“Hot Spots” and Priority Watersheds Identified for Imperiled Freshwater Mussels and Fishes

Aquatic Hot Spots and Priority Watershed Analysis Poster

By Ronald Cicerello and Greg Abernathy

INTRODUCTION
Kentucky’s native freshwater fish and mussel faunas are among the richest in North America (NA), the center of worldwide freshwater mussel and temperate freshwater fish biodiversity (1, 2, 3). Thirty-five percent of the NA freshwater mussel fauna (297 taxa) and approximately 30% of the NA freshwater fish fauna (ca. 800 taxa) are known from Kentucky (4, 5). The Kentucky fish and mussel faunas rank third and fourth, respectively, in species richness among the states. Both groups are dependent upon good physical habitat and water quality, but mussels also are dependent ecologically on fishes, which serve as hosts for mussel larvae. Mussels and fishes are among the most imperiled taxonomic groups nationally (3); the distribution of these groups in Kentucky is well documented (4, 6, 7). During the last century, habitat destruction and degradation (e.g., dams, pollution, introduced non-indigenous mussels) caused the extirpation or extinction of 21% and 4% of Kentucky’s mussel and fish taxa, respectively. Of the extant taxa, 41% of mussels and 25% of fishes are imperiled because of significant declines in diversity, numbers and distribution. Efforts to conserve Kentucky’s imperiled mussels and fishes are underway (e.g., The Green River Bioreserve project by The Nature Conservancy, USFWS, KY Department of Fish and Wildlife Resources et al.), but priority areas for conservation have not been assessed. Priority areas must be identified so limited conservation funds can be expended wisely. Our objectives were to identify hot spots, watersheds with the highest species richness, and priority watersheds for conservation of imperiled freshwater mussels and fishes in Kentucky.

MATERIALS AND METHODS
We followed methods used by Master et al. (3). Using a Geographic Information System, we scored each of 616 Kentucky watersheds (11-digit U.S Geological Survey hydrologic unit codes (HUC)) for post-1984 records of imperiled mussels (33 taxa) (freshly-dead or living specimens) and fishes (50 taxa) in the KSNPC Natural Heritage Program database as of 6 October 2004 (Figure 1, Table 1). Imperiled mussels and fishes are those listed as endangered, threatened, or of special concern or are candidates for listing as endangered or threatened by the USFWS (8, 9, 10), NOAA (11), and/or the KSNPC (12). The data were analyzed as follows:

Hot Spot Analysis:

We summed the number of imperiled taxa in each watershed.
Hot Spots are watersheds with > 8 imperiled fish and/or mussel taxa.

Priority Watersheds Analysis:

We calculated a rarity-weighted richness index (RWRI) (13, 14) for each taxon. Each imperiled taxon was scored, as 1 divided by the number of watersheds the taxon inhabits. A taxon inhabiting only one watershed was scored 1.0, and one inhabiting 20 was scored 0.05. The RWRI for each watershed is the sum of scores for each taxon occurring in that watershed. The minimum RWRI for inclusion as a priority watershed was 1.23, which equals the mean RWRI and 1 standard deviation (mean = 0.44, SD = 0.79, n = 190).
Criteria for Identifying Priority Watersheds to Conserve Imperiled Taxa in each of 17 drainages (Figure 2):
- Watersheds with RWRI > 1.23 or with > 5 taxa;
- Watersheds with the highest RWRI value in each drainage; and
- Add watersheds with the highest RWRI value or the most viable population to ensure all imperiled taxa are included at least twice (except taxa restricted to one watershed).

