Growth, Mortality, and Harvest of Hybrid Striped Bass and Walleye in an

Iowa Urban Lake: Implications for Regulation Reductions

Authors: Randall D. Schultz and Benjamin J. Dodd

Growth, exploitation, and natural mortality of hybrid striped bass and walleyes were investigated in Lake Manawa during 2005 and 2006.  The major objectives were to assess the contribution of these popular sport fish species in an urban situation, and to determine the potential benefits of regulation reductions.  Lake Manawa is an 800 ac natural lake in Council Bluffs, Iowa.  Currently hybrid striped bass are not regulated, and walleyes are regulated only with a creel limit of 5 and possession limit of 10.  Growth of hybrid striped bass (through age 4) was average to slightly lower than that of other North American populations, while growth of walleyes (through age 9) was average to slightly above average.    Significantly more hybrid striped bass and walleyes were caught than harvested; exploitation rates were less than 15% for walleyes and less than 25% for hybrid striped bass.   Total annual mortality (A) for hybrid striped bass and walleyes were 0.46 and 0.24, respectively.  Natural mortality estimates were 0.24 (51% of A) for hybrid striped bass and 0.09 (40% of A) for walleyes.  We conclude that natural mortality plays a greater role in the abundance and fishing quality hybrid striped bass and walleyes in this urban lake than do angler affects, and regulation changes are not warranted.