Biological Opinions - Bureau of Reclamation

Table 11.9. Daily average mainstem flows (cfs) where the proposed action will likely reduce coho salmon fry
habitat availability to below 80 percent of maximum (orange highlight).
Iron Gate Dam to Shasta
Shasta to Scott Rivers Scott to Salmon Rivers
River
Exceedance March April May June March April May June March April May June
95% 999 1308 1173 1020 1266 1480 1317 1104 1860 2082 1894 1284
90% 1028 1324 1190 1045 1327 1543 1369 1144 2056 2296 2060 1414
85% 1105 1339 1238 1113 1430 1619 1453 1224 2261 2623 2225 1564
80% 1287 1399 1341 1166 1672 1689 1569 1283 2592 2791 2492 1685
75% 1505 1719 1436 1207 1910 1966 1756 1359 3030 3007 2814 1805
70% 1664 1853 1597 1261 2090 2135 1898 1432 3315 3343 3258 1942
65% 1812 1980 1731 1323 2245 2340 2097 1504 3633 3771 3519 2148
60% 2052 2158 1898 1384 2612 2570 2254 1585 3994 4068 3791 2362
55% 2413 2318 2055 1458 2890 2795 2492 1676 4334 4569 4071 2540
50% 2773 2549 2276 1580 3336 3091 2699 1819 5215 4945 4389 2705
45% 3048 2801 2417 1667 3674 3387 2891 1945 5678 5345 4952 3002
40% 3239 3099 2602 1804 3980 3684 3123 2102 6003 6014 5381 3341
35% 3512 3501 2894 1925 4368 4221 3451 2320 6473 6546 5961 3702
30% 3880 3873 3129 2058 4744 4567 3779 2442 7324 7100 6309 4056
25% 4369 4235 3428 2186 5250 5026 4057 2535 8196 7753 6778 4554
20% 4889 4810 3695 2409 5983 5516 4324 2896 9278 8268 7259 5157
15% 5780 5520 4192 2817 6910 6233 4902 3382 10361 8865 7801 5687
10% 6781 5964 4565 3360 7987 6778 5423 3911 11844 9686 8651 6418
5% 7585 6513 5027 3996 9086 7602 5981 4663 14036 10615 9817 8045
11.4.1.2.3.2 Coho Salmon Juvenile
As discussed in the Environmental Baseline section, coho salmon juveniles are present in the
mainstem Klamath River throughout the year. However, the period from March to June
represents the peak of coho salmon juvenile presence (Justice 2007). While coho salmon
juveniles are present in the mainstem Klamath River in the summer, their habitat is limited to
areas that provide suitable cooler water temperatures during this period (i.e., thermal refugia).
Therefore, NMFS will analyze the proposed action’s effects on coho salmon juvenile rearing
habitat during spring using the Hardy et al.’s (2006) flow-habitat curves. However, NMFS will
analyze the effects of the proposed action on the integrity of thermal refugia in the summer
period.
As discussed earlier, the proposed action reduces flow volume in the mainstem Klamath River
generally throughout the year, and the effects of flow reduction on juvenile coho salmon habitat
availability in the mainstem Klamath River vary spatially and temporally downstream of IGD.
The steeper the relationship between flow and percent of maximum habitat, the greater the
magnitude of habitat reduction is when flows are reduced (Figure 11.18).
In the Trees of Heaven reach (RM 175), coho salmon juvenile habitat is reduced when flows
range from 1,000 to 1,224 cfs and 2672 to 4449 cfs at that reach. When the proposed action
270