areas searched at zorinsky lake

Zorinsky Lake Zebra Mussels
FINDINGS
AREAS SEARCHED AT ZORINSKY LAKE
FOR EMERGED ZEBRA MUSSEL SHELLS DURING THE 2010/2011 DRAWDOWN
OF THE ZORINSKY LAKE
ZEBRA MUSSEL SURVEY
• A total of 907 emerged zebra
mussel shells were found in the eight
delineated areas that were searched
when the reservoir was drawn down.
• The zebra mussel population in
Zorinsky Lake was widespread.
Emerged zebra mussel shells were
found from the dam to the upper
reaches of the reservoir.
• The density of emerged zebra mussels
shells found in Zorinsky Lake was
less than 1 per square meter. This
compares to zebra mussel densities of 5,000 to 30,000+ per square
meter commonly found in other
infested waters.
• The vast majority of emerged zebra
mussel shells found in Zorinsky
Lake were associated with “hard”
substrates (Figure 1).
• No emerged zebra mussel shells
were found below elevation 1100 ftNGVD29 (Figure 2).
• Size and growth ring analysis of the
collected zebra mussel shells indicate
the presence of up to four yearclasses of zebra mussels in Zorinsky
Lake (Figure 3).
• The zebra mussel population in
Zorinsky Lake is believed to have
been limited by water quality, hardsubstrate availability, and siltation.
W2
N10
• Fish predation may have also played
a role in limiting the zebra mussel
population in Zorinsky Lake.
S7
Area W2
Number of Zebra Mussel Shells Found: 11
Elevations of Shell Occurrence:
Range: 1103.2 to 1108.8 ft-NGVD29
Median: 1108.2 ft-NGVD29
Occurrence by Substrate:
Gravel/Cobble: 27.3%
Riprap: 72.7%
Number of Zebra Mussel Shells Found: 183
Elevations of Shell Occurrence:
Range: 1101.4 to 1109.1 ft-NGVD29
Median: 1106.0 ft-NGVD29
Occurrence by Substrate:
Riprap: 98.4%
Soil: 1.6%
Area S4
Area N10
Number of Zebra Mussel Shells Found: 17
Elevations of Shell Occurrence:
Range: 1105.4 to 1108.6 ft-NGVD29
Median: 1105.8 ft-NGVD29
Occurrence by Substrate:
Gravel/Cobble: 41.2%
Riprap: 58.8%
Number of Zebra Mussel Shells Found: 171
Elevations of Shell Occurrence:
Range: 1100.3 to 1108.7 ft-NGVD29
Median: 1104.8 ft-NGVD29
Occurrence by Substrate:
Bottle: 0.6%
Concrete: 0.6%
Gravel/Cobble: 0.6%
Riprap: 95.9%
Soil: 1.8%
Woody Debris: 0.6%
Area B1
Number of Zebra Mussel Shells Found: 262
Elevations of Shell Occurrence:
Range: 1102.0 to 1107.8 ft-NGVD29
Median: 1105.1 ft-NGVD29
Occurrence of Shells by Substrate:
Gravel/Cobble: 65.6%
Riprap: 29.4%
Soil: 5.0%
N6
• The zebra mussel population in
Zorinsky Lake may have been in
an “equilibrial” state controlled by
environmental factors, or in a “lag”
phase capable of significant growth in the future.
Area S7
S4
Area D4
ZEBRA MUSSEL SURVEY
B1
CONCLUSIONS
D1
• The winter 2010/2011 drawdown
of Zorinsky Lake is believed to
have diminished the zebra mussel
population to the maximum extent possible.
D4
Number of Zebra Mussel Shells Found: 147
Elevations of Shell Occurrence:
Range: 1103.4 to 1108.2 ft-NGVD29
Median: 1104.8 ft-NGVD29
Occurrence by Substrate:
Gravel/Cobble: 86.4%
Riprap: 12.9%
Tire: 0.7%
• Zebra mussels can be reintroduced to
Zorinsky Lake if adequate controls
are not put in place and followed.
FIGURE 1. SUBSTRATE OCCURRENCE
OF COLLECTED ZEBRA MUSSEL SHELLS
Substrate Occurrence
of 907 Zebra Mussel Shells
Figure 1. Substrate Occurrence
of Collected
Collected Zebra Mussel Shells
Bottle (0.1%)
Concrete (0.1%)
Gravel/Cobble (41.0%)
Rip Rap
56.2%
Gravel/Cobble
41.0%
Rip Rap (56.2%)
Soil (2.2%)
Tire (0.2%)
Wood (0.1%)
FIGURE 2. ELEVATION OCCURRENCE
OF COLLECTED ZEBRA MUSSEL SHELLS
Area N6
Number of Zebra Mussel Shells Found: 26
Elevations of Shell Occurrence:
Range: 1102.6 to 1109.0 ft-NGVD29
Median: 1105.8 ft-NGVD29
Occurrence by Substrate:
Riprap: 96.2%
Tire: 3.8%
Area D1
Number of Zebra Mussel Shells Found: 90
Elevations of Shell Occurrence:
Range: 1103.4 to 1106.5 ft-NGVD29
Median: 1105.0 ft-NGVD29
Occurrence by Substrate:
Gravel/Cobble: 68.9%
Riprap: 30.0%
Soil: 1.1%
FIGURE 3. POSSIBLE ZEBRA MUSSEL
YEAR CLASSES PRESENT IN ZORINSKY LAKE