Results and Discussion
Greenback cutthroat trout were found or introduced in 68 waters as part of recovery activities (table 1). Only waters used in an attempt to create a self-sustaining population were included -- we did not consider waters used solely to provide a sport fishery. We also restricted this list to waters that were believed to contain genetically pure fish during recovery, though some of these populations now appear to be hybridized. Nearly all waters were qualitatively surveyed during recovery efforts, and quantitative estimates were obtained in 53 waters (table 2). In streams, the mean abundance of greenback cutthroat trout greater than 100 mm was 24 fish/100 m (SD, 12). In lakes, the mean catch rate was 12 fish/gill-net-hour (SD, 9).
Samples from 22 waters were subjected to genetic analyses (table 3). Most evaluations before 1995 relied on meristic and morphometric analyses, with more advanced techniques employed thereafter. It seems likely that the precision and accuracy of these approaches will continue to improve, and that current tallies of pure and hybridized populations will change. For example, the most recent analyses (Evans and Shiozawa 2001) determined that four populations -- previously used to found broodstocks and other wild populations -- were introgressed to varying degrees with Yellowstone cutthroat trout (O. c. bouvieri) or rainbow trout. The proposed federal policy of protecting hybridized populations (USFWS 1996) may assume a greater role as the ability to estimate the amount and source of introgression increases.
Of the 68 recovery waters, 41 were treated with antimycin or rotenone to remove nonnative salmonids prior to introductions of greenback cutthroat trout (table 4). Because of this intensive use of toxicants, many protocols for their application were developed (for example, Tiffan 1992). Although most nonnative salmonid populations were successfully eliminated, periodic failures of artificial barriers, illegal introductions by anglers, or incomplete removals have permitted invasions in 15 waters (cf. Harig and others 2000).
Transfers of fish from different waters and different hatcheries have been extensive (table 5). The median number of fish introduced into streams was 4,862 (range, 900-28,456) and into lakes 4,696 (range 85-59,500). We caution that there is substantial uncertainty in these estimates because of the consistent lack of consensus among literature sources. Most transfers involved fish reared or produced by three hatcheries: the Bellvue Fish Research Hatchery (BFRH) in Bellvue, Colorado; the Bozeman Fish Technology Center (BFTC) in Bozeman, Montana; and the Saratoga National Fish Hatchery (SNFH) in Saratoga, Wyoming. The Pueblo State Fish Hatchery in Pueblo, Colorado, also distributed limited numbers of fish beginning in 1997, but did not develop broodstocks, hence we did not include it in our analysis of hatchery activities. Roaring Creek was historically stocked, though the population appears to be genetically pure.
Greenback cutthroat trout arrived in hatcheries as juveniles, adults, fertilized eggs, and milt (table 6). Attempts to minimize inbreeding depression involved the use of milt from wild males to fertilize eggs of hatchery females at the BFTC (Dwyer and Rosenlund 1988) or avoidance of sister-brother spawning at the BFRH by using 3-year-old females and 2-year-old males (Schler, personal communication). Strategies for developing broodstocks varied among hatcheries (table 7), as did protocols for selecting spawning groups. Typical spawning practice at the BFRH was to spawn three females with two males with milt from males added sequentially to the eggs of all females, though 1:1 matings were conducted when fish were abundant (Schler, personal communication). One:one ratios of females to males were typically attempted at the SNFH. At the BFTC, milt from males was frequently limited and occasionally as many as six females were fertilized with the milt from one male (Dwyer, personal communication). In addition, milt from wild males was generally stored individually but occasionally mixed in a single vial.
Records of the origin and number of fish spawned were inconsistent for the BFRH and BFTC. Particularly for the latter, many females were respawned, thus reports of total spawnings exaggerated the number of females used. Also, shipments of milt to this hatchery were occasionally unsuccessful, as were the attempts to fertilize eggs of hatchery females with milt from wild males, which accounts for the differences in fish shipped to hatcheries (table 6) and those used to produce year classes (table 7).
From 1985 to 1996, over 639,000 fish were distributed as part of the recovery of greenback cutthroat trout (table 8). Unfortunately, discrepancies between the number of fish shipped from hatcheries and the number of fish reported as stocked were typical. In some cases, more fish were shipped than reported stocked, which was partly attributable to fish being sent to nonrecovery waters. In other instances, mortality of fish in transport was reported and ranged from 5 to 40 percent, in which case our estimates of fish stocked (table 5) relied on reports from biologists responsible for stocking. Alternatively, if fewer fish were reported shipped than reported stocked, stocking totals were adjusted proportionately downward. Hatchery records were regarded as more reliable because the weight of fish shipped and the number of fish per unit weight were usually measured.
The bibliography contains materials that could be attributed to specific individuals, groups, or agencies; with few exceptions this material was not peer-reviewed. Much additional information that could not be cited was made available through personal communications or from agency files. Although we attempted to obtain all data relevant to the recovery of greenback cutthroat trout, we undoubtedly have overlooked some sources. We trust that our omissions will be corrected by others with access to additional information. Also, despite repeated checking of data, there most assuredly are errors in the tables that we hope will be remedied in later revisions.
After undergoing this effort, our primary recommendation is the creation of a formal process for reporting data and establishment of an easily accessible database to assist with future management of greenback cutthroat trout, as has been recommended for other federally listed species (James 1999; Safford 1995; Tear and others 1995). The often obscure and disparate sources of data (frequently limited to hand-written notes and in at least one instance, on a napkin) consulted to prepare this document are a reminder that current data reporting strategies risk the loss of much precious information, and that the availability of such data to all participants in endangered species management will lead to better-informed decisions.
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Title: RMRS-GTR-88WWW:
Results and Discussion
Electronic Publish Date: January 2002
Last Update: January
20, 2010