Final Mitigated Negative Declaration and Response to Comments

2009. Initial surveys estimated this infestation at approximately 3.5 acres in size just inside
and on the south side of the mouth of Emerald Bay, in water depths of 6 to 30 feet. Surveys
in 2011 showed the infestation had spread to approximately 5.5 acres, an increase in
infestation size of over 40% in only two years. An expansion of the Emerald Bay infestation
similar to that seen in South Lake Tahoe would result in considerable ecological and
recreation impacts.
The invasion and establishment of AC can lead to a variety of significant negative impacts.
The clams can dominate native benthic invertebrates and plants which are important
components of the food web in Lake Tahoe, and the presence of AC may increase the habitat
suitability for other non-native invasive species such as zebra and quagga mussels and
promote algal growth. Water quality can be degraded through concentrated nutrient excretion
and associated algal blooms. The extended algal blooms supported by clam populations can
have far reaching impacts on nearshore conditions. When algae die and wash ashore, they
decompose and rot on beaches and rocks where they impact the aesthetic beauty of the lake
and influence water quality and clarity.
The infestation in Emerald Bay is currently a relatively sparse population presumed to still be
in the early stages of invasion. This level of infestation offers the opportunity to prevent
further spread and contain or control the existing infestation. If the population goes untreated
for even a short duration of time, this small and sparse infestation could potentially expand as
seen in the populations in South Lake Tahoe. An expanded infestation will become extremely
difficult and expensive to control.
A small scale experiment by UC Davis researchers in 2009 using 10’ by 10’ EDPM pond
liners reduced the dissolved oxygen available to AC and resulted in 100% mortality after 28
days at peak summer temperatures. Additional work utilizing this technique has shown that it
is a good method with which to cause AC mortality. There is some subsurface water flow
through the sill in the mouth of Emerald Bay, so benthic barrier deployment at this site will
require barriers to be in place for an extended duration to increase mortality, and alternative
treatment methods may be required to supplement the benthic barrier treatment method.
MITIGATION MEASURES:
The following mitigation measures have been incorporated into the scope of work for the
Fuels Reduction and Understory Burning Project and will be fully implemented to avoid or
minimize averse environmental impacts identified in this MND. These mitigation measures
will be included in contract specifications and instructions to all personnel involved in
implementing the project.
MITIGATION MEASURE BIO-1: Nesting Osprey and Bald Eagle
To the extent possible, project activities would occur outside of the osprey (April 1 –
August 15) and bald eagle (February 15 – August 15) breeding seasons.
If work is required during the breeding season, a DPR-approved biologist would
conduct surveys to document reproductive activity of the established osprey and eagle
nests within 0.25 and 0.5 miles, respectively, of the project area.
3
Asian Clam Control Project
Final Mitigated Negative Declaration and Response to Comments