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Keywords:

  • Conservation planning;
  • fish diversity;
  • freshwater protected areas;
  • National Parks;
  • threat assessment

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

We assessed the representation of freshwater fish diversity provided by the National Park Service (NPS) and the potential for parks to serve as freshwater protected areas (FPAs) in the United States. Although most parks were not designed with freshwater conservation in mind, nearly two-thirds (62%) of native U.S. fishes reside in national parks. However, only 18% of the nation's highly imperiled fish species are represented within the NPS. The ability for parks to serve as protected areas depends on activities upstream from their boundaries and we found that a substantial part of these watersheds has some form of conservation status. Using a conservation planning approach that integrates fish diversity representation provided by parks and their current and future ecological threats (i.e., climate change, dams, watershed impervious surface, invasive species) and management challenges (i.e., land stewardship beyond park boundaries), we identify 50 parks that could serve as core members of a nationally comprehensive FPA system. While the NPS has limitations as the potential basis for an FPA network, it provides considerable representation of freshwater fish diversity that should be taken into account during systematic conservation planning for freshwaters.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

Globally, freshwater ecosystems are under severe anthropogenic pressure and as a result their rich biological resources are rapidly diminishing (Dudgeon et al. 2006; Vörösmarty et al. 2010). Humans now appropriate >50% of available freshwater runoff (Jackson et al. 2001; Sabo et al. 2010), over 1 million dams fragment river systems (Nilsson et al. 2005; Poff et al. 2007), species invasions are globally widespread (Leprieur et al. 2008), and projected climate change will introduce both new challenges and interact with the many other stressors to which fresh waters are exposed (Rahel & Olden 2008; Woodward et al. 2010). The end result is that freshwater faunas are among the most imperiled worldwide (Viéet al. 2009; Olden et al. 2010), where extinction rates far exceed their marine and terrestrial counterparts (Ricciardi & Rasmussen 1999; MEA 2005).

Scientists have recently begun to explore the potential of establishing freshwater protected areas (FPAs) as one approach to curtail biodiversity loss in freshwater ecosystems. Originally developed for terrestrial areas, and applied over the past two decades to marine systems, protected areas have emerged as a leading tool for conservation. The challenges of planning protected areas for freshwater ecosystems are great due to their hydrologic requirements of longitudinal, lateral, and groundwater connectivity (Barmuta et al. 2010). Thus, many contemporary design ideas for terrestrial and marine protected areas are not transferable to FPAs (Abell et al. 2007; Nel et al. 2009a). Additionally, FPAs must be implemented at the appropriate spatial scale, as many threats originate outside of protected area boundaries.

One of the first steps in designing a representative network of FPAs is taking stock of what is contained within current protected area systems, given that many existing terrestrial reserves house freshwater habitats. Reserves that combine protection for terrestrial and freshwater resources could be prioritized to promote efficient spending of limited conservation dollars (Abell et al. 2010). While some regional U.S. assessments of aquatic resources have been completed (e.g., USGS Aquatic GAP program), national scale empirical information on freshwater resources within terrestrial protected areas is lacking. Of the few national studies that have inventoried freshwater species contained within existing protected areas (Lyle & Maitland 1992—UK; Keith 2000—France; Tognelli et al. 2008—Chile), none have considered the current and future anthropogenic threats or the management challenges that may jeopardize the long-term conservation of biodiversity within those protected areas.

In this study, we provide the first national assessment of representation for native freshwater fishes provided by the National Park Service (NPS), America's longest standing conservation system. Although many NPS units were established for the conservation of terrestrial features, parks are found across a majority of North American ecoregions and thus have potential to provide national-scale representation for freshwater fish diversity. The persistence of freshwater ecosystems is strongly tied to the health of their contributing watersheds, so we quantified the ecological threats to park watersheds including percent impervious land surface, hydrologic alteration and fragmentation by dams, invasive species, and projected climate change. We also assessed the management challenges to utilizing NPS units as FPAs based on the amount of park watersheds in some form of conservation status. We used a conservation planning approach to integrate these results (i.e., fish diversity representation, ecological threats, and management challenge) to identify priority parks that could serve as the core members of an FPA network to protect freshwater fish diversity across the United States. Prioritization is key since funding is limited and the actions required to protect freshwater ecosystems contained in NPS units have high potential costs, including protracted legal action to secure water rights to parks, and the need to develop cooperative management agreements across multifarious stakeholders to protect the upstream watersheds of a park outside of park boundaries. Finally, we identify watersheds in the United States that should be prioritized for future conservation action to provide representation for native fish species that are not currently in the NPS.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

