The red eared invaders spread across Bulgaria

Featured photos: 

  1. Flag map of Bulgaria by PavelD Wikipedia commons
    1. https://en.m.wikipedia.org/wiki/File:Flag_map_of_Bulgaria.svg 
  2. Red-eared slider by Rhondle Wikipedia commons
    1. https://commons.wikimedia.org/wiki/File:Red-eared_slider.jpg

Publication: Kornilev YV, Lukanov S, Pulev A. 2020. The Alien Pond Slider Trachemys scripta ( Thunberg in Schoepff , 1792 ) in Bulgaria : Future Prospects for an Established and Reproducing Invasive Species. Acta Zool Bulg. 72(4):571–581: http://www.acta-zoologica-bulgarica.eu/00SIO_1_09

The invader in red 

The red-eared slider turtles (Trachemys scripta elegans) are listed as one of the 100 worst invasive species in the world. It is estimated that more than 52 million turtles were exported from their native range in the United States globally via pet markets. In England, they connect the pet trade popularity with the rise in popularity of the Ninja Turtles. Turtles generally are long-lived pets and unfortunately, many pet owners are thought to have released unwanted pets to ponds and other freshwater bodies. These sturdy animals were then able to reproduce and have established wild populations. Another consequence of their long age span is their significant ecological impact, which is proportional to their longevity. The species can be a predator and a competitor of native animals that live in freshwater bodies. Because of this, many states currently regulate the collection and exportation of red-eared slides (check out my previous post about this topic here). However, in countries where the turtles have already been introduced, the spread continues.

Drop by drop the whole lake becomes

–Bulgarian proverb

Figure 1: Red-eared slider turtle by Sheila Sund wikimedia. The turtle is known for its bright red band behind the eyes and the bright yellow color in its shell.

Red-eared sliders are the only invasive reptile or amphibian in Bulgaria. Like many other countries, the pet trade in the 1990s is attributed to a massive intentional and/or accidental release to the wild. In 2007, when Bulgaria joined the European Union, the import of Trachemys scripta was banned as per the regulation established by the Union in 1997. By 2014, three subspecies of Trachemys scripta were also included in this importation ban. However, in Bulgaria, the species remains readily available as a pet through illegal imports or from breeders within the European Nation (hyperlink to titular article). Because of this, Georgi Popgeorgiev (National Museum of Natural History & Bulgarian Academy of Sciences) and collaborators set out to map the current and potential distribution of Trachemys scripta in Bulgaria.

The team found that most sightings of Trachemys scripta occurred in close proximity to human settlements. This could be an indicator that the invasive turtles are largely using the habitats they were released in. Additionally, this study found that turtles now inhabit most of the lowlands of Bulgaria (Figure 2). The team also found that there are still more habitats that the turtle can use, potentially increasing the spread of the invasive turtle throughout Bulgaria. The study didn’t find any evidence of the invasive turtle displacing or harming the two native Bulgarian freshwater turtle species. However, the authors are concerned that as the species continues to spread this balance could be disrupted.

Figure 2: Map of the sightings of the invasive turtle in Bulgaria. Green squares represent previously published sightings, blue circles are new sightings and red triangles are new sightings and published sightings. The new species is spreading southeast along the lowlands where the climate is favorable for it

Every frog has its pond

— Bulgarian proverb

The spread of invasive species is a complicated issue with financial, political and biological implications. In some cases, citizens rely on income associated with pet trade and import regulations fall short in light of illegal sales and breeding. Furthermore, once a species is established it can become difficult to manage the invasive populations. If you own a pet that needs a new home, remember the Bulgarian proverb, every frog has its pond. Do not release your pet to the home of others, and instead find other solutions with local pet stores via adoption or animal control agencies. 

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Kevin Aviles Rodriguez

I am in the process of completing my PhD in Ecology and Evolutionary Biology at the University of Massachusetts in Boston. I am interested in human environmental changes as natural experiments to test hypothesis about the evolution of animals. Specifically, I study small lizards known as anoles and how living near human households impacts their ecology and behavior. I love fieldwork because often it takes me away from the cold and towards the sunny beachy islands that I love the most.

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