Published on Friday, December 22, 2000 by Agence France Presse
Salmon in Gender Crisis
Pollution seen as probable cause
SEATTLE - Sexual identity may be a problem facing the Pacific Northwest's endangered wild salmon runs, according to the findings of new research into gender of the fish.
A study of the chinook-salmon run in the Columbia River's most fertile spawning ground late last year found that 80 percent of the spawning female fish probably began life as males.
The findings surprised the study's lead author, James Nagler, a University of Idaho zoologist.
"The research raises more questions than answers," Nagler told AFP.
He believes that the sex changes could be caused by pollutants or water temperature changes.
However, ruled out as a cause is radiation seeping from the nearby Hanford Nuclear Reservation. The amount of radioactivity known to be going into the river is too small to have produced such changes, according to the study's authors.
The possible "sex reversal" of salmon could have a significant impact on efforts to preserve the genetic traits of wild runs.
The study by Nagler, Gary Thorgaard, a fish geneticist at Washington State University, and two other researchers, was published last week in Environmental Health Perspective, a journal of the National Institute of Environmental Sciences.
Researchers sampled 50 female and 50 male chinook in Hanford Reach, the last free-flowing stretch of the Columbia River -- and its most fertile spawning ground. Most of the female fish carried a genetic marker found only in male salmon.
"What we've got is an interesting observation with many unknowns," said Nagler.
"This could be a contributing factor, coupled with all the other burdens on the backs of these fish, that tweaks the health of these populations. It could be the tip of a pretty significant iceberg," he said.
"There's no reason this couldn't happen," said Paul Bentzen, a geneticist at the University of Washington Fisheries Department. "Sex determination is more relaxed in fish than in humans or other animals."
Nagler said the sex of salmon has been changed under laboratory conditions, usually through the concentrated use of hormones. For example, aquaculture farms sometimes transform male salmon into females because the females often grow larger and produce more desirable meat.
But the phenomenon has never been seen in wild salmon stocks, according to Nagler and other researchers.
Nagler's major concern about sex reversal in wild runs is that it might create a "supermale" fish whose characteristics in the wild are unknown.
Indeed, this may already have happened, the researchers conceded.
Normally, female fish carry two X chromosomes, while males carry an X and a Y chromosome. The altered females, which produced eggs, spawned and died in the normal cycle, also had an X and Y chromosome. Half their offspring could wind up with two Y chromosomes, Nagler said.
"It would be frightening if we're whittling down the female population and female genetic traits," said Nagler. "It might just be a correcting thing but my gut tells me that if you reduce female genetics in a species it's got to have an impact."
However, Nagler said that the effects on the offspring can be studied no further until the salmon return to the Hanford Reach to spawn. Future expanded studies are being planned to determine if the sex reversals were a one-time event or if other wild salmon runs have undergone similar changes.
Thorgaard believes the most likely cause of the reversal is pollution from agricultural or industrial chemicals, which may act like estrogens.
By contrast, a study of fish from the same genetic stock from the nearby Priest Rapids Fish Hatcher showed no evidence of sex-reversal.
"It's unlikely this is naturally occurring," said Thorgaard.
Copyright © 2000 AFP