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  • Writer's pictureJenni Foshey

Why You Should Care About Mink Frogs

Updated: Sep 30, 2020

Introduction 

Lithobates septentrionalis, commonly known as the Mink frog, is a species of concern when it comes to conservation. According to the Natural Heritage Inventory, the Mink frog is ranked as a G5, meaning its species is secure worldwide and has a very low risk of extinction because of their expansive distribution and abundant populations. However, the species is ranked as an S3 specifically in the state of Wisconsin, meaning they are considered vulnerable due to declining populations from various threats to them and their habitats. 

The above global and Wisconsin conservation statuses from the Natural Heritage Inventory are relatively recent. The Natural Heritage Inventory seems to have ranked the Mink Frog as S3 in Wisconsin primarily by analyzing their habitats (Wisconsin DNR). The way this species was ranked is believable because of the data provided by NatureServe Explorer (NSE); NSE provides distribution of the Mink frog in some states as well as Canadian provinces. Distribution here shows Wisconsin as vulnerable (S3), which is consistent with the ranking of the Natural Heritage Inventory. 


Threats

Mink frogs live near slow moving water with abundant vegetation nearby and are rarely found on land (Ontario Nature). Mink frog adults and tadpoles hibernate underwater and feed on small invertebrates they find in aquatic plants. Since these frogs depend on water for survival, their biggest threats come when their water habitats are affected.  

It is likely that this species is ranked as a G5 by the Natural Heritage inventory because of climate change. Since climate change impacts worsen each year, it’s thought that Mink frogs will be impacted more in the coming decades. According to the Northeastern States Research Cooperative, climate change is likely to harm Mink frog populations because of their specific habitat preferences of cold water. Climate change will increase water temperatures, which will in turn impact their distribution and the survival of eggs (Northeastern States Research Cooperative), and overwintering survival (Wisconsin DNR Wildlife Action Plan 2015). Popescu and Gibbs (2009) conducted a study on Mink frog pond occupancy by analyzing 46 ponds in New York to understand the species’ population and conservation status. Like the Northeastern States Research Cooperative, Popescu and Gibbs state that climate change is the prominent threat for the future of Mink frog populations. In order for embryos to survive, there must be an average monthly temperature of 21 degrees Celsius or less, and an increase in just one degree can drastically impact Mink frog survival (Popescu and Gibbs 2009). 

Though not specifically a threat to Mink frogs alone, the Chytrid fungus (Batrachochytrium dendrobatidis) is deadly to amphibians worldwide as it causes skin to thicken. Many amphibians absorb water and nutrients through their skin, so when the skin becomes thicker, water and nutrients cannot be absorbed, and therefore cause death (AmphibiaWeb). 


The first detection of the fungus was in Queensland, Australia, in 1995, which was after a massive decline and extinction of the Eungella Gastric-Brooding frog. The cause of extinction at the time was unknown, but since the Eungella Gastric-Brooding frog shared a similar habitat of cool waters year-round, their extinction acts as a warning to Mink frogs and other amphibians with similar habitat preferences. To understand this fungus more, a study was conducted in Queensland, Australia, by Retallick et al. (2004) on the frog species Taudactylus eungellensis and Litoria lesueuri. They examined 474 toes of these species for Batrachochytrium dendrobatidis and of this sample, 15% were positive for the fungus. This study is important because it helps ecologists and biologists understand the number of frogs affected. Batrachochytrium dendrobatidis was most prevalent in the cooler months and shown to peak at about 23 degrees Celsius, which is the preferred temperature of Mink frog waters. Therefore, Mink frog populations could have a similar percentage of infected individuals since they live in cooler waters than the Eungella Gastric-Brooding frog. Between climate change and the Chytrid fungus, I consider the Chytrid fungus to be more of a threat because it is currently occurring in amphibian species worldwide, whereas climate change is a threat that could worsen and affect populations over time. 

Conservation Efforts

There are not many, if at all, conservation efforts in effect for the Mink frog. Since so many amphibians are in decline due to similar reasons, like climate change, most management plan actions group the Mink frog with other amphibians under a generalized category. 

