|My co-blogger, Dr. Carin Bondar|
In her part of this co-blogging effort, entitled "Further Thoughts on Introduced Sportfish," Dr. C examines the ecological impacts of salmonid (i.e. trout) sport fish introduction on the food webs surrounding and woven through mountain lakes. When introduced fish were allowed in Canadian lakes, an artificial environment of competition was developed between the fish and several other species, including birds and amphibians, all of whom rely on native insect species for food. At the same time, as Dr. C and I discussed during formulation of this collaborative effort, the hydrology of the lakes may simply not be adequate for the natural propagation of the introduced species, not providing appropriate spawning habitat or environmental conditions . We came to two obvious results from this idea. First, this lack of species-appropriate habitat and spawning grounds provides a compelling explanation for the absence of these species from the lakes in the first place. Second, the introduced species cannot find appropriate spawning habitat, such that each stocked cohort is either fished out or dies over the winter season, bringing about the need for another stocking effort every year and propagating the policy by tradition. Canada, recognizing the both the ecological imposition and ultimate futility of such efforts , eventually halted the practice in favor of "returning to nature" the lakes that had been altered up to that point. As Dr. C showed in the work of her student associate, the ecological impacts of the sport fishing era on competing fish species and other associated fauna are still evident even a decade after the ban on stocking practices was enacted.
In the US, no such ban on stocking of sport fish has been introduced to the policy debate. For that matter, there seems to be no such policy debate; fish rearing and stocking activities are a basic function of the US Fish and Wildlife Service (USFWS). Questions surrounding the practice have become evident in relevant scientific literature and have floated through the years with little notice from the professional (that is, government) policy-makers. It is only recently, coincidentally since the Canadian ban was enacted, that researchers in the US have begun to demonstrate more seriously and in greater detail the ecological impacts of introduced species on native fish and other fauna in mountain lakes and rivers of the US Rocky Mountains and Sierra Nevada, as well as the effort that may be required to re-establish native species that have been crowded out or become endangered over time. Many of these researchers are looking in from the outside, however: the decision-making process is still managed by those government agencies that develop and control the natural areas, national parks, rivers, lakes and reservoirs in the mountain regions. Competing goals are just part of the problem; competing bureaucratic interests often obscure the goals entirely.
|from Dunham et al. (2002) as listed below|
|from Metcalf et al. (2008) as listed below|
One final issue for this overview, which must be recognized in an eventual debate on the topic, is an inevitable effort to re-establish the native species in their traditional habitats while, or after, the introduced fishes are removed. Scientists have found that translocated cutthroat trout, even within the ranges of their traditional geographic distribution, do not always successfully re-establish "native" populations in their traditional or former habitats for several reasons [7, 8]. Not only do we understand little about salmonid habitat preferences and tolerances over their life cycle even as our management practices have all but eliminated native species, but we must recognize that where there was once "native" habitat previously, the introduction of competing species and human practices may have modified the habitat (e.g., the thermal environment  and the altered food web ) beyond the tolerances of the returning cutthroat trout. What was once their home, for reasons of adequate spawning and feeding grounds and food availability that we are still attempting to understand, has been modified to an intolerable environment by the time of their return. It is certainly a tragedy to find that your old home has changed beyond recognition in the years since you last saw it.
 Rosenfeld, J., 2003: "Assessing the habitat requirements of stream fishes: An overview and evaluation of different approaches." Trans. Am. Fisheries Soc., v. 132, pp. 953-968. DOI: 10.1577/T01-126
 Schindler, D.W., 2000: "Aquatic problems caused by human activities in Banff National Park, Alberta, Canada." Ambio, v. 29, pp. 401-407. DOI: 10.1579/0044-7447-29.7.401
 Knapp, R.A., P.S. Corn, and D.E. Schindler, 2001: "The introduction of nonnative fish into wilderness lakes: Good intentions, conflicting mandates, and unintended consequences." Ecosystems, v. 4, pp. 275-278. DOI: 10.1007/s10021-001-0009-0
 Bahls, P.F., 1992: "The status of fish populations and management of high mountain lakes in the western United States." Northwest Sci., v. 66, pp. 183-193. (open-access pdf)
 Dunham, J.B., S.B. Adams, R.E. Schroeter, and D.C. Novinger, 2002: "Alien invasions in aquatic ecosystems: Toward an understanding of brook trout invasions and potential impacts on inland cutthroat trout in western North America." Rev. Fish Biol. Fisheries, v. 12, pp. 373-391. DOI: 10.1023/A:1025338203702
 Metcalf, J.L., M.R. Siegle, and A.P. Martin, 2008: "Hybridization dynamics between Colorado's native cutthroat trout and introduced rainbow trout." J. Heredity, v. 99, pp. 149-156. DOI: 10.1093/jhered/esm118
 Harig, A.L., K.D. Fausch, and M.K. Young, 2000: "Factors influencing success of greenback cutthroat trout translocations." North Am. J. Fisheries Manage., v. 20, pp. 994-1004. DOI: 10.1577/1548-8675(2000)020<0994:FISOGC>2.0.CO;2
 Harig, A.L., and K.D. Fausch, 2002: "Minimum habitat requirements for establishing translocated cutthroat trout populations." Ecol. Appl., v. 12, pp. 535-551. DOI: 10.1890/1051-0761(2002)012[0535:MHRFET]2.0.CO;2
 Bear, E.A., T.E. McMahon, and A.V. Zale, 2007: "Comparative thermal requirements of westslope cutthroat trout and rainbow trout: Implications for species interactions and development of thermal protection standards." Trans. Am. Fisheries Soc., v. 136, pp. 1113-1121. DOI: 10.1577/T06-072.1
 Eby, L.A., W.J. Roach, L.B. Crowder, and J.A. Stanford, 2006: "Effects of stocking-up freshwater food webs." Trends Ecol. Evol., v. 21, pp. 576-584. DOI: 10.1016/j.tree.2006.06.016