2009 NORTHEASTERN NATURALIST 16(3):355–364 Modern Records of the Pink Heelsplitter Mussel, Potamilus alatus (Say, 1817), in the Ottawa River Drainage, Québec and Ontario, Canada Isabelle Picard1, Jean-François Desroches2, Frederick W. Schueler3, and André L. Martel4* Abstract - Potamilus alatus (Pink Heelsplitter) is a rare freshwater mussel in the Ottawa River drainage (Ontario/Québec, Canada), at the northeastern limit of its distribution. There are few historical records, and one old specimen from an uncertain locality. The discovery of the Pink Heelsplitter in the Ottawa River drainage dates from 1863. A few specimens were reported up to 1901, but it was August 2001 before another specimen was found in the Ottawa River, as an empty shell at Upper Duck Island, near Ottawa. From 2001 to 2005, the authors found this freshwater mussel at four localities along the Ottawa River, and two in the tributary South Nation River. Records include 4 living specimens and 12 empty shells, of which 8 were in fresh condition. The Pink Heelsplitter seems to persist sparsely in the Ottawa River, but it may have been extirpated from one of its tributaries (South Nation River) before its discovery due to mortality associated with Dreissena polymorpha (Zebra Mussel). Introduction Potamilus alatus (Say) (Pink Heelpsplitter) is a freshwater mussel (Mollusca: Unionidae) considered to be uncommon or rare in Canada, where it has been reported from the provinces of Manitoba, Ontario, and Québec, in large, slow rivers. Fish-linkage studies indicate that in rivers in the United States it uses the Aplodinotus grunniens Rafinesque (Freshwater Drum) as host for the dispersal and development of its morphologically unusual glochidia larvae (Clarke 1981, Watters 1994). It is distributed throughout the Mississippi River drainage and in the St. Lawrence River drainage from Lake Huron to Lake Champlain (Parmelee and Bogan 1998), with the Ottawa River drainage (Fig. 1) being the northeastern extremity of its distributional range. With a large thin shell and a prominent postero-dorsal “wing,” the Pink Heelsplitter became an ideal substrate for attachment by the introduced Dreissena polymorpha (Pallas) (Zebra Mussel). Mortality associated with Zebra Mussels has nearly extirpated Potamilus alatus from the Laurentian Great Lakes (Gillis and Mackie 1994, Nalepa et al. 1996). Lake Erie, whose 11050-1 Saint-Marc, Sherbrooke, PQ, Canada, J1K 2T7. 2Cégep de Sherbrooke, Techniques de Bioécologie, 475 du Parc, Sherbrooke, PQ, Canada, J1K 4K1. 3Bishops Mills Natural History Centre, RR2, Bishops Mills, ON, Canada, K0G 1T0. 4Life Sciences, Malacology, Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, ON, Canada, K1P 6P4. *Corresponding author - amartel@mus-nature.ca. 356 Northeastern Naturalist Vol. 16, No. 3 populations of unionid mussels have basically been wiped out by the Zebra Mussel, may previously have contained the bulk of Canada’s Pink Heelsplitter populations. The Pink Heelsplitter is not yet listed as a “species at risk” by the Committee on Endangered Wildlife in Canada (COSEWIC 2009), but in a recent report on the national status of unionid mussels, Metcalfe-Smith and Cudmore-Vokey (2004) evaluated the status of the Pink Heelsplitter as “sensitive” in Canada. Currently this mussel is listed as “sensitive” in the province of Ontario and “at risk” in the province of Québec (Metcalfe-Smith and Cudmore-Vokey 2004). The species has been known in the Ottawa River drainage from a few historical records, including the Ottawa River proper near Ottawa (LaRocque 1938; Latchford 1882a, 1882b, 1889, 1906), the Ottawa River at the mouth of Rouge River (Whiteaves 1863), the Quyon River (tributary to the Ottawa upstream of Ottawa, below the present Chats Falls Dam; Latchford 1904), as well as one record around Montreal, without details on locality (Clarke 1981). No specimens have survived from these records, and no specimens from Québec are found in the collections of the Canadian Museum of Nature (CMN) or the Redpath Museum (verified in 2001–2002); one exception is a specimen collected in 1901 by H.M. Ami at an unknown location (Big[s?] over Spring) along the Ottawa River and