To assess national fish faunal representation provided by the NPS, we collated records for all freshwater species that presently occur within 147 park service units using the NPSpecies database (native occurrences only) and compared them to fish occurrence across all major watersheds of the United States (six-digit Hydrologic Unit Code, HUC). A detailed description of all fish distribution datasets used in this study is provided in the online supplementary material. The 147 parks considered in this analysis were chosen from the broader set of parks evaluated by the NPS Inventory and Monitoring program (NPS I&M) (n= 283 parks), because these parks are managed first and foremost for conservation of their natural resources and thus have the greatest potential to serve as FPAs (see online supplementary material for more details on park selection). Although fish occurrence within the NPSpecies database is internally validated we undertook a secondary validation of each park species list. This validation consisted of a timed (30 minute) review where we compared park species lists from the NPSpecies database to scientific literature, NPS and USGS reports, and gray literature related to the park and, if necessary, contacted park managers for additional information. In 74 hours of effort, we added 226 occurrence records to the total 3,084 records of interest. We also evaluated ecoregion-scale (Abell et al. 2008) representation provided by parks by comparing the suite of species contained within the network of NPS units in a given ecoregion to the species that reside within all watersheds of that ecoregion (NatureServe 2004).

The ability of NPS units to serve as FPAs depends on both threats to their contributing watersheds and the capacity to manage activities in these watersheds (Hansen et al. 2011). To address these issues, we first delineated the watersheds of all parks considered here in a GIS (see online supplementary materials for details). We intersected each park's watershed layer with a series of threat metrics to develop a cumulative current and projected future ecological threat index for all parks. Threats computation was standardized, allowing for comparison of threats across parks (see below). Current threat was comprised of four metrics describing major sources of anthropogenic disturbance in each park's contributing watershed, including (1) percent impervious land cover, (2) habitat fragmentation (number of upstream dams/watershed area), (3) flow alteration (total upstream reservoir storage capacity/long-term mean annual discharge), and (4) degree of species invasiveness within parks (nonnative:native fish species richness). Future ecological threat was assessed as (1) projected percent impervious surface for 2100 (EPA Spatially Explicit Regional Growth Model; A2 greenhouse gas scenario), (2) projected climate changes in annual mean temperature and percent departure in annual mean precipitation (2100 A2 scenario), and (3) invasion potential, determined by adding all nonnative fish species in watersheds adjacent to or within a park's watershed but not yet in park boundaries to the current nonnative richness, and then recalculating the ratio of nonnative:native richness. Current habitat fragmentation and hydrologic alteration were also included in the future ecological threat index calculation since there are no available forecasts of how these threats will change.

We calculated a “management challenge” index for each park based on the total area of a park's watershed within its boundary, as well as the percent of a park's watershed in some form of conservation holding (i.e., federal, state, tribal and local governments, and conservation easements). Ecological threat and management challenge metrics were rescaled using a cumulative distribution frequency to develop a relative index of threat ranging from 0 to 1 and then treated additively to calculate each of the major threat indices (following Vörösmarty et al. 2010). Data sources used to generate each threat index are described in the online supplementary material.

Park threat indices and data on faunal representation were used in the conservation planning software Marxan to identify a minimum set of priority parks that could provide representation for all native freshwater fishes contained in the NPS. Marxan prioritizes sites based on the conservation features they contain, relative to the costs of utilizing a site within the reserve system, and solves the minimum set problem, that is, finding the smallest number of sites that provide adequate representation with the lowest costs (Possingham et al. 2000). In separate analyses, we determined the prioritization of parks based on the occurrence of species in each park and their (1) current ecological threats, (2) future ecological threats, and (3) management challenges, where threats were calculated as costs in Marxan (see online supplementary material for more details). We conducted a sensitivity analysis of park selection by Marxan to (1) determine the influence of the different threat layers on park prioritization, and (2) determine how rare species affected park choice (see online supplementary material). Finally, we conducted another conservation planning analysis to identify watersheds that contain the native fish species not currently within the NPS. To accomplish this, we ran Marxan using our national fish occurrence by watershed database with a goal of prioritizing watersheds that could capture the species not in the NPS (see online supplementary material for detailed methods). We report highly “irreplaceable” watersheds, that is, those watersheds that were selected frequently by our Marxan analysis.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

