An Evaluation of a Skimmer Dredge for Collecting Freshwater Mussels

Unionid bivalves and attached epizoic zebra mussels (Dreissena polymorpha) were collected at one index station in 1989, 1990, and 1991 and at 17 stations in 1991 in offshore waters of western Lake Erie of the Laurentian Great Lakes. Sampling at the index station revealed that the proportion of live unionids declined from 53% in September 1989 to 17% in May–June 1990 and to 0% in September 1990: this 100% mortality coincided with heavy infestation by zebra mussels. Quantitative sampling with a Ponar grab at the 17 stations in 1991 revealed a widespread and dramatic reduction in unionid populations. In 1982, five unionid species occurred at 35% of the stations at a density of 4/m2, whereas in 1991, no live unionid species were found. Qualitative sampling with an epibenthic sled at the 17 stations in 1991 yielded only 4 live specimens of 2 species (Amblema plicata plicata and Fusconaia flava) and 187 dead specimens of 10 species. These and other results indicate that unionid populations are being negatively affected by zebra mussels in the Great Lakes. Similar impacts on unionids are expected to occur where zebra mussels become abundant throughout North America.

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“…2). The sled was similar to that uxed by Miller et al ( 1989). The sled was repetitively pulled (ca.…”

Section: Methodsmentioning

confidence: 99%

Dramatic Decline of Unionid Bivalves in Offshore Waters of Western Lake Erie After Infestation by the Zebra Mussel, Dreissena polymorpha

Schloesser¹,

Nalepa²

1994

Can. J. Fish. Aquat. Sci.

142

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“…It has been shown that in lakes ever, several field and experimental studies (e.g. Lodge & Lorman, 1987;Hanson et al, 1990;Lodge et al, 1994) (Miller, Becket & Bacon, 1989;Blindow et al, 1993) and streams (Gregg & Rose, 1985) areas without vegetation have suggested that crayfish are efficient predators on snails. In the H ponds we found that the percentage have lower biomasses of invertebrates than those with macrophytes, and the permanence of the macrophyte biomass of snails, leeches and the mussel Pisidium decreased with crayfish abundance.…”

Section: Macrophytesmentioning

confidence: 99%

Patterns in benthic food webs: a role for omnivorous crayfish?

Nyström¹,

Brönmark²,

Granéli³

1996

Freshwater Biology

185

110

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1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty‐one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment‐dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte‐associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.

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“…Brailing can be useful for large-scale exploratory searches for mussel beds but has a low catch rate, is highly biased against some species and small size-classes, and is cumbersome to employ. A skimmer dredge pulled behind a boat can provide unbiased estimates of species richness, species relative abundance, and size structure in lakes or large rivers but is limited to sand or silt substrates with few obstructions, requires a powerful engine, and may be destructive to the habitat (Miller et al 1989). …”

Section: Other Sampling Methods For Mollusksmentioning

confidence: 99%