Common Carp – LIFE IN THE LOWER SUSQUEHANNA RIVER WATERSHED

June 10, 2025June 10, 2025

Photo of the Day

June 7, 2025June 10, 2025

Common Carp: A Menace Meant for the Dinner Plate

One of the earliest non-native fish species to be widely released into North American waterways was the Common Carp. Stocks brought to the United States were likely sourced from populations already naturalized throughout much of western Europe after introductions originating from the fish’s native range in Eurasia, probably including the Danube and other watersheds east through the Volga. In western Europe, the species promised to be an abundant and easily cultivated food source. Under the same premise, carp were transported to the United States during the early 1800s and widely introduced into streams, lakes, and rivers throughout the country.

Common Carp thrive in nutrient-rich waters, particularly those subjected to sewage discharge and agricultural runoff, conditions which were already prevalent during the Common Carp’s initial introduction and have remained widespread ever since. Within these polluted streams, lakes, and ponds, introduced carp feed aggressively on benthic organisms and plants, stirring up decaying organic matter (mulm) from the substrate. This process raises turbidity in the water column and releases excessive amounts of the nutrient phosphorus resulting in unusually large algal blooms. Algal blooms can block sunlight from the longer-lived oxygen-producing vascular plants that grow in submerged environs. Growing beneath a dense cloud or blanket of algae can compromise the vigor of oxygen-producing vascular plants and disable their biochemical functions within the aquatic ecosystem. As the short-lived algae die, the bacteria that decay them begin to place increased oxygen demands on the water. With less oxygen being produced by both the vascular plants and the algae, and with oxygen consumption increased by the activity of decomposers, conditions can become fatal for fish and other organisms. This process is known as eutrophication. Because Common Carp are among the species most tolerant of eutrophic conditions, they tend to thrive in the conditions they create while the native fishes perish.

Common Carp spawn in the spring, usually from late April through June, when the water temperature is as low as 58 degrees and as high as 83 degrees Fahrenheit. This activity is often triggered by a rapid increase in water temperature. In a small lake, this may be brought on by a string of sunny days in late April or May. On larger streams and rivers, the temperature spike that initiates the spawn may not occur until warm rains and runoff enter the stream during June.

Common Carp Spawning — In water that is often less than a foot in depth, male carp follow the breeding females into egg-laying areas among debris and emergent vegetation.

Common Carp are one of the most widely farmed and eaten fish in all the world. Here in the United States, they were introduced beginning two hundred years ago because they were favorable to the palate, grew to large size quickly, and were a source of much needed food. Today, the Common Carp is seldom found on the American dinner plate. Yet, pound for pound, it is one of the most abundant fish in many of our waters, particularly in man-made lakes. Like some of our other most invasive species—including Blue Catfish, Flathead Catfish, and Northern Snakehead—Common Carp are perhaps the most edible of our freshwater fishes. For many cultures, they are an important staple. For others, they are a delicacy or holiday treat. In America, they do horrendous damage to aquatic ecosystems following establishment as a food crop that almost never gets harvested. Did you realize that on the internet, there are literally hundreds of recipes and culinary videos available to show you how to prepare delicious dishes made with Common Carp? It’s true. And for the cost of a fishing license, you can catch all you want, usually several pounds at a time. So why not give the marine fisheries a break? Take the big leap and learn to eat invasive freshwater species instead.

Common Carp Breaching — Jumpin’ gefilte fish, it’s what’s for dinner!

January 9, 2021January 14, 2021

2020: A Good Year

You say you really don’t want to take a look back at 2020? Okay, we understand. But here’s something you may find interesting, and it has to do with the Susquehanna River in 2020.

As you may know, the National Weather Service has calculated the mean temperature for the year 2020 as monitored just upriver from Conewago Falls at Harrisburg International Airport. The 56.7° Fahrenheit value was the highest in nearly 130 years of monitoring at the various stations used to register official climate statistics for the capital city. The previous high, 56.6°, was set in 1998.

Though not a prerequisite for its occurrence, record-breaking heat was accompanied by a drought in 2020. Most of the Susquehanna River drainage basin experienced drought conditions during the second half of the year, particularly areas of the watershed upstream of Conewago Falls. A lack of significant rainfall resulted in low river flows throughout late summer and much of the autumn. Lacking water from the northern reaches, we see mid-river rocks and experience minimal readings on flow gauges along the lower Susquehanna, even if our local precipitation happens to be about average.

