Species Status Assessment Report for the Big Blue Springs Cave Crayfish (Procambarus Horsti) Version 1.1
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Species Status Assessment Report for the Big Blue Springs Cave Crayfish (Procambarus horsti) Version 1.1 Type locality for Big Blue Springs Cave Crayfish, Big Blue Spring, FL. (credit: Ryan Means, Florida Geological Survey) May 2017 U.S. Fish and Wildlife Service Region 4 Atlanta, GA Big Blue Springs Cave Crayfish SSA Report Page ii May 2017 This document was prepared by Peter Maholland (USFWS – Athens, GA Field Office) with assistance from Dr. Sean Blomquist (USFWS – Panama City, FL Field Office) and Patricia Kelly (USFWS – Panama City, FL Field Office). Valuable peer reviews of a draft of this document were provided by Chester Figiel (USFWS – Warm Springs Fish Technology Center), Chris Skelton (Georgia College State University), and David Cook (Florida Fish & Wildlife Conservation Commission). We appreciate the time and effort of those dedicated to learning and implementing the SSA Framework, which resulted in a more robust assessment and final report. Suggested reference: U.S. Fish and Wildlife Service. 2017. Species status assessment report for the Big Blue Springs Cave Crayfish (Procambarus horsti). Version 1.1. May, 2017. Atlanta, GA. Big Blue Springs Cave Crayfish SSA Report Page iii May 2017 Species Status Assessment Report For Big Blue Springs Cave Crayfish (Procambarus horsti) Prepared by the U.S. Fish and Wildlife Service EXECUTIVE SUMMARY This species status assessment (SSA) reports the results of the comprehensive status review for the Big Blue Springs cave crayfish (Procambarus horsti), documenting the species’ historical condition and providing estimates of current and future condition under a range of different scenarios. The Big Blue Springs cave crayfish is a hypogean species of crayfish endemic to several freshwater spring and sink caves within the panhandle of Florida. The Big Blue Springs cave crayfish has been collected from aquatic caves and limestone springs associated with the Woodville Karst Plain near and below (south of) the Cody Scarp, paralleling riverine karst areas of the Wakulla, St. Marks, and Wacissa rivers. The principal habitat feature supporting this species appears to be a flowing, freshwater, subterranean environment. The SSA process can be categorized into three sequential stages. During the first stage, we used the conservation biology principles of resilience, redundancy, and representation (together, the 3Rs) to evaluate individual Big Blue Springs cave crayfish life history needs. The next stage involved an assessment of the historical and current condition of species’ demographics and habitat characteristics, including an explanation of how the species arrived at its current condition. The final stage of the SSA involved making predictions about the species’ response to positive and negative environmental and anthropogenic influences. This process used the best available information to characterize viability as the ability of a species to sustain populations in the wild over time. To evaluate the current and future viability of the Big Blue Springs cave crayfish, we assessed a range of conditions to allow us to consider the species’ resiliency, representation, and redundancy. For the purposes of this assessment, populations were delineated using the three sites that Big Blue Springs cave crayfish has historically occupied. Limited access to aquatic cave habitat prohibits confirmation, but it is presumed that the species is actually found throughout the karst conduits of the aquifer, and that these sites are merely “windows” where Big Blue Springs cave crayfish can be observed. Big Blue Springs Cave Crayfish SSA Report Page iv May 2017 Resilience, assessed at the population level, describes the ability of a population to withstand stochastic disturbance events. A species needs multiple resilient populations distributed across its range to persist into the future and avoid extinction. These factors include (1) fresh water availability (water quantity), (2) sufficient water quality, and (3) appropriate habitat. If spring and sink ecosystems provide adequate fresh water, suitable water quality, and adequate habitat, we anticipate Big Blue Springs cave crayfish will survive and thrive in abundance. Each of these factors is discussed here (Table ES-1). As we consider the future viability of the species, more populations with high resiliency distributed across the known range of the species are associated with higher overall species viability. Redundancy describes the ability of the species to withstand catastrophic disturbance events. Redundancy is about spreading the risk and can be measured through the duplication and distribution of populations across the range of the species. The greater the