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Index of Subjects On 5/16/2014 4:29 PM, nancy dowd wrote: > Dusan Soudek wrote: >> any living specimens around? They would likely be in somewhat deeper water, not easily visible from land... > None that I saw. But I did not really scan closely either. I find mussels are often in any depth of water where the sediment is soft, fine sand. On this lake. this is often at depths of 1m plus but can also be in shallow water where the preferred sediment has deposited behind several rocks. > Lots of beaver on the lake. I have never seen a muskrat swim by but that does not mean they are absent. * Nancy sent me the pictures by attachment, and at least most of the shells are Elliptio complanata, which around here is the hardiest species for drought or anoxia. I don't know if any are resistant to freezing, but the ice wouldn't have been a metre deep. If there are lots of Beavers, you might check for nibbles on the edges of the shells, since these are characteristic of shells - at least some of them - in cases where Beavers are implicated. These Beaver-implicated cases of predation are also characterized by shells scattered all over the bottom, which the photos show. I've hypothesized that the Beavers eat the mussels under the ice in the winter, which is why nobody ever sees them doing it. In any event, it would be good to scoop up a common plastic garbage bag full of the shells (emphasising diversity in shape if you don't know the species), and deposit them in the NS Museum, so future investigators will be able to figure out whatever they can about the event. fred. ================================================ >>> On May 16, 2014 at 1:35 PM nancy dowd <nancypdowd@gmail.com> wrote: >>> >>> >>> Water levels have dropped just enough on L Torment to show about 6" of beach in places now but the shore has been completely submerged since last October. The number of mussel shells seen in these pictures is unusual: >>> >>> At the end of the path they are visible as far as you can see out into the water: >>> https://www.flickr.com/photos/92981528@N08/14196083311/ >>> >>> And it is this way the whole way along the shore. Another view 40' along the submerged beach: >>> https://www.flickr.com/photos/92981528@N08/14012727849/ >>> >>> This side of the lake has the prevailing onshore winds and waves and the shells are starting to collect in the exposed pockets: >>> https://www.flickr.com/photos/92981528@N08/14199406975/ >>> >>> Why so many empty mussel shells? Would the winter somehow have been hard on them- ice or cold or oxygen levels? Doesn't look like predation to me- too many shells. This is the first year I have ever seen anything like this. >>> >>> Any ideas? >>> >>> Nancy >>> Is everyone having problems seeing the photos? The links seem to be working for me when I click on them. If so I will try to set them up again or email the pictures to anyone interested. Lots of beaver on the lake. I have never seen a muskrat swim by but that does not mean they are absent. Nancy On 2014-05-16, at 4:59 PM, Fred Schueler <bckcdb@istar.ca> wrote: > On 5/16/2014 1:06 PM, David McCorquodale wrote: >> Muskrats are important predators of freshwater mussels in eastern North >> America, including NS. Often they pile shells in middens. >> >> In Blacketts Lake and Pottle Lake in CBRM piles of shells of several >> species of freshwater mussels, including the Yellow Lamp Mussel, are >> obvious. > > * these URLs just took me to a general flckr site, not to the individual photos. > > Muskrats and Beavers can process astonishing numbers of mussels, and often leave the shells quite undamaged - and nonhuman mammals, with weak connections of cultural memory can "discover" a food source and use it to depletion for one generation with the descendents never learning about it, giving the prey time to build up to high density. > > Freezing or anoxia can kill mussels, though they'd die buried in the substrate, and wouldn't be expected to be on the beach this early - also low water levels can cause mass mortality. Without being able to see the pictures, I can't say what species these are, but if they're Anodonta or Pyganodon "Floaters" the light-weight shells would be more likely to work loose from the substrate and blow onto a lee shore. >
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