Valentine National Wildlife Refuge Fisheries Assessment
The Valentine National Wildlife Refuge (NWR) was established in 1935 to provide feeding and resting areas for migrating waterfowl. Public recreation that is compatible with the purposes of the refuge, including hunting and fishing, is promoted. Management of the fisheries is defined in a 1978 Cooperative Agreement between the U.S. Fish and Wildlife Service (Service) and Nebraska Game and Parks Commission (NGPC).
The Valentine NWR contains 39 lakes. The majority of the lakes are small, shallow, potholes that are subject to frequent winter-kills. Nine Lakes are open to fishing: Pelican, Hackberry, Dewey, Clear, Willow, Watts, Duck, Rice, and West Long (Figure 1). These lakes have varying degrees of potential for fisheries management. All of the designated fishing lakes, except Rice Lake, are accessible by vehicles.
Figure 1. Map of the lakes that are open to fishing on the Valentine NWR. Direction of water flow is depicted by arrows and refuge trails are depicted dotted lines.
Common carp (Cyprinus carpio) gained access to the Valentine NWR lake system through Gordon Ditch, which was dug during the 1930's. Carp reproduce well in the shallow, highly-vegetated refuge lakes and generally dominate the fishery within 10 years after introduction. Degradation of aquatic habitats by carp is well documented and high numbers of carp are detrimental to waterfowl and game fish habitat. These refuge lakes have a long history of chemical renovation to remove carp. Historically, for about five years after a renovation and re-stocking game fish, angling is excellent, duck use is high, and then both decline due to carp-induced habitat degradation. Fisheries biologists from the Service and NGPC have experimented with the use of northern pike (Esox lucius) as a biological carp-control. Early attempts were unsuccessful because northern pike were introduced after carp were well established and subsequently too large to be controlled by predation.
In 1988, northern pike and largemouth bass (Micropterus salmoides) length limits were changed for Valentine NWR lakes in an attempt to increase abundance and size structure of predators. The size restrictions appeared to be successful as carp numbers stabilized in lakes where the restrictions were enacted. However, strong year classes of carp during years where northern pike populations were down have led to recruitment and higher abundance of carp populations in some lakes. Success has not been without perceived drawbacks. Predation by northern pike has likely reduced the abundance and altered the size structure of largemouth bass, yellow perch (Perca flavescens), and bluegills (Lepomis macrochirus). Environmental conditions have likely had greater affects on recreational fisheries such as a 1987-88 winter-kill, low reproduction and recruitment due to drought conditions during the summers of 1989 – 1990 and 2002-2007, and an extremely cool spring/summer during 1992 and 1993. The springs of 1994-97 were exceptionally wet, and these conditions provided good habitat and conditions for strong year classes for most fish species. However, high water levels also connected lakes that are usually isolated, which allowed fish movement.
Northern pike have been identified as a possible tool for controlling common carp, and evaluating their potential is a high priority for the refuge's fisheries. Many of the results from fishery assessments identified in this report are directed at: 1) evaluating northern pike as biological control agent for carp, 2) evaluating northern pike recruitment and condition in response to the special regulation allowing harvest of northern pike less than 28 inches, and 3) evaluating the impacts of the special northern pike regulations on other game fish populations.