Salmon & Survival
Why Native and Hatchery Salmon are Different
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The Coast Range Association
Salmon & Survival Why Native and Hatchery Salmon are Different |
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Domestication Selection
Why are hatchery fish so different? Salmon biologists point to the very foundation of the hatchery concept: the way hatcheries boost the numbers of eggs that survive to smolthood. Most scientists now believe that nature has good reasons for letting so many salmonid eggs and juvenile salmonids die in the wild. This high natural mortality early in the salmonid life cycle isn't random, even if humans don't know all the reasons for it. That natural selection ultimately strengthens stocks by weeding out the weak. Hatcheries bypass this natural process. Keeping more eggs alive unnaturally also alters the balance of traits in a salmonid population. The only known results of that altered balance are negative.
In the river, genes are selected for fitness in the wild. In a hatchery, fish are selected for just the opposite: domestication. Scientists say that this "domestication selection" in hatcheries is unavoidable, leads to lower survival of the fish in later life stages, creates fish less able to reproduce successfully and irrevocably adds genes to the general population that counter millennia of wild evolution. (Busack and Currens, 1995)
In a March, 2000 letter to the Wall Street Journal, the Oregon Department of Fish and Wildlife wrote that "practices at hatcheries maximize survival during the early life stages of the fish. Thus, weaker, inferior individuals are not selectively removed from the population as they are in the wild. Over time, this ultimately weakens fish populations. The second and third generation of hatchery fish do not produce viable offspring." (Wall Street Journal, 2000)
| Altered Reproductive, Life History and Behavioral Traits: |
| ·Reduced Egg Size and Numbers |
| ·Earlier Age-at-Maturation |
| ·Juveniles Feed Near Water Surface |
| ·Poor Predator Avoidance |
| ·Reduced Secondary Sex Traits |
Domestication selection sometimes occurs in the way that hatchery managers choose which fish to allow to reproduce. Early hatcheries took eggs from the first salmon to return to spawn. The next generation returned to spawn early, like their parents. And since there were no parents who spawned later, the whole hatchery run time was compressed to a small window in the season. Wild fish return over a longer period as a hedge against too much or too little rain, or other environmental factors. With the run time simplified by the choice of hatchery managers, the resulting fish are more vulnerable to predictably unpredictable weather events.
Humans also don't know how salmon choose their mates, but nevertheless play matchmaker among the fish in the hatchery. According to the National Research Council, "the practice of making artificial matings - now the dominant hatchery method - is a serious concern because it disrupts natural patterns of sexual selection with negative implications for fitness of hatchery fish in natural environments… The most effective breeders in general are few, implying that this process of sexual selection is extremely intense and important evolutionarily. In hatcheries, the whole process is bypassed… The human breeders have no way of identifying the genetic relatedness of spawners or fish that would be the best breeders. Although not all the effects of this inadvertent interference with natural selection are precisely known, it is almost certain that one result is loss of general vigor, adaptation to local environments, and evolutionary fitness." (National Research Council, 1996)
Some studies, for instance, have found substantial differences in the fertility of male chum salmon. If those differences have a genetic basis, then human intervention in the mating process could favor less fertile genes and add those genes in great numbers to the greater population. "Indeed, some direct evidence shows that genetic differences in reproductive behavior have resulted from the bypassing of sexual selection in hatcheries." The authors added that repeated artificial selection reduces the number of genes that adapted together, "closing off options for evolution and jeopardizing long-term persistence of the population." (National Research Council, 1996)
Other results of this domestication selection are that hatchery salmon survive less well to adulthood, produce both fewer and smaller eggs and return at a younger age to spawn. Their overall diversity is diminished, their survival is poorer and their offspring less likely to reproduce. One study found that it takes five times as many hatchery fish as wild fish to produce two adults for the next generation. (Fleming and Peterson, 2001). Another found that hatchery males had only 46 percent of the reproductive success of their wild counterparts while hatchery females had 82 percent of the reproductive success of wild females. (Fleming and Gross, 1993)
Perhaps the most chilling problem with domestication selection is that scientists say it is permanent. The natural selection hatchery fish face after they are released into the wild does not cancel out the domestication selection of the hatchery. In other words, hatchery fish, even in the very first generation after eggs are taken from the wild, will always be different from wild fish. And those diminished fish can and do harm their wild counterparts by their presence and by interbreeding.
