But not create a separate species as you go through the generations.
From deep in the link-vault, Nautil.us Oceans, November 26, 2015:
The fish market has become the site of an ontological crisis. Detailed labels inform us where each fillet is from or how it was caught or whether it was farmed or wild-caught. Although we can now tell the farmed salmon from the wild, the degree of differences or similarities between the two defies straightforward labels. When a fish—or any animal—is removed from its wild habitat and domesticated over generations for human consumption, it changes—both the fish and our perception of it. The farmed and wild both say “salmon” on their labels, but are they both equally “salmon?” When does the label no longer apply?
This crisis of identity is ours to sort out; not the fish’s. For us, the salmon is an icon of the wild, braving thousand-mile treks through rivers and oceans, leaping up waterfalls to spawn or be caught in the clutches of a grizzly bear. The name “salmon” is likely derived from the Latin word, “salire,” to leap. But it’s a long way from a leaping wild salmon to schools of fish swimming in circles in dockside pens. Most of the salmon we eat today don’t leap and don’t migrate.
We now manage salmon’s evolution—even to the point of genetically modifying them to grow faster.More than 90 percent of all the adult Atlantic salmon now on the planet are thought to be in salmon farms and almost all Atlantic salmon available in the United States at your local market is from a farm. This rise of the farmed salmon, and the decline of native ones, is casting the definition of species into doubt and in the process tweaking our relationship to nature. In a 1998 paper, Mart Gross, a conservation biologist, called for the recognition of a new creature, Salmo domesticus.
“Domesticated salmon are about as different from wild salmon as dogs are from wolves,” says Gross, a professor at the University of Toronto. Like dogs, these salmon now depend on humans for habitat and food, and we manage their evolution—even to the point of genetically modifying them to grow faster.....MUCH MORE
Salmon species aren’t the first to undergo this identity shift at our hands, but the transformation from a wild to domestic species has seldom happened as quickly. We are watching this one unfold within a single human lifetime. To Gross and other scientists, the rapid transformation epitomizes our Anthropocene epoch, where nature can no longer be separated from humans.
After Pacific and Atlantic salmon were separated, likely about 15 million years ago following the cooling of the Arctic Ocean, they continued to subdivide until, about 6 million years ago, today’s species emerged—one in the Atlantic and six in the Pacific. Over time, they further subdivided, in both ocean basins, into a multitude of genetically and morphologically distinct populations, custom-built for specific rivers and migration routes.
In the 1960s, a novel evolutionary event began to take place, and those distinctions began to fade. Norwegians began raising salmon in pens in fjords, industrializing the process so they controlled the entire means of production, roe to fillet. They weren’t the first to farm fish, but domesticizing a carnivorous fish that migrates thousands of miles through both fresh and saltwater was something new. The ecological impacts of raising such a fish in a concentrated pen aside, the farms provided a reliable, controlled supply of salmon for communities and, later, export.
That control also meant farmers could select for faster-growing, bigger, more docile fish, and over time the salmon inside the pens began to genetically diverge from the wild ones swimming by. Studies have described a “parallel evolution” in which wild and farmed salmon in Canada and Norway have become significantly different genetically over just five to seven generations of selective breeding. That artificial selection, through technological advances, is happening faster than the domestication of chickens, pigs, or cows.
Marianne E. Lien is an anthropologist at the University of Oslo. In 2015, she published a book, Becoming Salmon: Aquaculture and the Domestication of a Fish, on the history and transformation of salmon aquaculture. As salmon are bred toward an increasingly homogenous, market-ready ideal, she says, their origins—adaptations to natal rivers and specific migration routes—are gradually being erased.
That matters because net pens can tear and mooring lines can break. A storm in central Norway in August 2005, for instance, broke lines and set free nearly a half million farmed salmon. In the North Atlantic, those escapees can interbreed with the remaining wild fish, pushing Atlantic salmon as a whole down a new evolutionary path on a much faster time scale than ever before.
Studies have found “hybrid” farmed-wild offspring have weaker genetic adaptations for the rivers and migratory paths of the wild. One study has found these interactions could potentially cause an “extinction vortex in vulnerable populations.” Hybrids are also reversing the genetic divergence in which salmon have evolved to thrive in unique rivers and conditions. Another study has forecast a decrease in “population differentiation” between previously distinct populations. “Now, salmon are distinguished in a new way—through the traits you select for in farming,” says Lien.
As salmon are bred toward an increasingly market-ready ideal, their origins are gradually being erased.Over time, Atlantic salmon farming operations spread to new corners of the oceans. Farms in Chile and New Zealand brought Atlantic salmon to the other side of the world. Farms in British Columbia put Atlantic salmon right in the middle of Pacific salmon species’ habitat. There are now more Atlantic salmon on the planet than there have ever been before, a large proportion of them are nowhere near the Atlantic, and nearly all of them depend on humans for their habitat.
This is a direct reversal of the past hundred or so years of human-salmon interactions, in either ocean. In some ways, the domestication of salmon began long before large-scale farms came about, as they had to learn to adapt to living alongside our expanding communities, navigate dams and fish ladders and tolerating changing water conditions due to pollutants and lower water levels....