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Role of chytrid fungus in decrease in hellbender populations

This is a discussion on Role of chytrid fungus in decrease in hellbender populations within the Large Aquatic Salamanders (Hellbenders/Cryptobranchids, Necturus, Siren, etc.) forums, part of the Species, Genus & Family Discussions category; I'm hearing talk among Japanese biologists here about how hellbenders have been declining in numbers, apparently due partly to the ...

Large Aquatic Salamanders (Hellbenders/Cryptobranchids, Necturus, Siren, etc.) This topic covers Cryptobranchids like the hellbender and Asian giant salamanders, as well as sirens, mud puppies, and amphiumas.

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Old 14th January 2007   #1 (permalink)
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I'm hearing talk among Japanese biologists here about how hellbenders have been declining in numbers, apparently due partly to the spread of the chytrid fungus, leading them to fear that the Japanese giant salamander could suffer the same fate. But I can't find anything detailed about this on the Web. Can anybody confirm this for me and cite a study or two?

(Message edited by TJ on January 15, 2007)



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Old 14th January 2007   #2 (permalink)
russ
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I've never heard any talk of that. Here's a site with some good info on suspected hellbender problems:

http://www.hellbenders.org/



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Old 15th January 2007   #3 (permalink)
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Thanks for that link, Russ. I wasn't aware of that site and it's really informative. It cites five factors as possibly behind the decline of hellbenders, namely siltation of streams, the building of dams, the killing of hellbenders by fishermen, overcollection for the pet trade, and endocrine disruptors. No mention of chytrid fungus.

There's one paper I'm after that I didn't see in that site's huge publication list. It's this article from Conservation Biology:

Population declines of a long-lived salamander: a 20+-year study of hellbenders, Cryptobranchus alleganiensis (by Wheeler. Prosen, Mathis, Wilkinson)
http://www.dicer.org/jsp/journal/sho...-106-109-1-151

A summary of that paper says that over the 20 some years of the study, populations of hellbenders declined by an average of about 77%, and that "it is not known whether population declines for hellbenders have a single cause or whether each population has experienced independent declines." Can anybody send me the PDF?

So far, I've only found one reference on the Web of chytrid fungus affecting hellbenders, a blog entry at http://violet789.blogspot.com/2006_08_01_archive.html that said the chytrid fungus "has been running rampant in the Hellbender's habitats." But there's no elaboration.



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Old 16th January 2007   #4 (permalink)
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I have a copy of the article that you are looking for and I PMed you for an email address.



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Old 16th January 2007   #5 (permalink)
frank
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Hi Tim,

I think most people agree that chytrids pose an important threat on native amphibian wildlife. However, it would be to easy to blame all amphibian declines to chytrids. I have become extremely cautious about chytrids since we tried to inoculate recently metamorphosed Dendrobates in the lab with a massive dose (to test a treatment); the frogs didn't become ill and were even able to eliminate the infection... I think in nature, in many cases you need more than the fungus alone.



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Old 17th January 2007   #6 (permalink)
jonathan
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for the benefit of those who don't have the article, it also says:
"This decline was characterized by a shift in size (age) structure, with a disproportionate decrease in numbers of young individuals."
That seems to make chytrid an unlikely culprit, unless it targets young individuals, or adults are resistant to it in some way.



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Old 17th January 2007   #7 (permalink)
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Abrahm, I'll be happy to get that from you. Thanks a lot Click the image to open in full size. And thanks for those observations, Frank and Jonathan.

Indeed, it seems the hellbender has plenty to contend with without the chytrid fungus Click the image to open in full size. I haven't yet looked at the above-mentioned report, but I did see the Eastern Hellbender Status Assessment Report (2003), which identifies potential threats to eastern hellbender populations in various states as including:

* siltation due to deforestation, road construction, etc.
* problems cause by dams, including habitat loss, declines of dissolved oxygen concentration, increased water temperature
* industrial pollution, pesticide runoff, acid mine drainage, failing septic systems, municipal waste
* streambed gravel mining
* incidental take by anglers, collection of bait salamanders, collection for commercial, scientific or educational purposes
* predation by non-native game fish, catfish, exotic crayfish
* alteration of habitats for recreation, channelization of streams
* nutrient enrichment (not sure what this means...)
* lack of prey
* cannibalism (adults on eggs
* endocrine disruption
* climate change, low water pH, UV-B radiation

While there's no mention of chytrid fungus, on the subject of disease the report seems to echo what Frank just said about "in nature, in many cases you need more than the fungus alone":

"Nickerson and Mays (1973) describe various fungi, protozoans, nematodes, trematodes, cestodes, acanthocephalans, and annelids (leaches) as hellbender parasites. Krecker (1916) reported the worm Filaria cingula to be a skin parasite of C. alleganiensis. These factors can adversely affect individual eastern hellbenders although relative to the threatening factors associated with habitat degradation, it is doubtful that they have negatively impacted populations of eastern hellbenders, significantly. However, the cumulative effects of multiple environmental and biological stressors may increase hellbender mortality rates. For example, Kiesecker et al. (2001) describe how climate-induced changes in UV-B exposure increase susceptibility to pathogen outbreaks in western United States amphibian populations."

Here is a link to a PDF of the Eastern Hellbender Status Assessment report:
http://www.fws.gov/midwest/eco_serv/...ns/eahe-sa.pdf



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