Current Status
The New Zealand mudsnail is now reported from all fully western states, except New Mexico.
It is also reported in Port Alberni, British Columbia,
but this project made no provision to cover Canada!
In the image below (updated 2007 MAR 19),
positive states are orange and positive HUCs (cataloging units) are red.
Click on the image for a larger version that is suitable for hard-copy.
The 1995-2005 map is still available.
The snails were reported in 3 new western HUCs during the last year
(down from 8 during 2005 (see details).
It is not clear if this represents a slowing of the spread or a slowing of collection and/or reporting.
Santa Monica Bay and Aliso-San Onofre in southern California represent jumps into isolated HUC's.
The other addition is the Ruby River in Montana. This HUC had mudsnails on all sides,
but the 2 discovered populations are well isolated from other sources (and each other)
and thus also represent 2 more jumps.
See the interactive maps on the bottom of this page to get get more detailed, up-to-date maps,
or to get more information on the positive sites.
Database Recent additions (Archive)
- The database was last updated on 2007 Dec 19.
Mike Robertson added 8 samples from Bair Creek, a tributary of the Great Salt Lake, Utah.
Randal Benthin added 2 more samples from Shasta Lake, California.
The on-line database now contains 1508 collection records.
- The database was updated on 2007 Dec 11.
Two new Califonia HUCs are added to the positive list;
Marion Wittman added a sample from lake Shasta in the Sacramento headwaters,
and Doug Post added a sample from the American River, another tailwater site.
Again, this seems to be an area of active expansion.
More sites in the Sacramento drainage should be expected to fill the gaps.
- The database was updated on 2007 Nov 9.
Michael Kellogg entered a location on Alameda Creek in California.
This is the first report from the San Francisco Bay HUC.
This seems to be an area of active expansion.
- The database was updated on 2007 Nov 6.
Wyoming Game and Fish obtained a sample from a concerned angler from the Shoshone River below Cody.
This is the first report from that drainage and yet another tailwater population.
The snail ID was confirmed by Dan Gustafson. No other details are known.
- The database was updated on 2007 Oct 8.
Michelle Luebke added West Antioch Creek, the first site from the San Joaquin Delta in California.
- The database was updated on 2007 Sept 18.
Mark Vinson added 9 new records for springs in Northern Utah.
This is disturbing as the snail has previously not been prone to showing up in isolated sites.
Mark thinks that duck might be involved.
Robyn Draheim and colleagues added 7 more records from the Deschutes River area.
The Swan River site in Western Montana was removed from the active data as repeated collection
efforts there have failed to find a living population.
This site is now treated as the second possible example of a failed population (see below).
The table below provides direct links to the default maps for the indicated areas.
All maps are produced on-demand to ensure using the latest copy of the database.
Red dots represent positive collection sites and red HUCs indicated positive HUC cataloging units.
You can get additional information by clicking on the dots or HUCs and following the available links.
See the instructions page for the AIM mapping system for more information.
Technical update note:
The mapping system was updated in February 2005 so that the current year is the default year for all data entry.
This eliminates the need for annual updates on all involved pages and programs.
More importantly, all involved mapping programs were also modified so that
any future year is automatically reset to the current year.
This allows simple links to point to the normal default case of using all available data.
To make use of this feature, simply copy the link you want and replace the current year with a distant future year.
For example, when using data from 1900 through 2005, you would replace "19002005" with "19009999".
This will be good until the y10k bug hits, which is not my problem.
As usual with such links, you must not disturb the rest of the data contents.
Potential Failed Populations (points removed from the database)
Failed introductions of New Zealand mudsnails,
like most species introductions, are probably very common.
However, the chances of detecting such an event is naturally extremely low.
With the nzms this probability might be increased as the snail is typically introduced at
convenient access points and the population might get started fairly quickly in the summer
before dying out in their first winter.
The sites below are thought to have had valid nzms collections, but without an established population.
These sites have been removed from the database, which is intended to track successful introductions.
Note that no substantial population of nzms in western North America is known to have died out.
- Kalispell Creek in Northern Idaho:
Dan Gustafson collected a single mudsnail in a large sample
(sample W1459) on April 27 2001.
There was no other known source of mudsnails on the entire trip, so the record is thought to be real.
However, 2 followup samples on July 29, 2003 were completely negative,
so no population appears to be established here.
The stream community here is not similar to those where mudsnails typically occur,
which may indicate that this site is unsuitable for them.
- The Swan River at the Swan River FAS:
A routine sample by MTDEQ contained a single mudsnail collected live from this site on August 11, 2003.
The snail was not identified until Jan 2007 when Dan Gustafson was reviewing some
samples of western Montana hydrobiids (only 3 known native species).
It represented the first record in Montana west of the continental divide.
Repeated efforts to verify their status there have failed to find any more mudsnails.
So at this time, there are no known nzms sites in Montana west of the continental divide.
The stream community here is not similar to those where mudsnails typically occur,
which may indicate that this site is unsuitable for them.
2002 FEB 9, last updated on 2007 NOV 9