Back in October, when the river was about as low as it was going to get, we took a walk across the Susquehanna at Columbia-Wrightsville atop the Route 462/Veteran’s Memorial Bridge to have a look at the benthos—the life on the river’s bottom.

As we begin our stroll across the river, we quickly notice Mallards and a Double-crested Cormorant (far left) feeding among aquatic plants. You can see the leaves of the vegetation just breaking the water’s surface, particularly behind the feeding waterfowl. Let’s have a closer look.

An underwater meadow of American Eelgrass (Vallisneria americana) as seen from atop the Veteran’s Memorial Bridge at Columbia-Wrightsville. Also known as Freshwater Eelgrass, Tapegrass, and Wild Celery, it is without a doubt the Susquehanna’s most important submerged aquatic plant. It grows in alluvial substrate (gravel, sand, mud, etc.) in river segments with moderate to slow current. Water three to six feet deep in bright sunshine is ideal for its growth, so an absence of flooding and the sun-blocking turbidity of muddy silt-laden water is favorable.

Plants in the genus Vallisneria have ribbon-like leaves up to three feet in length that grow from nodes rooted along the creeping stems called runners. A single plant can, over a period of years, spread by runners to create a sizable clump or intertwine with other individual plants to establish dense meadows and an essential wildlife habitat.

An uprooted segment of eelgrass floats over a thick bed of what may be parts of the same plant. Eelgrass meadows on the lower Susquehanna River were decimated by several events: deposition of anthracite coal sediments (culm) in the late-nineteenth and early-twentieth centuries, dredging of the same anthracite coal sediments during the mid-twentieth century, and the ongoing deposition of sediments from erosion occurring in farm fields, logged forests, abandoned mill ponds, and along denuded streambanks. Not only has each of these events impacted the plants physically by either burying them or ripping them out by the roots, each has also contributed to the increase in water turbidity (cloudiness) that blocks sunlight and impairs their growth and recovery.

A submerged log surrounded by beds of eelgrass forms a haven for fishes in sections of the river lacking the structure found in rock-rich places like Conewago Falls. A period absent of high water and sediment runoff extended through the growing season in 2020 to allow lush clumps of eelgrass like these to thrive and further improve water quality by taking up nutrients, particularly nitrogen and phosphorus. Nutrients used by vascular plants including eelgrass become unavailable for feeding detrimental algal blooms in downstream waters including Chesapeake Bay.

Small fishes and invertebrates attract predatory fishes to eelgrass beds. We watched this Smallmouth Bass leave an ambush site among eelgrass’s lush growth to shadow a Common Carp as it rummaged through the substrate for small bits of food. The bass would snatch up crayfish that darted away from the cover of stones disturbed by the foraging carp.

Sunfishes are among the species taking advantage of eelgrass beds for spawning. They’ll build a nest scrape in the margins between clumps of plants allowing their young quick access to dense cover upon hatching. The abundance of invertebrate life among the leaves of eelgrass nourishes feeding fishes, and in turn provides food for predators including Bald Eagles, this one carrying a freshly-caught Bluegill.

These improvements in water quality and wildlife habitat can have a ripple effect. In 2020, the reduction in nutrient loads entering Chesapeake Bay from the low-flowing Susquehanna may have combined with better-than-average flows from some of the bay’s lesser-polluted smaller tributaries to yield a reduction in the size of the bay’s oxygen-deprived “dead zones”. These dead zones typically occur in late summer when water temperatures are at their warmest, dissolved oxygen levels are at their lowest, and nutrient-fed algal blooms have peaked and died. Algal blooms can self-enhance their severity by clouding water, which blocks sunlight from reaching submerged aquatic plants and stunts their growth—making quantities of unconsumed nutrients available to make more algae. When a huge biomass of algae dies in a susceptible part of the bay, its decay can consume enough of the remaining dissolved oxygen to kill aquatic organisms and create a “dead zone”. The Chesapeake Bay Program reports that the average size of this year’s dead zone was 1.0 cubic miles, just below the 35-year average of 1.2 cubic miles.

