Many economically important fish, like Chinook salmon (Oncorhynchus tshawytscha), have their habitats changed by dams built for hydropower and other reasons. We guessed that dams on the Rogue River, the Willamette River, the Cowlitz River, and Fall Creek cooled the water in the summer and warmed it up in the fall and winter. These thermal changes undoubtedly impact the behavior, physiology, and life histories of Chinook salmon. High temperatures in the fall and winter, for example, should speed up growth and development, allowing fry to come out early. Evolutionary theory provides tools to predict selective pressures and genetic responses caused by this environmental warming. To show this, we did a sensitivity analysis of the fitness effects of thermal changes caused by dams, which were mediated by the embryonic development’s thermal sensitivity. Based on our model, we think that the end result of building a dam in the Rogue River was probably bad for Chinook salmon. Still, these changes in population may have led to strong selection for ways to make up for it, like adults delaying mating or embryos growing more slowly. Because dams have different thermal effects at different times of the year, we think they had a bigger effect on late spawners than on early spawners. Similar analyses could shed light on the evolutionary consequences of other environmental perturbations and their interactions.
Although multiple factors have contributed to the decline of Pacific salmon (Oncorhynchus spp. Dams have probably played a big part in many places where they have been built in parts of their natural range (NRC 1996; Lichatowich 1999; Ruckelshaus et al. 2002). Big dams In particular, these dams have cut down on the space for spawning and raising fish, and they have changed the flows, sediments, and temperatures further downstream (PFMC 1979; Ward and Stanford 1979; Ligon et al. 1995).
Since the early 1900s, when the first big dams in the Pacific Northwest were built, many generations of salmon have hatched, grown, left, and then come back to spawn in the water downstream. Possibly, these fish have begun to adapt to the new thermal regimes caused by dams (Waples et al. 2008). We can’t draw conclusions about adaptation from the data we have access to, but we can guess how dams might affect evolution and talk about the kinds of data we would need to draw those conclusions. Under this premise, we present an exploratory analysis of Chinook salmon (Oncorhynchus tshawytscha) in four parts. First, we assess the historical changes in water temperatures downstream of large dams. Second, we review the effects of water temperature on physiological performance at specific life stages. Third, we estimate the degree to which changes in physiological performance would influence the fitness of genotypes. Finally, we assess the possibility of an evolutionary response to selective pressures imposed by dams.
Salmon have been swimming up rivers and streams to spawn for millennia. These amazing fish are born in freshwater, move to the ocean to eat and grow, and then go back to the streams where they were born to spawn and die. This migration is a part of their natural life cycle. But in the last 100 years, human infrastructure like dams has messed up this cycle and caused populations to drop sharply.
This article will talk about how dams affect the lives and reproduction of salmon. Dams physically block salmon migration routes, change the environments of rivers, and kill fish directly through turbine passage. Even though fish ladders and transport programs can help lessen the effects of dams, the presence of dams has ultimately caused the extinction of some salmon runs and put many more at risk. Find out the hidden story of how these famous Pacific Northwest fish are affected by dams by reading on.
Dams as Physical Barriers
One of the most obvious ways dams negatively impact salmon is by physically blocking their migration routes between the ocean and their spawning grounds. Salmon are anadromous fish, meaning they are born in freshwater, spend most of their adult life in the ocean, and then return to freshwater to spawn. Dams construct literal concrete walls across rivers that salmon historically used to access spawning habitat.
For example, over 40% of the historic spawning habitat for salmon and steelhead in the Columbia River Basin has been permanently blocked by dams. When the Grand Coulee Dam was built on the upper Columbia River in the 1930s, it eliminated access to over 1,000 miles of spawning habitat virtually overnight. Salmon populations that once returned to rivers like the Spokane and Upper Columbia were completely wiped out.
While fish ladders and trap-and-haul programs can help provide passage around dams they are not limitless solutions. Fish ladders have size and flow limitations, and trap-and-haul programs are costly and still have mixed success for fish survival. Essentially dams reduce and degrade accessible habitat for salmon reproduction. With less habitat, salmon populations decline.
Dams Alter River Habitats
In addition to physically blocking migration routes, dams drastically alter river habitats downstream in ways that are detrimental to salmon survival.
One major way dams impact downstream habitats is by submerging natural riverbanks and shoreline areas. Historically productive spawning areas have been permanently lost. For example, shoreline habitat was lost on the Columbia River behind John Day Dam and on the Snake River in Hells Canyon after dam construction.
