by Jason Moak, Research Scientist
Spring is here and so are the American shad! The American shad (Alosa sapidissima) is the largest species of fish in the Herring family (Clupeidae), and is found all along the Atlantic Coast of North America. Prior to the World War II, American shad were considered one of the most valuable food fish in the United States. In 2002, Pulitzer Prize-winning author John McPhee published an entire book chronicling the history of the American Shad: “The Founding Fish.”
Adults of American shad are typically 3-6 years old and are between 16 to 21 inches long. These fish are anadromous, meaning they spend most of their lives in the ocean, but migrate up freshwater rivers to spawn. Southern populations of American shad only spawn once, and die shortly afterwards. In the Savannah River, American shad can usually be found in between February and May, when water temperatures are between 14 and 21 degrees Celsius (57 to 70 degrees Fahrenheit).
North American commercial fisheries for American shad have existed since the 1800’s, but catches have declined sharply since the early 20th century. Numerous factors led to the decline of this species, including the construction of dams that blocked access to historical spawning grounds, habitat destruction, overfishing, and pollution. Efforts to recover populations of American shad include enhancement through stocking of hatchery-reared fish, construction of upstream fish passage structures at dams, reduction of pollution, and limits on commercial and recreational fishing.
One interesting method of helping shad recovery, similar to a fish elevator, is used at New Savannah Bluff Lock & Dam, the last dam on the Savannah River between Augusta and the Atlantic Ocean. The U.S. Army Corps of Engineers, based on recommendations from the South Carolina DNR, operates the locks to allow fish to pass upstream of the dam during spawning season. This has been accomplished by allowing water to flow into the lock chamber, which serves to attract the American shad. Then, the downstream lock doors are closed, the lock is filled with water until it is level with the upstream river, and the upstream lock doors are opened, allowing the fish to swim out and upstream into the Augusta Shoals where there is a large amount of ideal spawning habitat.
Despite large declines in Savannah River American shad populations, restoration is currently considered to be sustainable. A study in the early 2000’s documented that half of tagged shad were able to move upstream through the lock and estimated that the population of shad that reached the Lock and Dam may be higher than 200,000 fish.
Question Mark Butterfly
By Damon Mullis
This Question Mark Butterfly (winter form) was photographed in the park in February by L. Anderson.
Spring is in full bloom, and with it butterfly activity in the swamp is on the rise. To prime you for butterfly season, today we’ll explore a butterfly that sometimes gets overlooked while people are out searching for Monarchs and Swallow-tails: the Question Mark Butterfly (Polygonia interrogationis). It gets its name from the silver question mark-like marking seen when its wings are folded back. In this position, the butterfly looks remarkably like an old leaf, disguising its location from predators.
The Question Mark larvae are more opportunistic feeders than many other butterfly larvae. Unlike Monarch larvae that only feed on milkweed, they feed on many different plant species, with elm trees and nettles being some of their favorites. Interestingly, the adult females usually lay their eggs under the leaves of non-host plants and the hatchlings must search out a suitable plant species to feed on.
There are usually two generations of hatchlings per year with each brood having a different adult form. The upper hindwing surfaces of the summer form are largely black. The upper wing surfaces of the winter form are fringed with violet, and the hindwings are rich orange above. As adults, they like to feed on fermenting fruit, tree sap, dung, and carrion, and only feed on nectar if these sources aren’t available. In addition to Question Marks, many other butterfly species feed on a variety of non-nectar food sources. So, when you’re out searching for butterflies in the park, don’t just focus on the flowers.
Culiseta inornata female courtesy of Treasure Tolliver and Nathan D. Burkett-Cadena.
Culiseta inornata female caught by Phinizy Center.
Spotted: “Winter Mosquito”
By: Kelsey Laymon
Culiseta inornata is a species of mosquito uncommonly found in the Georgia area. However, this past week Phinizy Center Researchers were lucky enough to find two of these mosquitoes! They are easily identified by their black and white speckled scales on the edges of their wings and a hairlike “setae” found on the base of the wings. Fortunately for humans, these mosquitoes prefer to feed on deer, cows and horses. This particular species prefers to breed in pools, ditches and sometimes artificial water containers. They were found during early March, and typically are active during the winter; giving them the nickname “Winter Mosquito.”
