Host fish quality may explain the status of endangered Epioblasma torulosa rangiana and Lampsilis fasciola (Bivalvia:Unionidae) in Canada

Transcription

1 J. N. Am. Benthol. Soc., 2011, 30(1): by The North American Benthological Society DOI: / Published online: 14 December 2010 Host fish quality may explain the status of endangered Epioblasma torulosa rangiana and Lampsilis fasciola (Bivalvia:Unionidae) in Canada Kelly A. McNichols 1, Gerald L. Mackie 2, AND Josef D. Ackerman 3 Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1 Canada Abstract. Freshwater unionid mussels are among the most endangered groups of organisms in the world. They develop indirectly via a host, usually a fish, and this dependence appears to limit the reproduction and distribution of freshwater mussels. Epioblasma torulosa rangiana and Lampsilis fasciola are 2 endangered species in Canada. Epioblasma t. rangiana has a low abundance and limited distribution, whereas L. fasciola has a higher abundance and less-constrained distribution. Three known host species were examined for each mussel species. Results were that: 1) E. t. rangiana glochidia had significantly higher metamorphosis rates (i.e., proportion of attached glochidia that successfully metamorphosed to the juvenile mussel stage) on Etheostoma exile (mean 6 SE: %) and Cottus bairdi (42 6 6%) than on Etheostoma nigrum (10 6 3%) and 2) L. fasciola glochidia had significantly higher metamorphosis rates on Micropterus dolomieu (82 6 2%) and Micropterus salmoides (63 6 8%) than on C. bairdi (37 6 7%). Variation in the co-occurrence of mussels and their primary vs marginal host species (i.e., high vs low infestation and metamorphosis rates, respectively) appears to explain the distributions and abundances of these 2 endangered mussels in Canada. An understanding of the quality of different host fishes of endangered mussel species is needed to facilitate effective conservation strategies. Key words: metamorphosis, infestation, species at risk, endangered species, conservation, glochidia. Freshwater mussels play an important role in aquatic ecosystems in that they affect both water-column and sediment processes and, therefore, are considered indicators of ecosystem health (Vaughn and Hakenkamp 2001, Dextrase et al. 2003). They also are one of the most endangered groups of organisms in North America (Williams et al. 1992, Strayer 2008). Declines and extinctions have been attributed to anthropogenic factors including habitat modification and destruction, commercial exploitation, and invasive species (Bogan 1993, 2008, Lydeard et al. 2004). For example, of the 55 species of freshwater mussels in Canada, 8 are federally protected (as endangered) under Canada s Species at Risk Act (SARA), and an additional 4 have been proposed for protection (SARA 2010). In addition to the threats listed above, ecological factors can have direct and indirect detrimental effects on mussel populations particularly because unionid mussels develop indirectly and have a complex life 1 addresses: kmcnicho@uoguelph.ca 2 gmackie@sympatico.ca 3 To whom correspondence should be addressed. ackerman@uoguelph.ca 60 history involving their glochidia larvae, which parasitize a vertebrate host, usually a fish (Bogan 1993). Consequently, any changes in the behavior, physiology, or ecology of the host species also may affect the mussel s survival (Trdan and Hoeh 1982, Kirk and Layzer 1997). For example, the extirpation of the Alasmidonta heterodon (Dwarf Wedgemussel) in New Brunswick, Canada, is believed to have been caused by the elimination of the host species when the Moncton Riverview causeway was constructed in 1968 (DFO 2007, also see Strayer 2008). In Canada and elsewhere, identification and subsequent protection of host fishes are among the goals of mussel recovery strategies, which are designed to prevent the extirpation and extinction of mussel species at risk and to return populations to historical healthy, self-sustaining levels (Morris and Burridge 2006). Fortunately, the host species for many mussel species have been identified, and some of these mussel species use more than one host (Yeager and Saylor 1995, McNichols 2007, Strayer 2008). Unfortunately, both the infestation rate, i.e., the proportion of glochidia exposed to the host that attach, and the metamorphosis rate, i.e., the proportion of attached

2 2011] HOST FISH AND ENDANGERED MUSSELS 61 TABLE 1. Host-fish species identified in the laboratory for Epioblasma torulosa rangiana and Lampsilis fasciola. Mussel species Host-fish species Reference Epioblasma torulosa rangiana Lampsilis fasciola McNichols (2007) Cottus bairdi Watters (1996), McNichols (2007) Culaea inconstans a McNichols (2007) Etheostoma caeruleum a Etheostoma camurum b Watters (1996) Etheostoma exile McNichols (2007) Etheostoma nigrum McNichols (2007) Etheostoma zonale b Watters (1996) Percina caprodes a McNichols (2007) Percina maculata a unpublished data Salmo trutta Watters (1996) Micropterus Zale and Neves dolomieu (1982) Micropterus McNichols (2007) salmoides Cottus bairdi McNichols (2007) a Species with low infestation or metamorphosis rate b Species not present in Ontario glochidia that successfully metamorphose to the juvenile mussel stage (Dodd et al. 2005), may differ among hosts (Strayer 2008). In addition, female mussel fecundity also may be variable and generally increases with shell length and age (Haag and Staton 2003). Therefore, determining if and how metamorphosis rate varies among different host species and female mussels is relevant to identifying high-quality or primary host species vs low-quality or marginal host species. Such information could improve conservation efforts by: 1) improving understanding of the relationship between the quality of host fish and the status of endangered freshwater mussels, 2) identifying primary host fish to reintroduce into ecosystems, and 3) identifying primary host fish for rearing large numbers of