Daniel J. Schill

Hooking Mortality of Bait-Caught Rainbow Trout in an Idaho Trout Stream and a Hatchery: Implications for Special-Regulation Management

Abstract Mortality of rainbow trout Oncorhynchus mykiss caught and released by anglers using number 8 worm-baited hooks was investigated during 1990–1991 at the Hagerman (Idaho) State Fish Hatchery and within a 2-km segment of Badger Creek, Idaho. Cutting the line on deep-hooked rainbow trout reduced postrelease mortality by 36% in the hatchery and 58% in the wild during observations of 60 and 29–34 d, respectively. Seventy-four percent of hatchery rainbow trout and 60% of wild rainbow trout that had been hooked deeply and released by cutting the line shed hooks during the same periods. There were no significant differences (P > 0.05) in condition factors among surviving control, light-hooked, and deep-hooked hatchery rainbow trout. Seventeen percent of 281 wild rainbow trout on Badger Creek were hooked in the gills or esophagus. Overall, hooking mortality was estimated to be 16% for wild rainbow trout. No significant differences in the incidence of deep hooking were observed between small (<200 mm total ...

Comparison of day snorkeling, night snorkeling, and electrofishing to estimate bull trout abundance and size structure in a second-order Idaho stream

Abstract Biologists lack sufficient information to develop protocols for sampling the abundance and size structure of bull trout Salvelinus confluentus. We compared summer estimates of the abundance and size structure of bull trout in a second-order central Idaho stream, derived by day snorkeling, night snorkeling, and electrofishing. We also examined the influence of water temperature and habitat type on day and night counts of bull trout. Electrofishing yielded the largest estimates of abundance of age- 1 and older bull trout. Day snorkeling counts accounted for a mean of 75% and night snorkeling counts a mean of 77% of the fish estimated by electrofishing. Numbers of age- 1 and older bull trout observed during day counts did not differ from numbers observed at night. Water temperatures during underwater surveys were 9–13.5°C. Counts were not influenced by temperatures in this range; however, statistical power of the tests was low. The three sampling techniques yielded similar estimates of the size stru...

Reproductive demographics and factors that influence length at sexual maturity of Yellowstone cutthroat trout in Idaho

Abstract Length and age at sexual maturity for Yellowstone cutthroat trout Oncorhynchus clarki bouvieri vary across their historical range, but the factors that influence this variation are poorly understood. We collected 610 Yellowstone cutthroat trout from 11 populations across southeastern Idaho from streams and rivers with a variety of physical characteristics to determine length and age at sexual maturity and other reproductive demographics. The oldest Yellowstone cutthroat trout captured (age 10) was from the South Fork Snake River; most fish (90%) were between ages 2 and 4, and only three (<1%) were older than age 7 (all from the South Fork Snake River). Cutthroat trout from the South Fork Snake River did not mature until they were 300 mm long and 5 years of age, whereas cutthroat trout from other migratory and resident sites began maturing at ages 2–3 and lengths of 100–150 mm. Fish 100–250 mm long were much more likely to be mature if they were from sites with resident rather than migratory repro...

Evaluation of an Unsuccessful Brook Trout Electrofishing Removal Project in a Small Rocky Mountain Stream

In the western United States, exotic brook trout Salvelinus fontinalis frequently have a deleterious effect on native salmonids, and biologists often attempt to remove brook trout from streams by means of electrofishing. Although the success of such projects typically is low, few studies have assessed the underlying mechanisms of failure, especially in terms of compensatory responses. A multiagency watershed advisory group (WAG) conducted a 3-year removal project to reduce brook trout and enhance native salmonids in 7.8 km of a southwestern Idaho stream. We evaluated the costs and success of their project in suppressing brook trout and looked for brook trout compensatory responses, such as decreased natural mortality, increased growth, increased fecundity at length, and earlier maturation. The total number of brook trout removed was 1,401 in 1998, 1,241 in 1999, and 890 in 2000; removal constituted an estimated 88% of the total number of brook trout in the stream in 1999 and 79% in 2000. Although abundance of age-1 and older brook trout declined slightly during and after the removals, abundance of age-0 brook trout increased 789% in the entire stream 2 years after the removals ceased. Total annual survival rate for age-2 and older brook trout did not decrease during the removals, and the removals failed to produce an increase in the abundance of native redband trout Oncorhynchus mykiss gairdneri. Lack of a meaningful decline and unchanged total mortality for older brook trout during the removals suggest that a compensatory response occurred in the brook trout population via reduced natural mortality, which offset the removal of large numbers of brook trout. Although we applaud WAG personnel for their goal of enhancing native salmonids by suppressing brook trout via electrofishing removal, we conclude that their efforts were unsuccessful and suggest that similar future projects elsewhere over such large stream lengths would be costly, quixotic enterprises.

Status of Yellowstone Cutthroat Trout in Idaho

Abstract In this study, we electrofished 961 study sites to estimate the abundance of trout (in streams only) throughout the upper Snake River basin in Idaho (and portions of adjacent states) to determine the current status of Yellowstone cutthroat trout Oncorhynchus clarkii bouvierii and other nonnative salmonids and to assess introgressive hybridization between Yellowstone cutthroat trout and rainbow trout O. mykiss. Yellowstone cutthroat trout were the most widely distributed species of trout, followed by brook trout Salvelinus fontinalis, rainbow trout and rainbow trout × Yellowstone cutthroat trout hybrids, and brown trout Salmo trutta. Of the 457 sites that contained Yellowstone cutthroat trout, less than half also contained nonnative salmonids and only 88 contained rainbow trout and hybrids. In the 11 geographic management units (GMUs) for which sample size permitted abundance estimates, the number of 100-mm and larger trout was estimated to be about 2.2 ± 1.2 million (mean ± confidence interval); ...

