New Zealand Mud Snails(Potamopyrgus antipodarum)

Discussion in 'Fly Fishing Forum' started by Jeremy King, Feb 27, 2013.

  1. So lately while fly fishing on a couple of local rivers I've noticed a ton of these snails and hardly any caddisfly larva I called the wdfw (washington department of Fish and wild life) and they told me about the new zealand mud snails .I'm going to give them a sample to make sure it is an invasive snail but whatever it is there are less caddisfly larva and more snails. I started researching snail control and have lots of experience in farming and usually you control an invasive species by making an uncomfortable enviroment for them or releasing something that eats them or controls them. I've heard that brown trout will eat them the most but they dont get very much nutrients to be healthy also read in the forms that in New Zealand the reason its not infested with them is becasue they have a certain organism that keeps the population low. If you have any info please let me know.
  2. The NZ mud snail is extremely hard to kill and can reproduce asexually, so it only takes one little snail to colonize a new stream. They can live in damp felts for weeks. Not good.

    Which streams have you seen the snails in? They are documented in Thornton Creek in Seattle, Kelsey Creek in Bellevue, in a lake in Olympia(Capitol Lake) and possibly elsewhere in WA. They are in Montana and Idaho too. Freezing is probably the easiest way to decontaminate fishing equipment. WDFW has a fact sheet and an equipment decontamination protocol that they can give you.
    Do you have a photo of the critters?
  3. Invasive species are a HUGE issue as you are all well aware. It's VERY hard to eradicate a species once it gets a foothold in a new environment, and bio control agents (introducing one species to control another) are poor solutions at best (swaping once invasive for another), and can cause further ecological damage.
    Jim Wallace and jimmydub like this.
  4. While a well meaning and logical way to remove one 'introduction' is to introdcue it's predator too, the reality can out way worse. Look up cane toads in Australia and I think mongoose introduction in a few places went spectacularly wrong. The snails I'm sure will become a much bigger issue in the future in more watersheds and there's not a lot we can do. Imagine getting everyone in the NW to stop wearing felt boots. Not going to happen and as noted it only takes one....

    Happy Wednesdays,

    Jim Wallace likes this.
  5. Ha Ha, The Hawaiian example! Ua Mau Ke Ea O Ka Aina I Ka Pono! (The life of the land is perpetuated in righteousness!") Ya know you get a volcano island group out in the middle of a vast ocean that has species evolving in isolation, and then ignorantly bring in another species in an attempt to control it, then you get what you get. Same old story. Mongoose stay out in daylight, rats stay out at night. Oops!

    I just bought some expensive high end new felt-soled boots, and I expect to use then for maybe as long as the next ten years. But I won't wear them where I know of any problems with invasive organisms. I just won't fish in those places. I'm going to wait until there are some rubber soled wading boots available that offer better traction on slick river cobbles than is currently available, before I spend my $$ on some new non-felt soled boots. The current skinny is that rubber vibram soles on wading boots is almost suicidal.

  6. Skeena, that is always a great link.
  7. By the time felt soles are banned it will be too late!!!
  8. Well that is somewhat disheartening. Didn't know they were so prolific in the Columbia.
  9. Looks like I'm going to have to reserve space in my freezer for my boots. All I've got is the small one on the top end of my fridge. But there's plenty of space in there now that I'm down to one small Ling filet, a stocker trout from a lake, and a piece of tuna, as well as a triploid carcass awaiting delivery to a watershed for nutrient purposes, some "ice wraps" for my aching joints, and a bag of ice ready for my cooler (that fills the remaining void).
  10. [​IMG]

    Here is an ok image of a couple snails that i found, idk what species they are but there is thousands of them in the river
  11. I have found small black snails that resemble these (NZ Mud Snails) in one of my favorite tidal creeks that flows into Willapa Bay. However, the ones I've found seem to attain a larger size, up to anywhere between 1/3" and 1/2" in length. Lots of smaller ones, though.
    Are there indigenous snails that resemble the New Zealand Mudsnail in appearance, but are usually larger, and black?

    edit: Jeremy, just saw the photo you posted. Hmmmm, the ones I am seeing are more conical in shape than those, and closely resemble the pics I've seen of NZMS, except the ones in lower Smith Creek are larger and almost black.

    So I would like to know if there is an indigenous freshwater snail found in streams along the coast that fits that description. My searches have found a lack of info containing any descriptions that include line drawings or photographs on this subject. I am having difficulty hacking thru the taxonomic jungle.
  12. The most effective way to approach invasive species is to enhance the natural environment that they have taken hold in. Stressed ecosystems are more easily infected or infested, while healthy functioning ecosystems have natural constitution against invasive species and plagues. Invasives might appear in healthy ecosystems, but they do not take hold. Native species are far better equipped to outcompete in healthy ecosystems.

    As others have pointed out, introducing predators can lead to devastating consequences like the Cane Toad. Some attempts have been successful, like the Cinnabar Moth on invasive ragworts. I prefer having allowed the Cinnabar Moth to be introduced to combat ragwort infestation than need to continually apply herbicides or manual removal. It's far less intensive, and the moths have not been shown to have an impact on native veg or wildlife. Plus, those moths are seriously cool looking.
    Jeremy King likes this.
  13. I might not get back up that creek until June or July now that fishing has closed there for the season. I'll see if I can collect some samples then, and send them in somewhere for identification.
  14. Jeremy -

    It would help to have something for scale in the photo with the snails. I can't tell if they are 2 mm or 2 cm in diameter.

  15. Me too its crazy how many species of snails there are these are mostly like 2mm to 4mm their tiny but i cant find anything on them and the ones that resemble them are the NZMS
  16. If as Skeena88 stated,these snails have been found in Capital Lake and have probably been there for a while,I would assume it would be a simple matter for them to migrate or be carried to the upper Deschutes river. Question for you biologist folks,do they take over the habitat to a point where they limit the natural insects survival?
  17. The snails do occupy a large area of stream bed and can be found at densities of >500,000 critters per square meter. I have some papers at work that discuss effects of NZ mud snails on native invertebrates, but at that density they can significantly displace and compete with native bugs, so a reduction in invertebrate diversity is inevitable.
    There was a study that looked at water bodies in a specified radius (don't recall the distance but it wasn't small) around Capitol Lake and didn't find any snails. The snails can migrate upstream slowly at about 800 meters/yr in low gradient systems, but the colonization pattern isn't usually a spreading radius around a single focal point which would indicate a gradual expansion of a local population, but rather is sporadic and wide ranging which usually means that the bugs have jumped large distances by being transported by a host. The host could be boats, wading gear, animals etc.
  18. NZM are sensitive to cold weather, so they drained Capitol lake a few years ago in the winter to let the cold air kill the snails; it didn't get all of them, but apparently it did knock the population back. Of course, you can't drain the Madison river in the winter...

    The snails graze on microscopic algae that form the base of the food chain in freshwater ecosystems. At high density they can outcompete the native invertebrates for food, thereby truncating the food chain that trout rely upon.


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