Assessment of Cold Water Fisheries Resources in Northeast Iowa
Submitted by Greg Gelwicks, Fisheries Research Biologist, N.E. Regional Office
Fisheries managers are working to protect existing wild populations of Brook Trout, and expand efforts to restore self-sustaining populations of this native species in other streams with suitable conditions. There are many small headwater streams and spring branches in northeast Iowa that have not been sampled recently, if ever. It is possible that some of these streams support wild Brook Trout populations that are in need of protection. There may also be streams that have the conditions necessary for successful wild Brook Trout restoration that are currently unknown to fisheries managers. The South Pine Creek Brook Trout population provides a limited resource for propagation of fish for stocking, so it is important that restoration stockings are done on streams where there is the greatest probability that Brook Trout populations will be successfully established. The recent expansion of wild Brown Trout populations in northeast Iowa has also raised concerns for fisheries managers, due to potential negative impacts of the species on Brook Trout restoration efforts. Therefore, it is important to know the distribution of wild Brown Trout for both the management of Brown Trout populations and the planning of wild Brook Trout restoration work.
The goal of this project is to assess the status and distribution of Brook Trout and Brown Trout in northeast Iowa, and identify cold water streams where wild Brook Trout restoration has a high probability of success. Our general approach is to identify cold water streams using high resolution winter satellite images taken during very cold periods to identify stream reaches that do not freeze over, and therefore are likely to have suitable cold water spring flow (Figure 1a). We then select sites from these likely cold water reaches where we can sample fish and habitat conditions (Figure 1b). To date, we have sampled 40 sites in 10 sub-watersheds of the Upper Iowa River. Brown Trout were sampled at 24 of these sites. Brook Trout were sampled at three sites, and a Brook Trout X Brown Trout hybrid was sampled at one site where Brown Trout were collected. Twenty-four Brook Trout of various sizes were sampled at one of these sites, indicating a self-sustaining population (Figure 2). Fin clips from all sampled Brook Trout were collected for genetic testing to determine if they originated from the South Pine Creek population. If so, they can potential be used as a source of eggs for restoration stockings.
Several sites identified from winter satellite imagery were either completely dry, or had very limited spring flow that was not sufficient to support fish during late summer and fall. Conditions at 20 of these sites were documented with georeferenced photographs of dry reaches, beginning and end points of reaches with water, barriers to fish movement, and spring sources. This information will be used to help further refine site selection using remote imagery.
Information provided by this project will help guide wild trout management in Iowa. Discovery of additional self-sustaining wild Brook Trout populations could provide additional sources for wild Brook Trout fingerling production, and add to our understanding of the conditions necessary for sustaining wild populations. This understanding would improve our ability to protect these rare and valuable resources, and guide watershed, riparian, and instream habitat improvement efforts aimed at recreating these conditions in other streams. Additional information on the temperature, flow, and habitat conditions in NE Iowa’s cold water streams will aid in identifying streams that would be the best candidates for restoration stockings. This will lead to more efficient use of limited wild Brook Trout fingerling production.
A better understanding of wild Brown Trout distribution in Iowa will aid in wild Brook Trout restoration planning. It will also help identify streams that should be targeted for management actions such as angler access development, watershed land use improvement, and/or instream and riparian habitat improvement to increase opportunities for Iowa anglers to pursue wild Brown Trout. Further increases in self-sustaining Brook and Brown Trout populations would also allow redirection of limited hatchery capacity toward increasing catchable Rainbow Trout production. This could result in expanded trout fishing opportunities in NE Iowa trout streams and community trout fisheries.