Back on a stormy day in mid-November, 2020, we took a look at the tidal freshwater section of Chesapeake Bay, the area known as Susquehanna Flats, located just to the southwest of the river’s mouth at Havre de Grace, Maryland. We wanted to see how the restored American Eelgrass beds there might have fared during a growing season with below average loads of nutrients and life-choking sediments spilling out of the nearby Susquehanna River. Here’s what we saw.

We followed the signs from Havre de Grace to Swan Harbor Farm Park.

Harford County Parks and Recreation’s Swan Harbor Farm Park consists of a recently-acquired farming estate overlooking the tidal freshwater of Susquehanna Flats.

Along the bay shore, a gazebo and a fishing pier have been added. Both provide excellent observation points.

The shoreline looked the way it should look on upper Chesapeake Bay, a vegetated buffer and piles of trees and other organic matter at the high-water line. There was less man-made garbage than we might find following a summer that experienced an outflow from river flooding, but there was still more than we should be seeing.

Judging by the piles of fresh American Eelgrass on the beach, it looks like it’s been a good year. Though considered a freshwater plant, eelgrass will tolerate some brackish water, which typically invades upper Chesapeake Bay each autumn due to a seasonal reduction in freshwater inflow from the Susquehanna and other tributaries. Saltwater can creep still further north when the freshwater input falls below seasonal norms during years of severe drought. The Susquehanna Flats portion of the upper bay very rarely experiences an invasion by brackish water; there was none in 2020.

As we scanned the area with binoculars and a spotting scope, a raft of over one thousand ducks and American Coots (foreground) could be seen bobbing among floating eelgrass leaves and clumps of the plants that had broken away from their mooring in the mud. Waterfowl feed on eelgrass leaves and on the isopods and other invertebrates that make this plant community their home.

While coots and grebes seemed to favor the shallower water near shore, a wide variety of both diving and dabbling ducks were widespread in the eelgrass beds more distant. Discernable were Ring-necked Ducks, scaup, scoters, Long-tailed Ducks, Redheads, American Wigeons, Gadwall, Ruddy Ducks, American Black Ducks, and Buffleheads.

We noticed a few Canvasbacks (Aythya valisineria) on the Susquehanna Flats during our visit. Canvasbacks are renowned as benthic feeders, preferring the tubers and other parts of submerged aquatic plants (a.k.a. submersed aquatic vegetation or S.A.V.) including eelgrass, but also feeding on invertebrates including bivalves. The association between Canvasbacks and eelgrass is reflected in the former’s scientific species name valisineria, a derivitive of the genus name of the latter, Vallisneria.

Canvasbacks on Chesapeake Bay. (United States Fish and Wildlife Service image by Ryan Hagerty)

The plight of the Canvasback and of American Eelgrass on the Susquehanna River was described by Herbert H. Beck in his account of the birds found in Lancaster County, Pennsylvania, published in 1924:

“Like all ducks, however, it stops to feed within the county less frequently than formerly, principally because the vast beds of wild celery which existed earlier on broads of the Susquehanna, as at Marietta and Washington Borough, have now been almost entirely wiped out by sedimentation of culm (anthracite coal waste). Prior to 1875 the four or five square miles of quiet water off Marietta were often as abundantly spread with wild fowl as the Susquehanna Flats are now.”

Beck quotes old Marietta resident and gunner Henry Zink:

“Sometimes there were as many as 500,000 ducks of various kinds on the Marietta broad at one time.”

The abundance of Canvasbacks and other ducks on the Susquehanna Flats would eventually plummet too. In the 1950s, there were an estimated 250, 000 Canvasbacks wintering on Chesapeake Bay, primarily in the area of the American Eelgrass, a.k.a. Wild Celery, beds on the Susquehanna Flats. When those eelgrass beds started disappearing during the second half of the twentieth century, the numbers of Canvasbacks wintering on the bay took a nosedive. As a population, the birds moved elsewhere to feed on different sources of food, often in saltier estuarine waters.

Canvasbacks were able to eat other foods and change their winter range to adapt to the loss of habitat on the Susquehanna River and Chesapeake Bay. But not all species are the omnivores that Canvasbacks happen to be, so they can’t just change their diet and/or fly away to a better place. And every time a habitat like the American Eelgrass plant community is eliminated from a region, it fragments the range for each species that relied upon it for all or part of its life cycle. Wildlife species get compacted into smaller and smaller suitable spaces and eventually their abundance and diversity are impacted. We sometimes marvel at large concentrations of birds and other wildlife without seeing the whole picture—that man has compressed them into ever-shrinking pieces of habitat that are but a fraction of the widespread environs they once utilized for survival. Then we sometimes harass and persecute them on the little pieces of refuge that remain. It’s not very nice, is it?

