During my fishing two weeks ago I caught a tagged fish. Out of curiosity I emailed the director of the National Aquatic Monitoring Center (he lives and works in my hometown) to see if he knew what the tag was about. He sent my email on to Gary Thiede, a fishery biologist at our local university, Utah State University. Gary was nice enough to send a couple of publications regarding their research, as well as answering some of my questions.

One of the papers Gary sent was their annual report, titled, “Logan River whirling disease study: factors affecting trout population dynamics, abundance, and distribution in the Logan River, Utah.” Quite a mouthful, but this was a grant research project. Based on this research, they also published a paper in the North American Journal of Fisheries Management 27:593–604, 2007, titled, “Quantification of the Vital Rates, Abundance, and Status of a Critical, Endemic Population of Bonneville Cutthroat Trout.” Again, quite the verbiage.

The gist of the research is summed up in these words: “…we completed a comprehensive population assessment, including depletion-based abundance estimates and a mark–recapture study (1,050 tagged fish) of site fidelity, growth, and survival.” It was one of those 1,050 tagged fish I caught.

This was an important study conducted by these folk. In fact, they knew it too: “We provide some of the first robust estimates of density, growth, survival, and population trend for an imperiled subspecies of cutthroat trout based on field measurements and mark–recapture techniques.”

For some reason I have an affinity for cutthroat trout. Having cut my fly fishing teeth on the Logan River, it may help explain that affinity. As stated in the “Quantification…” piece:

“The Logan River contains one of the largest remaining populations of Bonneville cutthroat trout; the densities observed here are some of the highest reported densities of inland stream-type cutthroat trout. Survival and growth rates were also relatively high. These are all components of population persistence. Clearly, the remaining continuity and connectedness of habitat fragments in the Logan River and their large size have contributed to the persistence of this population.”

I learned to fish in those areas with the highest density of cutthroat. What kind of density, you might ask? “…densities ranging from lows of 48 fish/km [77 fish/mile] at low-elevation sites occupied by nonnative brown trout to highs of 2051 fish/km [3300 fish/mile]…”

These fish are not playing hide and seek, that’s for sure. 3300 fish per mile. That’s a pretty healthy population! Right here in my homewaters! No sir, there is not any trouble here in River City. Or so one might think.

“Nevertheless, abundance now appears to be declining at some sites, and survival and abundance were lower at sites where Bonneville cutthroat trout were sympatric with exotic brown trout than at sites of allopatry.”

Those are some fancy words, and what they mean is that in places where brown trout and cutthroat are together, the higher the brown population, the lower the cutthroat population. And some of those tested sites are showing a move in that direction.

Even though we have a healthy, mostly intact population locally, “…the subspecies is recognized as an imperiled species by the American Fisheries Society …” There just isn’t the numbers of Bonneville cutthroat there used to be in their historic range.

“As such, to ensure the long-term viability of this important population, we recommend that proactive management measures be considered, such as exotic brown trout removal and habitat restoration and protection.”

Let’s keep the pressure on the Utah Division of Wildlife Resources to do something about the invasive brown trout.

Some additional quotes from the study:

“Population density exceeded 1,500 cutthroat trout/km at high-elevation sites; this is substantially higher than most other reported densities of inland, stream-type cutthroat trout. Fish demonstrated extremely high rates of site fidelity on average (92%; SE ¼ 6%), and growth rates were also high (up to 0.50 g/d; mean ¼ 0.09 g/d). Cormack– Jolly–Seber survival rates (fish ” 100 mm) increased with age-class (group effect) and condition (individual covariate) and ranged from over 64% at high-elevation sites to approximately 30% at lower-elevation sites. Population growth rates (k) appeared to be declining overall; however, 95% confidence intervals of k frequently overlapped 1.0, indicating high variability that limited conclusions about future status. We recommend a precautionary approach to management of this endemic and important population; potential options include habitat protection or restoration and the removal of exotic brown trout.”

“…we observed much higher densities of 100-mm and larger Bonneville cutthroat trout at certain sites in this system than have been observed in other such populations and other subspecies of cutthroat trout (Table 3). Densities of Bonneville cutthroat trout in the Logan River averaged 694 fish/km across our sites and years, while densities of this subspecies in northern (129 fish/km) and southern (228 fish/km) Utah as well as Wyoming (128 fish/km) are much lower. Logan River Bonneville cutthroat trout densities are as much as 25 times the densities of Colorado River cutthroat trout O. clarkii pleuriticus in similar, albeit slightly smaller-sized, streams (Horan et al. 2000). Thus, the continuous and connected nature of Logan River habitat and large size of the remaining habitat area are important for maintaining a large population of cutthroat trout.”

“…we also observed relatively high annual growth and survival rates overall, especially at upper-elevation sites. At upper-elevation main-stem sites, fish grew as much as 0.5 g/d and annual survival rates of adult fish were as high as 75%. In contrast, observed survival rates at sites where exotic brown trout were present (Twin Bridges, Third Dam, and Temple Fork) were nearly half those observed at sites where brown trout were absent or occurred in extremely low abundance (Franklin Basin, Red Banks, and Forestry Camp).”

Logan River whirling disease study: factors affecting trout population dynamics, abundance, and distribution in the Logan River, Utah

by Phaedra Budy Associate Professor Assistant Coop Leader

Gary P. Thiede Fishery Biologist

Quantification of the Vital Rates, Abundance, and Status of a Critical, Endemic Population of Bonneville Cutthroat Trout (abstract available)
PHAEDRA BUDY,* GARY P. THIEDE, AND PETER MCHUGH
U.S. Geological Survey, Utah Cooperative Fish and Wildlife Research Unit, Department of Watershed Sciences, Utah State University, Logan, Utah 84322-5210, USA

North American Journal of Fisheries Management 27:593–604, 2007
Copyright by the American Fisheries Society 2007
DOI: 10.1577/M06-085.1

 Email This Post ⋅  Print This Post ⋅ Post a comment