Recovering threatened bull trout with conservation populations, an annotated bibliography

Al-Chokhachy, R., Moran, S., McHugh, P.A., Bernall, S., Fredenberg, W., & DosSantos, J.M. (2015). Consequences of actively managing a small bull trout population in a fragmented landscape. Transactions of the American Fisheries Society 144 (3): 515-531. https://www.tandfonline.com/doi/ abs/10.1080/00028487. 2015.1007162

Summary: Habitat fragmentation is a leading cause of Bull Trout declines in abundance and distribution. This paper looks at the difficulties of managing small local populations of Bull Trout. The case study transports juvenile Bull Trout from headwater tributaries to Lake Pend Oreille for rearing while returning adult bull trout to natal streams for spawning. The authors of the paper modeled various environmental scenarios on varying numbers and ages of juveniles and adults transported and found that many scenarios could actually be detrimental to the overall population.

Relevance: If we were to translocate a population of Bull Trout to High Lake, it would be a small, fragmented population. We are considering the implications of this, but this paper brings some of them into focus. Whatever we decide, we need to move slowly and carefully as this paper suggests.

Benjamin, J.R., Brignon, W.R., & Dunham, J.B. (2019). Decision analysis for the reintroduction of bull trout into the lower Pend Oreille River, Washington. North American Journal of Fisheries Management 39 (5): 1026-1045. https://afspubs.onlinelibrary.wiley.com/doi/10.1002/nafm.10334

Summary: Whether to conduct a reintroduction project is made difficult due to uncertainties and differing opinions on what constitutes success. This paper introduces a structured decision-making process that helps managers identify realistic objectives with various management alternatives. The process was applied to the reintroduction of Bull Trout in the lower Pend Oreille River in northeastern Washington. The model incorporated the views of a well-rounded stakeholder consortium and known biological information to generate possible scenarios. An optimal scenario provided the best recipient stream and the number and ages of individuals to reintroduce.

Relevance: With the support of the structured decision-making tool provided in the paper, we would have more confidence as to the likelihood of success if we were to translocate Bull Trout into High Lake. It would allow us a way to predict outcomes and help us define what success means to us. Ultimately, this could save us time, money, and resources that could better be directed elsewhere.

Brignon, W.R., Peterson, J.T., Dunham, J.B., Schaller, H.A., & Schreck, C.B. (2017). Evaluating trade-offs in bull trout reintroduction strategies using structured decision making. Canadian Journal of Fisheries and Aquatic Sciences 75 (2). https://cdnsciencepub.com/doi/abs/10.1139/cjfas-2016-0516

Summary: This decision support tool analyzes scenarios that permit the highest number of individuals to the recipient location without harming the donor population irrecoverably. The model predicts that the number of Bull Trout reintroduced, the juvenile survival in the reintroduced and donor populations, fecundity rates, and sex ratio are the factors that will have the largest influence over the outcome while survival of the captive-reared population and the juvenile carrying capacity of the reintroduced population will have the least influence.

Relevance: Although some of the variables tested are irrelevant to our potential plan, the results of this tool are valuable nonetheless. This model dives deeper into age demographics and reproduction variables that we may not have considered otherwise.

Dunham, J., Gallo, K., Shively, D., Allen, C., & Goehring, B. (2011). Assessing the feasibility of native fish reintroductions: a framework applied to threatened bull trout. North American Journal of Fisheries Management 31 (1): 106-115. https://afspubs.onlinelibrary.wiley.com/doi/abs/10.1080/02755947.2011.559830

Summary: This paper provides a decision support framework that seeks to address the feasibility of a reintroduction project prior to implementation. The framework is focused on the habitat quality of the reintroduction location and the ability of the donor population to provide the individuals needed to reintroduce successfully. It includes consideration of inherent uncertainties in available data and can quickly provide feasibility analysis for a proposed reintroduction. It was applied to the reintroduction of Bull Trout to the Clackamas River in Oregon and found the proposed project to have a high likelihood of success.

Relevance: The use of the framework provided in this paper would provide an additional metric to help us determine how successful a translocation of Bull Trout to the High Lake system might be. It would help us determine how to translocate or even whether to try at all.

