Black-knobbed Map Turtle
Encyclopedia
The black-knobbed map turtle (Graptemys nigrinoda) (formerly known as the black-knobbed sawback turtle) is a small to medium sized aquatic turtle
with light gray skin. Some of the most distinguishing characteristics of the black-knobbed map turtle, and the Graptemys
genus, are the protruding “spikes” on the turtle’s shell. This species resides mainly in the fall line
s of rivers in the Mobile Bay
drainage, in Alabama and Mississippi.
The shell of the turtle is dark olive-brown in color. Within each pleural, or “plate”, of the shell are yellow-green circular rings which are outlined in black. Hatchlings are similar in color to adults, but the colors tend to be more vibrant and contrasting. The knob-like processes are compressed laterally.
Their head is small and is dark brown with yellow stripes with yellow crescents behind the eye facing towards the posterior end of the turtle. These stripes continue on the legs of the turtle also, with the underside being lighter than the dorsal.
Sexual dimorphism
is evident in this species. Females are roughly twice the size of males. Also, females’ shells tend to be higher than males, though the males have longer tails than the females. Sizes have been recorded as ranging from 7.6-10.2 cm (3-4”) in males and 10.2-19.1 cm (4-7.5”) in females.
system and in the Black Warrior River
as far north as Jefferson County, Alabama. They are only able to survive in fresh water
, thus they are only found within fresh water river systems.
is a routine part of their day, occurring in the early morning and early afternoon. Thermoregulation
is thought to be the reason for basking, along with the removal of parasites and algae growth.
When approached, they jump into the nearby water. Once in the water, they seek protection between the branches of fallen trees on the river bottom. Most of the riverbeds they live in have sand and clay bottoms with moderate currents. Hatchlings prefer more sluggish waters off the main channel.
Little is known about foraging
behavior. However, this species has been observed to consume beetles and dragonflies that have fallen into the river. Upon examination of both female and male stomach matter, Lahanas found a distinction of food material percentages. Males had roughly 58% animal matter and 40% plant matter, while females had 70% animal matter and 29% plant matter. The three primary sources of animal matter came form freshwater sponges, bryozoans, and mollusks. The only plant matter found was a freshwater alga.
Males reach sexual maturity
at around 3–4 years and females reach it around 7–8 years. Females have a clutch
size of roughly 5 eggs and can lay 3-4 clutches in a year. Nesting occurs from May- August, and occurs nocturnally on the sandbank. This species feeds primarily on insects.
by the IUCN Red List
. The black-knobbed map turtle is most likely threatened by habitat degradation and encroachment
by humans. Humans have been known to remove dead logs that line the shoreline of rivers, which the turtle uses for basking in the sun. Also, indirect disturbances of nest sites may become an issue. Additionally, the turtle population could decline due to the consumption of their eggs by humans or other predators. Fisherman, though in most cases not purposely, can kill turtles via their trotlines, gill nets, and hoop nets.
Most of the lands encompassed by the species habitat are protected lands, but the rivers remain vulnerable. Mobile River Basin Aquatic Ecosystem Recovery Plan has been implemented to address the needs of 22 aquatic species. One of these species is the red bellied turtle(Pseudemys rubriventris), whose habitat overlaps with Graptemys nigrinoda, and therefore will be beneficial to the black-knobbed map turtle.
Captive breeding
has been an option for conservation efforts also. It has been determined that captive breeding is plausible for increasing population sizes in captivity. However, it remains unclear if captive bred black-knobbed map turtles can be released into the wild and breed on their own.
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
with light gray skin. Some of the most distinguishing characteristics of the black-knobbed map turtle, and the Graptemys
Graptemys
Graptemys is a genus of turtles known commonly as map turtles or sometimes sawback turtles. They are aquatic, freshwater turtles that are found throughout the eastern half of the United States and northward into southern Canada. They superficially resemble many other species of aquatic turtle,...
genus, are the protruding “spikes” on the turtle’s shell. This species resides mainly in the fall line
Fall line
A fall line is a geomorphologic unconformity between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock. A fall line is typically prominent when crossed by a river, for there will often be rapids or waterfalls...
s of rivers in the Mobile Bay
Mobile Bay
Mobile Bay is an inlet of the Gulf of Mexico, lying within the state of Alabama in the United States. Its mouth is formed by the Fort Morgan Peninsula on the eastern side and Dauphin Island, a barrier island on the western side. The Mobile River and Tensaw River empty into the northern end of the...
drainage, in Alabama and Mississippi.