RESULTS AND DISCUSSION
Hot Spot Watersheds
Only 31% of 616 11-digit watersheds in Kentucky had at least one imperiled taxa and only 1.9% support 8 or more imperiled taxa. The Green River near Munfordville is the top hot spot with 21 imperiled mussel and fish taxa (Figure 1, Table 2). The second and third most important watersheds are contiguous with the top watershed and harbor 18 and 13 taxa, respectively. These three watersheds are habitat for 24 imperiled taxa, including 8 USFWS/NOAA-listed or candidate species, and they are isolated from adjacent watersheds and mussel and fish populations by Green River Lake Dam upstream and by Lock and Dam 6 downstream. Terrapin Creek, a tributary to the Obion River in west Tennessee, has 11 imperiled taxa, all listed only by KSNPC, plus an undescribed, endemic form of Lampetra aepyptera not included in this analysis. Contiguous lower Ohio River watersheds each support 8 imperiled taxa, but when merged they include 14 species. The Green River near Munfordville also is the most important watershed for conservation of USFWS/NOAA-listed and candidate species (Figure 3, Table 3). Conservation of the top 10 hot spot watersheds (12 watersheds totaling ca. 403,653 hectares) would protect populations of 88% of imperiled mussel taxa and 58% of imperiled fish taxa.

Priority Watersheds to Conserve Imperiled Taxa
Conservation of 53 watersheds totaling ca. 1,490,896 hectares or 14% of Kentucky will protect all taxa restricted to one watershed and at least two watersheds for each of the remaining taxa (Figure 4, Table 2). Priority watersheds are concentrated in drainages extending from the Mississippi River to the upper Green and upper Cumberland rivers, areas with diverse habitats and high species richness. Eight of the top 10 priority watersheds are in three drainages (Mayfield and Obion Creeks and Bayou de Chien, the Upper Green River, and the Upper Cumberland below the Falls). Drainages extending from the Tradewater River to the Big Sandy River generally have lost imperiled taxa to habitat destruction and degradation. Terrapin Creek, the top priority watershed (RWRI = 7.11) and a focus of KSNPC conservation efforts, has five taxa restricted to one watershed and it exclusively shares two additional taxa with only one other watershed. These species are widely distributed and relatively abundant in the lower Mississippi River valley and in Gulf Slope drainages. Six drainages (3, 4, 10, 11, 13, and 17) support few imperiled or range limited taxa. Only the watershed with the highest RWRI score in each of these drainages is a conservation priority. Priority watersheds generally include populations with the best viability and integrity (i.e., size, condition, and landscape context). However, some priority watersheds have been severely degraded (e.g., Little South Fork Cumberland River and Horse Lick Creek) and the viability of imperiled taxa and entire taxonomic groups (e.g., mussels) in these watersheds is questionable (15, 16). Population size for Epioblasma obliquata obliquata, E. torulosa rangiana, and Obovaria retusa probably is below the minimum for viability and these taxa will likely be lost in Kentucky. Larger scale watersheds probably are required to ensure viability of some species. Migratory species such as lake sturgeon probably require larger watersheds to ensure that all life requisites are met. Removal of abandoned navigation dams on the Green River, for example, would reconnect and restore riverine habitat and probably increase the viability of mussels (e.g., Pleurobema plenum and P. rubrum). There are challenges to the conservation of these watersheds. Some watersheds are highly developed and conservation is at best a secondary priority (e.g., the Mississippi, Ohio, and lower Tennessee rivers). More than two populations of each taxon must be protected to ensure the long-term survival of imperiled mussel and fishes, requiring the protection of additional land. The large number and mean size (28,139 hectares) of priority watersheds overwhelms the resources required to protect them. Despite these and other challenges, efforts to protect several priority watersheds are already underway (e.g., the Rockcastle and Licking rivers). This preliminary assessment focused on imperiled mussels and fishes. A future assessment will use data for all native mussel and fish taxa to determine priorities for biodiversity conservation of these groups.