deposited at the CMN molluscs collection (CMN-Moll cat. num. 10157). In his 1880–1881 survey of the unionids of the Ottawa area, Latchford (1882b) concluded: “As I have not met with it in my many excursions, I think it must be rare in this vicinity, or at least be restricted to a small area.” Database searches of various major molluscs collections in the US, including that of Illinois Natural History Survey (INHS), Ohio State University (OSU), University of Michigan Museum of Zoology (UMMZ), National Museum of Natural History (NMNH; Smithsonian Institution), and Academy of Natural Sciences of Philadelphia (ANSP), revealed no additional historical or recent records of the Pink Heelsplitter from the Ottawa River drainage. Figure 1. Map showing the Ottawa River, between Quyon and Montréal, where Pink Potamilus alatus (Heelsplitter) has been reported. 2009 I. Picard, J.-F. Desroches, F.W. Schueler, and A.L. Martel 357 In 1995, when F.W. Schueler began resurveying the Ottawa drainage’s unionids, the Pink Heelsplitter was the only historically known mussel species that was not rediscovered in the first years of field work (Schueler 1996a, 1996b, 1997). This paper reports on the subsequent rediscovery of the Pink Heelsplitter in the Ottawa River, including (i) the first record since Ami's 1901 specimen, (ii) first specimens from the province of Québec, and (iii) first records from the South Nation River. Specimens are held in Isabelle Picard’s collection (IP numbers), the collection of the BMNHC (EOBM[MOLL]), or at CMN. Methods Beginning in 1993, we independently surveyed unionids along the Ottawa River and its tributaries (Fig. 1) by examining the nearshore shallow water littoral zone. One or more observers spent 30 to 120 minutes at each site looking for live animals or shells while walking or wading along shore. Localities were recorded by GPS or on regional navigation or topographical maps. A bottom viewer was occasionally used for observing the river bottom. At each site, we recorded habitat, relative water levels, all unionids found, and the presence or absence of Zebra Mussels, as well as other environmental variables required by our individual protocols. Snorkeling and SCUBA diving were also involved in many surveys during 1993–2007, especially in the Ottawa River proper and several of its main tributaries, such as the Mississippi River, the Rideau River and the Gatineau River. Surveys conducted using snorkeling or SCUBA diving last 30 to 120 min and involved two people who looked for and collected or photographed live animals or empty unionid shells. In this paper a “fresh” empty (dead) shell refers to a specimen whose valves displayed little or no sign of periostracum erosion, an unbroken or undamaged and sharp outer shell margin, as well as a shiny non-eroded nacre. Results No Potamilus alatus were found in 12 surveys by F.W. Schueler (FWS) of the St Lawrence River above Montreal, 10 I. Picard and J.-F. Desroches (IP & J-FD ) surveys of tributaries of the lower Ottawa River, 199 surveys (FWS, 66; ALM, 133) of the Rideau River, 85 surveys (F.W. Schueler, 76; A.L. Martel, 9) of the Mississippi River, 9 surveys (IP & J-FD, 5; ALM, 4) of tributaries of the Gatineau River, 8 ALM surveys of the Gatineau River proper, or 38 surveys (FWS, 23; IP & J-FD, 7; ALM, 8) of the Ottawa River above the Chats Falls dam. In 15 surveys by IP & J-FD of rivers around the islands of Montreal, and 92 shore and snorkeling/SCUBA diving surveys of the lower Ottawa River (IP & J-FD, 10; FWS, 65; ALM, 17), and 38 FWS surveys of the main-channel South Nation River (below Spencerville), we found a very small number of Pink Heelsplitter in 7 surveys at 6 sites (Fig. 1), and were 358 Northeastern Naturalist Vol. 16, No. 3 given one shell collected by others. The rarity of Pink Heelsplitter across the Ottawa River drainage was made obvious by its occurrence in only 7 out of 506 (1.4 %) surveys (1993–2007). In the reaches of the rivers where we found Pink Heelsplitter, it occurred in 7 out of 145 (4.8 %) surveys. On 16 August 2001, ALM and Jacqueline Madill (CMN) conducted a unionid survey on the western shoreline and shallow littoral zone of Upper Duck