Dams also create reservoirs which slow down river flows The stagnant water becomes warmer, reaching temperatures lethal for salmon Dams disrupt natural flow regimes and sediment transport downstream, altering river channel structure and food-web ecology. Even “run-of-river” dams without large reservoirs impact habitat through flow regulation.
Essentially, dams fundamentally transform downstream habitats from the high velocity, cold, free-flowing rivers salmon evolved to thrive in. Warmer, slower reservoirs provide conditions where predators can flourish, food-webs are disrupted, and disease spreads more readily among fish.
Salmon Killed By Turbine Passage
Perhaps the most direct way dams kill salmon is through turbine passage. At hydroelectric dams, juvenile salmon migrating downstream must pass through dam turbines or spillways to continue their journey to the ocean.
Inside dam turbines, the pressure changes and violent collisions kill 10-15% of juveniles outright. Those that survive turbine passage are often left stunned, injured, or disoriented, making them easy prey for birds, fish, and other predators below the dam.
When multiple dams must be passed, the accumulating mortalities are extremely high. For example, on the Snake River, salmon must pass through eight total dams. Even with a relatively low mortality rate of just 10% per dam, only about half the juveniles would survive the entire journey seaward. Fish populations cannot sustain these losses indefinitely.
While surface passage such as spillways help reduce turbine mortalities, dams remain an obstacle course where salmon regularly die. Protecting downstream migrants continues to be a challenge at all dams.
Can Salmon Coexist With Dams?
Dams provide many benefits like electricity, irrigation, and navigation. But they come at an enormous cost to native salmon populations. Extensive habitat loss and persistent direct mortality have led to the extinction of some Columbia Basin salmon runs and the endangerment of many more.
Mitigation measures like fish ladders and spillway passage have not fully addressed fish losses. Hatcheries produce more salmon, but those fish have lower reproductive success and genetic diversity. Salmon are resilient, but their population dynamics require diverse habitat and sustainable mortality rates.
In the ongoing debate between dams and salmon, there are no easy solutions. However, continuing to improve dam passage effectiveness, restoring surrounding habitats, enforcing harvest regulations, and reintroducing salmon to historic spawning areas will be key. With commitment from dam operators and fisheries managers, perhaps salmon can persist despite river changes caused by dams.
The iconic salmon migration is an important part of Pacific Northwest ecology, culture and economy. As we continue benefitting from dams, we must also continue seeking creative solutions that will allow salmon to complete their ancient migration cycle. By understanding the untold ways dams impact salmon survival, we can make more informed decisions about how to proceed. With dedication and care, wild salmon and dams may be able to coexist into the future.
Impacts of dams on water temperature
To figure out how much the water temperature changed downstream of a dam has changed, you need to know where the dam is, when it was built, and how hot or cold it was at different times. To connect changes in temperature to the behavior of Chinook salmon in particular, we need to know more about where populations are located. We compiled these data from a variety of sources (Willingham 1983; Myers et al. 1998; USACE 2000b; StreamNet 2005; City of Tacoma 2005; Kimbrough et al. 2006; Herrett et al. 2006; USGS 2007), and then imposed five criteria to identify several dams for our analysis. First, the dam had to reside upstream of a gauge that recorded water temperatures. Second, the gauge had to keep records for a number of years before and after the dam was built. Third, the dam had to be built on a river or big creek in Washington, Oregon, California, or Idaho that had Chinook salmon. Fourth, the gap between the gauge and the dam had to be Finally, no other large dam could exist upstream of the focal dam prior to its construction. Using these criteria, we selected four dams for analysis ( , ).
| Dam | Type | Location | State | Gauge number* | Dam-gauge distance (km) | Date of operation† | Beginning of record | End of record |
|---|---|---|---|---|---|---|---|---|
| Mayfield | ER | Cowlitz River | WA | 14238000 | 2.3 | 1962 | 1954 | 1982 |
| Fall Creek | HR | Fall Creek | OR | 14151000 | 1.8 | 10/1965 | 1951 | 2007 |
| Hills Creek | HR | Willamette River | OR | 14148000 | 17.9 | 1961 | 1950 | 1987 |
| Lost Creek | MR | Rogue River | OR | 14337600 | 4.5 | 2/1977 | 1970 | 2007 |
The gauges downstream of these dams contained two types of gaps in their records of temperature. The first group was made up of days when the lowest and highest temperatures were recorded but not the average temperature. For these days, we estimated the mean temperature by averaging the minimal and maximal temperatures. The second type comprised days when both the mean temperatures and extreme temperatures were missing. In these cases, we estimated the means by regression or interpolation (see Appendix A).
