F. Sherwood Rowland was an atmospheric scientist who studied inert gases, namely chlorofluorocarbons (CFCs), widely used as refrigerants and aerosol propellants. In a 1974 paper in Nature, he first recognized the threat that CFCs posed to the Earth’s ozone layer. As the story goes, one evening he remarked to his wife, Joan, that the research “is going very well, but it may mean the end of the world.” His research and associated “fear and doom” led to global environmental action to eliminate CFCs, which were eventually banned. Rowland’s research saved the planet; it did not mean the end of the world.
Today, most atmospheric scientists accept the reality of global climate change and each year new records are set (Feltman 2017). Yet, many atmospheric scientists who study global climate are criticized for framing the climate change with language that connotes fear and doom. Researchers Michael Mann and Lee Kump, in Dire Predictions: Understanding Climate Change, present the evidence to support the contention that climate change is real, caused by human activities, and is already a threat. There is no longer any excuse for delaying a shift away from fossil fuel energy. The research is based on basic principles of physics and chemistry that allow us to predict that the Earth will warm as concentrations of greenhouse gases increase. Of course, Mann and Kump have been criticized for creating alarmism in the climate sciences.
|Number of years per decade that had above-average temperatures—and how many of those years rose a half, or even a whole, degree above the norm (Feltman 2017).|
We do not know how fishes will adapt to a warmer earth. The science involves physics and chemistry of aquatic ecosystems as well as many other fields of inquiry. Those who fish have already observed changes in their catches as warm-water fish are increasing observed in northern latitudes or high elevation waters. Managing fish in a warming world will prove to be extremely complicated as fish re-distribute or adapt to the changing conditions.
Some changes are already evident. For example, Neala Kendall, Gary Marston, and Matthew Klungle, from the Washington Department of Fish and Wildlife, reported on the decline in ocean survival and abundance of Steelhead Trout (anadromous Oncorhynchus mykiss), raising concerns about long-term viability of stocks in the Puget Sound and south. However, over the study period, temperature does not have a simple relationship to smolt survival. This region has also undergone an ecosystem shift of the past several decades leading to demersal fish declines and increases in harbor seal Phoca vitulina and harbor porpoises Phocoena phocoena (both smolt predators). Consequently, forecasting future changes will be highly uncertain depending on behavior of multiple predators.
Perhaps fish in other smaller, inland systems will be easier to understand. In Michigan, streams with higher relative groundwater inputs are less sensitive to temperature changes and, therefore, more suitable for Brook Trout (Salvelinus fontinalis), Brown Trout (Salmo trutta), and Rainbow Trout (Oncorhynchus mykiss) (Carlson et al. 2017). Observed stream temperatures in Shenandoah National Park were also less sensitive to air temperature due to the moderating effect of shallow groundwater inputs (Snyder et al. 2015). Consequently, these coldwater thermal refugia will become even more important in the future. Policymakers and stakeholders should map and protect these habitats to conserve salmonid populations as the climate warms. Moreover, this management action is correct no matter whether the water temperature increases 2 or 4 °C in the next 50 years. Perhaps, the action can be generalizable to other regions (Isaak et al. 2015; Myers et al. 2017).
However, much of the research to date assumes the species traits and other aspects of aquatic communities do not change. Novel research to explore shifts in species traits (Ayllón et al. 2016) is necessary to realistically evaluate long-term changes in response to climate change. Evidence of evolutionary responses to climate change is limited to observations of shifts in timing of migration and spawning.
|Species distribution model predictions of probability of occurrence for the Kanawha Minnow Phenacobius teretulus and Appalachia Darter Percina gymnocephala in the New River drainage (Huang et al. 2016).|
Freshwater fishes face losses due to many factors in addition to climate change. Habitat loss, fragmentation of habitat, pollution, hydrologic alteration, invasive species, and overexploitation are pervasive issues. Compared to salmonids, relatively little work has been done to assess the risk of climate change on other freshwater fishes. Species distribution models have been applied to fishes in the United States. Because the distributions are very sensitive to climate and land use, they may prove useful to projecting new distributional patterns given an altered climate (Bouska et al. 2015; Huang et al. 2016). In southern Appalachia, many cold and coolwater fishes on private lands are most at risk for local extirpations. The species distribution models for two coolwater endemic fishes, Kanawha Minnow Phenacobius teretulus and Appalachia Darter Percina gymnocephala, demonstrate the importance of remaining coolwater fragments that support the only surviving populations of these species. Similarly, some rare headwater fishes, such as the Clinch Dace (Chrosomus sp. cf. saylori), have no other cool places to move when temperatures rise.