juvenile mussels to augment/reintroduce populations in the field (O Beirn et al. 1998, Hoftyzer et al. 2008). Epioblasma torulosa rangiana (Northern Riffleshell) and Lampsilis fasciola (Wavyrayed Lampmussel) are endangered unionid species that use multiple host-fish species and have contrasting trends in abundance and distribution in Canada. Epioblasma t. rangiana is severely limited. The Ontario population is 1 of the remaining 4 reproducing populations in its range (Staton et al. 2000, Strayer 2008). The distribution of L. fasciola, on the other hand, is not as constrained. The species is considered one of the more abundant endangered mussel species in Canada (Metcalfe-Smith et al. 2000) and is nationally secure in the US (NatureServe 2009). Whether the differences in abundance and distribution of E. t. rangiana and L. fasciola are the result of the distribution and quality of host fish remains to be determined. Our objectives were to determine whether infestation and metamorphosis rates of E. t. rangiana and L. fasciola glochidia differ among host species and whether these differences might explain their abundances and distributions in Canada. Known host species Methods Epioblasma torulosa rangiana. Etheostoma exile (Iowa darter), Etheostoma nigrum (Johnny darter), and Cottus bairdi (mottled sculpin) were chosen as host fish for our study because they have been identified previously as host species (Watters 1996) and they have produced the largest number of juveniles in trials with other potential host species in our laboratory (McNichols 2007; Table 1). They currently or historically occur(red) in the Sydenham and Ausable Rivers where E. t. rangiana are found, and they are readily available and easy to capture. Lampsilis fasciola. Micropterus dolomieu (smallmouth bass), Micropterus salmoides (largemouth bass), and C. bairdi (mottled sculpin) were chosen as host species because they have been identified as hosts for L. fasciola (Zale and Neves 1982, McNichols 2007; Table 1). Acquisition of host fish Fish were collected in lakes and rivers that did not contain E. t. rangiana and L. fasciola to limit the possibility of acquired immunity by potential hosts (Dodd et al. 2005). In addition, the gills of each fish were examined to ensure that no glochidia were present before transport to the laboratory. Seine nets, minnow traps, small hand nets, and electrofishing gear were used to collect the fish, which were transported to the Hagen Aqualab at the University of Guelph in an aerated cooler. The fishes were transferred to recirculating Aquatic Habitat units (AHAB; Aquatic-Ecosystems, Inc., Apopka, Florida) and were fed frozen bloodworms (Chironomus sp.,, g) 3 times/wk. Acquisition of mussels Epioblasma t. rangiana were collected in late September to mid October in 2006 in the Sydenham River (lat 42u N, long 81u W) by manually sieving through the bottom sediment in known mussel habitat. Lampsilis fasciola were collected in mid June 2005 in the Grand River (lat 43u N, 80u W). Underwater viewing boxes (41-cm high box with a PlexiglasH bottom) were used to identify gravid mussels with swollen marsupial gills. Mussels were transported in an aerated cooler to the

3 62 K. A. MCNICHOLS ET AL. [Volume 30 Hagen Aqualab for extraction of glochidia, and then returned to their collection site. Adult mussels were fed cells of commercial microalgal diet (Nanno 3600 and Shellfish Diet, Reed Mariculture, Campbell, California) every other day. Artificial infestation of host fish Glochidia were flushed from either ½ or a part of each of the marsupial gills with a water-filled syringe so that female mussels could release glochidia naturally in the rivers upon return. All glochidia were collected in a dish, and the viability of a subsample of,100 glochidia was determined by exposure to a 24% NaCl solution in which viable glochidia adducted their valves rapidly (ASTM 2006). The batches of glochidia were considered to be of comparable quality because the results of the viability tests were comparable for each female in each experiment (i.e., % response by E. t. rangiana glochidia and % by L. fasciola glochidia), female mussels were collected during the same time of year, and the glochidia were removed and used on the same day for each respective experiment. The glochidia from each of the 3 E. t. rangiana females were split into 3 subsamples with a modified Motodo plankton splitter and were poured onto 12 individuals of a given fish species held in 1 L of water with an airstone. After 60 min of exposure, the 12 fish were separated among 3 replicates, each in a 9-L tank containing 4 individuals, which were placed into separate AHAB units (each AHAB contained E. exile, E. nigrum, and C. bairdi infested with glochidia from a given female; Appendix 1). The glochidia of each of the 6 L. fasciola females were similarly split into 3 subsamples and poured onto 12 individuals consisting of 4 M. dolomieu, 4M. salmoides, and 4 C. bairdi held in L of water with airstones. After 60 min of exposure, the fish were removed and separated into species-specific 9-L tanks, each containing 4 individuals, which were placed in separate AHAB units (each AHAB unit contained 1 replicate of M. dolomieu, M. salmoides, and C. bairdi infested with glochidia from 6 females; Appendix 2). The 3 AHAB units were maintained at uC (mean 6 SE) and ph of Water chemistry (NH 3, NO 3, and NO 2 ) was monitored weekly when fish were introduced into each AHAB unit. If one of these variables was high ( mg/l NH 3,.3 mg/l NO 3,.0.2 mg/l NO 2 ),,50 L of water were replaced with fresh well water. Once these variables stabilized, monitoring was undertaken on a monthly basis. Mean NH 3,NO 3, and NO 2 levels were , , and mg/l, respectively, throughout the experiments. Recovery filters consisting of 100-mm mesh glued onto sections of polyvinyl chloride (PVC) pipe were added to the back of each tank to prevent the loss of the glochidia or juvenile mussels from