Elimination of Myxobolus cerebralis in Placer Creek, a Native Cutthroat Trout Stream in Colorado

Abstract

Placer Creek, a tributary of Sangre de Cristo Creek in Colorado's San Luis Valley, supported an allopatric core conservation population of native Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis during much of the 20th century. After the failure of gabion barriers in the late 1990s, Brook Trout Salvelinus fontinalis infected with Myxobolus cerebralis invaded from Sangre de Cristo Creek. By 2005, whirling disease (WD) and competition from Brook Trout reduced Rio Grande Cutthroat Trout numbers to less than 10% of the total trout population. New barriers were constructed in 2006 and the stream was treated with rotenone in 2007 and 2009 to eliminate all fish prior to the reintroduction of Rio Grande Cutthroat Trout. Results of WD research studies in Montana, California, and Colorado indicated it might be possible to break the life cycle of the parasite in some situations. Our management interventions included (1) reducing the fish population in the stream to zero for approximately 14 months, (2) introducing lineage V and VI Tubifex tubifex worms, which are not susceptible to M. cerebralis, and (3) eliminating a small off-channel pond that provided optimal habitat that sustained a localized high-density population of lineage III T. tubifex, the oligochaete host susceptible to M. cerebralis. Electrofishing during the fall of 2009 and spring of 2010 indicated the drainage was devoid of fish. Fry, juvenile, and adult Rio Grande Cutthroat Trout were stocked in September and October of 2010 and 2011. Approximately 975,000 lineage V and VI T. tubifex were introduced into Placer Creek between 2010 and 2012 as possible oligochaete competitors for the lineage III worms. The off-channel pond was filled in, and the surface was reseeded in April 2012. No evidence of M. cerebralis infection was detected among more than 280 Rio Grande Cutthroat Trout tested between July 2012 and July 2016, indicating the parasite had been eradicated from the Placer Creek basin upstream of the barriers.

The Use of Barriers to Limit the Spread of Aquatic Invasive Animal Species: A Global Review

“…Research has focussed on the Laurentian Great Lakes area, primarily to reduce sea lamprey access to spawning habitat in tributary streams (e.g., Swink, 1999;Johnson et al, 2014;Miehls et al, 2017) and to prevent the intrusion of "Asian carp" species into Lake Michigan (e.g., Ruebush et al, 2012;Parker et al, 2015). The other main focus area within the United States has been in the western states where physical barriers have been installed to prevent nonnative salmonids from reaching upstream areas that harbour endangered populations of native trout (e.g., Novinger and Rahel, 2003;Avenetti et al, 2006;Nehring et al, 2018). Canadian examples (10 studies) include the exclusion of common carp (Cyprinus carpio) from bays in Lake Manitoba in order to help restore the quality of marsh habitat (Caskenette et al, 2018).…”

“…These are frequently implemented through augmenting existing natural waterfalls (e.g., Lintermans, 2000). Although construction of barriers in streams is not as technologically demanding and less costly compared to rivers, high flow events and bedload movements can still cause failures (Nehring et al, 2018).…”

“…While short term experiments can provide useful insights, long term studies are needed to evaluate the effectiveness of AIS barriers under a broader range of conditions. For example, physical barriers can fail during high flow events (Nehring et al, 2018), some taxa can disperse terrestrially (Thomas et al, 2019), electrical barriers can suffer power-outages (Clarkson, 2004), and AIS can become habituated to behavioural deterrents (Vetter et al, 2015) as well as chemical barriers (Schneider et al, 2018). Promising results from short term studies need to be treated with caution.…”

Increasing copper concentrations do not affect Myxobolus cerebralis triactinomyxon viability

“…Because sublethal concentrations of copper can reduce immune function and increase susceptibility to diseases in salmonids (Anderson et al, ; Dethloff & Bailey, ; Elsasser et al, ; Mushiake et al, ; O'Neill, ), the effect and spread of whirling disease are potentially greater in fish populations stressed by copper, and further research investigating this scenario is needed. At lethal levels of copper, the absence of either host ensures that the parasite could be extirpated from an ecosystem within 14 months (Nehring, Alves, Nehring, & Felt, ). Such disease‐free locations may be priority candidates for mine reclamation efforts.…”

“…At lethal levels of copper, the absence of either host ensures that the parasite could be extirpated from an ecosystem within 14 months (Nehring, Alves, Nehring, & Felt, 2018). Such disease-free locations may be priority candidates for mine reclamation efforts.…”