https://cpw.cvlcollections.org/files/original/f3765c1433774294773bad86716b3a07.pdf ceae0bd0614c51e321eb2aa81ff3e646 PDF Text Text C O L O R A D O P A R K S & W I L D L I F E Brown Trout Life History EVALUATING BROWN TROUT POPULATION STRUCTURE AND LIFE HISTORY IN THE SOUTH PLATTE RIVER Brown Trout Ecology Brown Trout are native to Europe, Western Asia, and Northern Africa, and have been introduced to every continent except Antarctica. Across their native and introduced ranges, Brown Trout show a large diversity in life-history traits. For example, some Brown Trout stay within a small section of stream their entire life. Some populations consist of fish that spawn only once, while in other populations, fish spawn multiple times over their lifetimes. There are also populations that are anadromous, where fish move up freshwater rivers from the ocean to spawn, as well as adfluvial populations, where fish migrate between rivers and lakes. Along with these differences in life history, the physical appearance of Brown Trout varies greatly, which could be related to genetics, habitat use, diet, and fish age, among other factors. However, the connection between life-history traits, factors affecting physical appearance, and management in North America is not well studied. Black (top), intermediate (middle), and red (bottom) spotting patterns of Brown Trout from the Middle fork of the South Platte River. Brown Trout were first introduced to the United States in 1883, and subsequently introduced into Colorado in 1890. Different source populations were used to establish these wild Brown Trout fisheries, including lake populations from Scotland and river populations from Germany. Brown trout populations in Colorado are generally considered a mix of these two, and exhibit physical and behavioral characteristics of both as part of their life histories. Understanding Brown Trout life history is an important aspect of managing these populations throughout the state. Brown Trout in the South Platte River The Brown Trout population in the Middle Fork of the South Platte River near Hartsel is of interest to both anglers and mangers due to the unique angling opportunities provided by both Spinney Mountain Reservoir and the state wildlife areas along the South Platte River. Between 2006 and 2011, a stream restoration project was completed in a small section of the Middle Fork of the South Platte to create deeper pools for overwinter habitat and to hold big fish throughout the rest of the year. Between 2013 and 2016, CPW biologists and researchers conducted a tagging study to investigate habitat use by Brown Trout throughout the river. Fish were tagged with passive integrated transponder (PIT) tags containing a unique identification number that can be used to track the location of fish through physical recaptures and scanning during population estimate, and by river-spanning COLORADO PARKS & WILDLIFE • 317 West Prospect Road, Fort Collins, CO 80526 • (970) 472-4436 • cpw.state.co.us �antennas placed in the river that can detect the tags when the fish move past their location. These antennas record the date and time when movements are made year-round. Over the course of the study, three Brown Trout spotting patterns were identified: those with only black spots, those with red spots, and an intermediate spotting pattern between the two. To determine if spotting pattern explained observed movement patterns or the life history of the Brown Trout population in the Middle Fork of the South Platte River, additional data was collected in 2016, including stable isotopes, a technique used to identify chemical signatures in the fish tissue and characterize their diets and where feeding occurred, scales for aging fish, and genetic samples. South Platte River Brown Trout Population Structure and Life History A total of 1,259 Brown Trout were PIT-tagged over the three year study. Brown Trout with typically black spots and larger sizes moved longer distances, crossing all four of the stationary antennae at least once during the study. Although some PIT-tagged fish made long-distance movements, most moved less than 9 miles, with the majority of the fish moving 1 mile or less, suggesting many were river residents. Larger movements were made in the fall (September through October) as well as the spring (March through May). Fall movements occurred during the Brown Trout spawning period, whereas spring movements occurred when the ice was melting. Brown Trout primarily used the section of river at the upstream end of the study area, and Spinney Mountain Reservoir. When Brown Trout chose to move, they generally moved between these two locations fairly quickly, bypassing the habitat in between, including the deep pools in the restoration section, to reach favorable spawning areas or overwinter habitat in the reservoir. Brown Trout with black spots were older than Brown Trout with red spots, and fish with an intermediate spotting pattern fell between the two, suggesting spotting pattern changed as fish got older. Isotope data indicated that black spotted fish and red spotted fish each eat different foods and reside in different parts of the system. Black spotted fish spend most of their time within the reservoir, entering the river to spawn in the fall, and the red spotted fish live primarily within the river. Fish with an intermediate spotting pattern are likely transitioning from life in the river to life in the reservoir as they get older. Genetic testing indicated that the Brown Trout with black spots, red spots, and the intermediate spotting Average age (95% confidence intervals) of Brown Trout with pattern were related and form one adfluvial Brown black, intermediate, and red spotting patterns from the Middle Fork of the South Platte River. Trout population. Brown Trout in the Middle Fork of the South Platte River rely on both the river and the reservoir to complete parts of their life history (e.g., spawning and juvenile rearing versus overwinter habitat and growth), and change spotting patterns as the fish age and use these different habitats. Management of Brown Trout This study allowed biologists to better understand the life history of Brown Trout in the South Platte River. Based on the suite of data collected, these Brown Trout represent one population with an adfluvial life history incorporating characteristics of lake and river source populations historically used to establish Brown Trout in Colorado and North America. The connection between the reservoir and the upstream spawning habitat is important to the life history of the Brown Trout in this system, providing habitats needed to complete different parts of their life cycle. This information will help inform management of the fish in both the Middle Fork of the South Platte River and Spinney Mountain Reservoir, promoting their persistence, and ultimately providing more angling opportunities in both systems. Additionally, knowledge of the life history can be used to guide future river restoration activities in this and other rivers around the state to maximize their success. Associated Literature Avila, B. W., E. R. Fetherman, M. C. Kondratieff, E. E. Richer, D. A. Kowalski, M. R. Baerwald, A. Goodbla, and J. Spohn. In preparation. Brown Trout population structure and life history in the South Platte River, Colorado. COLORADO PARKS & WILDLIFE • 317 West Prospect Road, Fort Collins, CO 80526 • (970) 472-4436 • 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/. 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Title A name given to the resource Brown Trout Life History Creator An entity primarily responsible for making the resource Colorado Parks & Wildlife Extent The size or duration of the resource. 2 pages Date Created Date of creation of the resource. 2024 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> Type The nature or genre of the resource Fact Sheet Format The file format, physical medium, or dimensions of the resource application/pdf Language A language of the resource English