INTRODUCTION

Unregulated pollution by coal mine drainage and industrial effluents decimated the aquatic biota of many streams in western Pennsylvania by the early 1900s (Ortmann 1909). Ortmann (1909) singled out the Clarion River in northwestern Pennsylvania as “possibly one of the worst streams in the state” with regard to water pollution. Eight tanneries, 11 wood chemical plants, and a large paper mill operated on the river, chiefly in Elk County, releasing a cumulative 98 million liters of industrial effluent daily in addition to mine wastes entering the river from tributaries (Department of Health of the Commonwealth of Pennsylvania 1915). Ortmann's description of the condition of the Clarion River at the time was stark: “The water of [the] Clarion River. . .is black like ink, and retains its peculiar color all the way down to where it empties into the Allegheny [River].” He later concluded that the aquatic fauna of the Clarion River was “entirely destroyed” (Ortmann 1913) but acknowledged that no historical mussel records were known from the stream (Ortmann 1919).

Mussels remained unknown from the Clarion River until 1993, when biologists conducting an odonate survey made a chance discovery of four living individuals of Strophitus undulatus, the Creeper, near Clarington, Forest County (Carnegie Museum and Western Pennsylvania Conservancy 1993). The authors suggested that S. undulatus might be slowly recolonizing formerly degraded habitat but doubted that the river could support substantial mussel populations; however, they gave no specific reasons for their doubt.

I conducted qualitative shell surveys from 2007 to 2019 to document past and present mussel distribution along a 55-km reach of the Clarion River. I measured and aged a representative sample of recently dead S. undulatus shells to provide demographic information about the population. I discuss my findings with regard to the potential recovery of the mussel fauna of the Clarion River.

Figure 1.

Map of the Clarion River, Pennsylvania, with study reach and key locales. Insert map shows the four-county region drained by the river.

STUDY AREA

The Clarion River is a tributary of the Allegheny River in northwestern Pennsylvania. The Clarion River watershed encompasses 2,850 km² located in two sections of the nonglaciated Appalachian Plateau physiographic province: the Allegheny High Plateau in the north and the Pittsburgh Low Plateau to the south (Commonwealth of Pennsylvania 2018). Landscapes of the High Plateau include broadly rounded uplands of moderate to high relief with deep, angular valleys; those of the Low Plateau consist of irregular to smooth, undulating uplands of low to moderate relief with relatively shallow valleys. Drainage patterns in both sections are dendritic with sandstone, siltstone, and shale as the predominant bedrock types (Commonwealth of Pennsylvania 2018). Forestry and oil and natural gas extraction are dominant land uses on the High Plateau. On the Low Plateau, agriculture and strip mining for bituminous coal are common (Williams 1995).

The Clarion River proper forms at Johnsonburg, Elk County, at the confluence of the East Branch and West Branch and flows 164 km southwest to meet the Allegheny River upstream of Parker's Landing, Armstrong County (Fig. 1). The watershed has two major dams, Piney Dam, completed in 1924 on the mainstem in Clarion County for flood control and hydropower generation (Williams 1995), and East Branch Dam, completed in 1952 on the East Branch Clarion River for flood control and summer flow enhancement (USACOE 2021). Piney Dam both isolates the upper Clarion River from the rich aquatic fauna of the Allegheny River and creates irregular flows downstream that can affect aquatic biota (Bardarik 1965).

Efforts to abate industrial pollution of the Clarion River began in the 1940s with improved waste treatment technologies and effluent retention facilities, particularly at the paper mill in Johnsonburg (Anonymous 1949; Camp, Dresser, and McKee, Consulting Engineers 1949). Water quality improved significantly from the 1960s to the 1980s as additional point source pollution and abandoned mine drainage issues were addressed (Williams 1995). These efforts were largely successful: in 1996, an 83-km reach of the Clarion River upstream of Piney Dam was given National Wild and Scenic River status. Presently, the Clarion River is an important recreational resource for the region and was named Pennsylvania River of the Year in 2019 (POWR 2019).

