https://cpw.cvlcollections.org/files/original/af33a2755dd8063711d58c3ac7f6f595.jpg dc2d0c5e0506476f2f96667f77db4f7d https://cpw.cvlcollections.org/files/original/025cc91e2456893ced0194e9128c84f1.jpg 7c1740b1b954f5ef0e22ab22fa80ad4e https://cpw.cvlcollections.org/files/original/ecd4e5f8954ae9b4b69501494f0e345a.jpg 33e15b297e499c3bdf1831f633130884 https://cpw.cvlcollections.org/files/original/36c9b19a91c6867c26ea8b9aa4418883.jpg 6630f1e5612b43d34ef505c38ba07124 https://cpw.cvlcollections.org/files/original/cad43d31ddb75fdea808df7db5c98f76.pdf b872c5ec2dbdc345834aa49d483918a0 PDF Text Text C O L O R A D O P A R K S & W I L D L I F E Blue Mesa Lake Trout ACHIEVING LAKE TROUT AND KOKANEE FISHERY OBJECTIVES THROUGH LAKE TROUT HARVEST Can trophy lake trout and kokanee be maintained through increased harvest of small lake trout? Kokanee fry survival has declined since lake trout began naturally reproducing within Blue Mesa Reservoir beginning in the early 1990's. This decline was due to higher predation from the expanding and now larger population of predatory-sized lake trout (Figure 1). Anglers value opportunities to fish for both kokanee and lake trout. Kokanee provide the greatest draw for overall catch and harvest while lake trout provide the greatest draw for their trophy potential. Lake trout over 50 pounds and 44 inches in length have been caught. However, lake trout require plentiful kokanee as prey to achieve such large size (Figure 2). Improving kokanee fry survival by reducing predation from small lake trout is necessary for maintaining abundant kokanee and associated benefits to anglers seeking to catch and eat kokanee or seeking trophy lake trout. Recent study: managing for coexistence of kokanee and trophy lake trout Unsustainable levels of predation by lake trout can lead to rapid declines in kokanee abundance and in lake trout growth and body condition. Immediately following a 90% decline in kokanee abundance during the 2000’s, CPW initiated fall netting efforts for lake trout in 2009 to recover kokanee while still providing for a trophy lake trout fishery. Additional harvest of lake trout is needed to achieve these management objectives. Recent research demonstrated that increased removal of primarily small, young lake trout could improve kokanee fry survival, the overall abundance of kokanee, and produce more trophy lake trout. It is possible that this increased harvest could be achieved through a lake trout harvest incentive program, but may require additional netting if angler harvest is not sufficient. Figure 1. Reconstructed population trajectory of predatorysized lake trout over time (years) based on abundance estimates from netting (SPIN) and mark-recapture surveys. A harvest incentive tournament can lead to improved angler involvement and efficient fisheries management: Fall netting by CPW supplemented angler harvest by removing ~1,200 lake trout annually from 2009 through 2017 while returning trophy-sized lake trout to the water. Angler harvest averaged ~6,000 lake trout annually over this period (Figure 3). As a result of these joint efforts, the abundance of predatory-sized lake trout has decreased recently (Figure 1) and kokanee survival and abundance has improved. However, recent lake trout monitoring surveys indicate that numerous small lake trout are now growing larger and expected to switch to preying on fish. CPW feels there is an opportunity to further encourage angler harvest through a lake trout harvest incentive program which could more efficiently remove enough small lake trout such that netting would not be required. Ninety-six percent of lake trout harvested by anglers and netted by CPW were smaller than 24 inches in length. Figure 2. Average number of kokanee (KOK) per predatory-sized lake trout (MAC) present in Blue Mesa Reservoir over time (years) in relation to when state-record fish were caught. Lake trout harvest incentive tournament details:  Only heads from lake trout less than 24 inches will be accepted.  Tournament dates: February 1 st through July 31st, 2020.  Prizes for most heads turned in: $1,000 for most, $500 second most, $250 third most.  Prize for each tagged fish turned in: $250 (tags are not visible).  Twenty $200 prizes randomly selected with one chance for each head turned in.  Head drop off locations: Iola, Elk Creek, and Lake Fork Marinas; Gunnison and Montrose CPW offices.  