Meet the Double-crested Cormorant, a strangely handsome bird with a special talent for catching fish. You see, cormorants are superb swimmers when under water—using their webbed feet to propel and maneuver themselves with exceptional speed in pursuit of prey.
Double-crested Cormorants, hundreds of them, are presently gathered along with several other species of piscivorous (fish-eating) birds on the lower Susquehanna River below Conowingo Dam near Rising Sun, Maryland. Fish are coming up the river and these birds are taking advantage of their concentrations on the downstream side of the impoundment to provide food to fuel their migration or, in some cases, to feed their young.
In addition to the birds, the movements of fish attract larger fish, and even larger fishermen.
The excitement starts when the sirens start to wail and the red lights begin flashing. Yes friends, it’s showtime.
Within minutes of the renewed flow, birds are catching fish.
Then the anglers along the wave-washed shoreline began catching fish too.
The arrival of migrating Hickory Shad heralds the start of a movement that will soon include White Perch, anadromous American Shad, and dozens of other fish species that swim upstream during the springtime. Do visit Fisherman’s Park at Conowingo Dam to see this spectacle before it’s gone. The fish and birds have no time to waste, they’ll soon be moving on.
To reach Exelon’s Conowingo Fisherman’s Park from Rising Sun, Maryland, follow U.S. Route 1 south across the Conowingo Dam, then turn left onto Shuresville Road, then make a sharp left onto Shureslanding Road. Drive down the hill to the parking area along the river. The park’s address is 2569 Shureslanding Road, Darlington, Maryland.
A water release schedule for the Conowingo Dam can be obtained by calling Exelon Energy’s Conowingo Generation Hotline at 888-457-4076. The recording is updated daily at 5 P.M. to provide information for the following day.
And remember, the park can get crowded during the weekends, so consider a weekday visit.
Within the last few years, the early-summer emergence of vast waves of mayflies has caused great consternation among residents of riverside towns and motorists who cross the bridges over the lower Susquehanna. Fishermen and others who frequent the river are familiar with the phenomenon. Mayflies rise from their benthic environs where they live for a year or more as an aquatic larval stage (nymph) to take flight as a short-lived adult (imago), having just one night to complete the business of mating before perishing by the following afternoon.
In 2015, an emergence on a massive scale prompted the temporary closure of the mile-long Columbia-Wrightsville bridge while a blizzard-like flight of huge mayflies reduced visibility and caused road conditions to deteriorate to the point of causing accidents. The slimy smelly bodies of dead mayflies, probably millions of them, were removed like snow from the normally busy Lincoln Highway. Since then, to prevent attraction of the breeding insects, lights on the bridge have been shut down from about mid-June through mid-July to cover the ten to fourteen day peak of the flight period of Hexagenia bilineata, sometimes known as the Great Brown Drake, the species that swarms the bridge.
After so many years, why did the swarms of these mayflies suddenly produce the enormous concentrations seen on this particular bridge across the lower Susquehanna? Let’s have a look.
Following the 2015 flight, conservation organizations were quick to point out that the enormous numbers of mayflies were a positive thing—an indicator that the waters of the river were getting cleaner. Generally, assessments of aquatic invertebrate populations are considered to be among the more reliable gauges of stream health. But some caution is in order in this case.
Prior to the occurrence of large flights several years ago, Hexagenia bilineata was not well known among the species in the mayfly communities of the lower Susquehanna and its tributaries. The native range of the species includes the southeastern United States and the Mississippi River watershed. Along segments of the Mississippi, swarms such as occurred at Columbia-Wrightsville in 2015 are an annual event, sometimes showing up on local weather radar images. These flights have been determined to be heaviest along sections of the river with muddy bottoms—the favored habitat of the burrowing Hexagenia bilineata nymph. This preferred substrate can be found widely in the Susquehanna due to siltation, particularly behind dams, and is the exclusive bottom habitat in Lake Clarke just downstream of the Columbia-Wrightsville bridge.
Native mayflies in the Susquehanna and its tributaries generally favor clean water in cobble-bottomed streams. Hexagenia bilineata, on the other hand, appears to have colonized the river (presumably by air) and has found a niche in segments with accumulated silt, the benthic habitats too impaired to support the native taxa formerly found there. Large flights of burrowing mayflies do indicate that the substrate didn’t become severely polluted or eutrophic during the preceding year. And big flights tell us that the Susquehanna ecosystem is, at least in areas with silt bottoms, favorable for colonization by the Great Brown Drake. But large flights of Hexagenia bilineata mayflies don’t necessarily give us an indication of how well the Susquehanna ecosystem is supporting indigenous mayflies and other species of native aquatic life. Only sustained recoveries by populations of the actual native species can tell us that. So, it’s probably prudent to hold off on the celebrations. We’re a long way from cleaning up this river.