number of populations a species has distributed over a larger landscape, the better it can withstand catastrophic events. For the Big Blue Springs cave crayfish, we considered whether the distribution of resilient populations was sufficient for minimizing the potential loss of the species from such an event. Representation characterizes a species’ adaptive potential by assessing geographic, genetic, ecological, and niche variability. Representation can be measured through the genetic diversity within and among populations and the ecological diversity of populations across the species’ range. The more representation a species has, the more it is capable of adapting to changes in its environment. In the absence of species-specific genetic and ecological diversity information, we evaluate representation based on the extent and variability of habitat characteristics within the geographical range. The Big Blue Springs cave crayfish historic range was limited to three sites in Florida’s panhandle. Maintaining those populations provides redundancy, and the species is currently represented across most of the known geographic extent of the species. We have assessed the Big Blue Springs cave crayfish’s levels of resiliency, redundancy, and representation currently and into the future by ranking the condition of each population, as delineated for this assessment. Together, the 3Rs comprise the key characteristics that contribute to a species’ ability to sustain multiple distinct populations in the wild over time (i.e., viability). Using the principles of resiliency, redundancy, and representation, we characterized both the species’ current viability and forecasted its future viability over a range of plausible future scenarios. To this end, we ranked the condition of each population by assessing the relative condition of occupied sites using the best available scientific information. Rankings are a qualitative assessment of the relative condition of spring and sink ecosystems based on the knowledge and expertise of U.S. Big Blue Springs Cave Crayfish SSA Report Page v May 2017 Fish and Wildlife Service and Florida Fish and Wildlife Conservation Commission staff, and recent spring/sink condition reports. The most significant stressor to Big Blue Springs cave crayfish is the future loss of spring and sink ecosystems that individuals and populations need to complete their life history. The primary source of potential future habitat loss is groundwater depletion resulting in reduced or eliminated available fresh water in subterranean caves. Groundwater withdrawal is not anticipated to influence spring flow dramatically in the Woodville Karst Plain region due to the large areas of public ownership, changes to surface water flow and stormwater management, and sea level rise causing more freshwater to remain in the karst system instead of discharging into the Gulf of Mexico. The viability of the Big Blue Springs cave crayfish depends on maintaining multiple resilient populations over time. Given our uncertainty regarding if or when sites occupied by Big Blue Springs cave crayfish will experience a reduction or elimination of adequate fresh water in the future, we have forecasted what the Big Blue Springs cave crayfish may have in terms of resiliency, redundancy, and representation under three future plausible scenarios: (1) All or most springs and sinks occupied by Big Blue Springs cave crayfish experience no measureable drop in fresh water availability; (2) Available fresh water in springs and sinks occupied by Big Blue Springs cave crayfish is reduced but not eliminated; and (3) All or most springs and sinks occupied by Big Blue Springs cave crayfish experience an extreme reduction or elimination of available fresh water. We used the best available information to forecast the likely future condition of the Big Blue Springs cave crayfish. Our goal was to describe the viability of the species in a manner that will address the needs of the species in terms of the 3R’s. We considered a range of potential scenarios that may be important influences on the status of the species, and our results describe this range of possible conditions in terms how many and where Big Blue Springs cave crayfish populations are likely to persist into the future (Table ES-1). Big Blue Springs Cave Crayfish SSA Report Page vi May 2017 Table ES-1. Summary results of the Big Blue Springs cave crayfish Species Status Assessment. 3Rs Needs Current Condition Future Condition (Viability) Projections based on cave freshwater availability • Adequate • Two populations scenarios: Resiliency availability of fresh across range have high • No change: All populations are likely to remain (Large water resiliency, one extant into the future populations able • Sufficient water population has • Fresh water is reduced: Most populations are to withstand