By Jason Moak
Researchers at Phinizy Center monitor the oxygen levels in the Savannah and Ogeechee Rivers to better understand how they function and ensure the health of aquatic organisms that live there. Most of us know that oxygen is one of the essential requirements for human life. Oxygen in our bodies is a vital component of many life-sustaining chemicals and processes. The same is also true for most organisms that live in our lakes, rivers, and streams. Just as we humans depend on the oxygen present in the air we breathe, aquatic organisms depend on the oxygen present in the water they “breathe.” As those organisms breathe, they use up the oxygen in the water and it must be replenished. But how?
One source of oxygen in water is diffusion from the atmosphere. Based on the laws of physics, there is a maximum amount of oxygen that water can contain. To understand this, imagine if you were to add a couple of tablespoons of sugar to water and stir. After some time, the sugar granules would dissolve in the water. You could add a couple more tablespoons of sugar and stir and the sugar would again dissolve in the water. At some point, though, once the water becomes full or saturated, the sugar you keep adding would no longer dissolve. The same holds true for how much oxygen can be dissolved in water. If water does not contain the maximum amount of oxygen it can hold (it is undersaturated), then oxygen present in the air above the water can dissolve or diffuse into the water, just like the sugar. This diffusion process is pretty slow, but it can be sped up by turbulence, such as when water falls over a dam or passes through steep, rocky sections of a river or stream.
The other source of oxygen in water is photosynthesis. On land, plants absorb the energy from the sun and carbon dioxide from the atmosphere, use them to grow, and put out oxygen as a byproduct. Similarly, organisms like algae and phytoplankton that live in the water emit oxygen into the water during the day as they grow. Sometimes, these photosynthetic aquatic organisms can be so productive that they actually supersaturate the water with oxygen. When this happens, there are only two ways for that extra oxygen to get out of the water: diffusion (also called off-gassing), or respiration. Diffusion in this case is simply the reverse of what was described above, except here the excess oxygen dissolves from the water into the atmosphere. The other process, respiration, occurs when aquatic organisms like fish or bacteria “breathe” in the oxygen in the water using it for their own growth.
Based on state and federal laws, the waters in our local rivers and streams are required to have a daily average of at least 5 milligrams per liter of dissolved oxygen to ensure that they remain healthy. If you are interested in the dissolved oxygen levels of the places Phinizy Center monitors, check out our website at https://phinizycenter.org/projects/river-monitoring/.
By: Matt Erickson
Frog choruses can usually be heard on warm, wet nights, but February is right in the middle of calling season for the southern chorus frog. Calling in the winter and spring with cold weather has some advantages. It allows them to breed in temporary wetlands that might not hold water in the summer months and helps them avoid predators like snakes that are only active during warmer periods. Their call is a high-pitched, slow trill that sounds like a ratchet or something dragging the teeth of a comb. These frogs are common and abundant, so there is a good chance you’ll hear them if you listen for them. They spend time in wet, grassy areas and can often be found around retention ponds and roadside ditches.
Using Freshwater Invertebrates in River Monitoring
By: Damon Mullis
In the summer of 2014, we implemented a quarterly macroinvertebrate sampling regime to complement our continuous water quality monitoring programs on the Savannah and Ogeechee Rivers. Macoinvertebrates are any of a wide variety of invertebrates that live in aquatic habitats and are large enough to be seen without the aid of a microscope. Examples include crayfish, snails, segmented worms, and insects. The tolerance level of these diverse, localized populations to environmental stressors varies widely. As a result, their community structures are reliable indicators of changing environmental conditions over time and space. This characteristic makes macroinvertebrate assemblages ideal indicators of aquatic ecosystem health and quality. In addition, macroinvertebrates play an important role in freshwater food webs, serving as prey for other organisms including fish, amphibians, and wading birds. However, their role in processes like breaking down organic matter and nutrient cycling is likely their most significant contribution to the ecosystem. In fact, we initiated these biomonitoring projects because of the ecological importance and environmental utility of macroinvertebrate communities.
We collect macroinvertebrates by deploying Hester-Dendy multiplate samplers tied to floats that suspend them approximately 2 feet below the water’s surface. These samplers do not trap invertebrates; rather, they supply a stable substrate for them to inhabit. Fungus and bacteria start to grow on the samplers soon after they enter the water. This growth encourages the presence of species of macroinvertebrates that feed on these colonies. Other species use the stable substrate as a place to attach and filter food out of the flowing water. Predatory macroinvertebrates soon show up to feed on these other groups. After 30 days, the samplers are retrieved and the macroinvertebrates are identified, measured, counted, and classified into groups based on their ecological roles and tolerances to pollution. This data allows us to calculate abundance and biomass. We also use it to estimate diversity, biotic integrity, and functional roles for each community. Using this information in conjunction with data collected from our continuous monitoring stations allows us to detect changes in water quality and see how these changes directly impact biological communities.