|Clinch Dace is a headwater specialist with very limited distribution in Virginia. Photo: D.J. Orth|
The Smallmouth Bass Micropterus dolomieu is a popular game species whose distribution will shift northward as thermal regimes warm. However, the Smallmouth Bass may contract in the southern extent of its range where groundwater refugia are lacking. In the southern parts of the range, growth is slow and summer growth may be limited by climate (Brewer 2013).
|Seasonal growth curve for Smallmouth Bass from a stream at the southern edge of the native range. Median length at age is typically 20% longer. (Orth et al. 1983).|
Lynch et al. (2016) reviewed 31 studies that documented fish responses to climate change in inland waters of North America. Most have dealt with the valuable stocks of Pacific salmon. In Ontario lakes Smallmouth Bass may demonstrate enhanced recruitment, survival, and dispersal with warming temperatures. In the arid southwest, climate change changes flow, thereby influencing reproductive phenology of fishes and reducing river-floodplain connectivity. In the diverse streams of southeastern US, the interaction of climate change and pervasive anthropogenic influences makes it difficult to separate the interacting causes. However, many stenothermic fishes are replaced by more eurythermic fishes. Lynch et al. (2016) make a number of recommendations for future research. Importantly, they highlight the importance of identifying processes that buffer fishes from climate change, such as groundwater upwelling, phenotypic plasticity, and adaptive microevolution. Research on resilience is lacking.
|Documented responses of fishes in the southeastern USA to climate change. Green arrows indicate an increase or earlier seasonal response, and gray arrows indicate a decrease or later seasonal response (Lynch et al. 2016).|
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Bouska, K.L., G.W. Whitledge, and C. Lant. 2015. Development and evaluation of species distribution models for fourteen native central U.S. fish species. Hydrobiologia 747: 159. doi:10.1007/s10750-014-2134-8
Brewer, S.K. 2013. Groundwater influences on the distribution and abundance of riverine Smallmouth Bass, Micropterus dolomieu, in pasture landscapes in the midwestern USA. River Research and Applications 29:269-278.
Carlson, A.K., W.W. Taylor, K.M. Schlee, T.G. Zorn, and D.M. Infante. 2015. Projected impacts of climate change on stream salmonids with implications for resilience-based management Ecology of Freshwater fish 26:190-204.
Feltman, R. 2017. Don’t believe our planet is warming up? Look at this. Popular Science. July-August. Accessed July 13, 2017, at http://www.popsci.com/climate-change-infographic-our-warming-planet
Huang, J., E.A. Frimpong, and D.J. Orth. 2016. Temporal transferability of stream fish distribution models: can uncalibrated SDMs predict distribution shifts over time? Diversity and Distributions 22:651-662.
Isaak, D.J., M.K. Young, D. E. Nagel, D. L. Horan, and M.C. Groce. 2015. The cold-water climate shield: delineating refugia for preserving salmonid fishes through the 21st century. Global Change Biology 21:2540-2553.
Lynch, A.J., B. J. E. Myers, C. Chu, L.A. Eby, J. A. Falke, R. P. Kovach, T.J. Krabbenhoft, T.J. Kwak, J. Lyons, C.P. Paukert, and J.E. Whitney. 2016. Climate change effects on North American inland fish populations and assemblages, Fisheries, 41(7):346-361.
Middaugh, C.R., B. Kessinger, and D.D. Magoulick. 2016. Climate-induced seasonal changes in smallmouth bass growth rate potential at the southern range extent. Ecology of Freshwater Fish DOI: 10.1111/eff.12320
Myers, B.J.E., C.A. Dolloff, J.R. Webster, K.H. Nislow, B. Fair, and A.L. Rypel. 2017. Fish assemblage production estimates in Appalachian streams across a latitudinal and temperature gradient. Ecology of Freshwater Fish DOI: 10.1111/eff.12352
Orth, D.J., D.D. Oakey, and O.E. Maughan. 1983. Population characteristics of smallmouth bass in Glover Creek, southeast Oklahoma. Proceedings of the Oklahoma Academy of Science 63:37-41.
Pease, A.A., and C.P. Paukert. 2013. Potential impacts of climate change on growth and prey consumption of stream-dwelling smallmouth bass in the central United States. Ecology of Freshwater Fish 23:336-346.