National parks provide representation for 61.7% of the native freshwater fishes that occur in the United States (478 out of 775 total species), and cover a broad range of fish families (Table S1). NPS units afford variable faunal coverage for their associated ecoregions, with an average representation of 49.5% of species (SD = 21.9%, Figure 1). Representativeness is not a function of species richness of the surrounding ecoregion; ecoregions with high native richness are not more or less represented by their network of national parks than ecoregions with low richness (R2= 0.01, P= 0.47). Seven ecoregions lacked NPS units that meet our criterion for analysis, three of which occur completely within the United States (Apalachicola, Lahontan, Oregon Lakes) and four of which only marginally occur within the United States (≤17% of total ecoregion area in the United States, Guzman—Samlayuca, Sonora, St. Lawrence, Upper Saskatchewan). Parks provide relatively poor representation for species of conservation concern, currently supporting populations of 27 of the nation's 153 highly imperiled fish species (17.6%). Highly irreplaceable watersheds that contain the fish species not currently represented by parks are broadly distributed across 29 different U.S. ecoregions, but are located primarily in the speciose southeastern United States, and species-poor but highly endemic faunas of the southwest and western ecoregions (Figure 2).

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Figure 1. Percent of native fish species represented by parks for each ecoregion, with NPS units selected (filled circles) and not selected (open circles) in our systematic planning analysis. Park symbols represent their geographic centroid, but are not drawn to scale. Ecoregion and park identification can be found in the online supplementary materials (Figure S1, Table S1).

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Figure 2. Irreplaceability (i.e., selection frequency by the Marxan conservation planning software) of watersheds in the United States that contain the remaining 297 freshwater fish species that do not occur in any NPS unit.

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Using Marxan, we identified 50 priority parks that could provide representation for all native species within the NPS (Figure 1, Table S2). With a goal of capturing at least one occurrence of all 478 species currently in the park network, each Marxan analysis (current and future ecological threat and management challenge as costs) selected parks similarly. The average Pearson's correlation coefficient among analyses was 0.93, with a range of 0.89–0.95 (see sensitivity analysis in the online supplementary material, Table S3). Overall, the 50 parks prioritized were comprised of a minimum set of 46, 47, and 46 parks chosen based on current, future threats, and management challenge cost layers, respectively, with a high degree of overlap in their solutions (i.e., only four parks were chosen by a single threat index). Approximately one-third (29.7%) of all native fish species contained in the NPS occur in only one park across all parks considered in this study (n= 147 parks, Figure 3A), and 42.7% of the species had only a single representation within the network of 50 parks prioritized in the Marxan analysis (Figure 3B).

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Figure 3. Number of park occurrences for native U.S. species (n= 478) within the NPS. (A) Frequency of species occurrence in all NPS units considered in this study and (B) within NPS units prioritized by the Marxan conservation planning analysis.

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The optimal solution derived from the prioritization analysis was driven by the large number of species that are rare within the NPS, defined as species occurring in ≤2 parks, which account for 212 of the 478 native U.S. fishes. Parks containing these species (66 parks of the 147 total) have significantly higher current and future ecological threats and lower management potential than parks not containing rare species (Table 1). Together, the large number of rare species distributed across disparate parks (45% of the parks assessed) constrained the Marxan solution to include parks with high threats in the conservation portfolio (Table S2). Parks were chosen differently based on whether rare species were required in the Marxan solution (Tables S2 and S3).

Table 1.  Median (M) current and future ecological threat and management challenge for parks with and without rare species. Differences in median threats between these sets of parks were tested using the Mann–Whitney Rank Sum test. All were statistically significant (P < 0.05)
 Parks that contain rare species (n= 66)Parks that do not contain rare species (n= 81)P-value
M25%○75%○M25%○75%○
Current ecological threat0.590.360.790.410.150.680.003
Future ecological threat0.590.350.770.440.190.730.04 
Management challenge0.640.370.800.410.140.66<0.001

In terms of watershed management challenges, 61 (41%) of the NPS units we assessed have ≥90% of their upstream watersheds outside of park boundaries while only 24 parks (16%) contain their own headwaters (<1% of park watershed outside of the park boundary, Figure 4A). However, 58 parks (39%) have ≥ 90% of their upstream watersheds in some form of conservation status (i.e., federal, state, local government land, private land with conservation easements, and tribal land, Figure 4B). We also assessed the congruence of ecological threats and management challenges across the park network to identify potential conservation opportunities. Sixteen of the 50 parks (32%) prioritized by Marxan have below average current ecological threats and management challenge, representing parks with high FPA potential (relative threat indices <0.5 for both; Figure 5, lower left quadrant). Over one-third (36%) of the parks chosen by Marxan have both above average current ecological threat and management challenge (Figure 5, upper right quadrant). These units were selected largely because they contain rare species, whereas their ecological threats and management challenges make their conservation potential relatively low.

