Aquatic Food Web Dynamics in Del Valle Reservoir: Implications for Managing Mercury Concentrations in Sport Fishes

Joe Sullivan Fisheries Program Manager

Natural and Cultural Resource Committee February 21, 2018 Statewide TMDL for Mercury

• 132 reservoirs listed as impaired by EPA • Del Valle, Shadow Cliffs, Lake Chabot, Contra Loma • 2 year pilot study • Development of statewide mercury control program Sources of Mercury: Natural and Anthropogenic

Del Valle Mercury 2016 1.40

1.20

1.00

0.80 Total Hg (ug/g) Total 0.60

Do Not Eat 0.40

2 servings/week 0.20 3 Servings/week 0.00 Mercury Management

• Increase stocking of hatchery trout • Culling large fish • Biomanipulation • Oxygenation Aquatic Food Webs Aquatic Food Webs

Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg Hg

Hg Hg Hg

Hg Aquatic Food Webs Assessing Aquatic Food Webs: You Are What You Eat!

13C and 15N Stable Isotopes: 13C and 15N

15N = Trophic Position

13C = Diet Source Del Valle Food Web 6.00

LMB (Adult) STB Primary Predators 5.00

BG (adult) ISS SMB (Adult)

CARP Trophic Position Secondary Consumers 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) BG (YOY) TFS

RSCF 3.00

Zoop Primary Consumers

2.00

Algae Primary Producers

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 6.00 Open Water Bottom

LMB (Adult) STB 5.00

ISS

BG (adult) SMB (Adult) CARP 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) BG (YOY) TFS

RSCF 3.00

Zoop

2.00

Algae

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 Diet Source 6.00 Open Water Bottom

LMB (Adult) STB 5.00

ISS

BG (adult) SMB (Adult) CARP Trophic Position 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) BG (YOY) TFS

RSCF 3.00

Zoop

2.00

Algae

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 Diet Source Striped Bass are Open Water Feeders

Spring 2016 Winter 2013

16% 100% Mysid 6% Threadfin shad Unknown Fish

Crayfish 78% 6.00 Open Water Bottom

LMB (Adult) STB 5.00

ISS

BG (adult) SMB (Adult) CARP Trophic Position 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) BG (YOY) TFS

RSCF 3.00

Zoop

2.00

Algae

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 Diet Source Largemouth Bass More Bottom Oriented

Spring 2016

4% 7% Unknown Fish 15% Crayfish

Bluegill

74% Invertebrate 6.00

Open Water Bottom

LMB (Adult) STB 5.00

ISS

BG (adult) SMB (Adult) CARP Trophic Position 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) BG (YOY) TFS

RSCF 3.00

Zoop

2.00

Algae

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 Diet Source Smallmouth Bass Open Water & Bottom

Spring 2016

5% Mysid

Unknown Fish

50% Invertebrate 45% 6.00

LMB (Adult) STB 5.00

ISS

BG (adult) SMB (Adult) CARP 4.00 SMB (YOY) RBT (Hatchery) LMB (YOY) Hg BG (YOY) TFS

RSCF 3.00

Zoop

2.00

Algae

1.00 -35.00 -33.00 -31.00 -29.00 -27.00 -25.00 -23.00 -21.00 -19.00 Diet Source Conclusions

• All 3 top predators excessively high in Hg • Mercury accumulation through multiple pathways • Rainbow trout have little influence on Hg accumulation Mercury Management

• Increase stocking of hatchery trout • Culling large fish • Biomanipulation • Oxygenation • Remain status quo? Thank You!