Island (45º28'01"N, 75º37'28"W), ON, downstream of Ottawa, where they found, partly buried in the sand of the shallow littoral zone, an old empty shell of Pink Heelsplitter (Fig. 2). This specimen, although partly eroded and represented by a single valve (100 mm), still clearly displayed the characteristic prominent postero-dorsal “wing” and brightly colored pink nacre. This specimen is currently being accessioned at the CMN Molluscs collection. The site where this Potamilus specimen was collected was dominated by shells of Elliptio complanata Lightfoot (Eastern Elliptio), Lampsilis radiata (Gmelin) (Eastern Lampmussel), and L. cardium Rafinesque (Plain Pocketbook), the latter being particularly common. On 3 October 2001, F.W. Schueler and B. Wigney were surveying unionids and the extent of Dreissena in the South Nation River, Prescott and Russell counties, ON, Canada. At the foot of the High Falls, in Casselman, (45º19'25"N, 75º5'42"W), they found an old, broken 85-mm Pink Heelsplitter valve in 30–50 cm deep rocky bedrock flats at the foot of the shallow Figure 2. Photograph of the first modern specimen of the Pink Heelsplitter (Potamilus alatus), which was collected near the shore of Upper Duck Island, in middle of the Ottawa River, near the Québec-Ontario boundary, on 16 August 2001. The specimen measured 100 mm (shell length). 2009 I. Picard, J.-F. Desroches, F.W. Schueler, and A.L. Martel 359 bedrock falls (EOBM[MOLL]00415). Zebra Mussels were scattered or dense under rocks there, the largest seen was 32.5 mm; other unionids noted included one each of Lasmigona costata (Rafinesque) (Flutedshell), Eastern Elliptio, and Eastern Lampmussel. At Jessups Falls Conservation Area (45º33'33"N, 75º3'45"W; Fig. 1), near the mouth of the South Nation, on a trampled bedrock shore of the muddy river, they found an old broken valve of the Pink Heelsplitter (greatest dimension = 96 mm EOBM[MOLL]00205). Zebra Mussels were abundant, and no living Unionidae were seen: Leptodea fragilis (Rafinesque) (Fragile Papershell) was abundant in the shell piles, with lesser numbers of Pyganodon grandis (Say) (Giant Floater) and Eastern Elliptio, and single shells of Utterbackia imbecillis (Say) (Paper Pondshell; not previously reported from the South Nation; F.W. Schueler, unpubl. data), and Ligumia recta (Lamarck) (Black Sandshell) (not previously reported from the South Nation). On 31 July 2002, Tim Haxton and student assistants from the Ontario Ministry of Natural Resources were seining for fish in the Ottawa River at the Petrie Islands (approximately 45°29'40"N, 75°30'50"W) and picked up a fresh 101-mm Pink Heelsplitter empty shell, which was donated to the BMNHC in 2005 (EOBM[MOLL]00363). The collection was made ≤5 m off shore in water 2 m deep; the substrate was 20% sand and 80% clay/silt. This stretch of the river was disturbed by decades of gravel extraction, which has recently ended. Other collections of unionids from the Petrie Islands include, in decreasing order of abundance, Eastern Elliptio, Eastern Lampmussel, and Plain Pocketbook. On 14 September 2002, a 112-mm freshly dead Pink Heelsplitter shell (IP-M0201) was found by IP & J-FD in the Ottawa River at Lac des Deux- Montagnes, west of Montreal Island, Québec, in a bay called Anse-à-l'Orme (45°27'4''N, 73°56'21''W), at the junction of Pierrefonds and Senneville. The shell was in shallow water, the water level of the lake being exceptionally low at this time. The other species of freshwater mussels found at Anse-à-l'Orme are, in decreasing order: Eastern Lampmussel, Elliptio spp. (mostly Eastern Elliptio), Fragile Papershell, Plain Pocketbook, and Anodonta implicata Say (Alewife Floater; first record in Quebec since 1976). Pink Heelsplitter was the least frequent species. The Zebra Mussel is absent from this locality. On 28 May 2005, two freshly dead Pink Heelsplitter shells and a single living individual were found in the Réserve Faunique de Plaisance, at the Pentecôte Bay of the Ottawa River, PQ (45°36'18''N, 75°3'51''W; IP-M0240, IP-M0241). At the same place, on 3 June, within 2–3 hours, an additional four fresh shells were collected (IP-M0248) and two live Pink Heelsplitters were observed (Fig. 3). Pink Heelsplitters found at this locality ranged from 82 to 114 mm. Other unionids found were, in decreasing order of abundance, Eastern Lampmussel, Fragile Papershell, Giant Floater, Eastern Elliptio, and Black Sandshell. The two latter species were less frequent than Pink Heelsplitter. No Zebra Mussels were observed. 