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Figure 4. Frequency distribution of NPS units based on (A) the percent of each park's watershed outside of that park's boundary and (B) the percent of a given park's watershed in some form of conservation status (i.e., federal, state, local government land, private land with conservation easements, and tribal land).

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image

Figure 5. Park current ecological threat as a function of management challenge (based on the percent of a park's watershed in some form of conservation status), with NPS units selected (filled circles) and not selected (open circles) in our systematic planning analysis. Parks with a square outline contain at least one rare species.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

Overall, NPS units contain almost two-thirds of the freshwater fish species within the United States, providing the first evidence that the NPS could broadly contribute to a nationally comprehensive FPA system. By applying a systematic planning approach that considers the distribution of fish species across the park network, as well as an assessment of the current and future ecological threats to parks, we identified 50 national parks that provide representation for all freshwater fish in the NPS. The conservation planning approach employed here was constrained by the fact that many fishes are rare within the park system, and these rare species are present in disparate parks (i.e., not all rare species are present within a few parks of the NPS). Thus, many high-risk parks had to be included in the conservation portfolio. We recognize that there are other means to employ conservation planning software to prioritize parks. For example, high-threat parks could be excluded, or “locked out,” from potential conservation planning solutions. In an exploratory analysis, we found that if all parks with ≥0.75 threats (for any of the three threat indices, range 0–1, n= 60 parks) were excluded from the prioritization process, 83.7% of native U.S. fish species (400/478 species) in the NPS could still be represented in as few as 35 national parks.

The representation provided by the NPS is encouraging given that most parks were not established for the conservation of freshwater features. Of the 38% of native fish species unrepresented by parks (n= 297 species), more than half (n= 171) are highly endemic (i.e., nationwide they are present in ≤2 HUC6 watersheds), so it is not surprising that parks designed mainly for terrestrial conservation did not include these species. Further, nearly half (n= 126) of the 297 fish species not currently represented within the NPS are considered nationally imperiled and 80% (n= 101) of these imperiled species are highly endemic. The relatively low representation of imperiled species within national parks highlights one limitation of using the NPS as a foundation for a national FPA network. Conservation efforts often prioritize the most threatened fauna, so unless parks are established that contain these species, conservation investment for imperiled freshwater fishes will have to be directed outside of the NPS. Our study also identified watersheds that could be prioritized for future conservation action to provide representation for the remaining fish species not presently represented in the NPS (Figure 2). These watersheds may contain non-NPS protected areas that, if managed in conjunction with the priority parks we identified, could provide representation for all U.S. native freshwater fishes. The highly irreplaceable watersheds we identified also inform the NPS or other conservation organizations where new protected areas could be placed to establish a fully comprehensive system of freshwater fish representation.

A major constraint to utilizing NPS units as FPAs is that their ecological integrity is subject to anthropogenic disturbances that occur outside of park boundaries. This is one of the main criticisms of applying the terrestrial protected area approach to freshwater ecosystems (Dudgeon et al. 2006; Abell et al. 2007; Nel et al. 2009b). Our findings illustrate that while most parks have the vast majority of their watersheds outside of park boundaries, the contributing watersheds of many NPS units are held in some form of conservation status. Although public ownership of land does not guarantee protection of its waters (Pringle 2000), it increases the feasibility of establishing an integrated watershed protection program. Forming partnerships with surrounding land owners (both public and private) will be essential to maintaining the aquatic resources currently contained within parks. Establishing these sorts of partnerships is easier said than done, but there is precedent for such cooperation within the NPS (Hamin 2001), and the recently introduced National Fish Habitat Conservation Act (S. 1214, H.R. 2565) aims to further enhance cooperation across government entities to provide regional and national scale conservation planning for freshwater resources.