In the absence of man-made lighting, male Great Brown Drakes congregate over waterways lit often by moonlight alone. The males hover in position within a swarm, often downwind of an object in the water. As females begin flight and pass through the swarm, they are pursued by the males in the vicinity. The male response is apparently sight motivated—anything moving through their field of view in a straight line will trigger a pursuit. That’s why they’re so pesky, landing on your face whenever you approach them. Mating takes place as males rendezvous with airborne females. The female then drops to the water surface to deposit eggs and later die—if not eaten by a fish first. Males return to the swarm and may mate again and again. They die by the following afternoon. After hatching, the larvae (nymphs) burrow in the silt where they’ll grow for the coming year. Feathery gills allow them to absorb oxygen from water passing through the U-shaped refuge they’ve excavated.
Several factors increase the likelihood of large swarms of Great Brown Drakes at bridges. Location is, of course, a primary factor. Bridges spanning suitable habitat will, as a minimum, experience incidental occurrences of the flying forms of the mayflies that live in the waters below. Any extraordinarily large emergence will certainly envelop the bridge in mayflies. Lights, both fixed and those on motor vehicles, enhance the appearance of movement on a bridge deck, thus attracting hovering swarms of male Hexagenia bilineata and other species from a greater distance, leading to larger concentrations. Concrete walls along the road atop the bridge lure the males to try to hover in a position of refuge behind them, despite the vehicles that disturb the still air each time they pass. The walls also function as the ultimate visual attraction as headlamp beams and shadows cast by moving vehicles are projected onto them over the length of the bridge. Vast numbers of dead, dying, and maimed mayflies tend to accumulate along these walls for this reason.
The absence of illumination from fixed lighting on the deck of the bridge reduces the density of Great Brown Drake swarms. Some communities take mayfly countermeasures one step further. Along the Mississippi, some bridges are fitted with lights on the underside of the deck to attract the mayflies to the area directly over the water, concentrating the breeding mayflies and fishermen alike. The illumination below the bridge is intended to draw mayflies away from light created by headlamps on motor vehicles passing by on the otherwise dark deck above. Lights beneath the bridge also help prevent large numbers of mayflies from being drawn away from the water toward lights around businesses and homes in neighborhoods along the shoreline—where they can become a nuisance.
Edsall, Thomas A. 2001. “Burrowing Mayflies (Hexagenia) as Indicators of Ecosystem Health.” Aquatic Ecosystem Health and Management. 43:283-292.
Fremling, Calvin R. 1960. Biology of a Large Mayfly, Hexagenia bilineata (Say), of the Upper Mississippi River. Research Bulletin 482. Agricultural and Home Economics Experiment Station, Iowa State University. Ames, Iowa.
McCafferty, W. P. 1994. “Distributional and Classificatory Supplement to the Burrowing Mayflies (Ephemeroptera: Ephimeroidea) of the United States.” Entomological News. 105:1-13.
It was a routine occurrence in many communities along tributaries of the lower Susquehanna River during the most recent two months. The rain falls like it’s never going to stop—inches an hour. Soon there is flash flooding along creeks and streams. Roads are quickly inundated. Inevitably, there are motorists caught in the rising waters and emergency crews are summoned to retrieve the victims. When the action settles, sets of saw horses are brought to the scene to barricade the road until waters recede. At certain flood-prone locations, these events are repeated time and again. The police, fire, and Emergency Medical Services crews seem to visit them during every torrential storm—rain, rescue, rinse, and repeat.
We treat our local streams and creeks like open sewers. Think about it. We don’t want rainwater accumulating on our properties. We pipe it away and grade the field, lawn, and pavement to roll it into the neighbor’s lot or into the street—or directly into the waterway. It drops upon us as pure water and we instantly pollute it. It’s a method of diluting all the junk we’ve spread out in its path since the last time it rained. A thunderstorm is the big flush. We don’t seem too concerned about the litter, fertilizer, pesticides, motor fluids, and other consumer waste it takes along with it. Out of sight, out of mind.
Perhaps our lack of respect for streams and creeks is the source of our complete ignorance of the function of floodplains.