Galloway, B.T. (2014) Feasibility assessment for translocation of imperiled bull trout populations in Glacier National Park, Montana. Master’s thesis, Montana State University, Bozeman, Montana. https://scholarworks.montana.edu/items/d4c1221e-99c2-4dae-a897-2ad0562e3cfe  

Summary: Many of the reasons translocation projects do not produce the intended results is because of an inadequate accounting of biotic and abiotic factors prior to implementation. Invasive species in certain lakes in Glacier National Park are driving Bull Trout toward extirpation. The prospect of translocating many of these individuals to avoid this fate is being considered. This paper evaluated the spawning, rearing, foraging, and overwintering habitat of three stream and lake systems in Glacier National Park. The risk of translocations to negatively affect native aquatic biota, potential for the habitat to support a donor population, and ability of current populations to support a translocation were all considered. The three donor locations were then ranked in order of most likely to be successful.

Relevance: Evaluating the different types of habitat needed for a successful translocation project is what sets this paper apart. If any one of those habitat types is inadequate, the translocated population will fail.  

Galloway, B.T., Mulhfield, C.C., Guy, C.S., Downs, C.C., & Fredenberg, W.A. (2016). A framework for assessing the feasibility of native fish conservation translocations: applications to threatened bull trout. North American Journal of Fisheries Management 36 (4): 754-768. https://afspubs.onlinelibrary.wiley.com/doi/10.1080/02755947.2016.1146177

Summary: This paper outlines the importance of considering more drastic solutions to imperiled populations of fishes due to habitat loss, competition with invasive species, and climate change. It defines a conservation introduction as the act of moving individuals from an at-risk population to habitat that is more suitable for the species. Success is dependent upon an understanding that sufficient environmental factors exist in the recipient habitat. This paper addresses both lotic and lentic systems and provides a framework for analyzing the recipient habitat and community along with the donor population and future threats that might affect the relocated population. It develops a scoring system to rate the components based on those of healthy populations and high quality habitat. It then applies the scoring system to a planned reintroduction of Bull Trout in Glacier National Park, Montana.

Relevance: There is a direct correlation between the planned Bull Trout translocations in Glacier National Park and our project in the Malheur River watershed of eastern Oregon. The paper found that a population relocated within the same drainage was likely to succeed if the habitat and aquatic community were suitable. If we were to translocate Bull Trout to High Lake, the source population would be from the same drainage or from one nearby in the same watershed. We believe we likely have suitable habitat but we should use the framework provided in the paper to further analyze whether the aquatic community is suitable.

Harig, A.L., & Fausch, K.D. (2002). Minimum habitat requirements for establishing translocated cutthroat trout populations. Ecological Applications 12 (2): 535-551. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/1051-0761(2002)012[0535:MHRFET]2.0.CO;2

Summary: This paper outlines the importance of habitat in translocation projects. Cutthroat Trout habitat has been severely fragmented and translocated populations do not often succeed. Habitat quality is often cited as the limiting factor. The authors analyzed 27 translocation projects and determined the habitat characteristics most beneficial to success. The patch scale, rather than landscape scale, was determined most appropriate for determining habitat quality.

Relevance: A different but related species of trout was analyzed in this paper. The importance of high quality habitat is just as important, perhaps more important, for a specialist species like Bull Trout.

Harig, A.L., Fausch, K.D., & Young, M.K. (2011). Factors influencing success of greenback cutthroat trout translocations. North American Journal of Fisheries Management 20 (4): 994-1004. https://www.tandfonline.com/doi/abs/10.1577/1548-8675(2000)020%3C0994%3AFISOGC%3E2.0.CO%3B2

Summary: Although a different species, Greenback Cutthroat Trout are non-anadromous salmonids like Bull Trout. This paper looked at 14 successful translocations against 23 failures to determine the reasons behind the discrepancies. 48% of the failures were because of nonnative salmonid reinvasion and 43% because of inadequate habitat. Success was highest in locations of at least two hectares in size where trout were successful previously.