Savannah River Dinosaurs
By: Jason Moak & Kelsey Laymon
There are dinosaurs living in the Savannah River. While they may not be as fearsome as a Tyrannosaurus rex, they are every bit as primitive. These river dinosaurs are fish – the shortnose sturgeon (Acipenser brevirostrum) and Atlantic sturgeon (Acipenser oxyrinchus). Scientists have thought of sturgeon species as living fossils because their anatomy has not changed in over 100 million years. Sturgeons are long-lived, slow growing species that have been captured as a source of food and caviar which has contributed to their decline and landed them on the list of federally endangered species since 1967.
SCDNR Reasearcher with Shortnose Sturgeon
Sturgeon are unique among bony fishes because their skeleton is almost all cartilaginous. Unlike most fish, they are covered with bony plates called scutes instead of scales. They have an elongated body and barbels, similar to a catfish’s whiskers, which help them find their food, commonly aquatic insects, mollusks, and crustaceans. Both of these species can live more than 60 years, and while shortnose sturgeon typically grow to about 3 feet long, some Atlantic sturgeon reach lengths of up to 14 feet!
Atlantic and shortnose sturgeons are found in rivers, estuaries and the sea all along the Eastern coast of North America. They are anadromous, a fisheries term meaning they spend most of their time in saltwater, but migrate up freshwater rivers from time to time for reproduction. In the Savannah River, the shortnose sturgeon spawns in the spring, but typically begin their upstream migration in January or February. Atlantic Sturgeon spawn from spring to fall, and can be found in the freshwater portion of the river throughout the year.
Phinizy Center Research Scientists Downloading Sturgeon Logger
Phinizy Center scientists have worked with other researchers since 2009 to study the movements of these fish in the Savannah River. Currently, we help monitor a network of underwater sensors that detect when a tagged sturgeon swims past. The sensors record the date and time, as well as the unique ID of the tagged fish. Using this data, researchers are gaining a better understanding of which habitats are most important for these species and when they migrate to spawn.
Distinctively Colored Mayfly Nymphs Collected From the Ogeechee River
By: Damon Mullis
Recently while processing invertebrate samples from the Ogeechee River, I spotted six exceptionally colored mayfly nymphs. They were very small (2-4mm in length) and had striking pink markings. Upon further inspection, I discovered that they were a species of mayfly within the Tricorythode genus. There are thirteen species of Tricorythodes in North America, with four species regularly occurring in our area. While insect biologists have discovered characteristics to distinguish between these species in their adult life stage, no one has done the tedious work of rearing them in a laboratory to reveal differences in the nymphs. As a result, we are unfortunately only able to identify these nymphs to the genus level.
Tricorythode nymphs are typically found in areas of flowing water in large streams and rivers. They prefer slow moving water that is slightly acidic, making the rivers and streams of the Coastal Plain of Georgia an ideal environment. They feed on the dead plant material and diatoms that are plentiful in this habitat. These rivers and streams are also pretty silty, so these little insects have evolved specially adapted gills. The first pair of gills are thickened and plate-like and do not function to obtain oxygen. They cover the functional gills and protect them from being covered with silt, which would prevent them from obtaining oxygen. To obtain dissolved oxygen, they raise the plate-like gills slightly and circulate water under them by waving the functional gills back and forth.
Most folks in these parts have had the pleasure of consuming catfish at some point in their lives. You might know that some catfish species found in our area can grow quite large – the Georgia state record blue catfish caught in 2010 weighed 80 lbs! What you might not know is that there are some catfish in our local creeks and rivers that don’t get much bigger than your pointer finger.
Recently, while checking on a water quality monitor in the Savannah River, one of our researchers found one of these small catfish, called “madtoms,” hiding in the small cage that guards the probes. This particular species is a speckled madtom (Noturus leptacanthus), named for the numerous spots covering its body. This species grows to a normal length of about two inches and typically lives two to three years.
The speckled madtom are found in both small creeks (they are present in Butler Creek at Phinizy Swamp Nature Park) and large rivers. They typically spend most of their day hiding in crevices around rocks or fallen trees and limbs and come out at night to feed on prey, which is mostly made up of small aquatic insect larvae. To protect themselves from predators, madtoms have bony, sharp spines that actually contain venom. This biologist can confirm that being stuck by a madtom spine is fairly painful, so be careful if you ever encounter one of these tiny catfish!