Floodplains are formed over time as hydraulic forces erode bedrock and soils surrounding a stream to create adequate space to pass flood waters. As floodplains mature they become large enough to reduce flood water velocity and erosion energy. They then function to retain, infiltrate, and evaporate the surplus water from flood events. Microorganisms, plants, and other life forms found in floodplain wetlands, forests, and grasslands purify the water and break down naturally-occurring organic matter. Floodplains are the shock-absorber between us and our waterways. And they’re our largest water treatment facilities.
Why is it then, that whenever a floodplain floods, we seem motivated to do something to fix this error of nature? Man can’t help himself. He has a compulsion to fill the floodplain with any contrivance he can come up with. We dump, pile, fill, pave, pour, form, and build, then build some more. At some point, someone notices a stream in the midst of our new creation. Now it’s polluted and whenever it storms, the darn thing floods into our stuff—worse than ever before. So the project is crowned by another round of dumping, forming, pouring, and building to channelize the stream. Done! Now let’s move all our stuff into our new habitable space.
The majority of the towns in the lower Susquehanna valley with streams passing through them have impaired floodplains. In many, the older sections of the town are built on filled floodplain. Some new subdivisions highlight streamside lawns as a sales feature—plenty of room for stockpiling your accoutrements of suburban life. And yes, some new homes are still being built in floodplains.
When high water comes, it drags tons of debris with it. The limbs, leaves, twigs, and trees are broken down by natural processes over time. Nature has mechanisms to quickly cope with these organics. Man’s consumer rubbish is another matter. As the plant material decays, the embedded man-made items, particularly metals, treated lumber, plastics, Styrofoam, and glass, become more evident as an ever-accumulating “garbage soil” in the natural floodplains downstream of these impaired areas. With each storm, some of this mess floats away again to move ever closer to Chesapeake Bay and the Atlantic. Are you following me? That’s our junk from the curb, lawn, highway, or parking lot bobbing around in the world’s oceans.
Beginning in 1968, participating municipalities, in exchange for having coverage provided to their qualified residents under the National Flood Insurance Program, were required to adopt and enforce a floodplain management ordinance. The program was intended to reduce flood damage and provide flood assistance funded with premiums paid by potential victims. The program now operates with a debt incurred during severe hurricanes. Occurrences of repetitive damage claims and accusations that the program provides an incentive for rebuilding in floodplains have made the National Flood Insurance Program controversial.
In the Lower Susquehanna River Watershed there are municipalities that still permit new construction in floodplains. Others are quite proactive at eliminating new construction in flood-prone zones, and some are working to have buildings removed that are subjected to repeated flooding.
There are two Conewago Creek systems in the Lower Susquehanna River Watershed. One drains the Gettysburg Basin west of the river, mostly in Adams and York Counties, then flows into the Susquehanna at the base of Conewago Falls. The other drains the Gettysburg Basin east of the river, flowing through Triassic redbeds of the Gettysburg Formation and York Haven Diabase before entering Conewago Falls near the south tip of Three Mile Island. Both Conewago Creeks flow through suburbia, farm, and forest. Both have their capacity to support aquatic life impaired and diminished by nutrient and sediment pollution.
This week, some of the many partners engaged in a long-term collaboration to restore the east shore’s Conewago Creek met to have a look at one of the prime indicators of overall stream habitat health—the fishes. Kristen Kyler of the Lower Susquehanna Initiative organized the effort. Portable backpack-mounted electrofishing units and nets were used by crews to capture, identify, and count the native and non-native fishes at sampling locations which have remained constant since prior to the numerous stream improvement projects which began more than ten years ago. Some of the present-day sample sites were first used following Hurricane Agnes in 1972 by Stambaugh and Denoncourt and pre-date any implementation of sediment and nutrient mitigation practices like cover crops, no-till farming, field terracing, stormwater control, nutrient management, wetland restoration, streambank fencing, renewed forested stream buffers, or modernized wastewater treatment plants. By comparing more recent surveys with this baseline data, it may be possible to discern trends in fish populations resulting not only from conservation practices, but from many other variables which may impact the Conewago Creek Warmwater Stream ecosystem in Dauphin, Lancaster, and Lebanon Counties.
So here they are. Enjoy these shocking fish photos.
Normandeau Associates, Inc. and Gomez and Sullivan. 2018. Muddy Run Pumped Storage Project Conowingo Eel Collection Facility FERC Project 2355. Prepared for Exelon.
Stambaugh, Jr., John W., and Robert P. Denoncourt. 1974. A Preliminary Report on the Conewago Creek Faunal Survey, Lancaster County, Pennsylvania. Proceedings of the Pennsylvania Academy of Sciences. 48: 55-60.