[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
NFC: Minnessota Mussels
Yesterday we checked on four cages placed in the Prescott area back in
June.
Results below.
Upstream of Prescott in the St Croix -
Cage placed 6/06/01, we estimated several hundred young mussels, we think
mostly higginsi, most from 5-10 mm in length but including three that
ranged
from 25-32 mm in length. I don't know why the large size descrepancy
exists. We put the cage and its young mussels back in the river
relatively
undisturbed. I am now wondering if only the large individuals were
really
higginsi and the others are just too young to identify accurately. Why
else
two crops from one cage? The possibility that we only really raised
three
from the caged fish and all the others came from fish outside the cage
has
me scratching my head.
2 Cages placed 6/15/01, 1 young higginsi in each 8 mm length, several
Utterbackia imbecillus present in each cage. We seived the sediment from
each cage but this is all we found. Cages were removed from the river
and
the two young mussels placed in another cage that was not disturbed.
These cages had up to 12 small zebra mussels attached to the underside of
the bottom and to the legs.
Below Prescott in Mississippi River -
1 cage placed 6/15/01, 4 higginsi juveniles 8-15 mm length. Other
juveniles
included 17 U imbecillus, 11 Leptodea fragillis, 2 Potamilus alatus, 2
Potamilus ohiensis, 2 Corbicula, and at least 100 tiny Amblema plicata
and/or Obliquaria reflexa about 1-2 mm length. I would venture to guess
that the cage is acting as a refuge for other mussel species' juveniles
that
must have drifted into the cage from the mussel bed in which they were
placed. Could be that fish infected with mussel larvae are using the
cages
as structure, hanging around and loosing their little parasites close by,
we
did observe fish hanging out beneath one cage. This cage had filled with
silt up to 6 inches deep that buried the sand substrate placed in it back
in
June when the river was still high. We placed the young higginsi into
another cage that was not disturbed and removed this one from the river.
Several small zebra mussels were attached to the cage.
Very mixed results that illustrate to me that we still have a lot to
learn
about propagating mussels and the dynamics of life in the river. I would
like to place a couple of empty cages in the river next year to see what
shows up in them! Maybe protecting young mussels from large predators
accounts for the presence of so many other species in cages that were
supposed to only have higginsi in them.
Mike Davis
1801 S Oak St
Lake City, MN 55041
(651) 345-3331
(651) 345-3975 FAX
Robert Rice
NFC president
www.nativefish.org