The Large Reservoir team assists fisheries managers in charge of large impoundmentswith the research needed to improve management of fisheries populations utilizing the best science possible.
Management of Hybrid Striped Bass in Iowa
Hybrid striped bass have become a sought-after species both in Iowa’s large federal impoundments and in its urban fisheries. Although hybrid striped bass continue to expand their distribution through movement and additional stockings, little is known about managing these sport fish.
One of the objectives of this study was to identify an economical mark for hybrid striped bass. Freeze branding was effective on both 40 – 50 mm TL and larger hybrid striped bass. Mortality rates did not differ between freeze-branded and control fish Hybrid striped bass effectively retained their mark over a 6 ½ month period. Hybrid striped bass were also marked with oxytetracycline. Reader estimated mark quality did not differ between the two readers for the oxytetracycline treatments (500 ppm; 700 ppm) or structures (otoliths and dorsal spines). Mark quality was ranked significantly higher by two readers for hybrid striped bass otoliths treated at 700 ppm versus the 500 ppm treatment.This study also sought to initiate a standard sampling program (fall gill netting) to assess population characteristics (size distribution, condition, and catch-per-unit-effort) and growth of hybrid striped bass in Saylorville and Red Rock reservoirs. We determined that population characteristics were generally good, although numbers of hybrid striped bass stocked into these reservoirs could likely be increased.
Rathbun Lake Habitat and Zebra Mussel Assessment
During 2009 zebra mussel (Dreissena polymorpha) veligers were first detected in Lake Rathbun. Although research has been conducted on the effect of zebra mussels on Great Lakes food webs, little attention has been given to the possible effects of this invasive species on reservoir systems, due, in part, to the lack of larval fish, plankton, and water quality data prior to zebra mussel establishment in such systems. Fortunately, a 15-year data set of such information exists for Lake Rathbun prior to zebra mussel contamination. The objectives of this study are to determine current density and species composition of icthyoplanktonn in Rathbun Lake to document potential changes in ichthyoplankton following zebra mussels establishment in the Rathbun Lake.
An Evaluation of Walleye Stocking Methods in Big Creek Lake
Big Creek Lake was plagued with gizzard shad in the 1990’s. As a result, various predatory fish species, including additional walleye, were stocked in an attempt to control the introduced shad population. Special walleye regulations (3 fish daily bag limit; 15-in minimum length limit, with 1 fish over 20-in) were also implemented to increase walleye density. However, the harsh winter of 2000-2001 caused a complete shad kill in Big Creek Lake. Biologists began to speculate that walleye were experiencing slow growth rates due to the absence of gizzard shad. As a result, the 8-in walleye fingerling stocking rate was reduced from 10 to 5 fingerlings/ac. During 2012 we freeze-branded both 2– and 8-in walleye prior to stocking. We found little mortality related to freeze-branding. Fall electrofishing revealed fry-stocked walleye and advanced fingerlings stocked in 2011 and 2012 were the largest contributor to Big Creek’s walleye population. We were unable to document 2-in walleye recruitment in either 2011 or 2012. We will continue sampling during spring and fall 2013 to determine the cost/benefit ratios of the three walleye stocking strategies.
An Evaluation of Nonphysical Barriers for Deterring Walleye
Evaluating the Effects of Low-dose Rotenone Toxicity on Fish, Benthic Invertebrates, Freshwater Mussels and Zooplankton