The changes also happen fast: "Gene flow from hatchery fish also is deleterious because hatchery populations genetically adapt to the unnatural conditions of the hatchery environment at the expense of adaptedness for living in natural streams. This domestication is significant even in the first generation of hatchery rearing." (Reisenbichler, 1994)
Outbreeding Depression
When domesticated hatchery fish mate with wild fish, scientists say the well-adapted genes in the wild fish are diluted in a process called "outbreeding depression." Outbreeding depression is the exact opposite of the "hybrid vigor" well known to gardeners, in which a cross between two varieties of a plant produces hardier or more productive offspring. Because wild fish are so precisely tuned genetically to their native streams, the introduction of almost any non-native trait will reduce their ability to survive.
| Homing Ability of Native and Exotic Salmon | ||
| Treatment | Percent Accurate Homing | |
|---|---|---|
| Pure Native Stock | 86% | |
| Hybrid (Native x Exotic) | 46% | |
| Pure Exotic Stock | 22% | |
One 1976 study looked at the ability of native, non-native, and native-non-native hybrid hatchery fish to return to the streams in which they were born. The pure native stock returned to the right place 86 percent of the time. The hybrid stock - which had a percentage of local genes - returned accurately 46 percent of the time. The pure exotic stock returned only 22 percent of the time. The study concluded that salmon need more than rearing to know where home is - they also need something in their genes. The "degree of within-river homing in all hatchery-reared fish was strongly associated with frequency of inherited local genes," the authors reported. (Bams, 1976)
| Summer Steelhead Disease Resistance to Certatomyxa shasta by Stock in the Willamette River | ||
| Stock Crosses | Percent Mortality | |
|---|---|---|
| Skamania x Skamania (Native Columbia River) | 3% | |
| Umpqua x Umpqua (Non-Native, Coastal) | 99% | |
| Siletz x Siletz (Non-Native, Coastal) | 97% | |
| Native To Non-Native Crosses | Percent Mortality | |
| Skamania x Umpqua | 49% | |
| Skamania x Siletz | 68% | |
In 1982, the Oregon Department of Fish and Wildlife looked at disease resistance in Oregon's Willamette River of local, non-local and hybrid summer steelhead. Fish from the Skamania hatchery, on a tributary of the Columbia River, resisted the disease well - only 3 percent fell victim to it. Coastal Umpqua and Siletz river fish, taken from nearby but isolated rivers, nearly all perished - 99 percent of the Umpqua fish died, as did 97 percent of the Siletz fish. When the Siletz and Umpqua fish were crossed with the Skamania fish, the resulting hybrids did better than their non-local parent but much worse than their native one. Of the Skamania-Umpqua fish, 49 percent died. Of the Skamania-Siletz fish, 68 percent died. It is true that the pairing helped the non-native fish, but ultimately it did more harm to the native fish to introduce genes incompatible to the Columbia River system.
This type of effect is typical of mixing salmonid runs, which often occurs through hatcheries. The offspring of such crosses are less able to survive than their wild, native parents. Scientists believe that salmon have evolved groups or complexes of genes that all work together to help them thrive in their home rivers. Outbreeding breaks up those complexes and introduces genes that are not locally adapted. If those hybrid fish persist in the system, so will the genes that leave local runs open to disease. The simple act of introducing foreign fish - even from nearby, but isolated streams - significantly undercut thousands of years of evolution that allow the Skamania fish to thrive in the presence of disease.
