How Does the PRRIP Implement Science?

The Program has been implementing an Adaptive Management Plan (AMP) to reduce uncertainties related to the response of least terns, piping plovers, and whooping cranes to management actions on the central Platte River. Under this plan the Program investigates hypotheses related to whooping crane use, as well as least tern and piping plover use of and productivity on in-channel and off-channel habitat. This has been accomplished through the implementation of systematic monitoring and research of Platte River hydrology, geomorphology, and species response.

What is the PRRIP Adaptive Management Plan?

The Program’s AMP outlines two competing management strategies that reflect different paths to achieving the objectives of improving production of least tern and piping plover from the AHR and increasing use of the AHR and thus survival of whooping cranes. The first strategy is the Mechanical Creation and Maintenance (MCM) approach. This approach focuses on mechanical creation and maintenance of both in- and off-channel habitats for the species. For least terns and piping plovers this includes the construction of in-channel nesting islands, acquisition and restoration of off-channel sandpit habitat, and the construction of new off-channel sandpit habitat. For whooping cranes, this approach focuses on mechanical creation and maintenance of both in- and off-channel habitats including channel widening through management activities such as in-channel and bank line vegetation removal, the acquisition and restoration of off-channel wetland habitat, and the construction and preservation of wet meadow habitat.  

The second strategy is the Flow-Sediment-Mechanical (FSM) approach. This approach is river-centric with a focus on restoring channel width, improving sediment supply, and increasing annual peak flow magnitudes to increase sandbar height and maintain width. The FSM strategy is rooted in the view that the historical AHR provided critical suitable habitat conditions for whooping cranes and supported viable sub-populations of both the least tern and piping plover prior to the onset of water development and channel narrowing.

PRRIP Adaptive Management Experiment Example

The Program implemented an experimental design to evaluate least tern and piping plover selection of and productivity on in- and off-channel nesting habitat. This was accomplished through designed experiments where islands of various heights (i.e., overtopped by different levels of flow) and sizes were mechanically created near areas where existing off-channel nesting habitat existed.

We performed these experiments at two sites over the course of several years and learned least terns and piping plovers selected off-channel nesting habitat over in-channel islands and that use of in-channel islands resulted in very low productivity (21 nests; 4 successful nests; 7 chicks; 1 fledgling).

What Has PRRIP Learned?

Since 2007, the Program has been implementing an AMP to reduce uncertainties related to the responses of least terns, piping plovers, and whooping cranes to management actions on the central Platte River and to investigate hypotheses related to whooping crane use of in-channel and off-channel habitats and least tern and piping plover use of and productivity on in-channel and off-channel habitat. Implementation of SDHF releases, the physical process driver of the FSM management strategy, were hypothesized to produce suitably-high sandbar habitat for least tern and piping plover nesting in areas of sediment balance and to produce and maintain suitable riverine roosting habitat for whooping cranes within the AHR. Over this time, enough progress has been made to allow us to address critical uncertainties and assess the ability of the FSM and MCM management strategies to create suitable least tern, piping plover, and whooping crane habitat within the AHR.

Least Tern and Piping Plover Findings

Flow-Sediment-Mechanical (FSM)

Natural high flow events in 2008, 2010, 2011, and 2013, 2014 and 2015 all exceeded SDHF magnitude and duration; these high flow events failed to build suitable habitat as observed sandbar heights following these events did not exceed the Program’s minimum height suitability criterion in areas of sediment balance. Instead, the amount of suitable habitat has declined as constructed in-channel sandbar habitats that met the criterion were eroded. The disparity between observed and hypothesized beneficial effects of SDHF-magnitude flows on sandbar suitability can primarily be attributed to the prior assumption that sandbars build to the peak water surface during high flow events. Observational studies since 2007 indicate a height of 1.5 ft below peak water surface is a more reasonable estimate of sandbar height potential. When the prior height assumption is replaced with the estimated sandbar heights of 1.5 ft below peak flow, SDHF is no longer predicted to produce sandbars exceeding the minimum height criterion for suitable nesting habitat. Flow magnitudes of roughly twice SDHF may be necessary to create suitably-high sandbars in channel widths suitable for nesting.

As the negative indicators for FSM performance discussed above began to emerge, the Program’s Independent Scientific Advisory Committee (ISAC) and stakeholders requested the Executive Director’s Office (EDO) staff begin to compare and contrast the physical characteristics of the AHR and other regional river segments in an effort to glean additional management insights. The lower Platte River segment was an obvious choice for comparison given that the presence of viable species subpopulations in the historical AHR was inferred, in part, from contemporary species use of that segment of the river.

Both species arrive and begin initiating nests prior to the late-spring runoff which typically occurs in mid-June in the Platte basin. Given sandbar heights in relation to stage-discharge relationships in both the central and lower Platte River, nests initiated prior to the late spring rise are likely to be inundated. The timing of the late spring rise is especially problematic for piping plovers and it does not appear that either segment can support sufficient in-channel productivity to maintain a subpopulation of that species over the long term. The ability to maintain a stable least tern subpopulation is likely tied to the success of renesting following the late spring rise. Given the challenges of maintaining adequate productivity, these findings suggest that use and success on novel habitats like in-channel sand spoil piles and off-channel sand mines may be necessary to allow these species to persist in a river basin with hydrology that is not ideally suited to the species’ nesting ecology.

