Species Action Plan Eastern Pearlshell Mussel Natural Diversity Section June 2011 Species Action Plan: Eastern pearlshell (Margaritifera margaritifera) Purpose and Goals Purpose: This plan provides an initial five years blueprint for the actions needed to attain near-term and, ultimately, long-term goals for the conservation and recovery of the eastern pearlshell. The action plan is a living document and will be updated as needed to reflect progress toward those Figure 1. Eastern Pearlshell Mussel goals and to incorporate new information as (Margaritifera margitifera). Photo- it becomes available. PFBC. Goals: The immediate goal is to maintain Description: Linnaeus first described the the extant populations of eastern pearlshell eastern pearlshell in 1758. Strayer and Jirka in the Commonwealth and to protect its (1997) describe the shell characteristics as remaining habitat. The secondary goal is to “elongate, subelliptical to arched, thick (but enhance extant populations by improving often cracking when dried).” Shell size and increasing local habitat. Ultimately it is reaches up to 152 mm (Ortmann 1919). hoped the species will recover to the point Ortmann (1919) described the where it can be removed from the Pennsylvanian specimens (from the vicinity Pennsylvania list of endangered species (58 of Rene Mont) as the largest specimens ever Pa. Code §75.1). recorded for that time. Bogan (2005, Natural History correspondence) further notes that shell specimens are “somewhat inflated, somewhat cylindrical in cross-section, often becoming arctuate in older specimens.” Taxonomy: Class Bivalvia, Order Beak sculpture consists of longitudinal Unionoida, Family Margaritiferidae ridges, sometimes broken (Bogan 2005, (margaritiferids), Eastern Pearlshell correspondence). Periostracum dark brown (Margaritifera margaritifera, Linneaus to blackish, without rays. Pseudocardinal 1758). (Figure 1.) teeth are strong; however, lateral teeth Page | 1 Species Action Plan Eastern Pearlshell Mussel Natural Diversity Section June 2011 nearly or entirely absent. The eastern (Salvelinus fontinalis). These salmonid pearlshell’s nacre color varies from pearly species are found within the historic range white, to sometimes with pink or with purple of the eastern pearlshell and are stocked by tones. Pits are present where the mantle the Pennsylvania Fish and Boat Commission muscle attaches to the shell. These pits, (PFBC). Specific salmonid host fish use by when examined closely, have a trailing edge Pennsylvania’s eastern pearlshell has not not unlike a shooting star. been determined. The eastern pearlshell diet is unknown, but presumed to be bacteria, Habitat: The eastern pearlshell is found in detritus, phytoplankton, and zooplankton. clean, low nutrient, calcium-poor, fast- flowing areas of small creeks to medium- Distribution and Status sized rivers where often it is the only mussel species (Smith 1976). Life History: The eastern pearlshell has been Global and National Distribution: The described as the longest living invertebrate eastern pearlshell is a Holarctic species known and Bauer (1987) reports specimens found on the North American, Asian and > 100 years old. The eastern pearlshell is a European continents. Large populations short-term brooder (tachytictic), spawning remain in northern Russia (Varzuga River) yearly during mid-June through August and declining populations (little to no (Hastie and Young 2003, Young and recruitment) remain in Western Europe. Williams 1984). Conner (1909) noted that The North American distribution of eastern the Pennsylvania breeding season occurred pearlshell includes Atlantic Slope basins that during June and August. Hastie and Young range from Labrador south to Pennsylvania (2003) report glochidia being released into (Figure 2). In the United States, this species the water column beginning mid-July and is distributed from Maine to Pennsylvania. tapering off around the beginning of New York tributaries to Lake Ontario are September. The eastern pearlshell uses considered the western extent of the species salmonid species as its host, including range and Pennsylvania’s Delaware River rainbow trout (Oncorhynchus mykiss), basin the southern extent. brown trout (Salmo trutta) and brook trout Page | 2 Species Action Plan Eastern Pearlshell Mussel Natural Diversity Section June 2011 Pennsylvania Distribution: Historically, the eastern pearlshell’s Pennsylvania range probably included the entire Schuylkill River basin. Presently, only two populations are known to exist in that basin (Figure 3). The eastern pearlshell is also likely to have historically occupied portions of the Delaware River mainstem and tributaries. Live specimens were collected from the upper Delaware River mainstem in 2000 (Lellis 