Information on Salmon Genetics and Listing under the Endangered Species Act


Information on Salmon Genetics and Listing under the Endangered Species Act

Information on Salmon Genetics and Listing under the Endangered Species Act


4/14/2000 — — Contact:
*Jeff Reardon, New England Conservation Coordinator, Trout Unlimited, (207)882-4791;
*Leon Szeptycki, Eastern Conservation Director, Trout Unlimited, (804) 984-4919

Critics of the proposed listing of Atlantic salmon question the genetic lineage of Maine salmon. Due to stocking and/or introgression of genes from escaped aquaculture fish, these critics say, the genetic integrity of the wild salmon that once lived in Maine has been compromised. Therefore, the salmon swimming in Maine rivers today no longer have natural value and are not worth saving. This argument is at the heart of the state of Maine’s resistance to listing salmon under the Endangered Species Act (ESA).

The fact is that the available scientific information clearly demonstrates that Maine salmon retain distinctive genetic and biological characteristics that distinguish them from all other populations of Atlantic salmon. This information is of two primary kinds: (1) state-of-the-art genetic research that has been peer-reviewed and accepted for publication in internationally recognized scientific journals; and (2) over 120 years of empirical data on the life history traits of Maine, Canadian, and European salmon.

Genetic Evidence
Several kinds of genetic analysis using two kinds of DNA from Maine, Canadian, and European salmon show clear evidence that North American salmon are very divergent (or distinct) from European salmon. Within North America, there are also clear genetic differences between Maine salmon and Canadian salmon. These differences are dramatic enough that assignment tests-a statistical analysis of where an individual fits into a population-correctly distinguish between North American and European salmon greater than 99% of the time. The same tests correctly assign Maine vs. Canadian fish over 90% of the time.

This analysis alone is compelling evidence that there is such a thing as a “Maine salmon,” and that Maine salmon are distinct from other populations of the species. Another significant finding is that within the Maine population, individual rivers also show differences from each other. One population–in tiny Cove Brook, a tributary of the Penobscot River–is absolutely unique.

This evidence directly contradicts claims that the genetics of Maine salmon have been “mongrelized” or homogenized by stocking with fish from sources outside of Maine. That claim, made most prominently in the 1996 Report of the Salmon Genetics Committee of the Maine Atlantic Salmon Task Force, assumes that because large numbers of fish, especially Canadian fish, have been stocked in Maine rivers since the 1920s, they must have “swamped” the gene pool of Maine’s original wild salmon stocks.

This argument flies in the face of the documented genetic distinctions between fish from Maine and from Canada. In addition, peer-reviewed scientific journals have accepted the genetics work done by the U.S. Geological Survey, and relied on by the listing proposal. The Genetics Committee report has neither been peer reviewed nor published in the scientific literature.

Life History
Like all Atlantic salmon, Maine salmon return to the river they were born in to spawn, finding their natal river with 98% accuracy. Since 1960, only one fish from outside of the U.S. (not counting aquaculture fish) has ever been detected in a Maine river. The salmon’s homing instinct ensures that the fish are “reproductively isolated” from other salmon populations. Over the centuries, this isolation has allowed Maine salmon to develop traits that distinguish them from other salmon populations-and which make them uniquely suited to life at the far southern end of the Atlantic salmon’s range. Biologists noted many of these differences between Maine and Canadian salmon in the late 1800s, and they have persisted into the 21st century.

  1. Age at Maturity. In Canada, a large proportion of the salmon run consists of fish that mature and return to spawn after only one winter at sea (these fish are known as “grilse”). In Maine, grilse are quite rare, and the vast majority of salmon return as larger, two-sea winter salmon. These differences were first documented in 1874, and they persist today, despite stocking of fish from Canada and aquaculture strays. When Canadian salmon were used to stock Maine rivers, a larger proportion of the run was made up of grilse (as is normal in the river used for a broodstock source), but this characteristic did not persist in later generations.
  2. Habitat. Maine salmon exist at the far southern end of the North American range of salmon. The populations proposed for listing all inhabit relatively short coastal rivers with small drainage areas, as opposed to the large rivers with many tributaries more common in nearby sections of Canada.
  3. Persistence. In the rivers proposed for listing, wild salmon are well documented in the 1800s, 1920s, 1940s (when Maine still had a commercial salmon fishery), 1960s, 1980s, and today. Since the 1970s, over 80% of all fish that returned to Maine rivers were of wild, rather than hatchery, origin. In short, Maine salmon never went extinct, and, despite heavy stocking, the majority of fish that returned to spawn were the product of wild reproduction.

America’s Last Salmon
Even if Maine salmon were exactly like salmon in Canada-and many sources of empirical information demonstrate that they are not-they would still qualify for ESA listing. The clutter of scientific data and professional innuendo should not be allowed to obscure one very simple fact:

These populations–along with a few other wild populations not proposed for listing at this time–are the last remnants of the hundreds of thousands of salmon that once swam up U.S. rivers from the St. Croix to the Connecticut. Everywhere in the U.S. except Maine, wild Atlantic salmon have already been lost. Here, we have one tiny fragment left. Like bald eagles, puffins, and other creatures that are endangered in the U.S. but have healthy populations elsewhere, it is our responsibility to protect these last remnants using the tool that was designed for exactly this situation: the Endangered Species Act.

(Note: Bald eagles and puffins are no longer threatened with imminent extinction in the U.S. because of the unified state, national, and international effort inspired by their listing.)

Information in this document comes from three principal sources:

  1. “Review of the Status of Anadromous Atlantic Salmon (Salmo salar) under the U.S. Endangered Species Act.” Prepared by the Biological Review Team, July 1999
  2. “Maine Atlantic Salmon, A National Treasure.” Ed Baum. Atlantic Salmon Unlimited, 1997.
  3. “Atlantic Salmon Conservation Plan for Seven Maine Rivers.” The Maine Atlantic Salmon Task Force. December 1996 Draft.

Date: 4/14/2000