Description
The shell of Graptemys nigrinoda is slightly domed with the first 4 vertebrae possessing backward-projecting, knob-like processes, which are black in color. The second and third processes are more dominant in size compared to the first and fourth. With aging females the knobs are reduced to small swellings.The shell of the turtle is dark olive-brown in color. Within each pleural, or “plate”, of the shell are yellow-green circular rings which are outlined in black. Hatchlings are similar in color to adults, but the colors tend to be more vibrant and contrasting. The knob-like processes are compressed laterally.
Their head is small and is dark brown with yellow stripes with yellow crescents behind the eye facing towards the posterior end of the turtle. These stripes continue on the legs of the turtle also, with the underside being lighter than the dorsal.
Sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
is evident in this species. Females are roughly twice the size of males. Also, females’ shells tend to be higher than males, though the males have longer tails than the females. Sizes have been recorded as ranging from 7.6-10.2 cm (3-4”) in males and 10.2-19.1 cm (4-7.5”) in females.
Distribution
The black-knobbed map turtle is endemic to the southeastern United States. In Alabama, they are found in the Mobile Bay drainage. In Mississippi, they are found in the Tombigbee RiverTombigbee River
The Tombigbee River is a tributary of the Mobile River, approximately 200 mi long, in the U.S. states of Mississippi and Alabama. It is one of two major rivers, along with the Alabama River, that unite to form the short Mobile River before it empties into Mobile Bay on the Gulf of Mexico...
system and in the Black Warrior River
Black Warrior River
The Black Warrior River is a waterway in west central Alabama in the southeastern United States. The river rises in the extreme southern edges of the Appalachian Highlands and flows 178 miles to the Tombigbee River, of which the Black Warrior is the primary tributary...
as far north as Jefferson County, Alabama. They are only able to survive in fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
, thus they are only found within fresh water river systems.
Habitat and ecology
Black-knobbed map turtles are seasonally active in April- late November. BaskingEctotherm
An ectotherm, from the Greek εκτός "outside" and θερμός "hot", refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body...
is a routine part of their day, occurring in the early morning and early afternoon. Thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
is thought to be the reason for basking, along with the removal of parasites and algae growth.
When approached, they jump into the nearby water. Once in the water, they seek protection between the branches of fallen trees on the river bottom. Most of the riverbeds they live in have sand and clay bottoms with moderate currents. Hatchlings prefer more sluggish waters off the main channel.
Little is known about foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
behavior. However, this species has been observed to consume beetles and dragonflies that have fallen into the river. Upon examination of both female and male stomach matter, Lahanas found a distinction of food material percentages. Males had roughly 58% animal matter and 40% plant matter, while females had 70% animal matter and 29% plant matter. The three primary sources of animal matter came form freshwater sponges, bryozoans, and mollusks. The only plant matter found was a freshwater alga.
Males reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at around 3–4 years and females reach it around 7–8 years. Females have a clutch
Clutch (eggs)
A clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
size of roughly 5 eggs and can lay 3-4 clutches in a year. Nesting occurs from May- August, and occurs nocturnally on the sandbank. This species feeds primarily on insects.
Conservation
Currently this species is classified as Endangered by the U.S. Fish and Wildlife Service in sub category 3-C, but classified as Near ThreatenedNear Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
by the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
. The black-knobbed map turtle is most likely threatened by habitat degradation and encroachment
Encroachment
Encroachment is a term which implies "advance beyond proper limits," and may have different interpretations depending on the context. Encroachment may refer to one of the following:* Temporal encroachment* Structural encroachment...
by humans. Humans have been known to remove dead logs that line the shoreline of rivers, which the turtle uses for basking in the sun. Also, indirect disturbances of nest sites may become an issue. Additionally, the turtle population could decline due to the consumption of their eggs by humans or other predators. Fisherman, though in most cases not purposely, can kill turtles via their trotlines, gill nets, and hoop nets.
Most of the lands encompassed by the species habitat are protected lands, but the rivers remain vulnerable. Mobile River Basin Aquatic Ecosystem Recovery Plan has been implemented to address the needs of 22 aquatic species. One of these species is the red bellied turtle(Pseudemys rubriventris), whose habitat overlaps with Graptemys nigrinoda, and therefore will be beneficial to the black-knobbed map turtle.
Captive breeding
Captive breeding
Captive breedingis the process of breeding animals in human controlled environments with restricted settings, such as wildlife reserves, zoos and other conservation facilities; sometimes the process is construed to include release of individual organisms to the wild, when there is sufficient...
has been an option for conservation efforts also. It has been determined that captive breeding is plausible for increasing population sizes in captivity. However, it remains unclear if captive bred black-knobbed map turtles can be released into the wild and breed on their own.