METHODS

I conducted qualitative shell surveys from 2007 to 2019 at 157 sites along a 55-km reach of the Clarion River between river kilometer (rkm, measured from the mouth of the river) 64, just above the slack water of Piney Reservoir in Clarion County, to rkm 119 at the mouth of Spring Creek in Hallton, Elk County (Fig. 1). I chose this reach because it contained ample access points, and it included the 1993 collection site for S. undulatus at about rkm 97 (Carnegie Museum and Western Pennsylvania Conservancy 1993). I searched for shells by walking gravel point bars, wading the river, and kayaking. I classified shells as either recently dead, having intact periostracum and lustrous nacre; weathered shells, having weathered periostracum and nacre; or relic shells, having heavy wear and little periostracum, indicative of having been dead for an extended time (Blodgett and Sparks 1987; Sietman et al. 2001). Because this was an initial survey of mussel occurrence in the river, I made no consistent efforts to find live mussels, but I report incidental occurrences of live mussels encountered during shell surveys. Live mussels were returned to the area of collection after identification.

Figure 2.

Age-frequency distribution for recently dead shells (n = 60) of Strophitus undulatus collected from the Clarion River.

I measured and aged a random sample (n = 60) of recently dead shells of S. undulatus to provide demographic information on the species in the Clarion River. I measured the anterior-to-posterior shell length (nearest 0.1 mm) with digital caliper prior to sectioning. I selected one valve from each specimen and cut the valve radially from the umbo into two halves using a fine jeweler's saw. Instead of cutting thin sections from the valve (e.g., Neves and Moyer 1988), I lightly sanded the cut edge of the valve with 400-grit sandpaper and examined the wetted, cut edge under a dissecting microscope; wetting the shell accentuated shell rings. I identified annuli and distinguished them from nonannual rings as rings that could be traced from the umbo to the shell margin (Neves and Moyer 1988). Aging mussel species with slow growth and closely spaced annuli requires thin-sectioning techniques (Neves and Moyer 1988), but rapidly growing species such as S. undulatus can be aged effectively without thin sectioning (Neves and Moyer 1988; Haag and Commens-Carsons 2008; Harriger et al. 2009)). I examined the relationship between age and shell length with linear regression using QED Statistics version 1.5.1.456 (Pisces Conservation Ltd. 2015).

RESULTS

A total of 321 shells and living individuals of four mussel species were collected; at least one shell or mussel was collected from each of the 157 sites (Table 1). Two hundred forty-one recently dead shells, 58 weathered shells, and four live individuals of S. undulatus were collected from 146 sites (93% of total shells collected across sites; mean = 2.1 shells or live mussels/site at sites with S. undulatus). Twelve relic shells of Actinonaias ligamentina were found at 12 sites (3.7% of total shells collected across sites), five recently dead shells and one live Lampsilis fasciola were found at five sites (3.2% of total shells collected across sites), and one recently dead shell of Lampsilis ovata was found at one site (0.6% of total shells collected across sites). The few living individuals of S. undulatus and L. fasciola were found in slow-moving reaches of the river with substrates of fine sand and gravel.

Ages of 60 recently dead S. undulatus shells ranged from 2 to 16 yr, with a mean age of 8.0 yr (±1.0 SE; Fig. 2). Length of sampled shells ranged from 26.8 to 81.7 mm with a mean length of 29.8 mm (±0.5 SE). Shell length was positively associated with age (r² = 0.86, P = 0.005, shell length = 3.8[age] + 23.8).

DISCUSSION

Contrary to previous ideas that the Clarion River is unsuitable for mussels (Carnegie Museum and Western Pennsylvania Conservancy 1993), my results show that mussels, particularly S. undulatus, are of widespread occurrence, at least in my 55-km study reach. Species richness was low, and I have no information about the abundance of live mussels in the river. Nevertheless, the frequent occurrence of recently dead shells suggests that the study reach supports a substantial mussel population. Suitability of the river for mussels is further supported by a recent mussel relocation project; survival of several mussel species translocated from the Allegheny River to the upper Clarion River was 98% after 1 yr (Western Pennsylvania Conservancy 2015).

Strophitus undulatus possesses several life history traits that may allow it to readily recolonize streams recovering from severe pollution. First, S. undulatus is a host generalist whose glochidia can parasitize many different fish species (Cliff et al. 2001; Van Snik Gray et al. 2002; Ford and Oliver 2015). Second, S. undulatus is a widespread species and occurs across a range of environmental conditions (Ortmann 1919; Strayer and Jirka 1997), but it is predominantly found in smaller rivers and streams (Haag 2012). Finally, S. undulatus is classified as having a periodic life-history strategy, intermediate in position on the r–K continuum, with moderate life span, low to moderate age at maturity, and moderate to high growth rate, traits that can allow rapid population growth in some situations (Haag 2012). My results support a low–moderate life span of at least 16 yr. The wide range of ages represented in the population, including individuals as young as 2 yr old, suggests that natural recruitment is occurring in the river.

