Orconectes (Crockerinus) obscurus (Hagen, 1870)

Loughman, Zachary J. & Simon, Thomas P., 2011, Zoogeography, taxonomy, and conservation of West Virginia's Ohio River floodplain crayfishes (Decapoda, Cambaridae), ZooKeys 74, pp. 1-78 : 29-34

Orconectes (Crockerinus) obscurus (Hagen, 1870)

Cambarus obscurus Hagen 1870:69, figs. 72-75, 154.

Cambarus propinquus var. obscurus Faxon 1885:92.

Cambarus propinquus obscurus Hay 1899:960.

Cambarus (Faxonius) obscurus Ortmann 1905b:112; 1906:369, figs. 1, 2, 7.

Faxonius obscurus Creaser 1933:5.

Faxonius (Faxonius) obscurus Creaser 1933a:5.

Orconectes obscurus Hobbs 1942a:352; 1974:36, fig. 117. Crocker 1957:36, 53, 75, figs. 5-6. Fitzpatrick 1963:61; 1967:160, figs. 3, 11-15, 25. Taylor et al. 1996:31. Taylor et al. 2007: 384.

Orconectes (Orconectes) obscurus Hobbs 1942b: 154.

Orconectes (Crockerinus) obscurus Fitzpatrick 1987:50. Hobbs 1989: 36, fig. 155. Jezerinac et al. 1995:26-34, figs. 11 a– 11h. Loughman 2010: 50-53, fig. 16.

Diagnosis.

Rostrum with slightly converging margins, not thickened, with marginal spines or tubercles; median carina absent; postorbital ridges possessing a sharp spine. Cephalothorax ovoid, slightly, dorsoventrally compressed, without setae. Areola 3.7-6.6 times longer than wide, comprising 27-39% of TCL, with 2-3 rows of punctations across narrowest region; cervical groove interrupted just above cervical spine; lacking hepatic spines; suborbital angle obsolete. Antennal scale about 1.5 times as long as wide; basiopodite spine of antenna well developed. Ischiopodite of antenna without spine. Chelae smooth, broad and robust, length 91% of TCL; mesial surface of palm consisting of two well developed rows of tubercles; mesialmost row consisting of 7-11; dorsolateral row with 5-11; lateral margin of propodus smooth, dorsal surfaces of both dactyl and fixed finger of propodus with weak dorsolateral ridges; some elongate setae at base of fixed finger. First form gonopods short, comprising 33% of TCL, with two terminal elements about equal length; corneous central projection comprising 23% of pleopod length, tapering distally to point; mesial process non-corneous, spatulate, partially surrounding central projection; cephalic base of central projection with right angle shoulder. Form two male gonopod non-corneous, blunt, shoulder not prominent or absent. Female annulus ventralis deeply embedded in sternum, moveable, wider than long, cephalolateral prominences well developed, distinctly separated by a trough; fossa rather deep, sinus sinuate in caudal 67% of annulus.

Color in life.

Carapace, abdomen and dorsal surface of chelae brown; rostral margins, caudal edge of carapace, and anterodorsal surface of terga dark brown; tips of chelae and knob at base of dactyl orange; tubercles on mesial and lateral margins of dactyl, mesial margin of palm, and mesial margin of propodus, and two spines or tubercles on anterodorsal surface of carpus yellow; reddish stripe on lateral margin of chelae; ventral margins beige.

Specimens examined.

Orconectes obscurus were collected from six counties at 16 locations in the current study, as listed below.

