Brett High

Accuracy of Removal Electrofishing Estimates of Trout Abundance in Rocky Mountain Streams

Abstract Removal electrofishing is frequently used to estimate fish distribution and abundance in streams because it is simple and requires only one visit to a site. However, because the removal method usually overestimates capture efficiency and therefore underestimates fish abundance, some biologists have questioned its use in favor of less biased methods. In southern Idaho streams in the summers of 2006 and 2007, rainbow trout Oncorhynchus mykiss, cutthroat trout O. clarkii, and brook trout Salvelinus fontinalis were captured with backpack electrofishers using pulsed DC and marked and released in blocknetted sites; on the following day, four-pass electrofishing removals were conducted. Removal electrofishing underestimated the abundance of trout 10 cm and larger by 17% (four passes), 22% (three), and 25% (two); for trout less than 10 cm, the respective underestimates were 27, 27, and 37%. Removal estimates were biased in part because capture efficiency progressively decreased for fish 10 cm and larger ...

Survival and Dispersal of Hatchery Triploid Rainbow Trout in an Idaho River

Abstract Hatchery rainbow trout Oncorhynchus mykiss of catchable size (hereafter, “catchables”) are commonly released into streams to improve angler catch and harvest rates, but returns are often less than 50% and the fate of unharvested catchables is largely unknown, especially for sterilized hatchery trout. The survival and dispersal of triploid catchables were investigated using snorkel and telemetry techniques to quantify the persistence and dispersal of catchables stocked three times during the summer of 2006 (June, July, and August) into an Idaho river in which a minimum length regulation precluded harvest. Counts of catchables stocked with T-bar tags (n = 900) and catchables emitting active radio transmitter codes (n = 54) steadily declined throughout the three observation periods. Dispersal of T-bar-tagged catchables 30 d poststocking was generally downstream of the stocking point (median dispersal = 100 m). The median values of the maximum known downstream and upstream dispersal distances for cat...

Retention of Passive Integrated Transponder Tags in Stream-Dwelling Rainbow Trout

Abstract Passive integrated transponder (PIT) tags have been widely used as a tool for various monitoring and research needs, but the retention of PIT tags has rarely been tested in resident salmonids. We quantified the short-term (≤1 week), annual (1 year), and long-term (≥1 year) retention rates of PIT tags placed in the peritoneal cavity of small resident rainbow trout Oncorhynchus mykiss in 11 study streams and assessed whether fish size and gender affected tag retention. Short-term retention rates were at least 92% and averaged 96% for all streams, but a paired t-test nevertheless indicated that experienced taggers had significantly higher short-term retention rates (mean, 98%) than did inexperienced taggers (mean, 95%). Annual retention rates for PIT tags averaged 81% among all study streams, ranging from a low of 67% to a high of 92%. Annual retention rates were lower for larger rainbow trout than for their smaller counterparts. Long-term tag loss for females was the same as for males for fish smal...

Hooking Mortality and Landing Success Using Baited Circle Hooks Compared to Conventional Hook Types for Stream-Dwelling Trout

Abstract We estimated hooking and landing success and relative hooking mortality for stream-dwelling trout caught with baited circle and J hooks, J hook dry flies, and treble hook spinners (all hooks barbed). Trout were caught, individually marked, and released for 69 days. Deep-hooking rate was higher for trout captured with baited J hooks (21%) than for spinners (5%), baited circle hooks (4%), and dry flies (1%). Relative mortality rate was higher for trout captured with baited J hooks (25%) and spinners (29%) than for trout captured with baited circle hooks (7%) and dry flies (4%). Deep-hooking was two and six times higher for baited J hooks than baited circle hooks for fish caught actively and passively , respectively. For baited circle hooks, deep-hooking was over three times greater when using an active fishing method (i.e., an active hookset) compared to passive fishing method (no hookset), which conflicts with manufacturer&s recommendations on how circle hooks should be fished. Hooking success (ratio of hook-ups to number of fish strikes) was about one-third lower for baited circle hooks fished both passively and actively compared to other hook types and fishing methods, except for passively-fished baited J hooks. Once hooked, landing success (ratio of fish landed to number of hook-ups) was relatively high for all hook types and fishing methods (range 68–87%). Our results suggest that when bait fishing for trout in streams, circle hook use may reduce deep-hooking and hooking mortality (but also catch rate) regardless of whether anglers fish passively or actively.

Trends in the Distribution and Abundance of Yellowstone Cutthroat Trout and Nonnative Trout in Idaho

Abstract The distribution and abundance of Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri across their native range is relatively well-known, but evaluations of trends in distribution and abundance over time are lacking. In 2010–2011, we resurveyed 74 stream reaches in the upper Snake River basin of Idaho that were sampled in the 1980s and again in 1999–2000 to evaluate changes in the distribution and abundance of Yellowstone cutthroat trout and nonnative trout over time. Yellowstone cutthroat trout occupied all 74 reaches in the 1980s, 70 reaches in 1999–2000, and 69 reaches in 2010–2011. In comparison, rainbow trout O. mykiss and rainbow × cutthroat hybrid occupancy increased from 23 reaches in the 1980s to 36 reaches in 1999–2000, and then declined back to 23 reaches in 2010–2011. The proportion of reaches occupied by brown trout Salmo trutta and brook trout Salvelinus fontinalis was largely unchanged across time periods. Yellowstone cutthroat trout abundance declined from a mean of 40.0 fis...

Distinguishing Yellowstone Cutthroat Trout, Rainbow Trout, and Hybrids by Use of Field-Based Phenotypic Characteristics

AbstractNative and nonnative salmonids within the same genus sometimes hybridize, and the hybrids are often difficult to visually distinguish from parental species. We compared phenotypic delineations (based on several visual characteristics) and genotypic screening (using seven nuclear DNA loci) for 323 fish collected from an Idaho stream where Yellowstone Cutthroat Trout O. clarkii bouvieri were introgressed with Rainbow Trout O. mykiss to evaluate our ability to visually distinguish Yellowstone Cutthroat Trout from Rainbow Trout and hybrids. Assuming that the genotypes were 100% accurate, correct phenotypic classification was highest for Yellowstone Cutthroat Trout (the genotype confirmed the phenotype 94% of the time), followed by hybrids (79%) and Rainbow Trout (71%). All errors were between pure and hybrid fish. All of the measured phenotypic characteristics were useful for differentiating Yellowstone Cutthroat Trout from hybrids, but the most informative characteristics were the lack of a white lea...

Purifying a Yellowstone Cutthroat Trout Stream by Removing Rainbow Trout and Hybrids via Electrofishing

AbstractThe South Fork of the Snake River in Idaho supports one of the few remaining fluvial populations of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri, but long-term persistence of Cutthroat Trout in the drainage is threatened by introgression with introduced Rainbow Trout O. mykiss. We completed eight backpack electrofishing removals from 2010 to 2015 to remove Rainbow Trout and Rainbow Trout × Cutthroat Trout hybrids from a 9.3-km isolated reach of Palisades Creek (a tributary of the South Fork) in an attempt to improve the purity of the population. For two removals, fish from a subsample of Oncorhynchus were genetically screened at seven diagnostic nuclear DNA loci. A total of 14,092 fish were captured across all removals, of which 3,446 were putative Rainbow Trout or hybrids, which were removed from the stream. The proportion of the total catch that Yellowstone Cutthroat Trout comprised (across all size-classes combined) increased slowly over time, from 67% in 2010 to 86% for the second...