the flowthrough system in the AHABs. The water in each tank was siphoned through a 100-mm-mesh sieve every 2 to 3 d until juvenile mussels were observed, after which time they were siphoned every other day. The number of glochidia that sloughed from fish, the time required for glochidia to slough from fish, and the time required for juvenile mussels to metamorphose were recorded, as was any fish mortality. Dead fish were dissected, and the number of glochidia remaining on the body, fins, or gills of the fish was recorded. Siphoning was discontinued after 1 wk without detection of juvenile mussels. Analysis All results were expressed as the mean of a given number of replicates, each of which consisted of 4 individual fish of a given species in one 9-L tank at the beginning of the study. Infestation rate (%) was determined from the mean number of glochidia that attached to the fish from the number of glochidia present in the infestation container (i.e., glochidia concentration 3 volume). The metamorphosis rate (%) was determined from the mean proportion of attached glochidia that successfully metamorphosed to the juvenile mussel stage of a given fish species (e.g., mean of all E. exile replicates). The transformation rate for a given female was determined from the mean proportion of attached glochidia that successfully transformed into juvenile mussels on all fish species replicates infested with her glochidia (mean of E. exile, E. nigrum, and C. bairdi that were infested with glochidia from female X). Data were analyzed using 1- and 2-way analyses of variance (ANOVAs) with host species and female mussel as factors. Assumptions of the ANOVAs were tested with Shapiro Wilks test for normality and Bartlett s test for homogeneity of variances. Pairwise differences were examined with a Tukey test. If assumptions of the ANOVA could not be met through transformation, the nonparametric Kruskal Wallis test was used. All data analyses were done in Statistica (6.1: StatSoft Inc., Tulsa, Oklahoma). Results Epioblasma torulosa rangiana (Northern riffleshell) The shell length of the female mussels ranged from 3.68 to 6.14 cm and the mean number (6 SE) of glochidia removed per female was (Appendix 1). The concentration of glochidia in the

4 2011] HOST FISH AND ENDANGERED MUSSELS 63 and % on C. bairdi (Fig. 1C). These differences were statistically significant (2-way ANOVA, F 2,18 = 11.52, p, 0.001) using arcsine!(x)-transformed data. Both E. exile and C. bairdi had significantly higher metamorphosis rates than E. nigrum (p, 0.001). Significant differences also were found with log(x)- transformed values of the mean number of juvenile mussels produced (2-way ANOVA, F 2,18 = 34.19, p, 0.001; on E. exile,36 1onE. nigrum,206 5onC. bairdi). Significantly fewer juveniles metamorphosed on E. nigrum than on the other 2 species (Fig. 1C). The female mussel transformation rate also varied (29 6 8% from female 1, % from female 2, % from female 3). The overall mean was %. These differences might be considered marginally significant (F 2,18 = 2.95, p = 0.077) after arcsine!(x)-transformation. Female 2, the largest of the female mussels, had a marginally higher metamorphosis rate than female 3, the smallest of the females (p = 0.07). No significant interactions were found between fish species and female mussels for E. t. rangiana (F 4,18 = 1.24, p = 0.326). Lampsilis fasciola (Wavyrayed lampmussel) FIG. 1. Mean (61 SE) concentration of glochidia (glochidia/l) in Epioblasma torulosa rangiana infestation container (A), infestation rate (B), metamorphosis rate and number of juveniles transformed (C) on Etheostoma exile, Etheostoma nigrum, and Cottus bairdi. Bars with the same letter are not significantly different (p, 0.05). infestation containers varied from glochidia/l for C. bairdi to glochidia/l for E. exile (Fig. 1A). These differences were statistically significant (ANOVA, F 2,24 = 6.33, p, 0.05), and a Tukey test revealed that E. exile were exposed to a significantly higher concentration of glochidia than were other species. The infestation rate ranged from % on E. nigrum to 6 6 1% on E. exile (Fig. 1B), and these differences were statistically significant (Kruskal Wallis test, H 2,n=27 = 10.30, p, 0.05). Etheostoma exile and C. bairdi had significantly higher infestation rates than did E. nigrum. Metamorphosis occurred between days 15 and 31 post infestation. Mean metamorphosis rate varied with host species: % on E. exile,106 3% on E. nigrum, All 6 L. fasciola females displayed a brown fish-like lure, which is 1 of 4 distinct mantle displays found in this species (Zanatta et al. 2007). The shell length of the female mussels ranged from 4.83 to 5.50 cm, and the mean number of glochidia removed per female was 27, (Appendix 2). The concentration of glochidia in the infestation containers varied from glochidia/l for M. salmoides to glochidia/l for C. bairdi (Fig. 2A). These differences were not significant (1-way ANOVA, F 2,37 = 0.29, p. 0.05). Infestation rates were % on C. bairdi, % on M. salmoides, and 5 6 1% on M. dolomieu (Fig. 2B). These rates were significantly different (F 2,37 = 15.93, p, 0.05) using arcsine!(x)-transformed data. The infestation rate was significantly higher on M. dolomieu than on M. salmoides and C. bairdi. Metamorphosis occurred between days 15 and 49 post infestation. Fish mortality occurred in the M. salmoides and M. dolomieu replicates (7 of each species). Mean metamorphosis rate varied with host species: % on C. bairdi, 636 8% on M. salmoides, and % on M. dolomieu (Fig. 2C). The rates were significantly different (2-way ANOVA, F 2,23 = 4.20, p, 0.05) using arcsine!(x)-transformed data. Glochidia had significantly higher metamorphosis rates on M. dolomieu and M. salmoides than on C. bairdi (p, 0.05). Significant differences were also found using log(x)- transformed values of the mean number of juvenile mussels produced (F 2,23 = 22.00, p, 0.001; on C. bairdi, on M. salmoides, on M.