Speed of Changes
Not only do the genetic incursions of hatchery fish remain permanently in the wild population, genes can change after just one hatchery generation.
A 1992 study of spring chinook salmon in the Tucannon River of southeastern Washington found that the returning hatchery fish were younger and smaller than their wild counterparts of the same age. They also were less fertile compared to wild fish of the same size. It is not clear why these changes occurred, but scientists say it is significant that such a substantial reduction in productivity occurred after a single generation in the hatchery. (Bugert, 1992)
Other studies have found that hatchery populations of chum salmon can develop at unusual rates because of changes in water temperature in those hatcheries. These changes showed up genetically in about 6 years, or about 3 generations. (Lannan, 1980)
Further complicating matters is the fact that the tools scientists have for looking at salmon genes don't tell us anything about the specific genes that matter most for survival - genes that determine how big a fish grows, when it returns to spawn, or how it survives diseases. According to Robin S. Waples, director of the conservation biology division of the National Marine Fisheries Service in Seattle, "this means that artificial propagation could substantially harm natural populations long before there is any reasonable expectation of being able to detect it." (Waples, 1999)
IN THE WATER
All of these theoretical issues have direct and measurable consequences in the waters where salmon live. The effects show up in every stage of the salmon's life, from hatching through spawning, and overall in terms of general ability to survive and in the diversity of traits that have helped salmon survive longer than most other species we know.
Salmon's basic survival strategy is to maintain in its population a broad diversity of precisely honed adaptations to the natural range of fluctuations in a given river. Hatchery fish reduce that diversity, and consequently impair the ability of the species to meet successfully an historic range of challenges.
One way the fish diversify to survive is by lengthening or shortening the time adults spend in the ocean. This is a hedge against one bad spawning year - for instance, a year in which a landslide smothers the eggs waiting to hatch - or even against two or sometimes three bad years. More time in the ocean is a risk for the fish, because it is more likely that they will be caught by predators. But if they survive, older, larger fish generally are more fertile, translating into a greater likelihood of successful offspring.
| Winter Steelhead Age of Wild and Hatchery Fish in Kalama River | ||
| Salt Water Age | Percent of Population Represented by Wild Steelhead | Percent of Population Represented by Hatchery Steelhead |
|---|---|---|
| 1 | 1.5 | 1.2 |
| 2 | 79 | 89.7 |
| 3 | 18.6 | 9.1 |
| 4 | 0.9 | 0.0 |
Age Diversity
In 1957, the Oregon Department of Fish and Wildlife compared wild and hatchery steelhead returning to the Alsea and Wilson Rivers. Most of the returning wild fish (66.4 percent) had spent two or three years (25.6 percent) in the ocean. A smaller number yet (5.4 percent) had spent only one year and an even smaller number (2.4 percent) had spent four years. The fish had a good spread of time in the ocean, taking advantage of a full range of possibilities - and traits to pass on to their surviving offspring. By contrast, the hatchery fish were almost all (89.9 percent) individuals that had spent two years at sea. Only 4.6 percent had spent one year out and 5.5 percent had spent three years. None had spent four years in the ocean. (Oregon Department of Fish and Wildlife, 1957)
The Alsea and Wilson rivers are not unique in this. In 1980, the Washington Department of Fish and Wildlife reported similar numbers when it considered wild and hatchery winter steelhead in the Kalama River. Among the wild fish returning, 1.5 percent had spent one year in the ocean, 79 percent had spent two, 18.6 percent had spent three and just under 1 percent had spent four. Like the Oregon coast fish, the wild Kalama steelhead spread their returns over four years with a substantial two- and three-year-at-sea component. Conversely, the hatchery steelhead again showed no four-year-at-sea returns, and a smaller percentage of one year (1.2 percent) and three year (9.1 percent) at sea fish. Most of the hatchery fish (89.7 percent) returned after two years in the ocean. (Chilcote, 1980)
These numbers are significant. Two to five times more wild fish took a third year in the ocean in these studies. That extra year at sea can as much as double the weight of a salmon and is generally understood to increase the fish's ability to produce numerous, healthy offspring. None of the hatchery fish waited until year four to return, also a loss of reproductive potential. If the hatchery fish lived to spawn, or spawn with wild fish, they would pass on traits that favor shorter ocean sojourns, decreasing the possibility of longer ocean terms and therefore greater reproductive success of the population as a whole.
