Biological Opinions - Bureau of Reclamation

though several major improvements to key structures (e.g., the A Canal fish screen) have been
implemented.
Nonnative fishes were identified as a potential threat to the LRS and the SNS at the time of their
listing because of potential competition and predation.
Lastly, mass mortality events in UKL are not new, but it is believed that as Aphanizomenon flosaquae
(AFA), a nitrogen-fixing blue-green alga or “cyanobacterium,” has increasingly
dominated the system, the frequency of extreme fish die-off events has also increased (NRC
2004). Although conditions are most severe in UKL and Keno Reservoir, listed suckers
throughout the Klamath Basin are vulnerable to water quality-related mortality (USFWS 2007a,
b).
7.3 New Threats Identified Since Listing
7.3.1 Climate Change
Since the 1950s, western North America has experienced changes in the timing and amount of
precipitation, including decreased snowfall, earlier snowmelt, and earlier peak spring runoff,
which appear inconsistent with historically normal fluctuations, suggesting effects from
anthropogenic sources (Hamlet et al. 2005, Stewart et al. 2005, Knowles et al. 2006). Climate
models indicate that these trends are likely to continue (Barnett et al. 2008). In the upper
Klamath Basin, 8 of the 10 lowest total annual inflows into UKL in the past 50 years occurred
between 1991 and 2009, and, over the past decade, inflows to the lake have been about 9 percent
less than over the previous 31 years. Additionally, the July through September inflows to UKL
have declined by over 50 percent during the past 50 years (Mayer 2008, Mayer and Naman
2011).
The LRS and the SNS evolved in a region with highly variable precipitation, often with extended
and severe droughts (Negrini 2002); however, given the current lack of recruitment into the adult
population of each species, the absence of population connectivity (even in wet years), poor
habitat conditions, and diminished abundance, LRS and SNS populations are highly vulnerable
to negative impacts from climate change, especially increased drought. Threats from climate
change not only include reduction in amounts of spring runoff and its timing, but are likely to
also result in increasingly reduced water quantity, the spread of disease and parasites, and
proliferation of invasive and nonnative species that could prey on or compete with suckers.
7.3.2 Disease, Predation, and Parasitism
Emerging information suggests that other natural factors may also be adversely affecting the
suckers more than previously thought. For example, fish-eating birds, such as the American
white pelican (Pelecanus erythrorhynchus), could have substantial negative impacts on adult
sucker populations, especially those in Clear Lake where they could be exposed to pelican
predation during the spawning migration in Willow Creek. Early data indicate that American
white pelican predation rates on sub-adult or adult suckers in Clear Lake Reservoir may be as
high as 20 percent in some years; however, additional research is needed to clarify the magnitude
of this threat (Roby and Collis 2011; D. Hewitt, USGS, pers. comm. 2012). Additional, recently
identified threats include algal toxins, which may have affected nearly 50 percent of 47 juvenile
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