Relevance: This paper is interesting in that it analyzes a large number of failed trout translocations. We do not anticipate nonnative trout reinvasion as a waterfall barrier separates the downstream population of Brook Trout. Thousands of Brook Trout currently occur in High Lake and the outflow and High Lake is larger than two hectares in size. Those factors indicate potential success, but different species can respond in very different ways.

Hayes, M.F., & Banish, N.P. (2017). Translocation and reintroduction of native fishes: a review of bull trout Salvelinus confluentus with applications for future reintroductions. Endangered Species Research 34: 191-209. https://www.int-res.com/abstracts/esr/v34/p191-209/

Summary: This paper compiles a history of Bull Trout translocation and reintroduction projects and tries to determine whether each was successful or not. By analyzing why some translocations or reintroductions of Bull Trout have been successful while others have failed, it attempts to provide guidance for future projects to realize goals. Incomplete records and documentation from previous attempts hamper the analysis, but the paper provides summaries of six successful projects and two failures. Interestingly, many previous projects did not even consider habitat complexity, stream width, climate change, water temperatures, or screen for diseases/parasites but were still successful. 

Relevance: The application is clear, but it is important to note that many of the projects discussed were in riverine systems which differ from lacustrine environments. The High Lake outflow is similar to the successful Sun Creek project in Crater Lake National Park, which is probably the most relevant to consider for our purposes. Many of the other projects introduced Bull Trout into systems with non-native fish established, a key difference with our High Lake project which will be fishless. Non-native fish can provide a prey base, but they can also spread diseases and parasites, provide competitive stressors, or even be a source of genetic dilution for Bull Trout if the two species can spawn with each other. The habitat of High Lake and its outflow is small, but based on some conclusions from the paper, appears to be of high enough quality to support a translocated population of Bull Trout. Habitat connectivity (an impassable waterfall barrier exists in the High Lake system which prevents upstream fish migration) and whether there is access to suitable spawning grounds are concerns, however. This could result in a genetically stunted translocated population.

Kissinger, B.C., Sullivan, M.G., Post, A.J., Meinke, A., & Post, J. (2024). Establishment of Bull Trout in a previously fishless lake by translocation. North American Journal of Fisheries Management 44 (2): 520-531. https://afspubs.onlinelibrary.wiley.com/doi/10.1002/nafm.10989

Summary: Bull Trout are a difficult species to translocate successfully with a roughly 50% success rate. This paper describes one such success story where the translocated population was not only maintained but increased fourfold over a period of 12 years. Large individuals and multiple age classes confirm success in Marie Lake, Alberta, Canada. Individuals from Marie Lake were discovered up to 13 kilometers downstream in the Marie Lake outflow many years later. This paper highlights the importance of donor population selection, recipient habitat conditions, recipient aquatic community structure, and future threats to consider to guide efforts to establish a translocated population of Bull Trout. These factors have been found to be relevant in previous studies of fish translocation projects.

Relevance: It makes sense to investigate success stories to try to emulate that success using lessons learned. In our system of High Lake, we will have a similar aquatic community as Marie Lake with no competing fish species once the Brook Trout are removed. Bull Trout are known to be top predators in the aquatic environment, so if we translocate, we will need to monitor effects on other aquatic species. The aquatic species present, however, have co-evolved with Bull Trout and this project would simply represent a small range expansion in the Malheur River watershed. We will also monitor Bull Trout condition factor and try to determine population dynamics as Bull Trout are known to cannibalize under certain circumstances. The High Lake system has similar habitat conditions as Marie Lake, but it is smaller and shallower. Our donor population would be located much closer than the population in Marie Lake was. This may increase our chances of success as we would be using a locally adapted population to draw from. In terms of future threats, the High Lake system is groundwater driven which buffers from increasing temperatures with climate change. High Lake is much less remote than Marie Lake, however, so effects from angling pressure will need to be considered.

Lepine, T.M. (2024). An experimental test of bull trout egg to alevin survival in the wild, with implication for conservation translocations in Alberta. Master’s thesis, University of Calgary, Calgary, Canada. https://prism.ucalgary.ca/items/baef4984-c1b0-4922-a3a4-507535ae22a3

Summary: This paper looks at conservation translocations from a different angle- instead of using adults or juveniles, what about Bull Trout eggs? The paper sought to determine which habitat variables were most important for survival (water temperature, substrate, etc.). The author had a high survival rate at her study sites and notes that number of freezing days is the variable with the highest negative effect on survival.