Ocean Survival
Many studies show that hatchery fish survive poorly after they are released to the wild. In Washington's Kalama River, wild, native steelhead survive six to 12 times better in the wild than do hatchery fish. (Washington Department of Fish and Wildlife, 1980)
A third more wild Alsea River coho survive (2.9 percent) compared to their hatchery counterparts (1.9 percent), their disease resistance is high while the hatchery coho's is low, and their ocean migration ranges all the way south to California while the hatchery fish stay in a narrow band along the Oregon coast.
Hatchery fish in general fare poorly in the ocean, an effect not just limited to Alsea and Kalama River fish. The Idaho Cooperative Fishery Unit, looking at data from the late '60s and early '70s, reported in 1983 that wild steelhead returns were phenomenally higher than hatchery returns. Even though fewer individual steelhead came back than hatchery steelhead, in 1969 for instance, 44 times more wild fish returned than hatchery fish as a percentage of the total run.
Returns from the first year of the release of juveniles from a spring chinook supplementation hatchery on the upper Yakima River indicate a similar if less dramatic effect. Although more than twice the number of hatchery smolts (386,048) were released in 1999 than were estimated to have been produced naturally in the river under optimistic assumptions (157,500), the absolute number of returning adults (age-3 jacks plus age-4 adults) was nearly identical (7,104 hatchery; 5,540 wild). The wild fish were nearly twice as likely to survive in the ocean as were the wild fish - 3.52 percent of the wild smolts returned as adults while only 1.84 percent of the hatchery smolts did. (Gayeski, 2002)
Survival was estimated for both wild and hatchery smolts from the 1997 brood year migrating from the upper Yakima River in 1999 to the return of 3- and 4-year-old adults in 2000 and 2001. The estimate of maximum numbers of wild smolts migrating from the upper Yakima in 1999 was based upon an the spawning of approximately 350 wild females with estimated fecundities of 4,500 eggs each, estimated egg-to-fry survival of 50%, and estimated fry-to smolt survival of 20%.
Run Timing
Run timing is also changed. By spreading the migration back from the ocean over a long period, a deme maximizes the possibility that some fish will be able to take advantage of optimal spawning conditions when they occur. Hatchery fish, because of their simplified genetics, return from the sea during a narrower window. For instance, wild steelhead returning to the Quinault River in Washington spread their return over a 17-week period. The hatchery run is all but petered out after about 10 weeks. While this may help fishermen maximize their catch in a short time, it only harms any wild fish with which the hatchery fish interbreed.
Reproductive Success
Hatchery fish also are less successful at reproducing themselves than their wild counterparts. According to Washington State research on the Kalama River, it takes 10 adult hatchery steelhead to get two adults back to the river, while only two wild adults are needed to achieve the same result.
"Available data suggest progressively declining fitness for natural rearing with increasing generations in the hatchery. The reduction in survival from egg to adult may be about 25 percent after one generation in the hatchery and 85 percent after six generations. Reductions in survival from yearling to adult may be about 15 percent after one generation in the hatchery, and 67 percent after many generations." (Reisenbichler, 1996)
Some transplanted stocks are less productive than locally adapted populations and hatchery populations are generally less productive in nature than native locally adapted populations. (Leider 1990, Reisenbichler 1996, Chilcote 1986) Introductions of hatchery fish into a river system can also displace wild fish or reduce their abundance. (Nickelson, 1986)