By the end of 2020, things on the Susquehanna were getting back to normal. Near normal rainfall over much of the watershed during the final three months of the year was supplemented by a mid-December snowstorm, then heavy downpours on Christmas Eve melted it all away. Several days later, the Susquehanna River was bank full and dishing out some minor flooding for the first time since early May. Isn’t it great to get back to normal?

The rain-and-snow-melt-swollen Susquehanna from Chickies Rock looking upriver toward Marietta during the high-water crest on December 27th.

Cresting at Columbia as seen from the Route 462/Veteran’s Memorial Bridge. A Great Black-backed Gull monitors the waters for edibles.

All back to normal on the Susquehanna to end 2020.

Yep, back to normal on the Susquehanna. Maybe 2021 will turn out to be another good year, or maybe it’ll just be a Michelin or Firestone.

SOURCES

Beck, Herbert H. 1924. A Chapter on the Ornithology of Lancaster County, Pennsylvania. The Lewis Historical Publishing Company. New York, NY.

White, Christopher P. 1989. Chesapeake Bay, Nature of the Estuary: A Field Guide. Tidewater Publishers. Centreville, MD.

May 28, 2020May 28, 2020

How Much Can a Bald Eagle Lift?

Here it is—just as it happened, recently in the lower Susquehanna valley.

The eagle glides in and grabs an unsuspecting Common Carp, the bird’s momentum and a head wind helping it to raise the fish out of the water. This particular carp appears to be eighteen to twenty-four inches in length. In that range, it could weigh anywhere from four to ten pounds or more.

But as the eagle tries to flap its wings to carry the carp skyward, it loses lift, and the weight of the fish drags the raptor down. A carp exceeding twenty inches in length usually weighs more than five pounds, approximately half the mass of a male (about 9 lbs.) or a female (about 12 lbs.) Bald Eagle. From a dead stop, trying to extricate a submerged fish weighing half as much again as it does is an impossible task for this or any other Bald Eagle.

The eagle fights briefly to pull the carp from the water, then abandons the effort to instead release its talons from the fish to prevent its own demise by drowning.

Free of its hold on the carp, the eagle flaps its wings briskly to get up and out of the potentially deadly situation.

Both the eagle and, presumably, the carp survive the encounter.

The eagle finds a nearby tree limb where it takes a much-needed break from fishing.

Such an event may have been fatal to an inexperienced younger Bald Eagle. Though not an adult, this bird is no spring chicken. Its plumage, particularly its white head with a dark line through the eye (often called an “osprey face”), is indicative of a bird in its fourth year of life. By this time next year, it should be sporting a full set of adult feathers. In the meantime, it should stick to eating suckers; there are plenty of those to go around.

Common Carp are classified as a minnow (Cyprinidae). They are indigenous to Europe and are raised as a food fish in many parts of the world. In the Lower Susquehanna River Watershed, Common Carp are an introduced species with negative impacts on native fisheries. Those exceeding twenty inches in length begin to gain girth and weight, sometimes reaching thirty pounds at thirty inches.

SOURCES

Sedaghat, Safoura, Seyed Abbas Hoseini, Mohammad Larijani, and Khadijeh Shamekhi Ranjbar. 2013. “Age and Growth of Common Carp (Cyprinus carpio Linnaeus, 1758) in Southern Caspian Sea, Iran”. World Journal of Fish and Marine Sciences. 5:1. pp.71-73.

June 28, 2018July 1, 2024

Shocking Fish Photos!

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.

Electrofishing on the Conewago Creek in Lebanon County, PA — Matt Kofroth, Watershed Specialist with the Lancaster County Conservation District, operates the electrofishing wand in Conewago Creek while his team members prepare to net and collect momentarily-stunned fish. Three other electrofishing units operated by staff from the Susquehanna River Basin Commission and aided by teams of netters were in action at other sample locations along the Conewago on this day.

Fishes of the Lower Susquehanna River Watershed: Common Carp — Really big fish, such as this Common Carp (Cyprinus carpio), were identified, counted, and immediately returned to the water downstream of the advancing electrofishing team.