LITERATURE CITED
(1) Page, L.M. and B.M. Burr. 1991. A field guide to freshwater fishes, North America north of Mexico. Houghton Mifflin Company, Boston, MA.
(2) Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18:6-22.
(3) Master, L.L., S.R. Flack, and B.A. Stein, eds. 1998. Rivers of life: critical watersheds for protecting freshwater biodiversity. The Nature Conservancy. 71 pp.
(4) Burr, B.M., and M.L. Warren, Jr. 1986. A distributional atlas of Kentucky fishes. Kentucky Nature Preserves Commission Scientific and Technical Series 4:1-398.
(5) Cicerello, R.R., and G.A. Schuster. 2003. A guide to the freshwater mussels of Kentucky. Kentucky State Nature Preserves Commission Scientific and Technical Series 7:1-62.
(6) Cicerello, R. R., M. L. Warren, Jr., and G. A. Schuster. 1991. A distributional checklist of the freshwater unionids (Bivalvia: Unionoidea) of Kentucky. American Malacological Bulletin 8(2):113-129.
(7) Kentucky State Nature Preserves Commission. 2004. Kentucky Natural Heritage Database. Kentucky State Nature Preserves Commission. Frankfort, KY. Available at www.naturepreserves.ky.gov.
(8) [USFWS] United States Fish and Wildlife Service. 1999. Endangered and threatened wildlife and plants. Department of the Interior, Washington, D.C.
(9) [USFWS] United States Fish and Wildlife Service. 1999. Endangered and threatened wildlife and plants; review of plant and animal taxa that are candidates or proposed for listing as endangered or threatened; annual notice of findings on recycled petitions; annual description of progress on listing actions; proposed rule; notice of review. Fed. Reg. 64:57533-57547.
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(11) [NOAA] National Oceanic and Atmospheric Administration. 1999. Endangered and threatened species; revision of candidate species list under the Endangered Species Act. Fed. Reg. 64:33466-33468.
(12) Kentucky State Nature Preserves Commission. 2004. Endangered, threatened, special concern, and historical biota of Kentucky. Kentucky State Nature Preserves Commission, Frankfort, KY. Available at www.naturepreserves.ky.gov.
(13) Williams, P., D. Gibbons, C. Margules, A. Rebelos, C. Humphries, and R. Pressey. 1996. A comparison of richness hotspots, rarity hotspots, and complementary areas for conserving diversity of British birds. Conservation Biology 10:155-174.
(14) Csuti, B., S. Polasky, P.H. Williams, R.L. Pressey, J.D. Lamm, M. Kershaw, A.R. Kiester, B. Downs, R. Hamilton, M. Huso, and K. Sahr. 1997. A comparison of reserve selection algorithms using data on terrestrial vertebrates in Oregon. Biological Conservation 80:83-97.
(15) Warren, M.L., Jr., W.R. Haag, and B.M. Burr. 1999. Status of the mussel resource in the Little South Fork Cumberland River. USDA Forest Service, Center for Aquatic Technology Transfer, Center for Bottomland Hardwoods Research, Forest Hydrology Laboratory, Oxford, MS.
(16) Haag, W.R., and M.L. Warren, Jr. 2004. Species richness and total population size of freshwater mussels in Horse Lick Creek, Kentucky in 2003. Final report. USDA Forest Service, Center for Bottomland Hardwoods Research, Forest Hydrology Laboratory, Oxford, MS.

ACKNOWLEDGMENTS
For information and assistance we gratefully acknowledge J.B. Burch and D. Ó Foighil, (University of Michigan Museum of Zoology), B.M. Burr (Southern Illinois University), K.S. Cummings and C.A. Mayer (Illinois Natural History Survey), R. Hershler and P. Greenhall (National Museum of Natural History), J.B. Layzer (Tennessee Technological University), G.A. Schuster (Eastern Kentucky University), and D.H. Stansbery and G.T. Watters (Ohio State University Museum of Zoology). We thank the KSNPC staff and individuals and institutions too numerous to list for sharing their expertise and assistance.

Large format poster of the "Hot Spots" and Priority Watersheds Analysis (~5 MBs PDF format)