Relevance: This study is highly intriguing to our planning process. Using eggs may be a safer way to implement our translocation strategy. It could be a way to test survival of Bull Trout before potentially using juveniles and/or adults in our translocation plan. Or it could be so successful that we might not even need to translocate older individuals at all. Ultimately, we want to first do no harm to an already struggling Bull Trout population. That number of freezing days had such a negative effect is concerning, however- High Lake is in an alpine setting at around 7500 feet in elevation.

Vincenzi, S., Crivelli, A.J., Jesensek, D., & De Leo, G.A. (2011). Translocation of stream-dwelling salmonids in headwaters: insights from a 15-year reintroduction experience. Reviews in Fish Biology and Fisheries 22: 437-455. https://link.springer.com/article/10.1007/s11160-011-9235-5

Summary: A thorough analysis of quantitative measures of success over 15 years, this paper discusses the demographic traits, compensatory responses, life histories, and population dynamics of marble trout in reintroduction efforts in Slovenia. To increase species viability, two new populations were created and subsequently monitored. The species is not currently at risk of extinction, but severe flooding causes local population extirpations, and the authors do not recommend reestablishing reaches prone to severe flooding events. The translocation activities of the marble trout have provided insights into ecological dynamics and vulnerabilities beyond the species itself.

Relevance: There is a lot of information provided by this paper that can help determine the success of a translocation project. It goes beyond establishing populations to quantify how different demographics function within the populations and how the ecology responds. It provides a great model to reference for determining success.

Whitesel, T.A., DeHaan, P.W., Doyle, J., Adams, B.A., & Sankovich, P.M. (2022). Evaluating the success of a conservation reintroduction: the case of bull trout in the Wallowa River. Conservation Science and Practice 4 (6). https://conbio.onlinelibrary.wiley.com/doi/10.1111/csp2.12674

Summary: After Bull Trout were extirpated from the Wallowa River in the 1950s, they were reintroduced from the nearby Imnaha River in 1997. This paper determines the success of that reintroduction effort. It finds that Bull Trout still occur in the Wallowa and that they most closely resemble the genetics of Imnaha individuals. Based on size, survival, and age, the captured individuals were unlikely to be remnants which suggests that the reintroduction effort was successful. Although spawning is occurring, there is also evidence of a genetic bottleneck which may present persistence issues in the future.

Relevance: This paper presents another success story of a Bull Trout reintroduction. The genetic concerns referenced parallel our own concerns with small populations. In our case, that population will also be disconnected as an impassable waterfall prohibits upstream migration. Bull Trout in the High Lake system, if translocated, will be able to leave but individuals will not be able to freely migrate back into the system. Should this become problematic, we may consider translocating additional individuals to bolster genetic diversity.

Zymonas, N.D. (2011). Re-introduction of bull trout in the upper Willamette River basin, USA. IUCN Global Re-introduction Perspectives: 2011: 44-48. https://www.researchgate.net/profile/Adam-Backlin/publication/261287408_Conservation_and_recovery_of_the_mountain_yellow-legged_frog_in_Southern_California_USA/links/02e7e533c867f3c7e4000000/Conservation-and-recovery-of-the-mountain-yellow-legged-frog-in-Southern-California-USA.pdf#page=59

Summary: This report addresses Bull Trout reintroduction successes and challenges in the Willamette River, Oregon. Overall, the effort was considered a success. Access to spawning and rearing habitat, historic prey base, genetic exchange, and little evidence of angling mortality were many of the reasons why. Fry were used in the reintroductions and adults were observed several years later indicating survival. Augmentation with additional reintroductions was sometimes needed. One of the tributaries was unsuccessful due to low numbers of fry introduced.

Relevance: The High Lake system differs in that it is smaller, will not provide the same quality prey base, may present issues with genetic exchange, and may experience greater angling mortality. These factors are important to consider in our planning efforts. Using fry instead of juveniles or adults is also worth considering.