Call (970) 641-7070 or email dan.brauch@state.co.us for more information. Figure 3. Estimated total harvest of lake trout (MAC) during different periods by anglers over time (years) in relation to CPW fall netting. References: Hansen, A.G., and D. Brauch. In review. Long-term population dynamics of lake trout in Blue Mesa Reservoir, Colorado: guidance for an angler harvest incentive program. CPW report. Pate, W.M., B.M. Johnson, J.M. Lepak, and D. Brauch. 2014. Managing for coexistence of kokanee and trophy lake trout in a montane reservoir. North American Journal of Fisheries Management 34:908–922. COLORADO PARKS & WILDLIFE • 300 W. New York Ave., Gunnison, CO 81230 • (970) 641-7070 • 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 Aquatics Research 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 Evaluating the Biological Effectiveness of Angler Harvest Incentive Programs Description An account of the resource Led By: Lake and Reservoir Researchers Study Area: Select reservoirs Project Status: Ongoing Research Objectives: 1. Monitor the response of target fishes to incentivized angling. 2. Monitor the participation and harvest dynamics of anglers. 3. Develop population models and other quantitative tools to inform the biological effectiveness of ongoing incentivized angling efforts. Project Description CPW strives to provide the best sport fishing opportunities that are appropriate for each water body in the state of Colorado. Opportunities in some locations may not be appropriate for others given differences in management objectives, the need to protect native fish species in sensitive locations, the need to maintain wild broodstocks that provide valuable eggs to the states hatchery system, or other ecological factors.  One example is the presence of nonnative predatory sport fish like smallmouth bass and northern pike stocked historically or illegally into some reservoirs on the western slope of Colorado that are located upstream of critical river and stream habitats for unique native fishes. The presence of these predatory fish undermines conservation efforts because they can escape the reservoirs, establish populations downstream, and eat or compete with native fish. One of CPW’s missions is to protect native species that represent the ecology and natural history of the state. Sometimes, management actions to limit nonnative predatory sport fish in unwanted locations is necessary. Therefore, CPW has been implementing fishing tournaments in locations like Ridgway (southwest Colorado) and Elkhead (northwest Colorado) reservoirs where anglers can win cash prizes by helping CPW remove unwanted predatory fishes from the reservoirs to favor more compatible sport fish species. Harvest of sport fish is also sometimes needed for reasons other than native fish protection. For example, the need to maintain predator-prey balance in systems like Blue Mesa Reservoir (southwest Colorado) where consumption of stocked kokanee salmon by naturally reproducing lake trout can become unsustainable. Here, periodic harvest incentives are used to remove overabundant small lake trout (greatest predation impact on juvenile kokanee based on previous research) to help maintain the adult kokanee population where needed for egg-collection purposes and to maintain angling opportunities for trophy (even world record) lake trout. In both contexts, Lake and Reservoir Researchers have been working alongside managers collecting additional biological information and developing quantitative survey or modeling tools to inform the effectiveness of these angler incentive programs, identify potential avenues for increasing effectiveness if necessary, and to enable adaptive decision making. Associated Publications Cristan, E.T. 2021. Angler incentives: lucrative lake trout in Blue Mesa Reservoir. Colorado Outdoors Magazine. September/October Issue, Vol. 70, No. 5. Hansen, A.G., J.M. Lepak, E.I. Gardunio, and T. Eyre. 2024. <a href="https://doi.org/10.1111/fme.12699">Evaluating harvest incentives for suppressing a socially-valued, but ecologically-detrimental, invasive fish predator.</a> Fisheries Management and Ecology 31:e12699. Pate, W.M., B.M. Johnson, J.M. Lepak, and D. Brauch. 2014. <a href="https://doi.org/10.1080/02755947.2014.923072">Managing for coexistence of kokanee and trophy lake trout in a montane reservoir.</a> North American Journal of Fisheries Management 34:908-922. Creator An entity primarily responsible for making the resource <a href="https://cpw.cvlcollections.org/items/show/482">Lake and Reservoir Researchers</a> 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>