Conservation Biology and Applied Zooarchaeology

4. Prehistoric Biogeography and Conservation Status of Threatened Freshwater Mussels (Mollusca: Unionidae) in the Upper Trinity River Drainage, Texas

68 CHAPtEr FoUr Prehistoric Biogeography and Conservation Status of threatened Freshwater mussels (mollusca: Unionidae) in the Upper trinity river drainage, texas Charles R. Randklev and Benjamin J. Lundeen Historically, north America contained the most diverse and abundant population of freshwater mussels in the world, with nearly 300 species (neves 1993). Unfortunately, habitat destruction stemming from sedimentation , impoundment of streams and rivers, release of environmental contaminants, and the introduction of invasive species has reduced this number (lydeard et al. 2004; neck 1982a; Strayer 1999). Current estimates suggest that 12% of the mussel species endemic to north America are now extinct and 23% are threatened or endangered (Galbraith et al. 2008 and references therein). the 52 species described in texas have also been impacted, and many local streams and rivers are unable to support mussel populations at levels that existed in the past (Howells et al. 1996, 1997). As a consequence, 15 texas species have recently been listed as threatened, and 11 of these are now the subjects of petitions for Biogeography and Conservation Status of Freshwater Mussels 69 protection under the Endangered Species Act (ESA) (texas Parks and Wildlife department [tPWd] 2009). listing a species under the ESA requires that decisions be made using the “best scientific and commercial (trade) data available” (nicholopoulos 1999:8). For these species, “substantial information” using biological and biogeographic (past and present) data must demonstrate one of the following: 1. the destruction, modification, or curtailment of habitat or range 2. overutilization for commercial, recreational, scientific, or educational purposes 3. Population decline related to disease or predation 4. inadequacy of existing regulatory mechanisms for protecting existing populations 5. natural or anthropogenic factors affecting a species’ continued existence (US Fish and Wildlife Service 2009) Presumably, this would also be the case for conservation listings at state or local levels. Unfortunately, for both rare and common species, modern and historical data regarding ecological preferences and biogeographic distributions are incomplete at best (Brown and lomolino 1998; national native mussel Conservation Committee 1998). For unionids, the absence of basic biological data stymies conservation efforts. As a result, a national strategy was established in 1997 to help organizations identify tasks needed for the long-term conservation of mussels (nnmCC 1998). included in this framework was a call for an increase in sampling effort as well as for the gathering and dissemination of historical records to better understand the current status of mussel populations. However, the call did not mention the potential of paleozoological data sets for examination of the long-term history of unionids. the potential value of such data is unprecedented because historic and modern data sets are often limited to some degree or biased temporally and spatially. it is therefore questionable whether modern data sets provide adequate baselines from which to infer biogeographic distributions and to measure species declines for the purposes of conservation and restoration. this is not to say that modern and historic accounts are not important but rather that they are insufficient to determine the longterm ecological processes responsible for mussel distributions (Humphries and Winemiller 2009; randklev, Wolverton, et al. 2010; chapter 3, this volume). Given that conservation efforts tend to be driven by recent, and often limited, historical accounts, the extent or magnitude of the decline of poorly known species such as unionids may not be fully recognized by 70 Randklev and Lundeen conservation biologists. As a result, the status of a given mussel species may be far worse than is recognized, regardless of whether that species is considered to be rare or common (régnier et al. 2009). mussel conservation efforts would benefit from information concerning the long-term history of unionids because of the high stakes involved in conservation, such as local extirpation. Paleozoological data sets could provide insight on (1) the distributions of threatened species prior to large-scale impacts (e.g., impoundments) and the degree to which their ranges have changed; (2) the ecological characteristics of those species that have experienced the greatest declines; and (3) locations of prehistoric hot spots for what are today threatened species, and whether or not these locations have been recently sampled. in this chapter, we discuss zooarchaeological data that pertain to several unionid species recently listed for protection, thereby providing information that should inform ongoing conservation efforts. Background the upper trinity river drainage is located in north central texas and is characterized by a humid subtropical climate that is also continental and therefore subject...