To figure out how each dam affected the temperature, we looked at the daily average temperatures from the years before and after the dam was built. Based on what we learned, the time of year affects how a dam changes the temperature of the water. During summer, water was generally cooler after a dam was built. Conversely, during the fall and early winter, water was generally warmer in the presence of a dam. This change from summer cooling to fall warming could be seen on the Rogue River as early as August and on the Cowlitz River as late as October.
Not only should the time of year affect how hot the water is after a dam, but so should the thermal stratification upstream and the depth of water released at the dam (Ward 1982; Crisp 1987; Poff and Hart 2002). If the reservoir upstream is thermally stratified and the dam draws water from below the thermocline (i. e. The water below the dam should be unusually cold in the summer and unusually warm in the fall and winter (the hypolimnetic layer). If the dam draws water from above the thermocline (i. e. , the epilimnetic layer), the water downstream should be unusually warm during the summer. Other dams draw water from multiple depths, enabling finer control over temperatures downstream. Since our sample had three different kinds of dams, we were surprised to find that they all had similar effects on water temperatures.
Consequences of dams for the performance of salmon
Salmon can be affected by dams in both direct and indirect ways, depending on how sensitive their bodies are to heat. Because temperatures in the fall can approach those that stress Chinook salmon (e. g. , see Fall Creek in ), warming by a dam could directly increase the mortality of embryos. Geist et al. found that short-term exposure to 2017%C2%B0C during embryonic development caused more than 2098% of the deaths that happened between fertilization and emergence (1). 2006). More likely, however, dams indirectly influence fitness by advancing the timing of emergence. Emergence is the stage of development when fry leave the interstitial gravel and enter the water column. This starts a long-term, free-swimming home in a stream or river. At this point in development, the yolk’s energy stores are almost gone, and the juvenile needs to start getting food from outside sources. Too many flows, too many predators, or not enough resources could kill plants that emerge too early or too late (Jensen and Johnsen 1999; Einum and Fleming 2000). A dam would warm the water in the fall and winter, which would speed up the development of embryos and cause them to come out early. Thus, a dam could disrupt a match between the actual and the optimal dates of emergence.
Adaptation of behavior or physiology would ameliorate the thermal effects of a dam. Because of seasonal cooling, if the salmon below the dam spawned later in the year, their young would be exposed to cooler temperatures (see). Because of this, development would move more slowly, and the time of emergence would be the same as it was before the dam. On the other hand, salmon could delay emergence even though the water below the dam is warm because of an evolutionary slowdown in the rate of development. It depends on how much each strategy costs and how it affects other parts of the life cycle to decide which would be more under selective pressure: spawning behavior or developmental physiology
As we’ve already talked about, the current models of thermal adaptation can’t give us a lot of information about how salmon react to dams. First, these models focus on physiological responses to environmental temperature (reviewed by Angilletta et al. 2002; Kingsolver and Gomulkiewicz 2003), ignoring the potential for behavioral responses that seem relevant to salmon (e. g. , timing of spawning, placement of nests). Also, these models think that temperature has a consistent effect on an organism’s ability to reproduce (Gilchrist 1995) or its ability to survive (Lynch and Gabriel 1987). As salmon grow, their thermal tolerances change, and so do the effects of dams on temperature. This means that simple models can’t accurately predict how strong selection will be. Here, we use a model that is based on age to look at how physical performance affects the fitness of a genotype. This approach should yield a better understanding of the selective pressures imposed by dams.
Debating Dams: What’s The Best Way To Protect Salmon?
How do dams affect salmon & steelhead?
Dams impact salmon and steelhead in a number of ways, from inundating spawning areas to changing historic river flow patterns and raising water temperatures. Dams block passage of salmon and steelhead between spawning and rearing habitat and the Pacific Ocean. Where fish passage is not provided the blockage is permanent.
Do dams block salmon spawning & rearing habitat?
Dams block passage of salmon and steelhead between spawning and rearing habitat and the Pacific Ocean. Where fish passage is not provided the blockage is permanent. More than 40 percent of the spawning and rearing habitat once available to salmon and steelhead in the Columbia River Basin is permanently blocked by dams.
How do dams affect salmon?
They are barriers to juvenile salmon migrating to the ocean, and an obstacle as adult fish return to their natal streams to spawn. Dams affect the way water moves down a river, by changing the amount and timing of flow, as well as its temperature and chemical characteristics.
How does a dam affect fish?
Changing a habitat from a river to a lake can have many negative effects on fish. Changing a habitat from a river to a lake can have many negative effects on fish. The presence of the dam may also change the way predators and prey interact. In many cases the negative effects of these changes are greater than the direct effects of the dam itself.