360 Northeastern Naturalist Vol. 16, No. 3 On 26 September 2007, F.W. Schueler and a South Nation Conservation crew surveyed islands in the Ottawa River at the mouth of the South Nation River. In the fine-sand/clay bottom near a marshy island in the river mouth (45.57543°N, 75.10286°W) at 50 cm depth, they found a living 107- mm Pink Heelsplitter that was extensively crusted with little Dreissena. At another site nearby (45.57207°N, 75.09270°W) they found an old 113-mm Pink Heelsplitter shell. Other Unionids found were, in decreasing order of abundance (all heavily fouled with Dreissena): Eastern Elliptio, Eastern Lampmussel, Giant Floater, and Fragile Papershell (shell only). Discussion These results confirm that the Pink Heelsplitter persists in the Ottawa River, and that it is present, though rare, between the historically known locations of Ottawa and Montreal. Main-channel sites above Ottawa to the historic site at Quyon have not been adequately investigated, and therefore we do not know if the species inhabits that unionid-rich section of the river. The South Nation River population may have been extinct before or shortly after their discovery, because of the invasion of that Ottawa River tributary by the Zebra Mussel, which began in 1999 (Naomi Langlois-Anderson, South Nation Conservation Authority, Berwick, ON, Canada, pers. comm.) Figure 3. Photograph depicting a live specimen of Pink Heelsplitter (Potamilus alatus), collected at Plaisance, QC, along northern shore of the Ottawa River, on 28 May 2005. This is the first live record of this species for the province of Québec. The specimen measured 114 mm (shell length). 2009 I. Picard, J.-F. Desroches, F.W. Schueler, and A.L. Martel 361 At the town of Casselman, the river is now much more heavily infested with Zebra Mussels than it was in 2001 (F.W. Schueler, pers. observ.), though our understanding of surviving unionid fauna in this deep muddy river is still preliminary (Michele Rodrick, South Nation Conservation Authority, Berwick, ON, Canada, pers. comm). The Pink Heelsplitter is no doubt very rare in Québec, where it has been given S1 species status (Paquet et al. 2005, Picard 2004), being listed “at risk” in that province in the report by Metcalfe-Smith and Cudmore-Vokey (2004). Its official current status in Ontario, where it was one of the first unionids to be severely impacted by the Zebra Mussel in the Laurentian Great Lakes (Gillis and Mackie 1994, Haag et al. 1993, Nalepa et al. 1996), is S3. In most of its distributional range, one of the major threats to the Pink Heelsplitter is the invasive Zebra Mussel. All unionids are affected by the presence of Dreissena (Martel et al. 2001, Nalapa et al. 1996), but members of the (former) subfamilies Anodontinae and Lampsilinae (Pink Heelsplitter is included in the latter) are more sensitive to Dreissena than the Ambleminae (Baker and Hornbach 1997, Haag et al. 1993). In Lake St. Clair, Gillis and Mackie (1994) found a 93% decline of Pink Heelspliter and Fragile Papershell soon after the Zebra Mussel invasion. Environment Canada's Lower Great Lakes Unionid Database was queried (Daryl McGoldrick, Environment Canada, Burlington, ON, Canada, pers. comm.). It confirmed that the only eastern Lake Ontario records of the Pink Heelsplitter were from the mouth of Marysville Creek on Hungry Bay, Bay of Quinte (44°10'N, 77°12'W)—two samples from 1965 and 1995. Strayer and Jirka (1997) doubted a record from Sodus Bay, NY, across from the Bay of Quinte, but it is possible that the species had at least these two isolated populations in Lake Ontario, between the main range of the species and the Ottawa drainage populations. Also, Pink Heelsplitter has not been reported from the St. Lawrence River or its tributaries in northern New York State (Strayer and Jirka 1997). If the species was found in