. The Big Blackfoot River restoration progress report for 2002 and 2003 . Fish populations; Fishes; Fishery management; Trout fisheries; Stream ecology; Blackfoot River (Mont. ). 2002). With regard to whirling disease status in the Blackfoot Watershed, many of these factors are discussed below. Sentinel cages provide an indirect measure of TAM abundance in tested waters, and were first deployed in the Blackfoot Watershed in 1998 (see methods). Sentinel cage Mean grade category Infection Level Description Low Medium High Very High Table 15. Mean grade categor
. The Big Blackfoot River restoration progress report for 2002 and 2003 . Fish populations; Fishes; Fishery management; Trout fisheries; Stream ecology; Blackfoot River (Mont. ). 2002). With regard to whirling disease status in the Blackfoot Watershed, many of these factors are discussed below. Sentinel cages provide an indirect measure of TAM abundance in tested waters, and were first deployed in the Blackfoot Watershed in 1998 (see methods). Sentinel cage Mean grade category Infection Level Description Low Medium High Very High Table 15. Mean grade category descriptions monitoring has continued through 2003 at established Blackfoot River sites and throughout tributaries in order to assess disease expansion. A mean grade is determined from histology results from sentinel fish exposed in each cage to determine infection severity at individual locations (Table 15). An important criterion for determining cage deployment dates is based on water temperatures. Previous studies have shown the highest infection levels coincide with a specific water temperature range of 50 to 61 °F (Baldwin et al. 2000; Downing et al. 2002; Vincent 2002). In the Blackfoot River, these temperatures coincide with an early summer (mid-June through early July) sampling period. Results of recent Blackfoot cages show progressive increases in the disease in the up-and downriver directions, and a corresponding expansion in the lower reaches of many tributaries (Figure 55). During the last two years, whirling disease in the mainstem Blackfoot River has 1) expanded (-20 river miles) to the upper mainstem above Lincoln, 2) increased infection levels in the lower Blackfoot River (below the mouth of the Clearwater River), and 3) appears to have stabilized in the middle Blackfoot River at moderate to high levels. The recent escalation of the disease is also expressing itself at two long- term Blackfoot River (Johnsrud and Scotty Brown Bridge) population 20 18- 16- 14
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