Researchers Find Link Between Contaminants, Decline Of Sturgeon In Columbia River
White sturgeon populations in the Columbia River may be declining due to the presence of elevated amounts of foreign chemicals including dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs) in their bodies, according to new studies announced on April 7 by researchers at Oregon State University (OSU). The research by Carl Schreck and Grant Feist, biologists in OSU's College of Agricultural Sciences, shows that white sturgeon living in the Columbia River in some areas above Bonneville Dam have high amounts of toxic contaminants in their livers, sex organs and muscle tissue.
"We don't know the exact source of contamination," Schreck said. "The fish move, the stuff they eat moves and the water and sediments bearing the contaminants moves. The Columbia receives input from numerous sources, so any population of fish at any one site can be exposed to a myriad of substances."
The OSU researchers say it is difficult to estimate the numbers of sturgeon in the Columbia, but there has been a noticeable decline in the number of young fish, indicating productivity is poor, especially in the impounded areas above dams.
In the past, any decreases in population were thought to be linked to the presence of dams, which have changed the temperature and flow of the river. And despite fish ladders in place for salmon, the bottom-dwelling white sturgeon rarely navigate dams successfully making it difficult for them to expand their habitat or access oceanic food sources.
Schreck and Feist studied white sturgeon from three reservoirs along the Columbia River and from areas downstream of Bonneville, the last dam on the river in its path to the Pacific Ocean. The researchers found some of the fish living in reservoirs behind the dams had concentrations of chemicals up to 20 times higher than the fish below Bonneville. The contamination was most significant in the reservoir behind the Bonneville Dam, the oldest dam on the river.
"We believe that some contaminants are accumulating behind the dams by settling out in the sediment as the water slows," Feist said, adding that at this point this is a hypothesis.
"Fish residing in the reservoir behind the oldest dam had the highest contaminant loads," Feist added, "and exhibited reduced growth and reproductive fitness when compared to fish sampled in other locations. These data suggest that some contaminants may be accumulating behind dams over time."
North America's largest freshwater fish, white sturgeon have always been an important food source for Oregon's Native Americans, and now as salmon runs diminish, white sturgeon fillets and steaks are increasingly sold in fish markets.
But because of their potentially high contaminant levels, Schreck cautions consumers to not eat the fish at every meal.
During the last 25 years, white sturgeon have experienced a sharp drop in population in the upper reaches of the Columbia River. In 1990, the Committee on the Status of Endangered Wildlife in Canada designated the white sturgeon as "vulnerable," only to reclassify it as "critically imperiled" in 1994.
Today, the fish, which are caught commercially and for sport on the lower Columbia, are listed as endangered in Canada. Fishing for white sturgeon is regulated by the state, with size limits precluding anglers from taking juvenile fish or large, older fish.
Carl Schreck: http://www.cgrb.oregonstate.edu/faculty/schreck/index.html
College of Agricultural Sciences: http://agsci.oregonstate.edu