Physical and biological constraints on the capacity for life-history expression of anadromous salmonids: an Eel River, California, case study

Recovery of anadromous salmonid populations is complicated by their complex life-histories. We examined the spatiotemporal interplay of stream temperature, geomorphic features, and a species’ thermal sensitivity mediated by biological interactions in a case study of steelhead trout (Oncorhynchus mykiss) and Chinook salmon (O. tshawytscha) in California’s Eel River watershed. We estimated habitat suitability and fish capacity for each salmonid run and freshwater life stage during average, cool, and warm years in each of the watershed’s subbasins, including a historically-occupied high-elevation subbasin upstream of an impassable dam. Our estimates varied depending on whether we accounted for exposure to the Sacramento pikeminnow (Ptychocheilus grandis), an introduced predator/competitor. Our results indicate that the dammed subbasin has substantial salmonid capacity relative to the rest of the watershed and could provide an important cool-water refuge during warm years and from pikeminnow, potentially improving the productivity and resilience of multiple anadromous salmonid populations. Our approach can be applied in any setting where spatially explicit habitat metrics can be estimated and population specific and life-stage specific habitat criteria can be specified.

The distribution of anadromy and residency in steelhead/rainbow trout in the Eel River, northwestern California

To inform management and conservation of the species, we investigated the distribution of anadromy and residency of steelhead/rainbow trout (Oncorhynchus mykiss) in the Eel River of northwestern California. We determined maternal anadromy versus residency for 106 juvenile O. mykiss using otolith microchemistry. To attempt to relate patterns of anadromy with environmental factors known to influence its distribution in O. mykiss in other places, fish were collected from 52 sites throughout the drainage covering a range of stream size (0.1–7.7 m3/s estimated mean annual run-off) and distance from the ocean (23–219 km). Sixty-one of 91 fish sampled below prospective barriers had anadromous mothers, while 1 of 15 fish sampled above barriers had an anadromous mother. We did not detect any influence of stream size or distance from the ocean on the occurrence of anadromy. Fish with resident mothers were found at 21 of 46 sites below barriers. The current broad distribution of fish with resident mothers indicates the importance of maintaining freshwater conditions suitable for resident adults and juveniles age-1 and older, such as preserving dry-season streamflows.

Explicit landslide characterization using high-resolution and multi-trajectory airborne UAVSAR data

<p>The spatial resolution and deformation-mapping capability of SAR remote sensing fit into the scope of scientific investigations of landslides that move slowly at millimeters to meters per year. The SAR technique has become an efficient tool to detect, monitor and characterize slow-moving landslides. However, north-south motions are nearly unresolvable for the present-day, spaceborne, polar-orbiting and side-looking Interferometric SAR (InSAR) line-of-sight (LOS) mapping systems, and unstable slopes may often not face favorable directions of SAR satellites. In addition, a complete 3D displacement field cannot be obtained with only two distinct InSAR LOS measurements from ascending and descending satellite orbits. Arbitrary assumptions such as simply no north-south motions or constraints imposed by topographic gradients can provide a quasi-3D displacement estimate, yet this is subject to large bias. The Uninhabited Aerial Vehicle SAR (UAVSAR) is an airborne SAR system deployed by NASA/JPL that can acquire measurements along user-specified flight paths. UAVSAR operates with an L-band wavelength (0.24 m) and the single-look pixel spacings along the azimuth and the range directions are as small as 0.6 m and 1.67 m, respectively. Here we will focus on the contributions of UAVSAR and satellite SAR systems to studying the Slumgullion landslide in Colorado, USA with persistent movements at 1-2 cm/day, and even slower-moving landslides (cm to m per year) in the San Francisco East Bay Hills and the Eel River catchment in California, USA. As a complement to InSAR LOS measurements, the high-resolution UAVSAR data and appreciable velocity at a level of m/yr (e.g., Slumgullion landslide and numerous Eel River landslides) make it possible to extract motions by tracking pixel offsets in both azimuth and LOS directions. The flexible trajectory of the aircraft and the additional information from UAVSAR’s sub-meter resolution and multiple flight trajectories allows for an optimal 3D displacement solution, which can be further used for quantitative analysis of the formation of morphological structures, landslide-fault interactions, inferring rheology, understanding slope channel modulation, and capturing the spatiotemporally dependent sensitivity to hydroclimatic variability. New knowledge gained on the precipitation thresholds, landslide volume, and the identification of potential nucleation zones of slope failures will directly assist landslide hazard mitigation and reduction.</p>

On the Ecology and Distribution of Steelhead (Oncorhynchus mykiss) in California’s Eel River

