, May 2007. Long Term Resource Monitoring Program Completion Report 2006APE34 submitted to the US Army Corps of Engineers, Rock Island, Illinois. 64 pp. + Appendixes A-M.
Thanks for your interest.
P Ronald L Benjamin
Mississippi River Fisheries Supervisor
3550 Mormon Coulee Road
Lacrosse WI 54601
Wisconsin Department of Natural Resources
(() phone: (608) 785-9012
(() fax: (608) 785-9990
(+) e-mail: [email protected]