You may find this hard to believe, but during the colder months in the lower Susquehanna valley, gulls aren’t as numerous as they used to be. In the years since their heyday in the late twentieth century, many of these birds have chosen to congregate in other areas of the Mid-Atlantic region where the foods they crave are more readily available.
As you may have guessed, the population boom of the 1980s and 1990s was largely predicated on human activities. These four factors were particularly beneficial for wintering gulls…
Disposal of food-bearing waste in open landfills
High-intensity agriculture with disc plowing
Gizzard Shad population boom in nutrient-impaired river/Hydroelectric power generation
Fumbled Fast Food
Earthworms lifted to the soil’s surface by plowing attracted Ring-billed Gulls by the thousands to Susquehanna Valley farmlands during the late twentieth century. (Vintage 35 mm image)Filter-feeding Gizzard Shad populations thrive in nutrient-rich waters like the Susquehanna. Their rambunctious feeding style stirs up benthic sediment deposits to release more nutrients into the water column and promote the algal blooms that often lead to detrimental eutrophic conditions. Decades ago, hundreds and sometimes thousands of gulls gathered below the river’s hydroelectric dams to feed on the seemingly endless supply of small Gizzard Shad disoriented by their passage through the turbines during electric generation. (Vintage 35 mm image)
So what happened? Why are wintering gulls going elsewhere and no longer concentrating on the Susquehanna? Well, let’s look at what has changed with our four man-made factors…
A larger percentage of the lower Susquehanna basin’s household and food industry waste is now incinerated/Landfills practice “cover as you go” waste burial.
Implementation of “no-till” farming has practically eliminated availability of earthworms and other sub-surface foods for gulls.
The population explosion of invasive Asiatic Clams has reduced the Gizzard Shad’s relative abundance and biomass among filter feeders.
Hold on tight! Fast food has become too expensive to waste.
The non-native population of Asiatic Clams in the Susquehanna and most of its larger tributaries exploded during the last two decades of the twentieth century. Its present-day biomass in the river is exceeded by no other macroinvertebrate species. The share of plankton and other tiny foods that the Asiatic Clam harvests from the water column is no longer available to native filter-feeders including Gizzard Shad. Hence, Gizzard Shad biomass has been reduced and far fewer are available to attract amazingly enormous flocks of hungry gulls to hydroelectric dams. (Vintage 35 mm image)
GULLS THIS WINTER
Despite larid abundance on the lower Susquehanna not being the spectacle it was during the man-made boom days, an observer can still find a variety of medium and large-sized gulls wintering in the region. We ventured out to catch a glimpse of some of the species being seen both within the watershed and very nearby.
By far, most of the gulls you’ll encounter in the Lower Susquehanna River Watershed right now are Ring-billed Gulls. Some of them still drop by at the business end of the drive thru lane looking for a lost order of fries and maybe a cheeseburger in paradise.First-winter (left), second-winter (center), and adult Ring-billed Gulls on the Susquehanna.Nearly every flock of gulls found in our area right now is composed exclusively of Ring-billed Gulls. The trick to finding other species, particularly rarities, is to look for slightly larger birds mixed among them, particularly American Herring Gulls like the first-winter (back row left) and third-winter (back row right) birds seen here. Herring and other species of similar-sized gulls seem to prefer each other’s company while on the wintering grounds.Five American Herring Gulls with smaller Ring-billed Gulls. The bird to the upper left and the bird hunkered down to its right are adult American Herring Gulls, the three brownish birds are in their first winter.Non-adult American Herring Gulls in flight. Always look for birds with all-pale wing tips when encountering herring gulls in flight.Midway in size between the Ring-billed Gulls in the foreground and the first-winter American Herring Gulls in the upper left and middle right of this image is a Lesser Black-backed Gull (dark-mantled bird resting at center). The similar-sized bird in the water behind it is a first-winter Iceland Gull (Larus glaucoides), a rare visitor from the arctic.Another look at the first-winter Iceland Gull from the previous image. Did you notice the all-white primary feathers and compare them to the dark wing tips on the Ring-billed Gulls seen here in its company?The conspicuously pale wings of the first-winter Iceland Gull, seen here bathing in the presence of two first-winter American Herring Gulls.Both this first-winter Iceland Gull and the bird from the previous three images are currently being seen just east of the Susquehanna watershed at Blue Marsh Lake in Berks County, Pennsylvania. Additional Iceland Gulls are currently being reported in Maryland on the Susquehanna at Conowingo Dam; on upper Chesapeake Bay in Baltimore County, Maryland; and in southeastern-most Bucks County, near Tullytown, Pennsylvania, at a busy landfill site that attracts tens of thousands of gulls each winter. Double-digit numbers of Iceland Gulls have been reported at this latter site during recent weeks.Lesser Black-backed Gulls like this one observed at Blue Marsh Lake are uncommon in the Lower Susquehanna River Watershed. They are progressively more likely as you travel east toward the aforementioned Bucks County landfills where hundreds of these birds make up a core Atlantic seaboard population.Great Black-backed Gulls are the most frequently encountered large gull on the Susquehanna. They’re easily identified by their enormous size and, as adults, their dark mantle.Rivaling the Great Black-backed Gull in size is the Glaucous Gull (Larus hyperboreus), another rare arctic visitor with pale wing tips. There are numerous reports of these unusual winter visitors from sites on Delaware Bay north to the Tullytown landfills on Delaware River where half a dozen or more have been occurring. Seen near the mouth of the Susquehanna on Chesapeake Bay at North East, Maryland, has been a first-winter bird similar to this one that we photographed at Blue Marsh Lake in Berks County, Pennsylvania.
For us, seeing a Glaucous Gull brought back memories of the last time we saw the species. It was forty-five years ago on New Year’s Day 1981 that we discovered two first-winter birds feeding on Gizzard Shad in open water on an otherwise ice-choked Susquehanna below the York Haven Dam powerhouse at Conewago Falls. Hey Doc Robert, do you remember that day?
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.
Seeing the exposed backs of Common Carp as they stir up mulm and other sediments while feeding along the edges of a body of water is not at all unusual.But carp pursuing other carp into the shallows is a sign that spawning has commenced.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.A fountain of splashes can ensue as males try to outdo one another for a chance to fertilize the female’s eggs.The males’ aggressive pursuit can even forced a large female to temporarily ground herself on the beach.
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.
