NOAA -Great Lakes Environmental Research Laboratory
LOWER TROPHIC LEVELS
Lake Whitefish Workshop
Steven Pothoven
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Similar abundance to 1980s, but lower than 1990s. No positive response to recent declines in fish. • Recent declines in lipid content.
Typology: Summaries
2022/2023
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NOAA - Great Lakes Environmental Research Laboratory
LOWER TROPHIC LEVELS
Lake Whitefish Workshop
Steven Pothoven
From Dolan and Chapra 2012
TP Loading (MTA)
Lake Huron
Lake Michigan
Phosphorus loading has been in decline since 1980s Target 5600 MTA Target 4360 MTA
Data from T. Nalepa
Mussel biomass has generally stabilized after 2010
Quagga Mussel
Data from T. Nalepa
Chlorophyll
a
(mg/m
Day of Year
Changes in Seasonal Trends in Offshore Chlorophyll (phytoplankton) Surface Mixed Layer-Lake Michigan example
“Spring Bloom”
The spring diatom bloom has largely disappeared
chl a (mg/m
Lake Michigan Offshore Spring Chlorophyll
Convergence in productivity among upper lakes Figures from : FAHNENSTIEL, G.L., M.J. Sayers, R.A. Shuchman, F. Yousef, and S.A. POTHOVEN. Lake-wide phytoplankton production and abundance in the upper Great Lakes: 2010-2013. Journal of Great Lakes Research 42(3):619-629 (DOI:10.1016/j.jglr.2016.02.004) (2016)
50 100 150 200 250 300 350
50 100 150 200 250 300 350
Declines in Chlorophyll and Phosphorus in Nearshore Regions
TP (mg/m
)^
chl a (mg/m
)^ Chlorophyll^ a
Total
Phosphorus
Day of Year
Grand Haven, MI
NALEPA, T.F., D.L. FANSLOW, G.A. LANG, K. MABREY, and M. ROWE. Lake-wide benthic surveys in Lake Michigan in 1994-95, 2000, 2005, and 2010: Abundances of the amphipod Diporeia spp. and abundances and biomass of the mussels Dreissena polymorpha and Dreissena rostriformis bugensis. NOAA Technical Memorandum GLERL-164. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 21 pp. (2014). Rapid declines in abundance of the amphipod Diporeia Historically, a high energy food source for many fish, including lake whitefish No signs of recovery since 2010
Diporeia spp.
Diporeia Mysis Bythotrephes Cladoceran Copepod
Biomass (mg/m
Loss of Diporeia represents a major shift in food availability for fish
Lake Michigan
Declines of Diporeia associated with declines in growth or condition for several fish species
1987 1988 1990 1991 1992 1993 1994 1995 1996 2009 2010
Lake Michigan Nearshore
(Muskegon)
Inner Saginaw Bay
Chironomids
- Seasonal abundance varies
- Substrate type
- Limited time series data
Number/m
2
Number/m
2
Other
Chironomidae
Other zoopl.
Bosminidae
Daphnia
Cyclopoida
% dry weight
Lake whitefish length class (mm)
Age-0 lake whitefish diets-Saginaw Bay
12 13 14 15 16 17 18 19 20 21 22 Frequency (proportion eating a prey) calanoid cyclopoid Chironomid
2014 Northern Lake Michigan
Whitefish length (mm) 3 9% Empty (≤ 21 mm)
0 5 10 15 20 25 30 35 40 45
Frequency (proportion eating a prey) 0 5 10 15 20 25 30 35 40 45 calanoid cyclopoid Bosmina Daphnia Chironomid
2014 Muskegon
Whitefish length (mm) Whitefish length (mm) 19% Empty (≤ 21 mm)