Ecology of the burrowing amphipod, Pontoporeia affinis, in Lake Michigan / by Wayne Paul Alley.

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It is difficult to interpret the similar patterns of amphipod abundance that occurred at stations C-2 through C-7. Samter and Weltner
(1.904), Ekman (1913), and Henson (1954) have shown that as smaller
oligotrophic lakes warm in the spring and summer, Pontoporeia has a
tendency to migrate to the colder hypolimnion. The investigations of
Wells (1960) and Marzolf (1963) have shown that larger Pontoporeia are
active swimmers and these larger amphipods could possibly represent
transient groups that move from area to area. However, a reexamination
of the size frequency histograms showed that there appeared to be little
exchange of size groups within the shallower waters of the lake. These
fluctuations in abundance also did not appear to be the result of reproduction9
It is possible that these changes in abundance were the result of
sampling error. The ship logs were examined to determine if the fluctuations in the amphipod counts resulted from samples being taken during
periods of high seas. Sampling in rough weather often caused the dredges
to close prematurely. There appeared to be no association between the
state of the sea at the time the samples were taken and the variation in
the amphipod counts. All persons involved in collecting and processing
the samples were well trained in the sampling procedures, thus the collecting and processing of the samples should not represent a source of
error,
Smith (1968) indicated that adult alewives are densely concentrated