5 64 K. A. MCNICHOLS ET AL. [Volume 30 FIG. 2. Mean (61 SE) concentration of glochidia (glochidia/l) in Lampsilis fasciola infestation container (A), infestation rate (B), metamorphosis rate and number of juveniles transformed (C) on Cottus bairdi, Micropterus salmoides, and Micropterus dolomieu. Bars with the same letter are not significantly different (p, 0.05). dolomieu). All pairwise comparisons of host fishes yielded significant differences (Fig. 2C). Transformation rate varied among female L. fasciola mussels ( % from female 1, % from female 2, % from female 3, % from female 4, % from female 5, and % from female 6). The overall mean was %. However, these differences were not statistically significant (F 5,23 = 0.27, p. 0.05) using arcsine!(x)-transformed data. No significant interactions were found between fish species and female mussels for L. fasciola (F 9,23 = 1.57, p. 0.05). Discussion Infestation and metamorphosis rates differed significantly among the host species of E. t. rangiana and L. fasciola. These differences indicate that it is possible to identify 2 types of host species: 1) primary hosts where rates of infestation and metamorphosis are high and 2) marginal hosts where rates are low. Barnhart et al. (2008) reported that good hosts may have.90% metamorphosis, but our results indicate that these rates are on the order of 40% and 60% for E. t. rangiana and L. fasciola, respectively. Such differences may be the result of factors inherent to endangered species or of experimental factors. Specifically, Epioblasma species capture their host fish and pump glochidia directly onto the head/gills of the fish, where the glochidia are gill parasites (Barnhart et al. 2008). In our infestations, fish were exposed to a bath of glochidia, and glochidia could have attached to other body parts where they may not have undergone successful metamorphosis. This difference in mode of infestation may explain the lower metamorphosis rates observed in our study. Differences in infestation and metamorphosis rates have been attributed to a number of factors, including variability in the fecundity of female mussels (Haag and Staton 2003), the immune response of individual fish (Dodd et al. 2005), and the linkages among mussels and their hosts within water drainages (Riusech and Barnhart 2000, Bigham 2002). In our study, female fecundity did not vary significantly, and host species were purposely collected from drainages without the target mussel species to limit immune responses. However, we could not account for host-fish specificity within drainages because many of the host species were found in low abundance or have been extirpated from the river systems examined. Therefore, the infestation and metamorphosis rates in our study were more probably caused by the quality (primary vs marginal) of the host fish, as has been reported elsewhere (Haag et al. 1999, Riusech and Barnhart 2000, Jones and Neves 2002, Haag and Warren 2003, Jones et al. 2004). We assert that these differences may help explain the differences in the distributions and abundances of 2 endangered species as described below. A severely restricted endangered species Etheostoma exile and C. bairdi should be considered primary hosts for E. t. rangiana based on the metamorphosis and infestation rates. Higher glochidia concentration during infestation appeared to be less important than host-fish specificity in our analysis. Unfortunately, E. exile has not been collected in the Sydenham and Ausable Rivers during recent surveys, which is where reproducing populations of E. t. rangiana occur (M. Poos, University of Toronto,

6 2011] HOST FISH AND ENDANGERED MUSSELS 65 TABLE 2. Occurrence of Epioblasma torulosa rangiana (E.t.r.) and Lampsilis fasciola (L.f.) and their host fishes in Canada. 1 = Ausable River, 2 = Grand River, 3 = Thames River. Mussel species/ Occurrence in host-fish species Habitat type 1 Sydenham River 2 Occurrence in other rivers 3,4 Epioblasma torulosa rangiana Cottus bairdi Culaea inconstans Etheostoma caeruleum Etheostoma exile Etheostoma nigrum Percina caprodes Percina maculata Lampsilis fasciola Micropterus dolomieu Micropterus salmoides Cottus bairdi Coarse sand, gravel, shallow riffle Present areas, swift current Sand, gravel bottoms of cool Present, not at E.t.r. sites streams and lakes Clear, cold, densely vegetated Present, not at E.t.r. sites water of small streams and spring-fed ponds Gravel bottom, shallow, Present historically, clear water not caught in 2003 Bottom of organic debris, sand, Present historically, peat, clear-water lakes and rivers, not caught in 2003 intolerant of turbid waters Wide variety of habitats, but most Present/abundant common on bottoms of sand, gravel, silt, weedy areas, or gravel riffles of streams, moderate to no current Sand, gravel, or rocky beaches Present/abundant in lakes and rivers Quiet regions/pools of Present/abundant medium-sized, gravel streams Gravel and sand stabilized with Extirpated, present cobble, boulders, riffle areas, historically clear water Varies with size and season; rocky, Present/low abundance sandy areas of lakes and rivers, moderately shallow water Small, shallow lakes or bays, Present/low abundance slow rivers, soft bottoms with vegetation Sand, gravel bottoms of cool streams and lakes Present, but not at E.t.r. sites 1 - present 1 - present, not at E.t.r. sites 1 - present 1 - present, not at E.t.r. sites 1 - present historically, not caught since 1947, extirpated? 