End the stocking of nonnative trout species over wild native brook trout in Pennsylvania.
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We, the undersigned, urge the Pennsylvania Fish and Boat Commission to end the practice of stocking waters where wild native brook trout are present.
Wild native brook trout (Salvelinus fontinalis) are of great ecological, cultural, and economic importance to the eastern United States, and their preservation and restoration is a growing focus of many state and federal agencies, non-profit organizations, educational institutions, and concerned citizens.
Surveys completed in 2005 as part of the Eastern Brook Trout Joint Venture’s range-wide assessment indicate that intact stream brook trout populations exist in only 5% of the watersheds assessed. Furthermore, "Wild stream populations of brook trout have vanished or are greatly reduced in nearly half of the watersheds. The vast majority of historically occupied large rivers no longer support self-reproducing populations of brook trout.”
A regional and state-level assessment (Hudy et al. 2005) indicates that “Pennsylvania had the greatest number of watersheds with brook trout populations classified as reduced, severely reduced, extirpated, or unknown” within the eastern brook trout’s native range.
According to the United States Geological Survey (USGS) and numerous scientific studies (references 1-39 below), stocking over wild native brook trout has a negative impact on the resident population.
Citations below provided by the USGS:
1. Bartholomew, J. L., and P. W. Reno. 2002. The history and dissemination of whirling disease. American fisheries Society Symposium 26:1-22.
DOI: Not available
The authors reviewed the history of whirling disease (Myxobolis cerebralis) and summarized physiological effects on salmonid fishes including brook trout. They reported the distribution of the pathogen and discussed research needs.
2. Blanchet, S., G. Grenouillet, O. Beauchard, P. A. Tedesco, F. Leprieur, H. H. Dürr, F. Busson, T. Oberdorff, and S. Brosse. 2010. Non-native species disrupt the worldwide patterns of freshwater fish body size: implications for Bergmanns rule. Ecology Letters 13:421-431.
The authors demonstrated that non-native species are often larger than their native counterparts, and this has increased the overall median body size of fishes worldwide. They compiled a global dataset from over 1000 river basins for this analysis.
3. Carlson, S. M., A. P. Hendry, and B. H. Letcher. 2007. Growth rate differences between resident native brook trout and non-native brown trout. Journal of Fish Biology 71:1430-1447.
The authors observed that introduced brown trout typically grew faster than native brook trout in a small stream system (West Brook, Massachusetts). Interspecific differences in growth were greatest during spring and early summer months when total growth rates were highest. Variation in growth rates also were linked to differences in body size between species.
4. Clark, M.E., and K. A. Rose. 1997. An individual-based modeling analysis of management strategies for enhancing brook trout populations in Southern Appalachian streams. North American Journal of Fisheries Management 17:54-76.
The authors compared management strategies for controlling rainbow trout to promote native brook trout conservation. They concluded that habitat alteration and angler harvest were less effective than electrofishing removal.
5. Cunjak, R. A. and J. M. Green. 1984. Species dominance by brook trout and rainbow trout in a simulated stream environment. Transactions of the American Fisheries Society 113:737-743.
The authors evaluated interactions between brook trout and rainbow trout in a natural setting. Brook trout exhibited competitive dominance in pool-type habitats compared to non-native rainbow trout of similar size. However, social status within species was a more important predictor of habitat use than interspecific interactions.
6. Densmore, C. 2020. Aquatic invasive species in the Chesapeake Bay drainage-research-based needs and priorities of U.S. Geological Survey partners and collaborators. U.S. Geological Survey Open-File Report 2020–1057.
The author listed research priorities for invasive species in the Chesapeake Bay watershed. In conjunction with state and federal partners, the author identified high-priority invasive species and science needs for management of these species.
7. DeWald, L., M. A. Wilzbach. 1992. Interactions between native brook trout and hatchery brown trout: effects of habitat use, feeding, and growth. Transactions of the American Fisheries Society 121:287-296.
The authors evaluated effects of brown trout on brook trout in an experimental stream system. The presence of brown trout caused brook trout to shift their spatial positions relative to single-species trials. Brook trout foraging rates also decreased in the presence of brown trout, demonstrating competitive effects of non-native brown trout. Moreover, a third of brook trout contracted a lethal fungal infection (Saprolegnia sp.) when brown trout were present but not when brown trout were absent, suggesting physiological effects of interspecific competition.
8. Epanchin-Niell, R. S., R. G. Haight, L. Berec, J. M. Kean, and A. M. Liebhold. 2012. Optimal surveillance and eradication of invasive species in heterogeneous landscapes. Ecology Letters 15:803-812.
