This essay was written as an assignment for a Fish Diversity & Conservation course at Utah State University taught by PhD candidate Jack McLaren. Unfortunately, superscript is not supported on Wix.
“Typically, the menu of decline always includes things like pollution or overfishing but you can put it into one-word, non-native species ”-Dr. Robert Behnke
“What makes a conservation success story?”
This question is in reference to the films Rising from the Shadows: The Return of the Cutthroat Trout (1) and The Return (2). Each of these films are based on the declining population of native cutthroat trout in the Western United States and the restoration efforts to save them from extinction. The Return (2) is a modern film focused specifically on the Yellowstone Cutthroat Trout while Rising from the Shadows (1) gives a broader view of the history of our western native trout. These videos told the story of once abundant populations of native cutthroat trout prior to the introduction of non-native trout species and the management that helped lead to their recovery.
Dr. Robert Behnke stated that typically, the menu of decline always includes things like pollution or overfishing but you can put it into one-word, non-native species (1). What Behnke is referring to is rainbow trout, brown trout, lake trout and brook trout which are not native to the range in which they have been introduced. Non-native species invasions threaten the future of native fish diversity worldwide (3,4,5). These introduced fishes impact native species through competition, introgressive hybridization, predation and disease transmission (6,7,8,9,10). While the Yellowstone Cutthroat Trout and lake trout interaction is highlighted in each film, rainbow trout hybridization with other, more rare trout species, affects the genetic integrity of the native fishes (11,12,13,14). This introgression has been a major factor in the declining numbers of native cutthroat trout (15).
Cutthroat restoration has been successful to this point due to conservation efforts by state, federal and nonprofit organizations. Projects discussed in the films focused on removal of non-native lake trout in Yellowstone Lake, captive rearing programs to preserve pure strain native fishes and fish barriers to block migration from non-native species into native fish waters. Formation of organizations focused on recovery and protection of native species has helped fund, fight for and raise awareness of these once dissipating fishes.
The future holds some promise, but our native trout species are not out of the woods. While the human population increases, so does our need for development and the demand for water. Each of those factors can contribute to loss of fish habitat which can decrease abundance, size, and condition of fishes. When decreasing stream flow, it can leave fish eggs exposed, covered with silt, or left without proper levels of oxygen in the water which directly increases mortality rates. It is also said that water velocities and the amount of appropriate substrate can be altered to the point that spawning sites become limited which increases the probability of hybridization between some species (16).
Habitat loss or destruction to remaining habitat caused by increasing feral horse populations is among one of many future threats to native trout. These herds are often concentrated in areas affecting native trout and contribute to the nonattainment of grazing allotment objectives and standards for rangeland health. In Nevada, excess population levels are expected to continue negatively impacting sensitive riparian areas relied upon by the Lahontan cutthroat trout. Excess grazing of the vegetative resources can result in declines in the healthy vegetative condition that may take years to recover (17). This can reduce riparian vegetation along native trout streams causing an impact to habitat, food abundance and increased water temperatures.
Another future threat to native trout is the increasing numbers of American White Pelicans in southern Idaho. Distribution changes resulting from colony inactivity and new colony establishment have redistributed populations of pelicans. Initial this change was the result of the historic colony loss in southern and central California, primarily from water diversion (18). A more recent collapse of Yellowstone Cutthroat Trout populations coincided with this rapid increase of pelican breeding colonies on Blackfoot Reservoir. Pelicans have been documented to frequently consume substantial portions of the spawning migration of native Yellowstone Cutthroat Trout in the Blackfoot River system. In 2004, 70% of adult Cutthroat Trout migrants exhibited wounds consistent with pelican attacks (19). Hazing actions by means of loud noises, pyrotechnics and nest destruction had limited effect on the pelicans which led to the necessary use of lethal reinforcement, and an egg take quota in an attempt to reduce pelican predation on migrating Yellowstone Cutthroat Trout.
While there are still apparent threats to our native trout populations, there has been a great success in conservation. All of the 21 species of native trout currently have self-sustaining populations. Protections have been placed on sensitive species to limit or prevent harvest where it is sustainable. There will be no end to the fight, but if we can learn from the mistakes of the past and move forward with the thought of these systems as a whole, there is a chance to minimize our mistakes in the future.
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(Walbaum, 1792): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=910, Revision Date: 9/12/2019, Peer Review Date: 4/1/2016, Access Date: 10/15/2019
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17. Bureau of Land Management. 2008. Effective Long-Term Options Needed to Manage
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19. Teuscher, D.M., M.T. Green, D.J. Schill, A.F. Brimmer, and R.W. Hillyard. 2015. Predation by American White Pelicans on Yellowstone Cutthroat Trout in the Blackfoot River Drainage, Idaho. North American Journal of Fisheries Management 35: 454-463.