BROOKE COUNTY: Buffalo Creek at RT 2 crossing in Wellsburg, 40.261375 -80.61508; 4 September 2005 - (WLU 05090402), 2 I♂, 3 ♀. Cross Creek at entrance to Bruin Drive adjacent to Brooke High School, 40.306442 -80.5997; 28 June 2005 - (WLU 05062803), 1 ♀; 4 September 2005 - (WLU 05090403), 2 I♂, 1 II♂, 2 ♀. (3.) RT 2 crossing of nameless tributary 2.27 km (1.41 mi) S of Beech Bottom, 40.23163 -80.6523; 28 June 2005 - (WLU 05062801), 4 II♂. RT 2 crossing of nameless tributary in Beech Bottom proper, 40.306442 -80.5997; 28 June 2005 - (WLU 05062801), 1 ♀. HANCOCK COUNTY: Hardin Run 0.81 km (0.5 mi) from CR 2-7/RT 2 intersection on CR 2-7, 40.533314 -80.60326; 23 August 2005 - (WLU 05082302), 2 I♂, 1 ♀. Holbert Run 1.61 km (1.0 mi) from CR 2-8/ RT 2 intersection adjacent to CR 2-8, 40.474045 -80.58584; 23 August 2005 - (WLU 05082303), 1 I♂, 1 II♂, 1 ♀. Kings Creek at RT 2 crossing, 40.435715 N / 80.592514 W; 17 October 2005 - (WLU 05101701); 3 I♂, 4 ♀. Tomlinson Run backwater at RT 2 crossing, 40.54026 -80.628075; 8, March 2005 - (WLU 06030801), 9 I♂; 30 March 2005 - (WLU 06033001), 1 I♂. MARSHALL COUNTY: Big Grave Creek at Ohio River confluence in Moundsville, 39.9046 -80.75731; 20 July 2005 - (WLU 05072003 1 ♀; 4 September 2005 - (WLU 05090401), 2 I♂, 1 II♂. Fish Creek at RT 2 crossing, 39.808643 -80.81616; 30 October 2005 - (WLU 05103002), 7 I♂, 2 ♀; 30 April 2006 - (WLU 06043001), 8 O♀. Little Grave Creek at RT 2 crossing in Moundsville, 39.920944 -80.748566; 28 July 2007 - (WLU 05072807), 1 I♂, 1 II♂, 4 ♀. Nameless tributary at RT 2 crossing adjacent to Columbia Chemical operations, 39.85933 -80.79305; 28 July 2007 - (WLU 05072809), 2 I♂. OHIO COUNTY: Short Creek at RT 2 crossing, 40.18312 -80.676865; 4 September 2005 - (WLU 05090404), 2 I♂, 2 ♀. PLEASANTS COUNTY: Ben’s Run at RT 2 crossing, 39.46337 -81.08457; 28 July 2005 - (WLU 05072802), 1 I♂, 2♀. WETZEL COUNTY: Fishing Creek at RT 2 crossing, 39.63576 N/ -80.85848; 20 July 2005 - (WLU 05072001), 2 II♂, 1 ♀. Proctor Creek at RT 2 crossing, 39.70037 N/ -80.81791 W; 20 July 2005 - (WLU 05072001), 2 II♂, 3 ♀.

Distribution.

Orconectes obscurus occurs in north-west New York south through western Pennsylvania and north-central West Virginia, east to Maryland’s portion of the Youghiogheny River system and west to the Flushing Escarpment of Ohio ( Hobbs 1989). Ontario populations are considered introduced ( Taylor et al. 2007). Orconectes obscurus distribution in western West Virginia appeared to be limited to the Upper Ohio North and Upper Ohio South drainages ( Jezerinac et al. 1995). Jezerinac et al. (1995) reported the southern extent of Orconectes obscurus range adjacent to the Ohio River as Proctor Creek at the Marshall/Wetzel counties line, and documented Orconectes sanbornii replacing Orconectes obscurus inFishing Creek, Wetzel County. Jezerinac et al. (1995) also documented Orconectes sanbornii as the dominant orconectid for the Middle Ohio North, Middle Ohio South, and Lower Ohio basins.

Orconectes obscurus has undergone a southern range expansion since Jezerinac’s surveys in the 1980's (Figure 19). The southern extent of its range currently is Ben’s Run, Tyler County. Orconectes sanbornii 's northern limit currently is Middle Island Creek, due north of Saint Mary’s, Pleasant County. Orconectes obscurus and Orconectes sanbornii divide the Middle Ohio North basin, with Orconectes obscurus inhabiting northern portions of the basin and Orconectes sanbornii inhabiting southern portions (Figure 19).

The southward expansion of the range of Orconectes obscurus could be natural or an anthropogenic event. Orconectes are used as bait because of their ease of capture and high densities ( Distefano et al. 2009b), so bait bucket release may explain the southward range expansion. Orconectes obscurus has a history as an invasive, with such populations present in New York and Ontario, Canada ( Crocker and Barr 1968; Taylor et al. 1996). Many of the streams containing Orconectes obscurus populations in the southern region of the Middle Ohio North basin are second or third order streams that do not harbor large game fish populations.

