Species Status Assessment Report Scott Riffle Beetle (Optioservus phaeus) Big Spring at Historic Lake Scott State Park. Photo by Kansas Department of Wildlife, Parks, and Tourism. U.S. Fish and Wildlife Service Mountain-Prairie Region Kansas Ecological Services Field Office Manhattan, Kansas & Region 6 Ecological Services Lakewood, Colorado Version 1.0, May 2019 Scott Riffle Beetle SSA 1 2019 Scott Riffle Beetle SSA 2 2019 Species Status Assessment Report for the Scott Riffle Beetle (Optioservus phaeus) Prepared by the Kansas Ecological Services Field Office U.S. Fish and Wildlife Service Executive Summary This species status assessment details the results of the comprehensive biological status review by the U.S. Fish and Wildlife Service (Service) for the Scott riffle beetle (Optioservus phaeus) and provides a thorough account of the species’ viability and extinction risk. The Scott riffle beetle is a small freshwater aquatic beetle endemic to only one known type locality: a spring (Big Spring) located in Historic Lake Scott State Park (state park) in Scott County, Kansas. No other populations are known or are thought to exist. There are no known additional historical records for this species of riffle beetle (Ferrington et al. 1991, p. 4). To evaluate the biological status of the Scott riffle beetle both currently and into the future, we assessed a range of conditions to allow us to consider the species’ resiliency, redundancy, and representation (together, the 3Rs). The future persistence of the Scott riffle beetle is dependent on five fundamental environmental factors associated with Big Spring (its only known habitat). These factors include: (1) consistent groundwater discharge (2) relatively shallow, unpolluted, oxygenated water (3) coarse substrate such as medium sized rocks or broken concrete (4) abundance of aquatic macrophytes, algae, and periphyton (5) availability of adjacent terrestrial habitat If the Big Spring ecosystem meets these five conditions, we anticipate the only known Scott riffle beetle population to exist into the future (Table I). As we consider the future viability of the species, it should be noted that only a discovery of a previously undocumented population would lead to a higher overall species viability. We have assessed the Scott riffle beetle’s levels of resiliency, redundancy, and representation at present and into the future by describing the condition of the one population in its current state and by projecting its condition under multiple future plausible scenarios (Table I). The assessments are qualitative and are based on the knowledge and expertise of the Kansas Department of Wildlife, Parks, and Tourism (KDWPT) and other natural resources professionals. The most significant future potential stressor to the Scott riffle beetle is groundwater depletion and the subsequent loss of the spring ecosystem within which the larvae and adults need to complete their life history. Groundwater withdrawals from the High Plains Aquifer will continue into the future with depletion and recharge rates depending on regional water usage (Butler et al. 2018, pp. 52-53) and climate change (Crosbie et al. 2013, p. 3949). Anthropogenic activities that could act as stressors, such as surface water contamination, habitat destruction, substrate removal, or the introduction of invasive species are currently minimal at Big Spring due to protective measures implemented by the state park. Scott Riffle Beetle SSA i 2019 The viability of the Scott riffle beetle depends on maintaining the only known population at Big Spring over time. Given the possibility that groundwater discharge may change into the future and that this variable is fundamental to the survival of the species, we forecasted Scott riffle beetle resiliency, redundancy, and representation under five plausible future scenarios, weighting regional groundwater usage (a proxy for spring groundwater discharge1 and a variable whose impact could increase or decrease depending on the magnitude of climate change) higher than other potential variables: (1) decreased regional groundwater usage; tree removal to reduce local water stress; decreased groundwater contamination risk; increased site protection; increase in habitat area; establishment of captive population and suitable rearing facility (2) decreased regional groundwater usage; tree removal to reduce local water stress; no change in groundwater contamination risk; increased site protection; no change in habitat area; no captive population established; establishment of suitable rearing facility (3) no change in regional groundwater usage; tree removal to reduce local water stress; no change in groundwater contamination risk; increased site protection; no change in habitat area; no captive