For over a decade, scientists have been studying the reproductive health of smallmouth bass in the upper Potomac River and a range of other rivers, like the Mississippi and Colorado, and National Wildlife Refuge to track the rise of the species. It wasn’t until 2009 that scientists began to notice something strange; an abundance of male fish that were sampled seemed to be carrying female germ cells, or eggs, in their testes. It’s a phenomenon that caused scientists to deem these fish ‘intersex’ because they exhibited physical traits of both males and females. Females also had egg production and release disrupted, which could lead to a decrease in the species’ population.
Findings for this intersex phenomenon range far and wide across North America, causing scientists to scratch their heads when it comes to naming any one source. While fish that were born near a sewage treatment plant exhibited these changes, so did ones from a wildlife refuge and also ones in urban and rural areas. One link that researchers point to is the causal relationship between those that nest near agricultural areas.
“We keep seeing . . . a correlation with the percent of agriculture in the watershed where we conduct a study,” said Vicki Blazer, a U.S. Geological Survey biologist who studies fish.
Since scientists know that these strange changes are caused by disruptions with the hormones, they started looking at what could be causing the disruptions. For areas that rely on agriculture, they suspect that the estrogen that comes from cows through waste and is then turned to manure makes it way via heavy rains into the nearby rivers. Too much estrogen can change the biology of the fish as they grow in their eggs, causing them to take on female characteristics. One other relation to agriculture is the pesticide use that is prominent for such areas; with a slew of chemicals used to keep bugs off, pesticides are sprayed into the air and inevitably land in the water, possibly poisoning it so much that it affected the fish.
Another cause that researchers have been looking into is the mass dumping of contraceptive pills into the sewage system that makes its way through the treatment facility and harms the fish. In one study, researchers put fish into an experimental lake and added a synthetic estrogen that is common in birth control pills. The estrogen caused fish to become intersex and disturbed the hormones of the fish so much that the population collapsed within a few years. This cause would most likely occur in urban areas, where flushing of inappropriate items like pills is a huge threat to bodies of water.
Despite evidence of contamination in rural and urban areas, what’s even more surprising is that intersex fish were also discovered in the lakes of National Wildlife Refuges, where the water is supposed to be undisturbed and uncontaminated.
“It’s really pretty staggering to be seeing these percentages in areas we would think of as pristine natural areas,” said Christopher Martyniuk, a fish biologist at the University of Florida.
There aren’t any proposed explanations for this finding in the refuge, and now scientists are just beginning to realize that the bodies of water in supposedly pure areas could be just as polluted as those outside of the refuge.
The widespread nature of this issue has thrown researchers from all different groups for a loop. For something that hasn’t been seen before, the fact that 60 to 100 percent of male fish tested were carrying eggs is extremely alarming.
“I did not expect to find it quite as widespread,” Blazer admitted.
Critics of these studies say that they are outdated because the samples were taken prior to the bay pollution cleanup plan, and they may be onto something. At the University of Waterloo in Canada, researchers studied fish that were downstream from a sewage treatment plant a decade ago and found that every single male was intersex. In 2012, this sewage treatment plant underwent an upgrade that improved its cleanup procedures and reduced pollution. Scientists studied the fish again and found that there was a significant decrease in the amount of fish that tested as intersex, leading many to believe that where cleanup plans occur, pollution and anomalies like these decline.
However, as Blazer points out, this doesn’t mean that humans and fish are out of the woods. The majority of the areas where intersex fish were found have not been cleaned up since the initial studies and, besides, these disruptions in the fish could be a sign of something bigger.
The fish is “an indicator that something else is really wrong,” Blazer said in support of stronger pesticide reporting. “What are these things doing to the natural environment? If we find these things in wild organisms, there’s a good chance they’re also affecting people.”