Fishes of the Lower Susquehanna River Watershed: Swallowtail Shiner, Fallfish, Red-breast Sunfish, and suckers. — Other fish, such as the Swallowtail Shiner, Redbreast Sunfish (Lepomis auritus), Fallfish, and suckers seen here, were placed in a sorting tank.

Fishes of the Lower Susquehanna River Watershed: Fallfish — Fallfish (Semotilus corporalis) are very active and require plenty of dissolved oxygen in the water to survive. Fallfish, Rainbow Trout (Oncorhynchus mykiss), and Smallmouth Bass (Micropterus dolomieu) were quickly identified and removed from the sorting tank for release back into the stream. Other larger, but less active fish, including suckers, quickly followed.

Fishes of the Lower Susquehanna River Watershed: Fathead Minnow — Small fish like minnows were removed from the sorting tank for a closer look in a hand-held viewing tank. This Fathead Minnow (Pimephales promelas) was identified, added to the tally sheet, and released back into the Conewago. The Fathead Minnow is not native to the Susquehanna drainage. It is the minnow most frequently sold as bait by vendors.

Fishes of the Lower Susquehanna River Watershed: a breeding male Bluntnose Minnow — A breeding condition male Bluntnose Minnow (Pimephales notatus).

Fishes of the Lower Susquehanna River Watershed: Cutlips Minnow — The Cutlips Minnow (Exoglossum maxillingua) is a resident of clear rocky streams. Of the more than 30 species collected during the day, two native species which are classified as intolerant of persisting stream impairment were found: Cutlips Minnow and Swallowtail Shiner.

Fishes of the Lower Susquehanna River Watershed: Central Stoneroller — The Central Stoneroller (Campostoma anomalum) is a benthic feeder in creeks over gravel and sand.

Fishes of the Lower Susquehanna River Watershed: Eastern Blacknose Dace — The Eastern Blacknose Dace (Rhinichthys atratulus) is found in clear water over pebble and stone substrate.

Fishes of the Lower Susquehanna River Watershed: Longnose Dace — The Longnose Dace (Rhinichthys cataractae) is another species of pebbly rocky streams.

Fishes of the Lower Susquehanna River Watershed: juvenile Golden Shiner — A juvenile Golden Shiner (Notemigonus crysoleucas). Adults lack the side stripe and grow to the size of a sunfish.

Fishes of the Lower Susquehanna River Watershed: Swallowtail Shiner — A Swallowtail Shiner (Notropis procne) and a very young White Sucker (Catostomus commersonii) in the upper left of the tank.

Fishes of the Lower Susquehanna River Watershed: Spotfin Shiner — A probable Spotfin Shiner (Cyprinella spiloptera).

Fishes of the Lower Susquehanna River Watershed: Margined Madtom — The Margined Madtom (Noturus insignis) is a small native catfish of pebbly streams.

Fishes of the Lower Susquehanna River Watershed: Banded Killifish — The Banded Killifish (Fundulus diaphanus) is adept at feeding upon insects, including mosquitos.

Fishes of the Lower Susquehanna River Watershed: a juvenile Rock Bass — A young Rock Bass (Ambloplites rupestris). This species was introduced to the Susquehanna and its tributaries.

Fishes of the Lower Susquehanna River Watershed: Greenside Darter — The Greenside Darter (Etheostoma blennioides) is not native to the Susquehanna basin. The species colonized the Conewago Creek (east) from introduced local populations within the last five years.

Fishes of the Lower Susquehanna River Watershed: Tessellated Darter — The Tessellated Darter (Etheostoma olmstedi) is a native inhabitant of the Susquehanna and its tributaries.

Fishes of the Lower Susquehanna River Watershed: American Eel — The stars of the day were the American Eels (Anguilla rostrata).

American Eels serve as an intermediate host for the microscopic parasitic glochidia (larvae) of the Eastern Elliptio (Elliptio complanata), a declining native freshwater mussel of the Lower Susquehanna River Watershed. While feeding on their host (usually in its gills), the glochidia cause little injury and soon drop off to continue growth, often having assured distribution of their species by accepting the free ride. Freshwater mussels are filter feeders and improve water quality. They grow slowly and can live for decades.

SOURCES

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.