1. New Zealand mud snails
(Potamopyrus antipodarum)
In Capitol Lake

4. • Small aquatic snail
• Parthenogenic
• High reproductive
potential
▫ 20-120 offspring/year
• High-density populations
▫ 100,000-500,000/m2
• Tolerant of moderate
salinity levels (17-24 pss)

5. Impacts
• Outcompete native gastropods by consuming large
quantities of primary production
• Do not serve as an equivalent food source – NZMS
pass through fish guts undigested.
• Restricted recreational opportunities.
• Increased costs to aquaculture and municipal water
control facilities.

6. Western Expansion

8. Vectors
• Fish hatcheries and associated stocking operations
• Recreational watercraft and trailers
• Anglers and hunters
• Sand and gravel mining, dredging
• Commercial shipping
• Pets, fish and wildlife
• Natural resource management activities

9. Response
▫ Fish and Wildlife –
state and federal
▫ General
Administration
▫ Ecology
▫ Natural Resources
▫ City of Olympia
▫ Invasive Species
Council
• October 2009 – snails found
• November 2009
▫ Agencies notified
▫ Response work group formed
▫ Closed lake
• December 2009
▫ Partial lake drawdown + Freeze
• March 2010
▫ Lake drained and filled with
water from Budd Inlet
• July 2010
▫ Survey around lake

12. Freeze results
0 1 2 3 4 5
Time (days)
0.0
0.2
0.4
0.6
0.8
1.0
Survivalrate
Day 0 ~ 20,000 NZMS/m2
Day 5 ~ 400 NZMS/m2

13. Saltwater back flush

16. • 25 sites sampled
• Day 1: Fill water 28.7 pss
• Salinity levels declined
with freshwater inputs
from Deschutes River
• NZMS likely exposed to
salinities above 20 for 7-
8 hours.

17. 12% mortality from backflush
Impact on NZMS

18. Impact on resident benthic invertebrates
• Negative impact
▫ Abundance
▫ Species richness
• Community could
recover to similar
diversity and
abundance
▫ Overall community
structure (based on
feeding groups)
remained similar before
and after backflush.
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Pre-Backflush Treatment Post-Backflush Treatment
AverageTotalAbundanceofBenthicMacroinvertebrate
Organisms/M2
Pre-Backflush Post-Backflush
AverageTotalAbundance/M2

19. What’s next?
• Continue containment
• Freeze
• Permanent plots established to look at long-term
response
• Small-scale trials of higher salt concentrations or
other treatments

20. www.invasivespecies.wa.gov
wendy.brown@invasivespecies.wa.gov