This study also allows park managers to understand the role each park plays in supporting freshwater fish diversity at the national scale. Prior to the NPS I&M (first phase completed in 2008), the NPS did not have biotic inventories to catalogue species contained within most parks (Stohlgren et al. 1995), let alone biodiversity data at broader scales. By combining NPS I&M data with our national fish database, this work will assist the NPS to understand each parks’ contribution to the broader national fish diversity puzzle, and could assist the development of new policy that supports a comprehensive, network-based conservation strategy. This approach is currently used in the National Wildlife Refuge System, whose policies explicitly put each refuge in the landscape context of all others (USFWS 2001). Additionally, by systematically assessing threats to park watersheds, we provide the NPS a means to compare and prioritize parks based not only on the diversity of freshwater fishes within park borders, but also based on the landscape potential to protect these fishes (Table S2). Prioritizing units within the NPS will be essential because the action required to protect the hydrologic regime of park watersheds will likely be time consuming and costly. For example, Pringle (2000) found that the NPS was engaged in legal adjudications to secure water rights for over 50 different parks.

Given data limitations, we could not address all possible watershed threats to NPS units. Additional research describing nutrient, heat, or chemical pollution to park watersheds and threats from nonfish invaders within parks is also needed to further characterize parks’ FPA potential. Migratory species that occur within parks will also be faced with downstream impediments to their movement into and out of a potential reserve, and nonmigratory species may still require other sites outside of park boundaries for spawning, rearing, or overwintering. Another limitation of our analysis is that the NPSpecies dataset only contains presence/absence data. The relatively high representation of fish species found in the NPS likely overestimates the ability for parks to serve as FPAs because some fish populations in NPS units may be in decline or represent only sink or migratory populations. Assessing the population status of fishes contained in the NPS, and particularly rare species contained in high-threat parks, will be essential to determine if parks are the best strongholds for U.S. fishes or if other sites with higher conservation potential would be better suited to their protection. Monitoring of some of these fish populations is planned or ongoing as part of the NPS Vital Signs Monitoring Program (Fancy et al. 2009). Information on population viability for fish species within the park system does not currently exist at a national scale, and should represent an area of active research if the idea of implementing protection of freshwater resources within parks is carried forward. Also, many (29.7%) native fish species that occur within the NPS are found in only one park unit (Figure 3). A single representation of each species is unlikely to provide adequate buffer against many of the threats that may impinge on fishes within the NPS. Thus, while NPS units may contribute to an FPA system for freshwater fishes in the United States, redundant representation of these species will be required to provide the much needed assurance that these species will not be lost in the future.

Finally, freshwater fish may not be good surrogates for other freshwater biodiversity such as amphibians, crayfish, or mussels (Lawler et al. 2003), and a more taxonomically comprehensive analysis would be valuable in identifying the utility of NPS units as potential FPAs more broadly. Such analyses may become possible as more national park inventories are completed, and our prioritization framework and delineation of park watersheds, threats, and management potential should be useful for this purpose.

Overall, this study contributes to the developing debate on the utility of protected areas for freshwater conservation by examining the role that existing terrestrial reserves may play in representing freshwater species. While the NPS has limitations as the potential basis for an FPA network, it provides considerable representation of freshwater fish diversity that should be taken into account during systematic conservation planning for freshwaters. We also hope that this nationwide analysis of freshwater fish representation in a terrestrial reserve network, combined with a simultaneous assessment of ecological threats and management challenges to these reserves, provides an evaluation framework transferable to other countries and regions.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

We would like to thank Tom Philippi of the National Park Service for providing us with the original NPSpecies dataset. This manuscript was improved with comments from David Dudgeon, Josh Lawler, Michele Thieme, and two anonymous reviewers. D.J.L. and J.D.O. were funded by the U.S. EPA Science to Achieve Results (STAR) Program (Grant No. 833834). D.J.L., E.R.L., C.R.L., M.C.M., T.K.P., and J.D.O. conceived the idea of the study and developed the datasets. D.J.L. conducted the data analysis. D.J.L. and J.D.O. wrote the manuscript.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  9. Supporting Information

Figure S1: Freshwater ecoregions of the United States and the geographic centroid of NPS units selected (filled circles) and not selected (open circles) in our conservation planning analysis.

Table S1: Families of freshwater fishes present in the NPS (n = 147 parks) and for the entire United States.

Table S2: Park threat ranking (0--1) and selection in the best solution by the Marxan conservation planning software.

Table S3: Pearson's correlation coefficients for the best solution chosen by Marxan with four different cost layers, with and without rare species included in the analyses.

Supplementary text: Additional methods and analysis description.

FilenameFormatSizeDescription
CONL_185_sm_FigureS1.doc883KSupporting info item
CONL_185_sm_TableS1.doc33KSupporting info item
CONL_185_sm_TableS2.doc244KSupporting info item
CONL_185_sm_TableS3.doc37KSupporting info item
CONL_185_sm_Suppmat.doc91KSupporting info item

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