The Department of Natural Resources Wisconsin Wildlife Plan (2015) states threats and issues of wildlife and their correlated action for protection. The threat of climate change to amphibians implies the expected temperature increase of water habitats, which will negatively impact Mink frog survival. Because climate change is continuously progressing, it is difficult to plan and execute a specific conservation strategy. To conserve amphibians from climate change impacts, the Wisconsin DNR aims to take an overall habitat protection approach. This approach entails habitat restoration projects, and maintenance of aquatic vegetation, which will keep water temperature and water quality in check. The challenge of this approach is having funds to implement it and having people dedicated to constant monitoring and maintenance of the sites. It may be hard to determine whether or not this approach will go into effect since there are other species with a higher conservation concern. In this case, the conservation funds would likely go to that species instead.  

The Wisconsin DNR does not directly state a plan of action for addressing the Chytrid fungus among amphibians. They state that amphibian health concerns would involve both state and local conservation groups and agencies who are knowledgeable of the health concern at hand. The most effective plan the DNR states for this approach is community involvement. This is helpful in the sense that anyone can report amphibian disease and mortality, but the accuracy of this approach if questionable. On the other hand, the transmission of Batrachochytrium dendrobatidis has been studied to determine how the fungus can be treated. Effective disinfecting treatments, according to Young et al. (2007), include sodium hypochlorite, ethanol, and a compound of ammonium, didecyl dimethyl ammonium chloride, and other chemicals at various concentrations. These chemicals are effective when used in amphibian husbandry, in the field, and on equipment, clothes, and shoes to prevent transmission between animals; however, these chemical disinfectants should be used carefully so they do not harm the environment in which they’re used (Young et al. 2007). Similar to my earlier statement, I consider the Chytrid fungus plan of action more effective than the plan for climate change because the plan for Chytrid fungus transmission is specific in chemicals to use and what the chemicals should be used on, versus the non-specific climate change plan of monitoring habitats. 

Habitat

Mink frogs are located in much of southern Canada, and the northern US from Minnesota to the east coast, with 43N latitude being the southern limit of distribution (Heeden 1986). Wisconsin is peripheral to the Mink frog’s range because it is the general middle of the total range. Throughout the entire range, populations are overall common (NatureServe Explorer). The lowest conservation ranking is S3, which accounts for both Wisconsin and Vermont. This being said, Wisconsin Mink frog populations are especially important because if the populations decline, Wisconsin would have the lowest rank of all states and provinces with Mink frog populations, making it the area of greatest conservation concern.  

Additionally, Wisconsin Mink frog populations only reside in the northern half of the state due to boreal forests (Heeden 1986), which are associated with cool water habitats and is a suitable habitat for the species. Without these forests, Mink frog populations would drastically decrease. Climate change, species migration, seed dispersal, and fire disturbances all pose threats to Wisconsin boreal forests (Scheller and Mladenoff 2005). To protect Wisconsin’s Mink frog population, forest conservation is important. Forests can be conserved by maintaining ecosystem quality, preventing industrialization near forest, preventing habitat fragmentation, and tackling climate change from the source (for example, lowering carbon emissions in areas of concern). If boreal forests, and the water ecosystems within them, are preserved, Mink frog populations can remain stable at an S3 status or improve to a S4. 

My Take on Mink Frogs

Assuming there are limited funds available for managing a rare Wisconsin species and only a few species can be helped, I would list Mink frogs with a conservation priority of 3 (low) and would favor the species of greater concern for two reasons. 

First, Mink frogs have a state conservation rank of S3, which is in the middle of the 1-5 range, meaning there are species listed as more threatened (S1 and S2). Species of higher concern (especially ones with a smaller range) should be a priority simply because they’re closer to extinction. Being at such risk for extinction not only means that species is lost, but their predators and prey will be affected, as well as their habitats (niche shifts).  