1 - present/abundant 1 - present/low abundance 1 - present/abundant 1 - present/low abundance 2 - present/abundant 3 - present/low abundance 1 - present/abundant 2 - present/abundant 3 - present/decreasing numbers 1 - present/abundant 2 - present 3 - present/decreasing numbers 1 - present 2 - present, but not at L.f. sites 3 - Present/decreasing numbers 1 Mussel habitat type from Metcalfe-Smith et al. (2005), fish habitat type from Scott and Crossman (1998) 2 Sydenham River fish data were supplied by M. Poos, University of Toronto, personal communication (2004) 3 Ausable River fish data were from Nelson et al. (2003) 4 Grand River fish data were supplied by A. Timmerman, Ontario Ministry of Natural Resources, personal communication (2007) personal communication; see nonimperiled species in Poos et al. 2008; M. Veliz, Ausable Bayfield Conservation Authority, personal communication). This absence may be partially the result of the high turbidity levels in the Sydenham and Ausable Rivers (Whitford 2001, Nelson et al. 2003) because E. exile prefers clear, high-visibility water (Table 2; Scott and Crossman 1998). High turbidity levels also may decouple the host parasite relationship, which is based on the visual detection of white mantle pads by the host (Barnhart et al. 2008). However, we do not think that turbidity alone is responsible for the decline in mussels because both the Sydenham and Ausable Rivers experience high turbidity and lack the primary host (E. exile), but the E. t. rangiana populations continue to reproduce via marginal hosts in both rivers. Moreover, the other primary host, C. bairdi, is not abundant nor does its distribution overlap with E. t. rangiana in the Sydenham River (Poos et al. 2008; K. Killins, Ausable-Bayfield Conservation Authority, personal communication). Therefore, E. t. rangiana probably relies heavily on marginal host(s), such as E. nigrum, which is abundant and widespread in the Sydenham and Ausable Rivers, because its 2 primary host species are not available. Epioblasma t. rangiana also might rely on other darter species, such as Etheostoma caeruleum (rainbow darter), Percina caprodes (logperch), and Percina maculata (blackside darter), but these species have produced very small numbers of juvenile

7 66 K. A. MCNICHOLS ET AL. [Volume 30 mussels (low infestation or metamorphosis rates) in our laboratory (McNichols 2007). Moreover, E. caeruleum is thought to have been extirpated from the Sydenham River, and its distribution does not overlap with E. t. rangiana in the Ausable River. Percina caprodes is present but at lower abundance than E. nigrum and P. maculata (Poos et al. 2008; K. Killins, personal communication). Etheostoma blennioides (greenside darter) has been examined in our laboratory, but no juvenile mussels transformed (our unpublished data). We have not examined Etheostoma microperca (least darter), Percina shumardi (river darter), Etheostoma flabellare (fantail darter), or Salmo trutta (brown trout) because the former 2 species do not overlap spatially with E. t. rangiana and the latter 2 are not abundant (Poos et al. 2008; K. Killins, personal communication). We think that the loss and continued absence of their primary host(s) may explain the decline in abundance of E. t. rangiana from their historical range (Staton et al. 2000). We also suggest that the reliance on marginal host species has affected E. t. rangiana populations, which are limited compared to their historical numbers but self-sustaining (Staton et al. 2000). In other words, the absence of a primary host fish and the reliance on marginal host species has restricted the populations of E. t. rangiana in Canada. A less-restricted endangered species Micropterus dolomieu should be considered the primary host species for L. fasciola because it had high infestation and metamorphosis rates and produced the largest number of juvenile mussels. All 3 fish species examined in our study are found in the Grand and Thames Rivers, where the healthiest, reproducing populations of L. fasciola occur in stable areas dominated by sand, gravel, and cobble substrates (Metcalfe-Smith et al. 2000). Fortunately, M. dolomieu tends to inhabit similar areas (rocks and sandy areas in moderately shallow water; Scott and Crossman 1998) and is more abundant in these rivers than the marginal hosts, M. salmoides and C. bairdi (A. Timmerman, Ministry of Natural Resources; J. Schwindt, Upper Thames River Conservation Authority; personal communications), which