Graptemys nigrinoda (Black-knobbed Map Turtle)

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Black Knobbed Map Turtle

The Black-knobbed Map Turtle is a small to medium-sized freshwater turtle native to the southeastern United States. Renowned for the distinctive black knobs along its shell’s central ridge, this species exhibits unique physical characteristics and behaviors that make it a fascinating subject of study for herpetologists and nature enthusiasts alike.

Other related species

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Scientific Classification

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Testudines
  • Family: Emydidae
  • Genus: Graptemys
  • Species: Graptemys nigrinoda

Common Names

  • Black-knobbed Map Turtle
  • Black-knob Map Turtle

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Identification

Description

The Black-knobbed Map Turtle features an olive to brown carapace adorned with prominent black knobs along the central keel, especially noticeable in juveniles and males. The carapace has intricate patterns resembling contour lines on a map, giving the species its name. The plastron is lighter, usually yellowish, with dark markings along the seams. The skin is gray to olive with yellow stripes on the neck, limbs, and head, including a distinct yellow spot behind each eye.

Sexual Dimorphism

Females are significantly larger than males, with shell lengths reaching up to 10 inches (25 cm), while males typically grow up to 5 inches (13 cm). Males have longer, thicker tails and more elongated foreclaws compared to females. The knobs on the carapace are more pronounced in males.

Native Origin and Distribution

Geographical Range

Endemic to the United States, the Black-knobbed Map Turtle is primarily found in the Mobile Bay drainage system, inhabiting river systems in Alabama and northeastern Mississippi. Their range includes the Black Warrior, Tombigbee, and Alabama rivers.

Preferred Habitat

These turtles prefer rivers and streams with moderate to strong currents and abundant basking sites like fallen logs and branches. They thrive in habitats with sand or gravel bottoms and avoid heavily polluted or dammed waters. Clean, free-flowing rivers with ample aquatic vegetation and invertebrate populations are ideal for their survival.

Behavior

Feeding Habits

Black-knobbed Map Turtles are primarily carnivorous. Their diet consists of insects, mollusks (especially snails and clams), crustaceans, and occasionally small fish. Juveniles tend to consume more insects, while adults shift towards mollusks due to their stronger jaws capable of crushing shells.

Predators

Natural predators include raccoons, birds of prey, large fish, and snakes. Eggs and hatchlings are particularly vulnerable to predation by mammals and birds.

Reproduction

Breeding Season

Mating occurs in spring and fall. Nesting typically takes place from May to July when females leave the water to lay eggs on sandy or soft soil banks.

Reproductive Method

Females lay 1 to 3 clutches per year, each containing 4 to 7 eggs. The eggs incubate for about 60 to 75 days, with hatchlings emerging in late summer to early fall. Temperature during incubation can influence the sex of the offspring.

Conservation

Extinction Status

  • IUCN Red List: Vulnerable

Threats

  • Habitat Destruction: Damming of rivers, pollution, and deforestation impact their natural habitats.
  • Illegal Pet Trade: Over-collection for the pet industry reduces wild populations.
  • Human Disturbance: Recreational activities can destroy nesting sites and basking areas.

Conservation Measures

  • Legal Protection: Regulations on collection and trade have been implemented in some states.
  • Habitat Conservation: Efforts to preserve and restore river habitats are crucial.
  • Public Awareness: Educational programs aim to reduce human impact and promote conservation.

Economic Importance

While they contribute to the pet trade due to their unique appearance, overharvesting can negatively affect wild populations. Responsible breeding programs and regulations help mitigate adverse economic impacts.

Interesting Facts

  • The Black-knobbed Map Turtle’s shell patterns are so intricate that they resemble the contour lines of a topographic map.
  • They are excellent swimmers, well-adapted to life in flowing waters.
  • This species is highly sensitive to environmental changes, making it an important indicator of river ecosystem health.

About Author

Muntaseer Rahman started keeping pet turtles back in 2013. He also owns the largest Turtle & Tortoise Facebook community in Bangladesh. These days he is mostly active on Facebook.