The authors develop a monitoring framework for invasive species that accounts for trade-offs between surveillance effort and management costs. They demonstrate that optimal solutions depend in part on the mechanisms of invasive species establishment and spread.
9. Fausch, K. D., and R. J. White. 1981. Competition between brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) for positions in a Michigan stream. Canadian Journal of Fisheries and Aquatic Sciences 38:1220-1227.
The authors demonstrated changes in brook trout microhabitat selection for resting positions following the removal of brown trout from a Michigan stream. This study provides experimental evidence for competition between native brook trout and introduced brown trout.
10. Flebbe, P. A. 1994. A regional view of the margin: salmonid abundance and distribution in the southern Appalachian mountains of North Carolina and Virginia. Transactions of the American Fisheries Society 123:657-667.
The author demonstrated links between elevation and trout species distributions in the southern Appalachians. Elevation was treated as a surrogate for temperature but did not account for localized processes such as groundwater-surface water interactions that also affect stream temperature.
11. Garcia-Berthou, E. 2007. The characteristics of invasive fishes: what has been learned so far? Journal of Fish Biology 71:33-55.
The author reviewed invasive fish species research, focusing on species traits and mechanisms of biological invasions. He found that that initial stages of non-native fish transport and release are least understood yet most important for management interventions. He also reviewed the role of functional traits for non-native fish establishment and spread.
12. Gallardo, B., M. Clavero, M. I. Sánchez, and M. Vilà. 2015. Global ecological impacts of invasive species in aquatic ecosystems. Global Change Biology 22:151-163.
The authors highlighted the importance of trophic interactions for understanding effects of invasive species at a global scale.
13. Halverson, M. A. 2008. Stocking trends: a quantitative review of governmental fish stocking in the United States, 1931 to 2004. Fisheries 33:69-75.
The author reviewed the history of fish stocking in the United States, including rainbow trout and brown trout within the range of native brook trout.
14. Halverson, A. 2010. An Entirely Synthetic Fish: How Rainbow Trout Beguiled America and Overran the World. Yale University Press.
DOI: Not available
The author reviewed the history of rainbow trout introductions and the impact it has had on native fishes including brook trout.
15. Havel, J. E., K. E. Kovalenko, S. M. Thomaz, S. Amalfitano, and L. B. Kats. 2015. Aquatic invasive species: challenges for the future. Hydrobiologia 750:147-170.
The authors provided a review of aquatic invasive species focusing on their functional trait and impacts on native species. The authors identified functional traits associated with invasive species and identified types of ecological communities most susceptible to invasion.
16. Heger, T., A. T. Pahl, Z. Botta-Dukat, F. Gherardi, C. Hoppe, I. Hoste, K. Jax, L. Lindstrom, P. Boets, S. Haider, J. Kollmann, M. J. Wittmann, and J. M. Jeschke. 2013. Conceptual frameworks and methods for advancing invasion ecology. Ambio 42:527-540.
The authors recognized several challenges for understanding the effects of non-native species, including societal perceptions of invasive species, context-dependency of invasion success, and imprecise hypotheses. They recommended steps to address each of these challenges.
17. Hitt, N., E. Snook, and D. Massie. 2017. Brook trout use of thermal refugia and foraging habitat influenced by brown trout. Canadian Journal of Fisheries and Aquatic Sciences 74:406-418.
The authors evaluated the effects of brown trout on brook trout behavior in an experimental stream system. They demonstrated that brown trout restricted brook trout movements and limited their foraging rates relative to single-species trials.
18. Isely, J. J., and C. Kempton. 2000. Influence of costocking on growth of young-of-year brook trout and rainbow trout. Transactions of the American Fisheries Society 129:613-617.
The authors demonstrated competition between juvenile (age-0) rainbow trout and brook trout in a raceway environment: juvenile brook trout grew faster in allopatry than in sympatry with rainbow trout.
19. Kopf, K. R., D. G. Nimmo, P. Humphries, L. J. Baumgartner, M. Bode, N. R. Bond, A. E. Byrom, J. Cucherousset, R. P. Keller, A. J. King, H. M. McGinness, P. B. Moyle, and J. D. Olden. 2017. Confronting the risks of large-scale invasive species control. Nature Ecology and Evolution 1:1-3.
The authors reviewed potential mistakes in the management of invasive species and recommended risk management strategies for invasive species control.
20. Larson, G. L., and S. E. Moore. 1985. Encroachment of exotic rainbow trout into stream populations of native brook trout in southern Appalachian mountains. Transactions of the American Fisheries Society 114:195-203.