Two alternative hypotheses explaining this expansion may include previous misidentification and natural expansion. Orconectes obscurus may have always been present historically where the species was collected in this survey, and misidentified by previous investigators. It is also possible that the species has expanded under natural conditions southward since the 1980's, specifically invading the Hannibal Pool of the Ohio River and replacing Orconectes sanbornii in the mainstem. After displacement of Orconectes sanbornii in the Ohio River mainstem, additional streams could be colonized via stream confluences.

Morphometrics.

The largest individual was a 39.0 mm TCL form I male collected in Tomlinson Run backwater in Hancock County. The largest female was collected from the confluence of Little Grave Creek and the Ohio River in Marshall County and possessed a 37.4 mm TCL. Mean TCL for the species was 29.2 mm (n = 82, SE = 8.77). Sexual dimorphism is displayed in this species, with form I and form II male chelae significantly larger (t(345) = 6.8201, p = 0.0001) than female chelae. Morphometric data for Orconectes obscurus is presented in Table 8.

Habitat and natural history.

Orconectes obscurus (Figure 20) occupy stream habitats throughout the central and northern regions of the floodplain. Habitats include first through fifth ordered streams and Ohio River backwaters. Healthy populations of Orconectes obscurus occur in all 3rd through 5th ordered streams from Ben’s Run, Tyler County, north to Tomlinson Run, Hancock County. Orconectes obscurus were frequently collected from streams within two specific macrohabitats. Slab boulders and leaf packs were utilized by all demographics; form I males were associated primarily with slab boulders. Leaf packs in pool thalwegs were utilized with increased frequency by Orconectes obscurus juveniles. Based on captive observations, leaf packs offer both structural protection and periphyton for foraging (Z. Loughman personal obs.).

Orconectes obscurus is also a tertiary burrower, creating minimal burrows under substrate items. Small gravel and cobble piles usually were present along margins of slab boulders harboring Orconectes obscurus . One significant behavioral difference between the genera Orconectes and Cambarus along the floodplain is the difference in expressed territoriality. Orconectes obscurus and other orconectids displayed limited territorality. In one instance in Cross Creek, Brooke County, 11 individuals were collected from a single slab boulder.

Orconectes obscurus were collected from two ephemeral streams. This habitat has not previously been reported for the species, and is rarely reported forany Orconectes species( Distefano et al. 2009a). In Brooke County, Orconectes obscurus were observed in a first order stream tributary to the Ohio River mainstem, foraging on large mats of Cladophora spp. In another headwater stream in Brooke County, they were collected 1.5 km from the river mainstem and had traversed three 1.0 m waterfalls and their associated plunge pools. It is likely that these crayfish inhabit the mainstem of the river and had migrated into the stream, returning to the river during periods of drawdown.

Jezerinac et al. (1995) described Orconectes obscurus 's and Orconectes sanbornii 's life cycle in West Virginia. Form I males are present from fall into winter and mate in the early spring. After spring mating, males molt into second form in late June and proceed throughout most of the summer in this condition (Table 9). Life history data collected during this study validate Jezerinac et al.'s (1995) findings. Beginning in late April and continuing through mid May, females extruded eggs and carried instars. Ovigerous females were collected on 8, 9, and 12 May 2007. Pleopodal egg counts averaged 113 (n = 8 females, SE = 18.2) with a mean egg diameter of 1.7 mm. There was no correlation between pleopodal egg number and TCL (r2 = 0.88, n = 8). Beginning in late June of both 2005 and 2006, young of the year were frequently captured, indicating their release from female’s pleopods. Males in late July and early August underwent a late summer molt into first form condition (Table 9). After this molt, mating effort increased through late summer and fall until winter hibernation. In addition to the late summer molt, males molted in mass during May at the same time that females became ovigerous. This life history mirrors that of Ohio populations as well ( Fielder 1972). Crayfish associates collected with Orconectes obscurus include Cambarus carinirostris , Cambarus bartonii cavatus , Cambarus robustus , and Cambarus thomai .

Conservation status within study area.

Orconectes obscurus populations are stable and expanding southward along the floodplain. Determining if this expansion is a natural or anthropogenic event is important for conservation of any crayfish species that Orconectes obscurus may ultimately extirpate.