Papers by Robert Gresswell
Canadian Journal of Fisheries and Aquatic Sciences, 2005
Potamodromous cutthroat trout express multiple life history strategies, linking seasonal habitats... more Potamodromous cutthroat trout express multiple life history strategies, linking seasonal habitats with movement across spatiotemporal scales. Much of the research on these life history strategies has been conducted in smaller systems where the total habitat for each strategy may be contained within a few small streams. In larger river systems, the same life history strategies exist, but little is known about the spatiotemporal extent of the stream network used by these strategies or the behavioral variability that may exist within each strategy. In order to explore the life history organization of native Snake River finespotted cutthroat trout Oncorhynchus clarki behnkei in the upper Snake River below Jackson Lake Dam, we surgically implanted radio transmitters in 248 cutthroat trout and monitored their movement patterns for a year. All cutthroat trout spawning occurred in side channels of the Snake River (fluvial) and tributaries or spring creeks complexes (fluvial-adfluvial), but ...
Potamodromous cutthroat trout express multiple life-history strategies that appear to be directly... more Potamodromous cutthroat trout express multiple life-history strategies that appear to be directly related to the physical habitat in which they evolved. Although there is a substantial amount of information concerning the habitat use and distribution patterns of cutthroat trout that live in lakes and ascend tributaries to spawn, information about populations in lotic environments is less abundant. Most of these studies have focused on the migration and spawning dynamics of cutthroat trout moving into tributaries to spawn. In larger river systems, however, spatiotemporal relationships between physical characteristics of the habitat and life-history organization of cutthroat trout may be more complicated. To better understand the life-history organization, distribution patterns, and habitat use of Snake River finespotted cutthroat trout Oncorhynchus clarkii behnkei in the upper Snake River, we implanted radio transmitters in 248 cutthroat trout and monitored movement patterns for 12 m...
We propose to address the question, what can be learned by comparing lake trout restoration in th... more We propose to address the question, what can be learned by comparing lake trout restoration in the eastern USA to lake trout suppression in the western USA? In the Laurentian Great Lakes, lake trout were historically dominant, but underwent catastrophic declines caused by over-fishing, non-native species invasions, and habitat degradation. Lake trout management in Laurentian Great Lakes now focuses on restoration or rehabilitation of the species. In contrast, lake trout were introduced into many western lakes and are now overwhelming fish assemblages in many of those lakes, with devastating effects on native species, such as bull trout, rainbow trout, and cutthroat trout. In many western lakes, fishery management now focuses on lake trout suppression to restore native depleted species. Our symposium proposes to borrow information learned for one purpose, such as how to restore a depleted species, for the opposite purpose, such as how to suppress an invasive species. The lake trout p...
Prediction in the biological systems is difficult, primarily because context plays a major role i... more Prediction in the biological systems is difficult, primarily because context plays a major role in the expression of any observed state at a given point and changes in state through time. In fact, spatial and temporal scales are elements of context that are especially important for understanding biological systems. Factors that influence distribution and abundance of aquatic organisms following disturbance fire are being investigated at a variety of spatial and temporal scales. For example, broad generalizations about fire are possible through understanding of physical, chemical, and biological characteristics of a watershed and long-term climate, but it is more difficult to predict the occurrence of fire at specific location in a watershed at any point in time. Following fire, watershed characteristics combine with postfire vegetation patterns and local weather events to influence the probability and magnitude of change. Because effects are greatest at spatial scales of 102-103 m a...
In 1995, the year following the discovery of lake trout (Salvelinus namaycush) in Yellowstone Lak... more In 1995, the year following the discovery of lake trout (Salvelinus namaycush) in Yellowstone Lake, the National Park Service (NPS) initiated a suppression program focused on limiting the negative effects of this nonnative predator on native Yellowstone cutthroat trout (Oncorhynchus clarkia bouvieri). Following suggestions of a panel of nationally renowned scientists (Schullery and Varley (1995), the suppression program was based on gill nets set by US Fish and Wildlife Service (until 1996) and NPS crews. The suppression program expanded as the lake trout population increased, and in August 2008, a scientific review panel was convened by the NPS to evaluate suppression and recovery activities and provide future direction for the program. The panel recommended that the suppression effort should be increased, and monitoring and research of the Yellowstone cutthroat trout and lake trout populations should be expanded. The panel also suggested that a formal lake trout suppression plan n...
Suppression of invasive species in order to restore historical species assemblages and ecosystem ... more Suppression of invasive species in order to restore historical species assemblages and ecosystem integrity has become more prevalent in the past several decades, but in many cases, these programs are hampered by inadequate institutional and public support and funding. External peer review is an important mechanism for program evaluation that provides critical assessment of progress and potential for success, and concomitantly, it can be used as a means of building program support. For example, peer review of the lake trout suppression program currently being conducted in Yellowstone Lake was used in the development and initiation of the program in 1995, and in 2008, a second review was used to assess interim status of the program. By addressing most of the barriers to success identified during this external review, managers have improved the probability of success directly through targeted changes, and indirectly through renewed interest and support generated by these responses. The...
Journal of animal science, 1999
Contemporary issues are defined by people who share diverse and often strongly defended views abo... more Contemporary issues are defined by people who share diverse and often strongly defended views about the topic. In Oregon, citizens are increasingly being asked or expected to participate in complex decisions that require a consensus. Rather than teach one professor's synthesis of a contemporary natural resource issue, faculty from six disciplines coach group process, interactive learning skills, and systems thinking as a way to address complex issues from multiple perspectives. Students learn by grappling with a natural resource issue of their choice within groups based on a diversity among majors, degree status, and gender. Students define situation (S), brainstorm new or different targets (T), and analyze two or more pathways (P), using an STP learning and action process. Exploring potential pathways involves defining possible consequences, stakeholder views, feasibility (ecological, social, economic, and political), and planning that includes expected behavior of the improved...
Arctic and Alpine Research, 1997
ABSTRACT Long-term limnological data from the four largest lakes in Yellowstone National Park (Ye... more ABSTRACT Long-term limnological data from the four largest lakes in Yellowstone National Park (Yellowstone, Lewis, Shoshone, Heart) are used to characterize their limnology and patterns of temporal and spatial variability. Heart Lake has distinctively high concentrations of dissolved materials, apparently reflecting high thermal inputs. Shoshone and Lewis lakes have the highest total SiO, concentrations (averaging over 23.5 mg L-'), apparently as a result of the rhyolitic drainage basins. Within Yellowstone Lake spatial variability is low and ephemeral for most measured variables, except that the Southeast Arm has lower average Na concentrations. Seasonal variation is evident for Secchi transparency, pH, and total- SiO, and probably reflects seasonal changes in phytoplankton biomass and productivity. Total dissolved solids (TDS) and total-SiO, generally show a gradual decline from the mid-1970s through mid-1980s, followed by a sharp increase. Ratios of Kjeldahl-N to total-PO, (KN:TP) suggest that the lakes, especially Shoshone, are often nitrogen limited. Kjeldahl-N is positively correlated with winter precipitation, but TP and total-SiO, are counterintuitively negatively correlated with precipitation. We speculate that increased winter precipitation, rather than watershed fires, increases N-loading which, in turn, leads to increased demand for TP and total SiO,.
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Papers by Robert Gresswell