Geoscience Reference
In-Depth Information
pattern of releases provides the best opportunity to
determine if it is feasible to rebuild and maintain
sandbars in a sustainable manner (US Geological
Survey, 2008). These conclusions on HFEs were
based on results available in September 2010 and
presented at the
River Conservation and Management
conference in York. Subsequent, more extensive
analyses of the HFEs have now been published
and include unexpected findings, notably the
response of non-native fish species (Melis, 2011;
http://pubs.usgs.gov/circ/1366/).
brown trout (
Salmo trutta
) were thought to prey
upon and compete with humpback chub and other
native fish, so they were removed experimentally
in large numbers from the area near the confluence
of the Colorado and Little Colorado Rivers - the
reach where most Grand Canyon humpback chub
are found. The removal experiment took place
during 2003-2006 and reduced the rainbow trout
population by 90% in the targeted area during
the experimental period (Coggins and Yard, 2010).
This removal experiment demonstrated that trout
populations below the dam could be controlled
effectively within limited reaches of Grand Canyon
National Park (Coggins, 2008; Coggins and Yard,
2010). However, there is still uncertainty about
whether such actions really benefit humpback
chub populations in the longer term. Habitat, flows,
water temperature, food availability, and non-
native fish populations have all varied over the
last 20 years and therefore confounded attempts
to explain more precisely the factors that limit
native fish reproduction and survival. Nevertheless,
a combination of experimental actions, drought-
induced warming of the river and other factors
have probably contributed to an approximately
Fish removal and translocation
experiments
By 2002, scientists and managers had also
identified non-flow experimental treatments and
conservation measures intended to benefit the
endemic, native fish species below the dam
(Table 26.3). In 2000 and 2001, when monitoring
efforts detected a significant decline in the Grand
Canyon humpback chub population, the Program
implemented an emergency plan to reverse the
decline. Rainbow trout (
Oncorhynchus mykiss
)and
Table 26.3
Non-flow experimental treatments implemented as part of the Glen Canyon Dam Adaptive
Management Program.
Non-flow treatments
and conservation
measures
Duration
Resource focus
Replication
Resources measured
Non-native fish
removal.
2003-2006.
Humpback chub
population trend.
No - one 4-year block
only, but control
reach was utilized
upstream of
treatment reach.
Numbers of
non-native fish
removed in
treatment reach,
chub population.
Fish translocation to
expand tributary
rearing habitat
(humpback chub
juveniles were
relocated upstream
within Little
Colorado River (LCR)
spawning habitat).
2002-2010 in the LCR;
also 2009-10 in
Shinumo Creek,
another tributary
further
downstream.
Humpback chub
juvenile recruitment
to increase adult
population in Grand
Canyon National
Park.
Yes - LCR annually,
using naturally
spawned, wild
juvenile chub from
the lower reaches of
the Little Colorado
River, juvenile chub
also moved from
LCR to Shinumo
Creek.
Humpback chub
growth rates and
adult population
abundance within
Grand Canyon
National Park.