population established; establishment of suitable rearing facility (4) no change in regional groundwater usage; tree removal to reduce local water stress; no change in groundwater contamination risk; increased site protection; no change in habitat area; no captive population established; no suitable rearing facility (continuation scenario) (5) increased regional groundwater usage; increased groundwater contamination risk; decreased site protection; possible decrease in habitat area; no captive population established A Scott riffle beetle management plan written by KDWPT details management actions that have already reduced or are likely to reduce many of the potential risks to the Scott riffle beetle (Hofmeier (a) 2018, pp. 6-7). The plausible future scenarios draw heavily on the management actions contained in this plan. The underlying risk of groundwater discharge reduction as a result of regional groundwater usage, however, may be outside the current scope of this plan. Our assessment of the future viability (in terms of resiliency, redundancy, and representation) for the Scott riffle beetle is summarized in Table I below. Scenarios one and two are the only scenarios in which we would expect the resiliency of the species to not decline. Species redundancy is expected to be low in all but Scenario one which includes the establishment of one additional population, in this case in captivity. The current population inhabits the entire known range of the species; therefore, establishment of additional populations is limited to captivity. The presence of only one known population in one ecological niche with unknown genetic diversity means representation is projected to remain low under all five scenarios. 1 Historic discharge rates at Big Spring are expected to differ from current discharge rates due to differences in measurement methods and changes in the spring run infrastructure, including the installation of a pipe, the lining of the spring run in concrete, and the subsequent destruction of the concrete lining (Hofmeier (d) pers. comm. 2018). Regional groundwater usage is a variable related to groundwater discharge at Big Spring and is more accurately assessed in a historical context and in plausible management scenarios. KDWPT installed a water quality and quantity monitor in May of 2018. Measurements from this monitor can be used to calibrate regional water usage trends. Scott Riffle Beetle SSA ii 2019 Table I. Species Status Assessment summary for the Scott riffle beetle (Optioservus phaeus). 3Rs Needs Current Condition Future Condition (Viability) o adequate groundwater o One population assumed Projections based on scenarios: discharge to have medium to high ● Scenario 1 (optimistic) decreased regional groundwater usage; decreased groundwater o sufficient water quality, resiliency contamination risk; increased site protection; increase in habitat area; establishment of including sufficient dissolved captive population and suitable rearing facility. POPULATION EXPECTED TO oxygen EXPERIENCE INCREASE IN RESILIENCY o presence of periphyton and ● Scenario 2 (less optimistic) decreased regional groundwater usage; no change in diatoms groundwater contamination risk; increased site protection; no change in habitat area; o suitable substrate no captive population established; establishment of suitable rearing facility. o terrestrial habitat POPULATION EXPECTED TO EXPERIENCE NO DECLINE IN RESILIENCY Resiliency ● Scenario 3 (more optimistic than continuation) no change in regional groundwater (large populations able to usage; no change in groundwater contamination risk; increased site protection; no withstand stochastic events) change in habitat area; no captive population established; establishment of suitable rearing facility. POPULATION EXPECTED TO EXPERIENCE DECLINE IN RESILIENCY ● Scenario 4 (continuation) no change in regional groundwater usage; no change in groundwater contamination risk; increased site protection; no change in habitat area; no captive population established; no suitable rearing facility. POPULATION EXPECTED TO EXPERIENCE DECLINE IN RESILIENCY ● Scenario 5 (pessimistic) increased regional groundwater usage; increased groundwater contamination risk; decreased site protection; possible decrease in habitat area; no captive population established. POPULATION EXPECTED TO EXPERIENCE RAPID DECLINE IN RESILIENCY o multiple populations o Low redundancy, only one Projections based on scenarios: throughout known range of known population ● Scenario 1 (optimistic) INCREASE IN REDUNDANCY WITH ESTABLISHMENT OF species CAPTIVE POPULATION (because of presumed increased ability to withstand a Redundancy catastrophic event) (number and distribution of ● Scenario 2 (less optimistic) SLIGHT INCREASE IN REDUNDANCY WITH