Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

to disease, decrease the ability of young salmon and trout to compete with other species
for food, and to avoid predation (Spence, Lomnicky et al. 1996; McCullough 1999).
Migrating adult salmonids and upstream migration can be delayed by excessively warm
stream temperatures. Excessive stream temperatures may also negatively affect
incubating and rearing salmonids (Gregory and Bisson 1997).
Sublethal temperatures (above 24ºC) could be detrimental to salmon by increasing
susceptibility to disease (Colgrove and Wood 1966) or elevating metabolic demand (Brett
1995). Substantial research demonstrates that many fish diseases become more virulent
at temperatures over 15.6ºC (McCullough 1999). Due to the sensitivity of salmonids to
temperature, states have established lower temperature thresholds for salmonid habitat as
part of their water quality standards. A water body is listed for temperature on the 303(d)
list if the 7-day average of the daily maximum temperatures (7-DADMax) exceeds the
temperature threshold (Table 27).
Table 27. Washington State water temperature thresholds for salmonid habitat. These
temperatures are representative of limits set by California, Idaho, and Oregon (WSDE
2006).
Category Highest 7-DADMax
Salmon and Trout Spawning 13°C (55.4°F)
Core Summer Salmonid Habitat 16°C (60.8°F)
Salmonid Spawning, Rearing, and Migration 17.5°C (63.5°F)
Salmonid Rearing and Migration Only 17.5°C (63.5°F)
Water bodies that are not designated salmonid habitat are also listed if they have a oneday
maximum over a given background temperature. Using publicly available GIS
layers, we determined the number of km on the 303(d) list for exceeding temperature
thresholds within the boundaries of each ESU (Table 28). Because the 303(d) list is
limited to the subset of rivers tested, the chart values should be regarded aslower-end
estimates.
While some ESU ranges do not contain any 303(d) rivers listed for temperature, others
show considerable overlap. These comparisons demonstrate the relative significance of
elevated temperature among ESUs. Increased water temperature may result in
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