Protecting Crayfish

Why this Species is Special
The Nashville crayfish (Orconectes shoupi Hobbs) was described by Robert S. Fleming in 1939 as Cambarus propinquus sanborni (Fleming, 1938-9), from specimens collected in Mill Creek (Miller et al., 1990, O’Bara et al., 1985).  Horton H. Hobbs Jr. reassigned the species to the genus Orconectes in 1948 and renamed it in honor of Dr. Charles S. Shoup, a Vanderbilt University biology professor of the time (Hobbs, 1948).  The species was later assigned to the subgenus Crockerinus (Fitzpatrick, 1987). 

The Nashville crayfish was listed as Endangered by the USFWS on October 27, 1986, due to its apparent restriction to the Mill Creek watershed and continuing threats from development to the same.  The species was subsequently listed as Endangered under state law by the Tennessee Wildlife Resources Agency (TWRA).  The federal recovery plan for the species was completed in 1988 (USFWS, 1988). 

Early accounts suggested that the species was limited solely to Mill Creek and it largest tributaries (including Sevenmile Creek), but research over the last 20 years has documented the species in progressively smaller waters.  Many of the recent surveys are in direct response to certain regulatory requirements either directly or indirectly following from the listing of the species and its protection under the Endangered Species Act (O’Bara, 1999, in part, by inference).  Though often not abundant in the most minor of Mill Creek tributaries, O. shoupi has managed to eke out an existence at many locations despite an overwhelming abundance of competing species.

The species is still believed to be limited to the Mill Creek basin in Davidson & Williamson counties, where its preferred habitat includes free-flowing waters dominated by a slabrock on bedrock substrate.  It is now known from twenty primary (directly connected) and eleven secondary Mill Creek tributaries.  But that apparently broad distribution within the Mill Creek system does not imply security, as a single catastrophic event could result in the loss of thousands of individuals from Mill Creek and its larger tributaries.  Pollution events in the watershed are not uncommon.

The Nashville crayfish remains the signature species for Mill Creek, and for whatever reason, calls nowhere else home.

Habitat Needs
Orconectes shoupi appears to be restricted to the bedrock- or cobble-dominated streams in the Mill Creek drainage.  Preferred habitat includes slabrock over bedrock or cobble substrates in free-flowing streams, although at least three exceptions involving impoundments have been reported (Carpenter, 2004; DNA Biotics, 2009; Walton, 2008). Several authors have noted the apparent absence of the species outside of the drainage, and have indicated that historic accounts outside of the basin were either in error or represented short-lived introductions (Barrociere, 1986; Bouchard, 1984; Miller et al., 1990; O’Bara et al., 1985; USFWS, 1988).  Although they typically are most abundant in the larger streams of the Mill Creek watershed – where they can be the most common species- they also will utilize flashy headwater streams when possible.  In these areas however they face increasing competition from species more tolerant of drought, and generally are not found in any great number.  Still, it remains important to protect headwater systems for the species, should downstream populations be subject to mass die-offs.
Species Discovery
Hobbs (1948) described Orconectes shoupi following close examination of a series of crayfishes from the Nashville area (Bouchard, 1984, from Barrociere, 1986).  Many authors have addressed the particular characters that distinguish the species from others in Mill Creek and the region (Hobbs, 1948; O’Bara et al., 1985; USFWS, 1988; Williams, 2001).  The most distinguishing features include elongate pincers with red tips and adjacent narrow black banding, a usually light-colored “saddle” on the carapace (back) extending from the posterior to the anterior and terminating as lateral stripes on either side, and distinctive gonopods (reproductive organs) markedly different from any of its nearby cousins.  Larger females can be easily identified by the geometry of the annulus ventralis (AV, sperm receptacle) under minimal magnification, and occasionally by the naked eye.  O. shoupi can be a rather large crayfish, ranging from young-of-the-year (YOY) at ~0.6 cm total length (TL) to adults ~17.8 cm (O’Bara et al., 1985). 

Other Orconectes reported from the Mill Creek watershed, including the fishhook crayfish (O. rhoadesi) and the saddle crayfish (O. durelli), can be easily distinguished from O. shoupi by gonopod structure and body coloration.  As noted by Bouchard (1984a), O. placidus, a Central Basin species strongly resembling O. shoupi, has never been reported from the Mill Creek watershed.  As such, even YOY crayfish from the Mill Creek drainage often can be comfortably identified as O. shoupi, as no other saddle-bearing species are present in the system.  That idea was borne out during Tennessee Natural Heritage Program surveys between 2005-2009, as the only adult Orconectes from the Mill Creek system with the characteristic saddle was O. shoupi.  Saddled YOY observed in the Mill Creek drainage, by inference, are likely O. shoupi as well. 

What Does it Mean to be on the Federally Endangered List, and
Why is the Nashville Crayfish Listed

Species of plants and animals are listed by the U.S. Fish and Wildlife Service as endangered or threatened for one or more of the following reasons:

  • The present or threatened destruction, modification, or curtailment of its habitat or range.
  • Overutilization for commercial, recreational, scientific, or educational purposes.
  • Disease or predation.
  • The inadequacy of existing regulatory mechanisms.
  • Other natural or manmade factors affecting its continued existence.

The Nashville Crayfish was listed as an endangered species on October 27, 1986.  It is endemic to Mill Creek and its tributaries in Davidson County and Williamson County.  Four of the five above-listed factors necessitated listing of the Nashville Crayfish. Foremost was the past and ongoing loss of the species’ habitat.  Much of Mill Creek and its tributaries are located within Metropolitan Nashville which is a highly developed urban environment. The remainder of the drainage is now under heavy development pressure as Nashville grows. Other factors included the potential use of the species for food and bait, limited protection afforded the species by State law, and its vulnerability, due to its restricted range, to pollution and spills of toxic materials into streams containing populations.

Addition of a species to the Federal list of Endangered and Threatened Plants and Animals means that the species is legally protected by the Federal Endangered Species Act.  All Federal agencies must consider impacts to the species and its habitat when funding, authorizing, or carrying out activities.  Those agencies must also utilize their authorities to further protection of listed species by carrying out programs for the conservation of endangered and threatened species.  Listing also provides funding to be used for recovery of listed species; funding is provided to the Fish and Wildlife Service and to State fish and wildlife agencies through cooperative agreements.  The Endangered Species Act also provides opportunities to non-Federal agencies, groups, and private citizens to protect listed species through development of Habitat Conservation Plans.

Regulations and Penalties
The Endangered Species Act prohibits “take” of listed species.  Take includes harming, harassing, killing, shooting, wounding, trapping, collecting, pursuing, hunting, or capturing listed species, or attempting to engage in those activities.  This provision applies to all agencies, groups, and citizens.  Violation of the take provision can result in fines and/or time in prison.