Grazing the ocean to death

Salmon farming in Alaska, also known salmon ranching, has been pumping billions of hatchery-raised smolts into the North Pacific for decades, causing a significant increase in competition for food with wild salmonids. Based on a recent study, these hatchery-raised fish may also be significantly altering the natural fitness of wild populations.

A study published last week, “A single generation of domestication heritably alters the expression of hundreds of genes”, by Christie et al., in the prestigious journal Nature Communications, clearly shows that, only after one generation of domestication, the genetic expression of steelhead (rainbow trout) is significantly altered.

The principal investigator, Dr Michael Blouin, said that this study shows at the genetic level, hatchery and wild fish are passing on different information to their offspring.

Declining wild populations of salmon have long been supplemented and restored by the intervention of hatcheries. However, as a kind of double-edged sword, substantial amounts of data indicates that hatchery fish have lower fitness in natural environments than wild fish, which could hinder the recovery of wild populations. However, the mechanism behind this decreased fitness has remained a mystery.

Blouin said their findings prove long-held suspicions about why the offspring of hatchery-raised fish are less likely to survive in the wild than the offspring of wild fish, and furthermore, that genetics plays a role.

The team conducted their study using wild and hatchery-raised steelhead from the Hood River, in Oregon. They bred the fish, then raised their offspring – batches of fertilized eggs with two wild parents, with two hatchery-raised parents, and with one wild parent and one parent from a hatchery – in identical conditions.

A comparison of the genetics of each class of fish revealed that fish with hatchery-raised parents differed in the activity of more than 700 genes when compared to fish with wild parents. The fish had all been reared in the same environment, and their parents had been caught in the same water.

"The only difference," Blouin said, "is who their parents were."

What is still unclear, is what environmental factors are driving the genetic difference, or what the traits are that are changing. These details may help hatcheries make changes to their facilities or fish-rearing conditions (eg, overcrowding) that would reduce the divergence.

Regardless, this study has much larger implications.

Currently, the largest population of “wild” hatchery-raised salmon is in Alaska – where billions of Pacific salmon (chum, pink, and sockeye) are raised in hatcheries and then released into the ocean to forage for feed, migrate back to the hatcheries, and then are commercially harvested and sold as “wild Alaskan salmon” – a practice known as “salmon-ranching”.

However, unavoidably not all ranched salmon are harvested, and according to this recent study, the multibillion-dollar Alaskan ranched salmon industry may be inadvertently reducing the genetic resilience of wild salmon populations by diluting the gene pool.

Over the past 15 years, on average, the Alaskan industry has introduced approximately 5 billion smolts/year. Not only does ranching create an artificially intense competition for food to native wild salmon (ranched salmon consume approximately 11 million tones of ocean-derived protein from the North Pacific a year) but (and perhaps the real threat here), ranching may also be significantly impacting the genetic diversity and resilience of wild populations.

This new and credible evidence will hopefully raise some serious questions about the validity of the targeted campaign against salmon farming in BC.

Instead of vilifying BC salmon farming – which has been shown to be significantly more efficient, produces healthy, affordable market fish all year round, does not compete with wild salmon for feed resources from the North Pacific, and does not have negative effects on genetic diversity of wild populations – why aren’t the protestors and people who “care about wild salmon” up in arms about the real, scientifically accepted threat committed by salmon ranching?

Farming fish by the billions in the common garden of the North Pacific has been allowed to operate, without constraint or public scrutiny, for a very long time. Perhaps this latest piece of scientific evidence will catalyze constructive debate around what aquaculture practices (farming or ranching) is truly the most sustainable one.

The wild salmon of the North Pacific depend on it.