Demographic Characteristics of an Adfluvial Bull Trout Population in Lake Pend Oreille, Idaho

Abstract

Introductions of nonnative species, habitat loss, and stream fragmentation have caused the Bull Trout Salvelinus confluentus to decline throughout much of its native distribution. Consequently, in June 1998, the Bull Trout was listed under the U.S. Endangered Species Act as threatened. The Bull Trout has existed in Lake Pend Oreille and its surrounding tributaries since the last ice age, and the lake once supported a world‐renowned Bull Trout fishery. To quantify the current status of the Bull Trout population in Lake Pend Oreille, Idaho, we compared the mean age, growth, maturity, and abundance with reports in a study conducted one decade earlier. Abundance was estimated by mark–recapture for Bull Trout caught in trap nets and gill nets set in Lake Pend Oreille during ongoing suppression netting of Lake Trout S. namaycush in 2007–2008. Bull Trout sampled in 2006–2008 were used to estimate age structure, survival, growth, and maturity. Estimated Bull Trout abundance was similar to that estimated one decade earlier in Lake Pend Oreille. Bull Trout residing in Lake Pend Oreille between 2006 and 2008 were between ages 4 and 14 years; their growth was fastest between ages 1 and 2 and slowed thereafter. Male and female Bull Trout matured at a similar age, but females grew faster than males, thereby maturing at a larger size. Our findings suggest that management has effectively addressed current threats to increase the likelihood of long‐term persistence of the Bull Trout population in Lake Pend Oreille. Received November 13, 2015; accepted June 29, 2016 Published online October 7, 2016

New Insights into the Ecology of Adfluvial Bull Trout and the Population Response to the Endangered Species Act in the North Fork Lewis River, Washington

“…For example, Bull Trout lengths at age from the North Fork Lewis River are generally similar to fluvial and adfluvial Bull Trout populations in northwestern Montana and Idaho (Fraley and Shepard ; Erhardt and Scarnecchia ; McCubbins et al. ) but are considerably lower than those reported in Oregon by Ratliff et al. ().…”

“…Finally, the differences in growth rates likely explain interpopulation differences in length at age. For example, Bull Trout lengths at age from the North Fork Lewis River are generally similar to fluvial and adfluvial Bull Trout populations in northwestern Montana and Idaho (Fraley and Shepard 1989;Erhardt and Scarnecchia 2016;McCubbins et al 2016) but are considerably lower than those reported in Oregon by Ratliff et al (1996). Together, these results demonstrate that the complex interactions of in situ conditions and foraging opportunities (e.g., Johnston and Post 2009;Furey and Hinch 2017) likely drive interpopulation and life history differences in growth rates and suggest the importance of local data when describing Bull Trout life history expressions.…”

“…; McCubbins et al. ). Here, we evaluated the age of Bull Trout in the Lewis River using nonlethal samples from individuals captured during field sampling at the head of Swift Reservoir and nearby Yale Reservoir in 2016.…”

“…Understanding age structure provides important information on the life history expressions of fish and on their growth trajectories and is a key aspect of age-or sizestructured population models used in directing Bull Trout conservation and management (Al-Chokhachy et al 2015;McCubbins et al 2016). Here, we evaluated the age of Bull Trout in the Lewis River using nonlethal samples from individuals captured during field sampling at the head of Swift Reservoir and nearby Yale Reservoir in 2016.…”

Population Dynamics and Temporal Trends of Bull Trout in the East Fork Salmon River, Idaho

“…However, considering that subadults comprised only a small portion of the overall catch (i.e., 16 fish or 0.8% of all fish captures), it is unlikely their inclusion affected estimates of Φ. Estimates of absolute survival are rare for Bull Trout populations but have been reported to be 0.54-0.66 in Lake Pend Oreille (Vidergar 2000;McCubbins et al 2016). It may seem surprising thatΦ is so similar for TABLE 3.…”