A final comparative investigation was conducted to identify regional river segments that do support species population densities similar to proposed recovery objectives for the AHR. Although these species nest sympatrically on several river systems in Nebraska, the only river segments in this region that support population densities approximating proposed AHR recovery objectives occur on the Niobrara River. Peak flow volumes and magnitudes on the Niobrara are quite similar to the contemporary AHR. However, the timing of the annual peak flow is typically earlier and base flows remain higher during the summer months. The earlier timing of the annual peak may be especially important in relation to piping plover productivity. There are also intractable differences in physical conditions between the two segments that are likely related to species occurrence. The width of the Niobrara River is highly variable due to the influence of bedrock outcroppings and the median bed material grain size is much finer than the AHR (0.24 mm vs. 0.96 mm). These differences likely contribute to the formation of large sand flats (~ 30 ac) that are used by the species on the Niobrara. Channel widths within the AHR can be mechanically manipulated and widened, but it is not feasible to attempt to shift the bed material grain size of the AHR into the range of the Niobrara from either a technical or cost perspective.

In summary, these investigations lead us to conclude implementation of the FSM management strategy will almost certainly not create suitable least tern and piping plover nesting habitat on an annual or near-annual basis. Moreover, intractable differences between physical conditions in the AHR and other regional river systems that are used by these species raise serious doubt that the Program can successfully manage flow and sediment to create and maintain suitable in-channel nesting habitat.

Mechanical Creation and Maintenance (MCM)

The MCM approach of creating in-channel and off-channel nesting habitat has been implemented within the AHR by various entities since the early 1980’s. Accordingly, there is little uncertainty about the ability to construct and manage mechanical habitats that are suitable nesting habitat for the species. Systematic monitoring of least tern piping plover occurrence and productivity has been conducted in the AHR since 1979 with very few nests being observed on in-channel islands. A few productivity studies were also implemented during this time. These investigations all identified low quantities of suitable in-channel nesting habitat and high levels of nest loss and chick mortality due to inundation of sandbars. However, off-channel nesting incidence has increased and productivity has consistently been above productivity levels deemed necessary for maintaining least tern and piping plover populations within the AHR.

Structured Decision Making

In 2016, the Governance Committee (GC) of the Program successfully completed a Structured Decision Making (SDM) process where numerous options were considered for providing additional in- and off-channel nesting habitat for least terns and piping plovers within the AHR. The SDM process concluded with a formal GC decision to (a) construct an additional 60 acres of off-channel habitat on a mixture of leased land, purchased land, and land already owned by the Program, (b) commit to a budget of $26,000 for developing on channel habitat using a Moving Complexes Approach (MCA), and (c) recommend to the U.S. Fish and Wildlife service that water should not be used solely for the purpose of nest initiation flows for least terns and piping plovers. This represents the first known successful implementation of a completed cycle of  an AMP.

Whooping Crane Findings

We used data collected systematically along the central Platte River during 2001-2017 to evaluate riverine habitat selection within the AHR. The goal of our analysis was to develop habitat models to be used to inform and direct management activities the Program is able to implement. We were unable to establish a relationship between whooping crane use and flow metrics or total channel width, but rather found unobstructed channel width and distance to the nearest forest were good predictors of whooping crane use. We also used telemetry data obtained over the course of seven years, 2010-2016, to provide an unbiased evaluation of whooping crane use of riverine habitat throughout the migration corridor. Based on findings from the use of Platte River data, we evaluated the influence of unobstructed channel width and distance to nearest forest on whooping crane selection of riverine habitat throughout the North-central Great Plains in the United States. Findings of both studies indicate the Program would have the potential to influence whooping crane use of the central Platte River through increasing unobstructed channel widths that are <650 ft and mechanically removing trees within areas where the unforested corridor width is <1,100 ft. Based on results of both investigations, the Program informally accepted unobstructed channel widths of at least 650 ft and unforested corridor widths of at least 1,100 ft as highly favorable whooping crane riverine roosting habitat.

We used annual delineations of total channel width and maximum unobstructed channel width throughout the AHR to evaluate several flow and mechanical management alternatives hypothesized to create and maintain whooping crane roosting habitat. Results of our analyses indicate a positive relationship between unobstructed channel width and disking and peak discharge. However, natural high flow events in 2007, 2008, 2010, 2011, 2013, 2014, and 2015 all exceeded minimum SDHF magnitude and duration and only with the extreme high flow event occurring in 2015 did average unobstructed channel width exceed 600 ft. Our results also indicate disking and flows substantially exceeding the magnitude and duration of a SDHF release are the only management activities able to create and maintain 650 ft unobstructed channel widths believed to be favorable for whooping crane roosting habitat. As such, our weight of evidence approach led us to conclude implementation of the FSM management strategy will not create or maintain favorable whooping crane riverine roosting habitat.

Pallid Sturgeon Findings

While evaluations of pallid sturgeon data are still ongoing, a few recent discoveries have been made that make the best path forward for detecting or dealing with potential Program impacts on pallid sturgeon (positive or negative) difficult to determine. Pallid sturgeon will be an upcoming focus for the Program.

How Can I Gain Access to PRRIP Data?

Interested parties may be able to access PRRIP data by submitting a data request proposal to the Executive Director’s Office of the Program that outlines what data is of interest, how the data will be used, what the data will be used for, and what the final products of the data use will be.