When: 7:00 PM, Tuesday, 10 February 2015
Where: Orca Books (509 East 4th Avenue, Olympia, Phone 360.352.0123)
*Our February Topic Is:*
Long-term population response of Coastal Cutthroat Trout to hydrologic and other environmental fluctuations in a temperate-rainforest stream
In the relatively pristine Irely Creek watershed (upper Quinault River drainage) within Olympic National Park (ONP), Coastal Cutthroat Trout**(CCT, /Oncorhynchus clarkii clarkii/) coexists (as a native-adfluvial run) with anadromous Coho Salmon (/O. kisutch/) and two resident (lamprey and sculpin) species. Each spring during 2001-2012, we counted cutthroat redds (nests) in mainstem and tributary habitats there. Trout redds and fry were abundant in the mainstem during 2001-2002 stream walks, particularly in its middle segment, with escapement estimates (twice the redd count) being 48-106. More recently, the adult population has declined by an order of magnitude, reflecting summer/fall dry-outs of adult habitat in Irely Lake; lowest runs (escapement estimates of four each) were seen during 2006, 2007, and 2010. Although redd counts have risen when summer/fall seasons have been wetter during 2003-2012, they haven’t reached 2001-2002 counts because of regular lake dry-outs, including two consecutive dry-outs during 2002-2003. Hence, the trout population is showing an overall downward trend with some smaller-scale oscillations associated with fuller lake levels in wet summers; cutthroat-escapement estimates during 2003-2012 were in the range of 4-32. During 2002-2003, the population also spawned in a headwater tributary, but (a) log-created waterfalls in the upper mainstem and/or (b) reduced run size hindered tributary spawning in other years. But cutthroat fry and juveniles have been consistently present in Irely Creek during our 12-year study, as assessed by stream-walk, netting, and snorkeling observations. Recent (2010-2011) upsurges in (a) Irely Lake water levels with wetter conditions and (b) the coho run (marine-derived nutrients)were associated with the cutthroat’s partial run recovery during 2011-2012, the first population increase for two consecutive years. Correlation, multiple-regression, and multivariate analyses for this ‘natural experiment’ showed that spring reproductive-season flows, incubation-scour floods, and the location of hydraulic-drop (HD) barriers weren’t important predictors of trout escapement. But fish-environmental relations were complicated by time lags, so past-year conditions appeared to be more important for trout-run success than same-year bioticand physical conditions. Hence, cumulative-year hydrologic indices were often-better predictors of trout-run size than were single-year environmental variables and flood-scour indices. Complication for biotic parameters were curvilinear responses, likely due in part to density dependence for the highest trout-escapement year (2002), but quadratic terms didn’t improve predictive ability. The mechanistically valuable variables for our best monotonic and quadratic regression models included (a) cross-year conditions for lake level (that assumed good biotic and physical recovery after past dry-outs) and peak-spawning temperatures (given the trout’s coldwater preferences); and (b) past-year cutthroat escapement and coho-carcass counts (as a proxy index of nutrient/food abundance). Hence, both biotic (stock/trophic) and physical factors appeared to be important for cutthroat productivity, in positive vs. negative ways, respectively. Soour best monotonic-regression modelcan realistically predict future trout escapements, based on changing environmental conditions from natural and human impacts.
Robert Vadas holds a B.A. in zoology/botany (Ohio Wesleyan University), M.Sc. in stream-fish ecology (University of Maryland), and Ph.D. on fish instream-flow issues (Virginia Tech). He has since worked for two consulting companies in Alberta and has completed two postdoctoral projects in British Columbia and California on fish-habitat and other issues, with collective focus on riparian and instream-flow impacts to freshwater and estuarine ecosystems. He has recently worked as a state-agency biologist, including past estuarine fish-habitat work with the Florida Marine Research Institute and present freshwater (especially
salmonid) work with the Washington Department of Fish and Wildlife. He focus has been on hydrologic, habitat, and dietary needs of fishes, using field sampling, statistical analysis, and ecological synthesis. Formal instream-flow training includes a postgraduate course at Virginia Tech in stream-hydraulic modeling, USFWS courses on field and modeling techniques for PHABSIM, and USGS courses on 2-D hydrodynamic modeling and natural-resource negotiations.
Vadas’ Washington work has included much field work (including snorkeling) on spawning and rearing habitat use of cutthroat and coho, laboratory gut analyses on coho and prickly sculpins, some spawning and rearing habitat work on Chinook salmon and bull trout, and spawning work on pink, chum, and sockeye salmon and steelhead. His British Columbia work, which had a riparian focus, included much field/lab work on habitat and food use by Chinook, steelhead, mountain whitefish, and various other fishes.
He’s also an active member of several environmental organizations in Olympia, often acting as a scientific advisor for them.He enjoy music and sports, including active roles, and regularly likes to express his odd sense of humor.