https://cpw.cvlcollections.org/files/original/2f78f54a17bf32bba7113a8b0b0c88bf.pdf 2f914de19404675093f6939bfd896658 PDF Text Text C O L O R A D O P A R K S & W I L D L I F E Lake Trout Population Monitoring RAPID ASSESSMENT OF LAKE TROUT POPULATION SIZE IN LAKES AND RESERVOIRS How are lake trout populations monitored? Lake trout are top predators, reproduce naturally, and are important sport and food fish for anglers in Colorado’s lakes and reservoirs. Keeping close tabs on their abundance and size structure is necessary for assessing the appropriateness of harvest regulations, ensuring lake trout remain in balance with prey fish populations, and determining whether management goals are achieved. However, estimating the abundance of lake trout in our large coldwater reservoirs at the frequency needed to inform management using conventional methods such as mark-recapture is impractical. Thus, CPW researchers and biologists evaluated the utility of “Summer Profundal Index Netting” (SPIN) for application to lake trout in Colorado beginning in 2011. Developed by the Ontario Ministry of Natural Resources, SPIN is a standardized gill netting method for estimating the density of lake trout ≥12 inches over a 1-2 week period. Colorado has since adopted SPIN for monitoring lake trout populations in Blue Mesa Reservoir, Grand Lake, Lake Granby, and Taylor Park Reservoir. Survey design, implementation, and results: Standard gill nets specific to this protocol are set for two hours during daylight along the bottom in random orientation when surface temperatures exceed 64°F. You may see these nets being set or pulled at these lakes by CPW personnel during the summer months. The number of sets depends on the surface area of the lake or reservoir. Set locations cover depth intervals of 6-32 ft, 32-64 ft, 64-96 ft, 96-128 ft, 128-192 ft, 192-256 ft, and >256 ft. Sampling is also conducted in different portions of the lake or reservoir if necessary to account for differences in lake trout habitat. Catch rates of lake trout in the gill nets set in Colorado systems are compared to catch rates of lake trout in the same type of gill nets in other water bodies where estimates of lake trout density were available. The advantage of this method is the use of data from numerous other systems as a calibration tool to quantify lake trout densities and abundances in Colorado. Please see Lepak (2011) and Hansen (2018) for additional information. Management implications: Results from each SPIN survey conducted to date shows that lake trout density varies 7-fold across study systems. This indicates that processes governing the productivity of lake trout vary or operate differently in each lake or reservoir. Thus, management plans and corresponding harvest regulations must be tailored to each individual lake trout population in order to achieve desired goals for the fishery. Map of Blue Mesa Reservoir showing gill net set locations (N = 83 dots) and the associated depth interval sampled (colors) during the 2016 SPIN survey: Summary data from each SPIN survey conducted to date. Asterisks indicate the presence of Mysis shrimp in the body of water. Survey year Number of lake trout caught Mean length (inches) Density (fish/acre) Total area surveyed (ha) Abundance estimate Blue Mesa 81 129 17.2 4.51 7,559 34,071 Grand Lake* 36 87 16.5 5.14 477 2,452 Taylor Park* 36 271 16.4 7.94 1,507 11,950 Blue Mesa 81 211 16.7 3.18 8,424 26,753 Lake Granby* 71 501 16.4 23.17 6,870 159,193 Blue Mesa 83 180 17.2 2.89 8,424 24,368 Grand Lake* 36 109 17.2 6.56 477 3,131 Blue Mesa 95 313 16.3 4.60 6,496 29,857 2011 2013 2014 References: Hansen, A.G. 2018. Summer profundal index netting for tracking trends in the abundance of lake trout in coldwater lakes and reservoirs of Colorado: results from 2018. Internal CPW report. 6 pages. Lepak, J.M. 2011. Evaluating summer profundal index netting (SPIN) as a standardized quantitative method for assessing lake trout populations. Internal CPW report. 10 pages. Number of gill net sets Lake or reservoir 2016 2018 COLORADO PARKS & WILDLIFE • 317 W. Prospect Rd., Fort Collins, CO 80526 • (970) 472-4432 • cpw.state.co.us � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Fact Sheets Type The nature or genre of the resource Fact Sheet Format The file format, physical medium, or dimensions of the resource application/pdf Description An account of the resource CPW Fact Sheets Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Lake Trout Population Monitoring Fact Sheet Date Created Date of creation of the resource. 2018 Rights Information about rights held in and over the resource <a href="http://rightsstatements.org/vocab/NoC-NC/1.0/">No Copyright - Non-Commercial Use Only</a>