Second, the species of greater concern could be an umbrella species, meaning that protecting them can also benefit other species. For example, if the species of higher concern is threatened similarly to Mink frogs, tackling that threat can revive both species’ populations. By protecting the species of higher concern, other species can benefit, their role in the ecosystem will be maintained or revived, and once they’re at a safe status, other species, like the Mink frog can be of focus. But as a general rule, I believe it is important for the most threatened species to be helped first, so it’s not too late to save them. 

 

References


AmphibiaWeb. Rana Septentrionalis. Lannoo M, editor. [accessed 2020 Feb 17]. https://amphibiaweb.org/cgi/amphib_query?rel-common_name=like&rel-family=equals&rel-ordr=equals&rel-intro_isocc=like&rel-description=like&rel-distribution=like&rel-life_history=like&rel-trends_and_threats=like&rel-relation_to_humans=like&rel-comments=like&rel-submittedby=like&max=200&orderbyaw=Genus+species&include_synonymies=Yes&show_photos=Yes&rel-scientific_name=contains&where-scientific_name=lithobates+septentrionalis&rel-genus=equals&where-genus=&rel-species=equals&where-species=&where-common_name=&where-clade=&where-subfamily=&where-family=any&where-ordr=any&rel-isocc=occurs+in&where-isocc=&rel-species_account=matchboolean&where-species_account=&rel-declinecauses=equals&where-declinecauses=&rel-iucn=begins+with&where-iucn=&rel-cites=equals&where-cites=&where-submittedby=



Heeden SE. 1986. The Southern Geographic Limit of the Mink Frog, Rana septentrionalis. JSTOR. https://www.jstor.org/stable/1444920?seq=1#metadata_info_tab_contents

Northeastern States Research Cooperative. Effects of Climate Change on the Mink Frog of the Northern Forest. 1970 Jan 1. [accessed 2020 Feb 17]. https://nsrcforest.org/project/effects-climate-change-mink-frog-northern-forest

Ontario Nature. Mink Frog: Reptiles & Amphibians in Ontario. [accessed 2020 Feb 17]. https://ontarionature.org/programs/citizen-science/reptile-amphibian-atlas/mink-frog/

Popescu VD, Gibbs JP. 2009 May 5. Interactions between climate, beaver activity, and pond occupancy by the cold-adapted mink frog in New York State, USA. Biological Conservation. https://www.sciencedirect.com/science/article/pii/S0006320709001712

Retallick RW, McCallum H, Speare R. 2004. of the Amphibian Chytrid Fungus Endemic Infection in a Frog Community Post-Decline. Public Library of Science. https://journals.plos.org/plosbiology/article/file?type=printable&id=10.1371/journal.pbio.0020351

Scheller RM, Mladenoff DJ. 2005 Jan 17. A spatially interactive simulation of climate change, harvesting, wind, and tree species migration and projected changes to forest composition and biomass in northern Wisconsin, USA. Wiley Online Library. [accessed 2020 Feb 16]. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2486.2005.00906.x?casa_token=rknRgfMYhwwAAAAA:EthvEdQrFUOJP2X9IGGbhL9vBCrtS5dX1GYNTi8vD06T7itS3hsI-FHgSnhReINY9Va5MwEwEJJlNXo8

Wisconsin DNR. Mink Frog (Lithobates septentrionalis). [accessed 2020 Feb 17]. https://dnr.wi.gov/topic/EndangeredResources/Animals.asp?mode=detail&SpecCode=AAABH01190

Wisconsin DNR. Wisconsin Wildlife Action Plan pdf. 2015. Pg. 4. Threats/Issues and Conservation Actions for Reptile and Amphibian Species of Greatest Conservation Need. https://dnr.wi.gov/topic/endangeredResources/documents/herpConservationActions.pdf

Young S, Berger L, Speare R. 2007 Apr 24. Amphibian chytridiomycosis: strategies for captive management and conservation. ZSL Publications. [accessed 2020 Feb 15]. https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/j.1748-1090.2007.00010.x?casa_token=1RoP9vJRtXcAAAAA:W--MCAEfTMaVWx-AlCfteVS6uwGvEgkD2veO9XC3LLa9kXyJwylPbx5EOvHbAPhwhxxLDpVbrc2qEk95











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