The authors reviewed evidence that introduced rainbow trout have reduced native brook trout abundance and distribution in the southern Appalachian mountains, focusing on Great Smoky Mountains National Park.
21. Lovell, S., S. Stone, and L. Fernandez. 2006. The economic impacts of aquatic invasive species: a review of the literature. Agricultural and Resource Economics Review 35:195-208.
The authors assessed economic costs of aquatic invasive species. They estimated species-specific costs and recommended strategies for more comprehensive and consistent assessments in this regard.
22. Magoulick, D. D., and M. A. Wilzbach. 1998. Effect of temperature and macrohabitat on interspecific aggression, foraging success, and growth of brook trout and rainbow trout pairs in laboratory streams. Transactions of the American Fisheries Society 127:708-717.
The authors evaluated pairs of juvenile rainbow trout and brook trout in experimental stream channels. They found that brook trout were more aggressive and had higher foraging rates than rainbow trout at 13 ⁰C and 18 ⁰C. However, macrohabitat conditions (i.e., pool and riffle habitats) did not yield interspecific differences.
23. Marschall, E. A., and L. B. Crowder. 1996. Assessing population responses to multiple anthropogenic effects: a case study with brook trout. Ecological Applications 6:152-167.
The authors used matrix population models to assess effects of introduced species (rainbow trout), water quality (pH), substrate quality (siltation), and angling pressure on brook trout populations. They found that the presence of rainbow trout may decrease survival of small brook trout and may decrease growth rates for all size classes of brook trout.
24. McKenna, J. E., M. T. Slattery, and K. M. Clifford. 2013. Broad-scale patterns of brook trout responses to introduced brown trout in New York. North American Journal of Fisheries Management 33:1221-1235.
The authors used a variety of statistical methods to evaluate the effects of introduced brown trout on native brook trout distribution and abundance. They found evidence for the decline of Brook Trout in the presence of introduced Brown Trout, and they recommended stocking protocols to minimize these effects. They also found that evidence for direct interactions (e.g., competition) was secondary to the overriding effect of brown trout stocking practices.
25. Moore, S. E., B. Ridley, and G. L. Larson. 1983. Standing crops of brook trout concurrent with removal of rainbow trout from selected streams in Great Smoky Mountains National Park. North American Journal of Fisheries Management 3:72-80.
This study empirically demonstrated increased brook trout biomass and abundance in response to experimentally reduced numbers of non-native rainbow trout over 4 years. The authors discuss the potential of backpack electrofishing for removal of non-native trout as a management strategy for native brook trout.
26. O'Grodnick, J. J. 1979. Susceptibility of various salmonids to whirling disease (Myxosoma cerebralis). Transactions of the American Fisheries Society 108:187-190.
The author evaluated the susceptibility of juvenile salmonid fishes to whirling disease (Myxobolis cerebralis) in a laboratory setting. He detected important interspecific differences: rainbow trout were the most susceptible and lake trout were least susceptible. Brook trout were more susceptible than brown trout.
27. Pejchar, L. and H. A. Mooney. 2009. Invasive species, ecosystem services and human well-being. Trends in Ecology and Evolution 24:497-504.
The authors reviewed case studies from South Africa, the Great Lakes, and Hawaii on invasive species effects, focusing on economic, cultural, and ecological outcomes.
28. Radinger, J. and E. García‐Berthou. 2020. The role of connectivity in the interplay between climate change and the spread of alien fish in a large Mediterranean river. Global Change Biology 00:1-16.
The authors modeled current and future distributions of invasive fishes under different scenarios of climate change. Their results highlighted the importance of stream network connectivity and fragmentation (e.g., periodic dewatering) on the impacts to native fishes. They also discussed barriers as management strategies for native fish conservation.
29. Rahel, F. J. and J. D. Olden. 2008. Assessing the effects of climate change on aquatic invasive species. Conservation Biology 22:521-533.
The authors provided a conceptual framework for understanding interactive effects of climate change and invasive species in freshwater ecosystems.
30. Rose, G. A.1986. Growth decline in subyearling brook trout (Salvelinus fontinalis) after emergence of rainbow trout (Salmo gairdneri). Canadian Journal of Fisheries and Aquatic Sciences 43:187-193.
The author evaluated growth of juvenile (age-0) brook trout and rainbow trout in a tributary to Lake Superior. He found that brook trout growth rates diminished after the emergence of rainbow trout in June. The authors hypothesized that interspecific competition during early life history stages may limit brook trout populations by limiting growth and size-dependent overwinter survival rates for juvenile fish.