prefer different types of habitat (Table 2; Scott and Crossman 1998). Historically, L. fasciola also was found in the Sydenham River, but no live individuals have been observed since 1970 (Metcalfe-Smith et al. 2000). The loss of L. fasciola from the Sydenham River may be partially the result of the decrease in abundance of its primary host species, M. dolomieu (Metcalfe-Smith et al. 2000) or the low abundances of its marginal hosts M. salmoides and C. bairdi (Poos et al. 2008). It is evident that L. fasciola relies heavily on its primary host, M. dolomieu, and this reliance helps to explain the relatively strong population of L. fasciola in the Grand River and the loss in the Sydenham River. Threats to host species also may threaten mussel populations because of their host parasite relationship. One such threat is the arrival of Neogobius melanostomus (round goby), which have recently invaded rivers in the region (Poos et al. 2010). Neogobius melanostomus has caused severe declines in C. bairdi, low-to-moderate declines in certain darter species (Jude et al. 1995), and negative effects on M. dolomieu including nest success (Steinhart et al. 2004). Moreover, it is a molluscivore that may prey upon juvenile or small unionids (Poos et al. 2010). Variability among host species may help to explain the differences in abundance and distribution of endangered mussel species. Specifically, the loss of a primary host species (E. exile) appears to be associated with highly restricted populations of E. t. rangiana in both the Sydenham and Ausable Rivers. Conversely, the high abundance of a primary host species (M. dolomieu) may explain the relatively strong population of L. fasciola in the Grand River. Continued use of marginal host species may allow mussel populations to remain relatively stable, but it also may limit opportunities for increases in abundance or distribution. Identification of the relationship between hostfish quality and the status of endangered freshwater mussels will provide important insight into effective mussel-conservation efforts. Acknowledgements We acknowledge the Endangered Species Recovery Fund (World Wildlife Fund, Environment Canada, and Ontario Ministry of Natural Resources), Species at Risk Coordination/ Espèces en Péril (Department of Fisheries and Oceans [DFO]) and Natural Sciences and Engineering Research Council (Discovery grant to JDA). We also thank our many summer and work study students, the Ontario Ministry of Natural Resources (OMNR) Stewardship Ranger program, our volunteers for their help in the field, and the Hagen Aqualab, Bob Frank, and Matt Cornish (Hagan Aqualab), J. Metcalfe-Smith (Environment Canada), Daryl McGoldrick (Water Science and Technology Directorate, Environment Canada), Todd Morris (DFO), Dave Zanatta and Daelyn Woolnough (Central Michigan University), John Schwindt (Upper Thames River Conservation Authority), Art Timmerman (OMNR), Mark Poos (University of Toronto), Muriel

8 2011] HOST FISH AND ENDANGERED MUSSELS 67 Andreae (St Clair Region Conservation Authority), Mari Veliz and Kari Killins (Ausable Bayfield Conservation Authority), and the various landowners in the Sydenham River Watershed who provided access to the river. All fish collections were undertaken via OMNR permit numbers and and by the University of Guelph Animal Utilization Protocol 04R107. All mussel collections were undertaken via Species at Risk Act permit numbers SECT 05 SCI 020 and SECT 06 SCI 007. Literature Cited ASTM (AMERICAN SOCIETY FOR TESTING AND MATERIALS) Standard guide for conducting toxicity tests with freshwater mussels (E ). American Society for Testing and Materials International, West Conshohocken, Pennsylvania. BARNHART, M. C., W. R. HAAG, AND W. N. ROSTON Adaptations to host infection and larval parasitism in Unionoida. Journal of the North American Benthological Society 27: BIGHAM, S. E Host specificity of freshwater mussels: a critical factor in conservation. MSc Thesis, Southwest Missouri State University, Springfield, Illinois. BOGAN, A. E Freshwater bivalve extinctions (Mollusca: Unionoida): a search for causes. American Zoology 33: BOGAN, A. E Global diversity of freshwater mussels (Mollusca: Bivalvia) in freshwater. Hydrobiologia 595: DEXTRASE, A. J., S. K. STATON, AND J. L. METCALFE-SMITH National recovery strategy for species at risk in the Sydenham River: an ecosystem approach. National Recovery Plan No. 25. Recovery of Nationally Endangered Wildlife (RENEW), Ottawa, Ontario, Canada. DFO (DEPARTMENT OF FISHERIES AND OCEANS) Recovery strategy for the Dwarf Wedgemussel (Alasmidonta heterodon) in Canada. Species at Risk Act Recovery Strategy Series. Department of Fisheries and Oceans, Ottawa, Ontario, Canada. (Available from: pwgsc.gc.ca/collection_2007/ec/en e.pdf ) DODD, B. J., M. C. BARNHART, C. L. ROGERS-LOWERY, T. B. FOBIAN, AND R. V. DIMOCK Cross-resistance of largemouth bass to glochidia of unionid mussels. Journal of Parasitology 91: HAAG, W. R., AND J. L. STATON