Prepared by: Bryce Oldemeyer, Adrienne Roumasset, BenVaage and Ryan Johnson

Blue Lake, Idaho Kettle Origin (Wetzel, 2001) Rainbow Trout and Bullhead “Bottomless” Dimictic Stratifies Turns over twice a year Google Earth

TroutBullhead Zooplankton Phytoplankton Trophic Levels in Blue Lake

Goals of Zooplankton Sampling Determine zooplankton abundance and distribution in Blue Lake. Make inferences about data concerning: Status of the lake Foraging of fish Trophic cascade

Methods Overview Measure photic zone using Secchi disk. Sample zooplankton at four points on the lake. At each point, sample above and below photic zone. PHOTIC ZONE: Upper depths of lake where light can penetrate and facilitate plant growth. (Wetzel, 2001)

Transects and Sampling Locations on East Side of Blue Lake Littoral Zone : Shallow zone, emergent macrophytes can grow Pelagic Zone: Deeper zone, free open water

EQUIPMENT Secchi disk: Measures photic zone Schindler trap: Collects zooplankton at discrete depths Plankton net: Collects integrated samples

Results of Chlorophyll-A in Blue Lake Four sites sampled in replicates of 3, and the average [Chla] was 4.43µg/L. And a range of µg/L.

Results of Total Phosphorus in Blue Lake Excluding outliers, average [TP] for Blue Lake was µg/L. And a range of 10-41µg/L.

Zooplankton Observed Ceriodaphniacyclopoid calanoid

Results of Pelagic Zooplankton -Two transects sampled in triplicates in both the photic and aphotic zone. Transect 1Transect 2

Results of Pelagic Zooplankton Overall, aphotic zone yielded fewer zooplankton counts. Transect 1Transect 2

Results of Littoral Zooplankton Sampled two transects in triplicates. Transect 1Transect 2

Results for Blue Lake Zooplankton -Average zooplankton for both transects in photic zone was 103/L -Aphotic zone average was 49/L -Littoral zone was 36 zooplankton/L. Transect 1Transect 2

Discussion: Macrophyte Removal Benefits Costs Remove macrophytes for a more aesthetically pleasing pond. Possibly better swimming waters. Absence of macrophytes reduces cover for large zooplankton (Wetzel, 2001). Increase phytoplankton numbers, due to lack of grazing (Wetzel, 2001). Macrophytes shade phytoplankton, especially lilies.

Macrophyte Management Suggestion Removing macrophytes may make Blue Lake less “blue”. Still large amounts of organic sediment and steep gradient. Leave macrophytes, increase large zooplankton populations, increase quality of fish, and keep water quality constant.

Fishery Management Relatively low nutrients * Following classifications given in Wetzel, 2001 Increasing fish abundance Potential resource strain OligotrophicBlue LakeEutrophic Chl A0.3-3 µg/L µg/L µg/L TP<5 µg/L µg/L >30 µg/L

Results of Resource Strain Stunted growth in fish (Kohler, and Hubert, 1999) Decreased quality of fish (Kohler, and Hubert, 1999) Altered zooplankton composition (Brooks, and Dodson, 1965) Increase in phytoplankton (Timms, & Moss, 1984) (+) “Small” Z.P. (-)“Large” Z.P. RBT and Bullhead (+) Phytoplankton

Zooplankton concerns Selective predatory pressure creates favorable conditions for smaller zooplankton. Smaller zooplankton consume less phytoplankton than larger zooplankton (Wetzel, 2001) Ultimately increases phytoplankton abundance (+) “Small” Z.P. (-)“Large” Z.P. RBT and Bullhead (+) Phytoplankton

“Green” water Large abundance of phytoplankton cause “green” water (Wetzel, 2001) Large ZP can help control phytoplankton (Timms, & Moss, 1984)

Management Suggestion Bullhead and RBT removal Catch and Keep A rainbow trout of 220 mm tends to feed upon zooplankton ranging from 1.2 mm to 2.4 mm (Haddix et al, 2005). Reducing number of trout will increase larger zooplankton in Blue Lake Remaining trout will have more available forage and will be healthier Larger zooplankton will become more abundant. Reduces chances of “green water” (+) “Small” Z.P. (-)“Large” Z.P. RBT and Bullhead (+) Phytoplankton

Results of Removal Remove RBT and Bullhead Increased fish forage Increased large ZP Increased phytoplankton consumption Increased H 2 0 clarity and decrease “green” H 2 0 possibility Decrease Intra and Inter species competition Better Quality Fish

Recommended Actions Catch and Keep! Begin removing all fish caught As time progresses, primarily target smaller fish Occasionally keep larger fish

References Kohler, C. and Hubert, W. (1999). Inland fisheries management in north america, 2nd edition. Maryland: American Fisheries Society. Wetzel, Robert. (2001). Limnology, Third Edition: Lake and River Ecosystems. Academic Press. Haddix, Tyler, P. Budy, R. Schneidervin (2005). Zooplankton size selection relative to gill raker spacing in rainbow trout. Transactions of the American Fisheries Society 134: Kohler, C. and Hubert, W. (1999). Inland fisheries management in north america, 2nd edition. Maryland: American Fisheries Society. Brooks, J, & Dodson, S. (1965). Predation, body size, and composition of plankton. Journal of the American Chemical Society, 85, 835 Timms, R, & Moss, b. (1984). Prevention of growth of potentially dense phytoplankton populations by zooplankton grazing, in the presence of zooplanktivorous fish, in a shallow wetland ecosystem. Limnology and Oceanography, 29(3),