31. Taniguchi, Y., F. J. Rahel, D. C. Novinger, and K. G. Gerow. 1998. Temperature mediation of competitive interactions among three fish species that replace each other along longitudinal stream gradients. Canadian Journal of Fisheries and Aquatic Sciences 55:1894-1901.
The authors evaluated effects of temperature on interspecific competition between brown trout, brook trout, and creek chub in a laboratory setting. Creek chub and brown trout gained a competitive advantage over brook trout as temperatures increased. Their results are supported by other studies demonstrating context-dependent competition between brown trout and brook trout (e.g., Rahel and Olden 2008; Hitt et al. 2017).
32. Tebo, L. B., and W. W. Hassler. 1963. Food of brook, brown, and rainbow trout from streams in Western North Carolina. Journal of the Elisha Mitchell Scientific Society 79:44-53.
DOI: Not available
The authors evaluated stomach contents of brook trout, rainbow trout, and brown trout in southern Appalachian streams. Their findings revealed substantial overlap among species for prey items, indicating the potential importance of food availability for interspecific competition between native brook trout and non-native trout.
33. Thresher, R. E., K. Hayes, N. J. Bax, J. Teem, T. J. Benfey, and F. Gould. 2014. Genetic control of invasive fish: technological options and its role in integrated pest management. Biological Invasions 16:1201–1216.
The authors reviewed genetic strategies for controlling invasive fish species, including triploidy and trojan Y karyotypes. They indicated that application of these methods may enhance traditional methods of invasive fish control (i.e., electrofishing removal and barrier placement).
34. Vitousek, P. M., D'antonio, C. M., Loope, L. L., Rejmanek, M., and R. Westbrooks. 1997. Introduced species: a significant component of human-caused global change. New Zealand Journal of Ecology 21:1-16.
DOI: Not available
The authors reviewed invasive species global impacts of introduced species on ecosystem function, biodiversity, and ecosystem services. They put these impacts into context of other anthropogenically-induced drivers of environmental change.
35. Wagner, T., J. T. Deweber, J. Detar, and J. Sweka. 2013. Landscape‐scale evaluation of asymmetric interactions between brown trout and brook trout using two‐species occupancy models. Transactions of the American Fisheries Society 142:353-361.
The authors used occupancy modeling techniques and demonstrated that brook trout occurrence probability decreases where introduced brown trout are present. They also demonstrated that the probability of brook trout occurrence decreases with increasing impervious surface area and decreasing forest cover.
36. Waters, T. F. 1983. Replacement of brook trout by brown trout over 15 years in a Minnesota stream: production and abundance. Transactions of the American Fisheries Society 112:137-146.
The author observed the replacement of native brook trout with introduced brown trout in a long-term dataset and suggested that changes in stream flow facilitated this process.
37. Whitworth, W. E., and R. J. Strange. 1983. Growth and production of sympatric brook and rainbow trout in an Appalachian stream. Transactions of the American Fisheries Society 112:469-475.
The authors evaluated trout growth rates in a stream with 3 spatial zones: rainbow trout only (downstream reach), both rainbow trout and brook trout (middle reach), and brook trout only (upstream reach). The authors found that growth rates were similar between species until year-2 at which point rainbow trout outgrew brook trout and maintained a size advantage afterwards.
38. Yoder, W. G. 1972. The spread of Myxosoma cerebralis into native trout populations in Michigan. The Progressive Fish Culturist 34:103-106.
The author documented the presence of whirling disease in wild brook trout populations and suggested introduced rainbow trout as the source of the infection.
39. Kentaro Morita, Assessing the long-term causal effect of trout invasion on a native charr, Ecological Indicators, Volume 87, 2018, Pages 189-192,
Abstract: Many studies have indicated that invasive species can drive declines in native species through interspecific competition. In freshwater ecosystems, brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) have been implicated in reducing native species, especially congeneric salmonid fishes. However, demonstrating causality in the wild is problematic because non-natives might replace natives in areas where the former were extirpated by other environmental changes. Using the recently developed technique of multispatial convergent cross mapping (CCM) and a long-term monitoring data set (2002–2017) with spatial replication on both introduced and native salmonids in a Japanese stream, I tested whether an increase in non-native trout caused a decrease in native charr (Salvelinus leucomaenis). Native charr decreased their population density over time in contrast to the non-native brown trout and rainbow trout. The dominant species changed from native charr (64%) in 2002 to non-native trout (97%) by 2017. Multispatial CCM identified significant causal forcing of the native charr by both rainbow trout and brown trout, lending support for the hypothesis of displacement, rather than replacement, of a native species by non-native species. These results therefore suggest that eradicating the invasive trout species may aid the recovery of native charr in the region.
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