2000, unpublished data). Additional populations may occur in other under- surveyed river basins (e.g. Susquehanna River) or stream reaches (e.g. West Branch Delaware River) or tributaries. Pennsylvania Legal Status: Endangered Figure 2. North American distribution of the Eastern Pearshell (M. margaritifera) State Rank: S1 – Critically Imperiled (NatureServe 2010). Global Status: G4 – Apparently Secure The eastern pearlshell will be considered for delisting when 80% of the historically- occupied streams contain three distinct naturally-reproduced year classes (PABS Bivalve Committee listing criteria). Figure 3. Distribution of the Eastern Pearlshell in Pennsylvania. (Source: PFBC) Page | 3 Species Action Plan Eastern Pearlshell Mussel Natural Diversity Section June 2011 Management Status peak production of coal. A number of streams which may have historically contained eastern pearlshell were probably destroyed by mine-related pollution. The majority of all of the historic streams have been visited at least once by PFBC Current Threats: staff. Comprehensive assessments of historic streams have been restricted due to limited Habitat degradation: Threats to eastern permissions from landowners and staff pearlshell include riparian habitat loss, availability. sedimentation, incidental harvest, non-point Population trends: source pollution from poor agricultural One population in the Schuylkill River basin practices, and pollution from coal mining appears stable while the status of the activities. Additionally, in the absence of Delaware River population is unknown. best management practices implementation, eastern pearlshell populations could be Threats negatively affected by actions such as road construction, stream channel modifications, logging activities, agricultural activities, The following is a description of past and land use changes, pesticide use, and other present threats that have lead to the decline projects or activities in the watershed (see of eastern pearlshell populations in Cosgrove and Hastie 2001). Furthermore, Pennsylvania. Where appropriate, specific populations inhabiting relatively short actions to reduce or eliminate threats are stream reaches having multiple bridges or included in the list of conservation and ford crossings are likely to have more recovery activities following this discussion. exposure to single catastrophic events such Historic Threats: Historically the eastern as toxic spills which could potentially pearlshell was highly sought for the high annihilate the population during a single quality freshwater pearls produced by the event. Several authors (e.g., Hastie et al. species (Kunz and Stevenson 1908). 2003, Galbraith et al. 2010) indicate that Ortmann (1919) indicated that the climate change may have deleterious effects “recklessness of the pearl-hunters has nearly on mussel populations. Eastern pearlshells exterminated it” from the Schuylkill River and their hosts would be particularly basin. vulnerable to elevated water temperatures and large flood events associated with an In addition to the pearl industry, portions of increase in precipitation. the Schuylkill River region were heavily mined for anthracite coal. The time of Flow alteration. A primary threat to the Ortmann’s 1919 publication was near the continued existence of eastern pearlshell is Page | 4 Species Action Plan Eastern Pearlshell Mussel Natural Diversity Section June 2011 flow and habitat alteration due to placement Pennsylvania’s eastern pearlshell or operation of existing impoundments. The populations. Further exacerbating potential effects of impoundments on mussel genetic problems, small population sizes populations are well documented (Watters reduce the intra-population reservoirs of 2000) Gene dispersal via glochidia transport genetic variability. The apparent small through the water column or passage of fish population size of one extant population around the dams on occupied streams has suggests that this population may suffer been rendered unlikely except during from reduced genetic variability. Loss of extreme flood events. The construction of genetic diversity could adversely affect the dams on historically occupied streams has species’ ability to evolve and respond to eliminated large stretches of lotic habitat. natural changes. Soule (1980) recommended The conversion of habitat from a lotic to a minimum of 500 individuals to maintain lentic environment has altered the thermal genetic variability and evolutionary potential and flow regimes within the impoundments within a population. by decreasing flow, increasing sedimentation, and creating thermal Invasive species. The effects of predation stratification. on native fish species and/or competition for food and breeding habitat from The operation