Variation in fecundity and other reproductive traits in freshwater mussels. Freshwater Biology 48: HAAG, W. R., AND M. L. WARREN Host fishes and infection strategies of freshwater mussels in large mobile basin streams, USA. Journal of the North American Benthological Society 22: HAAG, W. R., M. L. WARREN, AND M. SHILLINGSFORD Host fishes and host-attracting behavior of Lampsilis altilis and Villosa vibex (Bivalvia: Unionidae). American Midland Naturalist 141: HOFTYZER, E., J. D. ACKERMAN, T. J. MORRIS, AND G. L. MACKIE Genetic and environmental implications of reintroducing laboratory-raised unionid mussels to the wild. Canadian Journal of Fisheries and Aquatic Sciences 65: JONES, J. W., AND R. J. NEVES Life history and propagation of the endangered fanshell pearlymussel, Cyprogenia stegaria Rafinesque (Bivalvia:Unionidae). Journal of the North American Benthological Society 21: JONES, J. W., J. R. NEVES, S.A.AHLSTEDT, AND R. A. MAIR Life history and propagation of the endangered dromedary pearlymussel, (Dromus dromas) Rafinesque (Bivalvia:Unionidae). Journal of the North American Benthological Society 23: JUDE, D. J., J. JANSSEN, AND G. CRAWFORD Ecology, distribution, and impact of the newly introduced round and tubenose gobies on the biota of the St. Clair and Detroit Rivers. Pages in M. Munawar, T. Edsall, and J. Leach (editors). The Lake Huron ecosystem: ecology, fisheries and management. SPB Academic Publishing, Amsterdam, The Netherlands. KIRK, S. G., AND J. B. LAYZER Induced metamorphosis of freshwater mussel glochidia on nonhost fish. Nautilus 110: LYDEARD, C., R. H. COWIE, W. F. PONDER, A. E. BOGAN, P. BOUCHET, S. A. CLARK, K. S. CUMMINGS, T. J. FREST, O. GARGOMINY, D.G.HERBERT, R.HERSHLER, K.E.PEREZ, B. ROTH,M.SEDDON,E.E.STRONG, AND F. G. THOMPSON The global decline of nonmarine mollusks. BioScience 54: MCNICHOLS, K. A Implementing recovery strategies for mussel species at risk in Ontario. MSc Thesis, University of Guelph, Guelph, Ontario, Canada. METCALFE-SMITH, J. L., A. MACKENZIE, I. CARMICHAEL, AND D. MCGOLDRICK Photo field guide to the freshwater mussels of Ontario. St Thomas Field Naturalist Club Inc., St Thomas, Ontario, Canada. METCALFE-SMITH, J. L., S. K. STATON, AND E. L. WEST Status of the Wavy-rayed Lampmussel, Lampsilis fasciola (Bivalvia: Unionidae), in Ontario and Canada. Canadian Field Naturalist 114: MORRIS, T. J., AND M. BURRIDGE Recovery strategy for the Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy mussel and Rayed Bean in Canada. Species at Risk Act Recovery Strategy Series. Catalog no.: En3-4/ E-PDF. Fisheries and Oceans Canada, Ottawa, Canada. (Available from: ca/document/dsptext_e.cfm?ocid=4878) NATURESERVE NatureServe explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. (Available from: NELSON, M., M. VELIZ, S. STATON, AND E. DOLMAGE Towards a recovery strategy for species at risk in the Ausable River: synthesis of background information. Prepared for Ausable River Recovery Team, Exeter, Ontario, Canada. (Available from: on.ca/downloads/synthesis_report_final_.pdf)

9 68 K. A. MCNICHOLS ET AL. [Volume 30 O BEIRN, F. X., R. J. NEVES, AND M. B. STEG Survival and growth of juvenile freshwater mussels (Unionidae) in a recirculating aquaculture system. American Malacological Bulletin 14: POOS, M., A. J. DEXTRASE, A. N. SCHWALB, AND J. D. ACKERMAN Secondary invasion of the round goby into high diversity Great Lakes tributaries and species at risk hotspots: potential new concerns for endangered freshwater species. Biological Invasions 12: POOS, M. A., N. E. MANDRAK, AND R. L. MCLAUGHLIN A practical framework for selecting among single-species, community-, and ecosystem-based recovery plans. Canadian Journal of Fisheries and Aquatic Sciences 65: RIUSECH, F.A.,AND M. C. BARNHART Host suitability and utilization in Venustaconcha ellipsiformis and Venustaconcha pleasii. Pages in R. A. Tankersley, T. Watters, B. Armitage, and D. Warmolts (editors). Proceedings of the Captive Care, Propagation, and Conservation of Freshwater Mussels Symposium. March 6 8, Columbus, Ohio. Ohio University Press, Columbus, Ohio. SARA (SPECIES AT RISK ACT) Species at risk public registry. Government of Canada, Ottawa, Ontario, Canada. (Available from: ca/species/schedules_e.cfm?id=1) SCOTT, W. B., AND E. J. CROSSMAN Freshwater fishes of Canada. Galt House Publications Ltd., Oakville, Ontario, Canada. STATON, S. K., J. L. METCALFE-SMITH, AND E. L. WEST Status of the Northern Riffleshell, Epioblasma torulosa rangiana (Bivalvia: Unionidae), in Ontario and Canada. Canadian Field Naturalist 114: STEINHART, G. B., E. A. MARSCHALL, AND R. A. STEIN Round goby predation on smallmouth bass offspring in nets during simulated catch-and-release angling. Transactions of the American Fisheries Society 133: STRAYER, D Freshwater mussel ecology: a multifactor approach to distribution and abundance. University of California Press, Los Angeles, California. TRDAN, R. J., AND W. R. HOEH Eurytopic host use by two congeneric