Why are there so few mysids in Lake Huron?

Session: 29. - Preliminary Results from the 2017 CSMI Intensive Field Year on Lake Huron

Lars Rudstam, Cornell University Bio Field Station, Dept. of Natural Resources, [email protected]
Annie Scofield, Cornell University, [email protected]
Toby Holda, Cornell Biological Field Station, [email protected]
James Watkins, Cornell University, [email protected]

Abstract

Mysid densities in Lake Huron are lower than in the other deep Great Lakes.  This is not due solely to shallower depths, as mysid densities were also low in the deepest part of the lake (150m depth).  There are indications of poor food conditions for mysids in Lake Huron.  Zooplankton abundance is low compared to lakes Michigan and Ontario, and Diporeia densities, a potential benthic mysid prey, is low compared to Lake Superior.  Epilimnetic chlorophyll concentrations were also low in Lake Huron, although concentrations in the deep chlorophyll layer used by mysids were similar to Lake Michigan.  However, mysid length distribution in Lake Huron was similar to the other deep Great Lakes, as was the number of embryos carried per females and the lengths of gravid females, suggesting that low growth and low food availability may not be the problem.  We propose that the high water clarity in Lake Huron combined with the relatively shallow depth and perhaps the decline in Diporeia has increased mysid mortality during the day in Lake Huron compared to the other three deep Great Lakes.  Light measurements in July 2017 indicate sufficient light on the bottom for fish to visually feed on mysids.

1. Keyword
zooplankton

2. Keyword
acoustics

3. Keyword
phytoplankton

4. Additional Keyword
Mysids

5. Additional Keyword
Deep Chlorophyll Layer