Good News From Mayflies

National Wildlife, Oct-Nov, 1998

For the last three years, a species of mayfly called Hexagenia has plagued towns along the western basin of Lake Erie in springtime. Swarms of the winged creatures have made roads slick after being squashed by cars and have flown into peoples' clothes and mouths. A huge cloud of the insects even caused a brownout in northwestern Ohio after being attracted to the lights of an electrical substation and conducting electricity across insulators.

Believe it or not, aside from the inconvenience, all of that is good news--not just in spring but year-round. That is because the reappearance of Hexagenia is a sign the region is regaining a level of ecological health it has not experienced for almost half a century. The mayfly virtually disappeared from Lake Erie--as well as several other heavily populated Great Lakes locations and the upper Mississippi River--by the late 1950s, victim in part of algal blooms and decomposing sewage that robbed the lake bed of oxygen. Now the insect is showing up in many of those sites again, as well as thriving in Lake Erie.

Hexegenia nymphs live in the sediment of relatively shallow water--as deep as 40 or 50 feet--emerging at the end of two years for a single day or two of flight. No longer able to eat at that point in their life cycle, the winged creatures' only goal is to reproduce. For females, that not only means mating but also laying fertilized eggs on the surface of water. And that is part of the reason for the traffic problems associated with mayflies: A new study from Hungary reveals that when asphalt reflects light, mayflies lay their eggs on roads, presumably mistaking the surface for water.

Mayfly nymphs were once an important part of the aquatic and near-shore food web, and scientists have hope that the insect once again will dependably nourish fish and birds near the populated areas where it did so before.

Pollutants Spread By Salmon

Ever since persistant organic pollutants such as PCBs and DDT began showing up in animals and people inhabiting Arctic ecosystems, scientists have assumed all the contaminants have arrived by air. Now it turns out some of the chemicals also are carried into the otherwise pristine areas by migrating fish.

A recent study in Alaska by biologist Gran Ewald of Lund University in Sweden found that grayling in a lake used by spawning salmon carried more than twice the concentration of organic pollutants than grayling in a nearby lake with no migrant visitors.

The salmon had spent as many as three years traveling 255 miles into the Gulf of Alaska and beyond, gradually accumulating pollution in their fat. As the fish burned up fat reserves to make the arduous return trip, the toxics became more concentrated. And when the gray- ling ate the salmon carcasses and roe, they in turn became contaminated. The finding strongly indicates that the chemicals transported to the area by the salmon move from the migrants throughout the ecosystem's food chain.