Yellowstone Cutthroat |
2003 Idaho Fish & Game survey reveals startling cutthroat decline There is no easy way to reverse the trend By Lyn Benjamin The Yellowstone cutthroat trout is considered by many to be the flagship species of the Yellowstone ecosystem. However, unlike many land-dwelling creatures such as the elk or the grizzly, its status has not received much attention until recently. Fish biologists in the Rocky Mountain region, though, have been tracking cutthroat trout population trends. As 2003 drew to a close, serious range-wide cutthroat trout population declines became evident. Although the four-year drought plays a prominent role in the precipitous drop in cutthroat numbers, extended dry spells are only a part of the story.
Two sections of the Teton River were surveyed, one in the upper valley, one in the lower valley. Since 1998, in the upper valley section of the river, cutthroat populations have declined by 94%, rainbow and hybrid populations have increased by 51% and brook trout populations have increased by 166%. In the lower valley section of the river, cutthroat populations have decreased by 95% and rainbows and hybrids have increased by 319% (in 1998 there were too few brook trout to be part of the population estimate). This level of decline was one of the worst in the region and is particularly worrying because of the huge increase in non-native trout (rainbows and brook trout). What are some probable causes for this decline?
Cutthroat trout habitat loss results from siltation of spawning areas, reduced woody debris (resulting from devegetation of riparian areas) and the placement of dams and other migration barriers. As Rob Van Kirk discusses in his article on the South Fork of the Snake River (Spring 2004 Newsletter), alteration of the natural hydrologic regime can also have negative impacts on the cutthroat trout whose life cycle patterns have evolved to cues from snowmelt runoff. Although we don’t have a dam in the Teton Valley, diversion of the flood peak flows have likely altered timing and amount of streamflows. Additionally, the lack of flows in tributary streams through much of the summer and fall reduce connectivity between headwater streams and the mainstem river. The final potential factor, which Utah and Idaho State Universities and FTR are currently studying, is whirling disease, a neurological disease that can cause mortality in juvenile trout and a typical “whirling” behavior in surviving adults. This is a long list of probable causes for population declines, and as a result the formulation of recovery strategies is not an easy task. Fortunately, regional non-profits and local, state and federal agencies have recognized the critical need for collaboration and started conversations about a cutthroat recovery plan in January at the FTR offices. The goal of a recovery plan is to assure the long-term persistence of a species. The details of such a plan for the Teton Basin continue to be discussed but will most likely contain the following components:
What are possible recovery strategies for the Teton Basin?
First, because of the reproductive overlap with rainbow trout, any available spawning habitat will be used by both cutthroats and rainbows and likely lead to hybridization. Secondly, brook trout will also use available habitat and will out compete cutthroats for available food and space. Despite our best intentions, by restoring habitat we might be simply giving rainbow and brook trout another edge over cutthroats. A couple of strategies, discussed below, are currently being used to exclude non-natives. On five tributaries to the South Fork, weirs have been placed that enable biologists to sort fish that are swimming upstream to spawn. Cutthroat traffic is directed upstream to spawn while rainbows and brookies are sent downstream! A more controversial strategy employed in other western watersheds is electrofishing and killing brook trout in drainages where they are out-competing cutthroats. Moving further upstream in the Teton watershed, headwater tributaries including South Leigh, Darby and Teton Creeks were extensively surveyed for trout in 1998. Yellowstone cutthroat trout were found in 89% of the surveyed habitat and in 19% of that habitat were the only trout present. Darby and South Leigh Creeks held the strongest populations of just cutthroat trout. It is important to track these populations closely and protect them carefully because it is possible that if the Teton River population declines even further, these tributary populations will be the only native trout left in the watershed. Several other recovery strategies need to be discussed. First, the issue of stocking … planting fingerling or catchable size cutthroat trout creates a better fishery but doesn’t create a self-sustaining population. However, placing fertilized or “eyed” cutthroat trout eggs in fresh spawning gravels will hatch out a generation of young cutthroats with the scent of the natal stream in their system, which will drive them to spawn in those streams. In order to conduct an eyed egg project, a “brood stock” of parent trout needs to be created, which can be difficult when numbers are so low in the Teton Basin. Additionally, the new generation of cutthroat needs to be protected by the placement of barriers to non-native trout. Second, the petition to list the Yellowstone cutthroat trout under the Endangered Species Act (ESA) has been taken back to court by the group whose petition was originally rejected in 2001. A benefit from listing would be increased visibility, and ability to leverage funds for its recovery. However, many individuals feel that an attempt to list the cutthroat would waste critical resources that might better be invested in on-the-ground action. Finally, on the South Fork, fishing regulations have been changed to permit unlimited, year-round harvest of rainbows. On the Teton River regulations could be changed to prevent any harvest of cutthroat (currently the limit is two above 16 inches). However if we encouraged unlimited harvest of rainbows it is possible that nothing will replace them. There are no easy answers to this situation. Here at FTR we are committed to work hard to protect our native trout. It is hard for me to imagine what the Teton River would be like without the beautiful Yellowstone cutthroat trout. Thanks to Rob Van Kirk for invaluable assistance with this article.
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So what is the rest of the story, and, in particular, how much applies to the Teton River fishery? 
Brook trout compete successfully against cutthroat trout for food and cover from predators, particularly in small streams. Rainbow and cutthroat trout are able to cross-reproduce, however the hybridization always favors the rainbow trout so hybridized populations quickly lose cutthroat trout genetic markers. 
Spring creeks on the valley floor have historically provided spawning and rearing areas for trout. Habitat degradation resulting in siltation and decreased stream flows has contributed to loss of spawning areas. Although restoration of stream banks and gravel spawning beds in these streams are important components of recovery, there are two important concerns that need to be addressed as this work is undertaken.