The preservation of life history and other phenotypic complexity is central to the resilience of Pacific salmon stocks. Steelhead (Oncorhynchus mykiss) express a diversity of life-history strategies such as the propensity to migrate (anadromy/residency) and the timing and state of maturation upon return to freshwater (run-timing), providing an opportunity to study adaptive phenotypic complexity. Historically, the Eel River supported upwards of 1 million salmon and steelhead, but the past century has seen dramatic declines of all salmonids in the watershed. Here we investigate life-history variation in Eel River steelhead by using Rapture sequencing, on thousands of individuals, to genotype the region diagnostic for run-timing (GREB1L) and the region strongly associated with residency/anadromy (OMY5) in the Eel River and other locations, as well as determine patterns of overall genetic differentiation. Our results provide insight into many conservation-related issues. For example, we found that distinct segregation between winter and summer-run steelhead correlated with flow-dependent barriers in major forks of the Eel, that summer-run steelhead inhabited the upper Eel prior to construction of an impassable dam, and that both life history and overall genetic diversity have been maintained in the resident trout population above; and we found no evidence of the summer-run allele in the South Fork Eel, indicating that summer run-timing cannot be expected to arise from standing genetic variation in this and other populations that lack the summer-run phenotype. The results presented in this study provide valuable information for designing future restoration and management strategies for O. mykiss in Northern California and beyond.

How rivers incise to survive periodic inputs of immobile landslide-derived boulders

<p>Bedrock landsliding provides a strong negative feedback on bedrock river incision by causing long-lived burial events and hence hiatuses in downcutting.  Nevertheless, rivers in tectonically active settings carve deep canyons despite being periodically inundated with immobile boulders. How is this possible? In this contribution, we explore the processes through which rivers incise bedrock canyons within the Franciscan mélange in the actively uplifting California Coast Range. The Franciscan mélange is well known for its “melting ice cream topography” in which slow-moving landslides (“earthflows”) festoon the walls of river canyons and deliver car- to house-sized boulders to channels.  </p><p>Analysis of valley widths and river long profiles over ∼19  km of Alameda Creek (185  km<sup>2</sup> drainage area) and Arroyo Hondo (200  km<sup>2</sup> drainage area) in central California shows a very consistent picture in which earthflows that intersect these channels deposit immobile boulders that force tens of meters of gravel aggradation for kilometers upstream, leading to apparently long-lived sediment storage and channel burial at these sites. In contrast, over a ∼30  km section of the Eel River (5547  km<sup>2</sup> drainage area), there are no knickpoints or aggradation upstream of locations where earthflows impinge on its channel. Neither boulder supply nor transport capacity explains this difference. Rather, we find that the dramatically different sensitivity of the two locations to landslide blocking is linked to differences in channel width relative to typical seasonal displacements of landslides. The Eel River is ∼5 times wider than the largest annual seasonal displacement. In contrast, during wet winters, earthflows are capable of crossing and blocking the entire channel width of Arroyo Hondo and Alameda Creek. Hence, by virtue of having wide valley bottoms, larger rivers are more likely to simply flow around the toes of earthflows.  </p><p>For the smaller rivers in our study area that are chronically buried in landslide debris, our field observations provide evidence for two processes that may allow periodic bedrock river incision. Narrow channels in the Franciscan mélange that are buried in debris can incise epigenetic gorges around the margins of boulder jams during periods of earthflow dormancy when boulders are no longer input into channels.  Alternatively, during periods of earthflow dormancy, abrasion (and hence size reduction) of boulders in place from suspended sediment may ultimately render boulders mobile.  </p><p>Without explicit representation of these three processes, modeling the coupling of hillslope and channel evolution in this setting is not possible. </p><p><br><br></p>

On the ecology and distribution of steelhead (Oncorhynchus mykiss) in California’s Eel River

Preservation of life-history and other phenotypic complexity is central to the resilience of Pacific salmon stocks. Steelhead (Oncorhynchus mykiss) express a diversity of life history strategies such as the propensity to migrate (anadromy/residency) and the timing and state of maturation upon return to freshwater (run-timing), providing an opportunity to study adaptive phenotypic complexity. Historically, the Eel River supported upwards of one million salmon and steelhead, but the past century has seen dramatic declines of all salmonids in the watershed. Here we investigate life history variation in Eel River steelhead by using Rapture sequencing, on thousands of individuals, to genotype the region diagnostic for run-timing (GREB1L) and the region strongly associated with residency/anadromy (OMY5) in the Eel River and other locations, as well as determine patterns of overall genetic differentiation. Our results provide insight into many conservation related issues. For example, we found distinct segregation between winter and summer-run steelhead correlated with flow dependent barriers in major forks of the Eel; that summer-run steelhead inhabited the upper Eel prior to construction of an impassable dam, and that both life-history and overall genetic diversity have been maintained in the resident trout population above; and no evidence of the summer-run allele in the South Fork Eel, indicating that summer run-timing cannot be expected to arise from standing genetic variation in this and other populations that lack the summer-run phenotype. The results presented in this study provide valuable information for designing future restoration and management strategies for O. mykiss in Northern California and beyond.