central Lake Ontario only in the Bay of Quinte and Sodus Bay, and if these populations are now extirpated by the effects of the Zebra Mussel, then the Ottawa River population is an isolated outlier of increased conservation significance. The abundance of the Pink Heelsplitter in the Ottawa River drainage may be limited by the numbers of the host fish, the Freshwater Drum, present in the system. This fish is commonly caught by anglers in the Ottawa River (Brian Coad, CMN, Ottawa, ON, Canada, pers. comm.). The three records (preserved specimens) of Freshwater Drum deposited in the CMN fish collection (CMNfi1972-0142.1, 1972-0143.1, 1984-0257.11) and originating from the Ottawa River have all been collected in the lower Ottawa River, where historical and recent records of the Pink Heelsplitter also occur (this study). The Freshwater Drum is also present but not commonly caught in the South Nation River, where the Pink Heelsplitter has been recently reported (this study). In the South Nation Conservation's 2001 362 Northeastern Naturalist Vol. 16, No. 3 Near-shore Community Index Netting of the lower section of the South Nation River, 2 of 366 fish sampled were of this species (Naomi Langlois- Anderson, 2007 pers. comm.). CMN’s fish collection also contains one specimen of the Freshwater Drum, which was collected in a major tributary of the South Nation River, 2 km from the South Nation River proper (Castor River; CMNfi1975-0953.13). The North American distribution of the Pink Heelsplitter overlaps, more or less, with that of the Freshwater Drum (compare distribution maps of Pink Heelsplitter in Parmelee and Bogan [1998], and that of the Freshwater Drum in Lee et al. [1980]). Details on the possible relationships between the abundance and distribution of this fish in the Ottawa River drainage, as factors explaining the current pattern of abundance and distribution of the Pink Heelsplitter in the same drainage, remain to be elucidated. The vast Ottawa River drainage may represent a major refugium for the Pink Heelsplitter, and other unionids, in Canada. It is believed that acidic low-calcium water of the Ottawa River would not permit high densities of Zebra Mussels to exist (Strayer 1991). Nonetheless, larvae of the Zebra Mussel are flushed into the Ottawa River from the calciumrich Mississippi, Rideau, and South Nation rivers where this pest mollusc has caused severe devastation among unionid populations (Martel 1995; Martel et al. 2001, 2006a). Time will tell if the low-calcium waters of the Ottawa River will, as hypothesized, prevent the invasive Zebra Mussel from causing significant damage to the rich unionid populations, including the rare stocks of Pink Heelsplitter present in the river, particularly between Ottawa and Montreal. There is little that unites the character of the sites where the Pink Heelsplitter was found except that they are large-river sites with soft substrate and few macrophytes. The numbers and demography of the extant populations are not known. Further surveys in the same areas and elsewhere in the Ottawa River would allow a better assessment of the species status (Schueler 1999). Acknowledgments The authors thank Nicolas Lauzon, Benoît Lafleur, and Bev Wigney for field assistance, Tim Haxton for sending in shells collected by Ontario Ministry of Natural Resources field parties, and the South Nation Conservation for support of work in that drainage. They are also grateful to Janice Metcalfe-Smith and Daryl McGoldrick for consultation. Environment Canada’s Lower Great Lakes Unionid Database was helpful in allowing us to access Potamilus records from Ontario. We are indebted to Jacqueline Madill for her assistance in the field, as well as for producing the distribution map and for kindly helping with the final preparation of the manuscript. We also thank Kathy Klein for a critical review of the manuscript. This study was in part funded by support for the BMNHC by Frank Ross and Donna Richoux and by a CMN research grant to A.L. Martel. 2009 I. Picard, J.-F. Desroches, F.W. Schueler, and A.L. Martel 363 Literature Cited Baker, S.M., and D.J. Hornbach. 1997. 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