Barbed Hook Restrictions in Catch-and-Release Trout Fisheries: A Social Issue

Abstract We summarized results of past studies that directly compared hooking mortality of resident (nonanadromous) salmonids caught and released with barbed or barbless hooks. Barbed hooks produced lower hooking mortality in two of four comparisons with flies and in three of five comparisons with lures. Only 1 of 11 comparisons resulted in statistically significant differences in hooking mortality. In that instance, barbless baited hooks caused significantly less mortality than barbed hooks, but experimented design concerns limited the utility of this finding. Mean hooking mortality rates from past lure studies were slightly higher for barbed hooks than barbless ones, but the opposite was true for flies. For flies and lures combined, mean hooking mortality was 4.5% for barbed hooks and 4.2% for barbless hooks. Combination of test statistics from individual studies by gear type via meta-analysis yielded nonsignificant results for barbed versus barbless flies, lures, or flies and lures combined. We conclud...

Relative Return to Creel of Triploid and Diploid Rainbow Trout Stocked in Eighteen Idaho Streams

Abstract Introductions of fertile nonnative hatchery trout have led to interspecific and intraspecific hybridization of native salmonid stocks throughout North America. Use of sterile triploid hatchery trout in stream-stocking programs could reduce genetic risks to native stocks while addressing public demand for consumptive fishing opportunity. Techniques to produce triploid salmonids are well developed, and triploid rainbow trout Oncorhynchus mykiss are readily available from commercial sources. However, there is no published information on the return to creel of triploid trout in stream recreational fisheries. We purchased mixed-sex triploid and diploid rainbow trout eggs from a commercial supplier and reared the resulting fish to catchable size. Flow cytometry was used to verify triploid induction rates in the triploid group. Estimated cost to produce a triploid catchable rainbow trout was about 15% higher than for a diploid fish. We jaw-tagged and stocked 300 triploid and 300 diploid fish into each o...

Routine Use of Sterile Fish in Salmonid Sport Fisheries

Abstract Since 1997, Idaho Department of Fish and Game hatchery and research personnel have worked cooperatively to develop a sterile trout program with the primary goals of protecting the genetic integrity of native stocks while continuing to supply hatchery-reared trout for harvest-oriented anglers. Results of recent field evaluations of sterile rainbow trout (Oncorhynchus mykiss) demonstrate that they provide recreational fisheries of equal or superior quality to normal diploid fish when stocked as catchables in streams or as fingerlings in productive lentic systems. Our preliminary evaluations suggest that use of sterile trout in high mountain lakes may require stocking adjustments or may eventually prove problematic because of lower survival rates. Sterile trout eggs can be readily purchased from commercial sources or produced from agency broodstocks with nominal equipment and manpower costs. To gain a better understanding of sterile fish use by other agencies, we conducted a U.S. state phone survey ...

Healing of Electroshock-Induced Hemorrhages in Hatchery Rainbow Trout

Abstract We monitored healing in electroshock-induced hemorrhages of myomere blood vessels produced by individually exposing hatchery rainbow trout Oncorhynchus mykiss to direct current (N = 502) and pulsed direct current (N = 708). We used voltage gradients and exposure times that were suspected to produce high injury rates to facilitate observation of injury duration in muscle tissue. At 1 d postexposure, 86.1% of the test fish exposed to DC and 81.6% of those exposed to pulsed direct current (PDC) had at least one hemorrhage. Fish exposed to DC averaged 1.86 injuries at 1 d postshocking, and those exposed to PDC averaged 1.45 injuries. Number of hemorrhage injuries per fish began declining by 15 d postshocking in both groups. The severity of injuries initially increased through 15 d postshocking and then decreased through the remaining 3–5 weeks of the tests. At the end of the test, injuries induced by DC had declined by 78.0% (36 d postshocking), and those induced by PDC declined by 92.4% (57 d postsh...

Performance of Diploid and Triploid Rainbow Trout Stocked in Idaho Alpine Lakes

Abstract Increased growth, improved survival, and genetic protection of wild stocks have been suggested as benefits of stocking triploid (i.e., sterile) salmonids for recreational fisheries. We examined the return rates and growth of mixed-sex diploid (2N), mixed-sex triploid (3N), and all-female triploid (AF3N) rainbow trout Oncorhynchus mykiss across 28 alpine lakes. Equal numbers of each treatment group were stocked in 2001 and 2003 and sampled 3–4 years later. During 2004 and 2005, a total of 75 2N and 36 3N marked rainbow trout were recaptured. Taken together, the 2N fish accounted for an average of 0.68 of the total marked fish caught, and the combined proportions of test fish (including netting and angling) differed significantly between the test groups and were consistent across survey years. During 2006 and 2007, a total of 60 2N, 31 3N, and 208 AF3N marked rainbow trout were recaptured. The mean length of the test fish was similar between test groups within sampling years. Overall, the return of...