species of freshwater mussel (Pelecypoda: Unionidae: Anodonta). American Midland Naturalist 108: VAUGHN, C. C., AND C. C. HAKENKAMP The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46: WATTERS, G. T Hosts for the Northern Riffleshell (Epioblasma torulosa rangiana). Triannual Unionid Report 10:14. (Available from: FMCS/TUR/TUR10.html#p14a) WHITFORD, J Report to the Sydenham Recovery Team in Sydenham River Recovery Project: synthesis and analysis of background data. Jacques Whitford Environment Ltd., Ottawa, Ontario, Canada. (Available from: SynthesisReport.pdf) WILLIAMS, J. D., M. L. WARREN, K. S. CUMMINGS, J. L. HARRIS, AND R. J. NEVES Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9):6 22. YEAGER, B. L., AND C. F. SAYLOR Fish hosts for four species of freshwater mussels (Pelecypoda: Unionidae) in the Upper Tennessee River Drainage. American Midland Naturalist 133:1 6. ZALE, A. V., AND R. J. NEVES Fish hosts of four species of lampsiline mussels (Mollusca: Unionidae) in Big Moccasin Creek, Virginia. Canadian Journal of Zoology 60: ZANATTA, D. T., S. J. FRALEY, AND R. W. MURPHY Population structure and mantle display polymorphisms in the wavy-rayed lampmussel, Lampsilis fasciola (Bivalvia: Unionidae). Canadian Journal of Zoology 85: Received: 5 May 2010 Accepted: 15 October 2010

10 2011] HOST FISH AND ENDANGERED MUSSELS 69 APPENDIX 1. Conditions used to infest Etheostoma exile, Etheostoma nigrum, and Cottus bairdi with glochidia from Epioblasma torulosa rangiana. Twelve individuals of each fish species were infested with the glochidia from 1 female mussel a. Fish were assigned to 1 of 3 replicates, each with 4 fish. The duration of all infestations was 60 min and each took place in 1 L of water. Female mussel Glochidia concentration (no. glochidia/l) Fish species infested Mean (61 SE) total length of fish (cm) 1 b E. exile ; n = E. nigrum ; n = C. bairdi ; n = 4 2 c E. exile ; n = E. nigrum ; n = C. bairdi ; n = 4 3 d E. exile ; n = E. nigrum ; n = C. bairdi ; n = 4 a Part of a marsupial gill was used b Shell length = 4.41 cm, 4452 glochidia removed c Shell length = 6.14 cm, 3885 glochidia removed d Shell length = 3.68 cm, 3410 glochidia removed APPENDIX 2. Conditions used to infest Etheostoma exile, Etheostoma nigrum, and Cottus bairdi with glochidia from Lampsilis fasciola at the beginning and end (used in the analysis) of the experiment. Each replicate consisted of 12 fish (4 individuals of each species) infested by M of the glochidia from a given female. The duration of all infestations was 60 min and took place in a 1-L container of water (unless noted). n = number of fish in tank, = replicate lost to fish mortality. Female mussel (replicate) Glochidia concentration (no. glochidia/l) Fish species infested Mean (61 SE) total length of fish (cm) Beginning 1 (1) a C. bairdi ; n = ; n = 3 M. dolomieu ; n = 4 M. salmoides ; n = 4 1 (2) C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 M. salmoides ; n = 4 1 (3) C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 M. salmoides ; n = 3 4.5; n = 1 2 (1) b C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 4 M. salmoides ; n = 2 2 (2) C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 6.4; n = 1 M. salmoides ; n = ; n = 3 2 (3) C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 M. salmoides ; n = 4 3 (1) c C. bairdi ; n = ; n = 4 M. dolomieu ; n = 3 M. salmoides ; n = 2 5.0; n = 1 3 (2) C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 2 M. salmoides ; n = 3 8.9; n = 1 3 (3) C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 4 M. salmoides ; n = 4 5.0; n = 1 4 (1) d C. bairdi ; n = ; n = 4 M. dolomieu ; n = 3 M. salmoides ; n = ; n = 1 End

11 70 K. A. MCNICHOLS ET AL. [Volume 30 APPENDIX 2. Continued. Female mussel (replicate) Glochidia concentration (no. glochidia/l) Fish species infested Mean (61 SE) total length of fish (cm) Beginning 4 (2) C. bairdi ; n = ; n = 2 M. dolomieu ; n = 4 M. salmoides ; n = 4 4 (3) C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 2 M. salmoides ; n = 4 6.6; n = 1 5 (1) e g C. bairdi ; n = ; n = 3 M. dolomieu ; n = ; n = 3 M. salmoides ; n = 4 5 (2) C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 3 M. salmoides ; n = 4 4.7; n = 1 5 (3) C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 8.3; n = 1 M. salmoides ; n = 4 6 (1) f h C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 9.9; n = 1 M. salmoides ; n = 4 4.9; n = 1 6 (2) h C. bairdi ; n = ; n = 4 M. dolomieu ; n = 4 9.3; n = 1 M. salmoides ; n = 4 4.6; n = 1 6 (3) h C. bairdi ; n = ; n = 4 M. dolomieu ; n = ; n = 3 M. salmoides ; n = 3 4.7; n = 1 a Shell length = 5.41 cm, 32,850 glochidia removed b Shell length = 4.83 cm, 18,450 glochidia removed c Shell length = 4.71 cm, 6075 glochidia removed d Shell length = 5.42 cm, 33,075 glochidia removed e Shell length = 5.50 cm, 14,400 glochidia removed f Shell length = 5.16 cm, 58,500 glochidia removed g 1.35 L used in infestation container h 1.5 L used in infestation container End