The other three species found in the Clarion River were rare. Lampsilis fasciola and L. ovata both were represented by live individuals or recently dead shells, suggesting that at least small populations currently exist in the river. Actinonaias ligamentina was represented only by relic shells. These shells may indicate occurrence of the species in the river prior to severe water pollution, but the time of death of the specimens is unknown, and it is unknown if the river currently supports a natural population of the A. ligamentina.

Table 1.

Sites on the Clarion River sampled for mussel shells from 2007 to 2019.

continued.

Table 1.

The absence of any historical mussel records prior to severe pollution in the early 1900s or any contemporary mussel surveys prior to this study make it impossible to reconstruct the Clarion River's original mussel fauna and difficult to assess the extent to which the fauna may be recovering. Possibly, the river never supported a substantial mussel fauna, but this seems unlikely in a region characterized by diverse mussel faunas in most streams (e.g., Ortmann 1919). More likely, the Clarion River supported a diverse fauna similar to other tributaries of the Allegheny River. If so, the widespread occurrence of mussels in the river today may represent recovery of the river and recolonization by the mussel fauna.

Potential source populations and dispersal routes for recolonization of the Clarion River likely differ among mussel species. Actinonaias ligamentina and L. ovata are generally restricted to larger streams such as the Allegheny River, where A. ligamentina is a dominant species (Anderson 2000; Smith et al. 2001). The Allegheny River was likely the source population for both species prior to the completion of Piney Dam, but the dam is currently a barrier to recolonization. Strophitus undulatus and L. fasciola inhabit both small tributary streams and the mainstem Allegheny River (Ortmann 1919; Harriger et al. 2009). Populations of both species in the Clarion River could have originated from the Allegheny River, but they are uncommon in the latter river (Anderson 2000; Smith et al. 2001). The apparently substantial population of S. undulatus in the Clarion River suggests the presence of a nearby source population in a tributary stream. Many tributaries within the Clarion Basin escaped pollution in the early 1900s (Department of Health of the Commonwealth of Pennsylvania 1915), but it is unknown if they support mussel faunas that serve as source populations for recolonization of the Clarion River. Tributaries are proposed as source populations for recolonization of the historically polluted upper Illinois River by mussels (Seitman et al. 2001) and for recolonization of fishes in the Clarion River (Bardarik 1965).

Another possible source for recovery of the mussel fauna is the Clarion River itself—if some species survived severe pollution. This seems unlikely given the severity and duration of pollution. However, the conclusion that the aquatic fauna was eliminated (Ortmann 1913) was not based on a comprehensive survey, and the lack of subsequent mussel surveys makes it impossible to determine whether any species survived. A third possible source of mussel fauna is the release of fishes infected with glochidia from other populations (Hayes 2000), but to my knowledge, this possibility has not been examined.

The decimation of the aquatic fauna of the Clarion River by pollution is a great tragedy, but so is the fact that no record of the historical fauna exists. The shell collections made during this study provide a glimpse of what the mussel fauna of the Clarion River may have looked like. All four species I found are characteristic members of mussel assemblages in small to midsized streams in the Ohio River basin of western Pennsylvania (Walsh et al. 2007). Other characteristic species of these assemblages, such as Lasmigona costata, Alasmidonta marginata, Lampsilis cardium, and Ptychobranchus fasciolaris, were not collected during this study. However, in 2015, I found a relic shell of Lasmigona costata in the Clarion River below Piney Dam just above the mouth of Deer Creek (C. Williams, personal observation). My results show that the Clarion River is now capable of supporting mussel populations, but additional surveys are needed to document mussel abundance and provide a baseline for monitoring future natural recovery. Conservation actions meant to hasten mussel recovery, such as translocation from other populations or release of hatchery-propagated individuals, face the challenge of determining appropriate species for reintroduction or augmentation, and these decisions will need to be made based on assumptions about the original fauna of the river.