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The role of egg predation in Pacific herring population dynamics
in Puget Sound, WashingtonTessa Francis
University of Washington Tacoma
Phil LevinOle Shelton
Greg WilliamsShannon Hennessey
NOAA Northwest Fisheries Science Center
Photos: Max Bakken, Eiko Jones
Pacific Herring Range
0 ··
)' ___ -==== ___ -===:::::JI Miles 1800
, \.lk....., 0 750 1,500 2,250 3,000 Map represents approximate range of species. Inshore and offshore distances are approximate.
NMFS, Offi ce of Protected Resources November 2008
Pacific herring distribution
Map courtesy of NOAA
Photo: Rick Rae
Photo by Madeline Stevens
growth rate without preda.on
mortality due to preda.on
+
-‐
0 rate N
a$er Sinclair et al. 1998 Cons Bio
Puget SoundWashington, USA
The place
Puget Sound herring are declining in some locations
The problem
Siple and Francis, in press, Oecologia
Egg hatch rates vary by spawning “stocklet”
Pro
babi
lity
of h
atch
ing
Shelton et al. 2014, MEPS
Is variability in egg mortality rates associated with predation?
What are the implications for Puget Sound herring?
Methodsegg collection by SCUBAegg density estimateswith & without cage enclosures
à egg loss rate probability of hatching
Predator-driven egg mortality is highacross all spawning sites
76 – 99.6% of mortality is owing to predation
Predator abundance is lowerat beaches with higher egg survival rates
Egg survival is higher at beaches with higher herring abundance
0
1000
2000
3000
1970 1980 1990 2000 2010 2020
Quartermaster Harbor
0 500 1000 1500 2000 2500 3000
1970 1980 1990 2000 2010 2020
Port Madison
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2000
4000
6000
1970 1980 1990 2000 2010 2020
Quilcene Bay
0 1000 2000 3000 4000
1970 1980 1990 2000 2010 2020
Holmes Harbor
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5000
10000
15000
20000
1970 1980 1990 2000 2010 2020
Cherry Point
0.01 0.00001 0.00001
0.1 0.06
Low egg survival rates are associated with declining trends in biomass
Predation pressure combined with low abundance may lead to Allee-type effects in Puget Sound herring.
Inverse density dependence may be an important consideration for fisheries management.
Early life stages of herring are important for population models.
Recovery of Puget Sound herring may depend on early life stage dynamics.
Conclusions
xis(t+τ)=xis(t)e-(Zhs
+εhs
)τ
i = station s = site τ = # days
yis(t)=xis(t)eδ δ ~ N(0,ω2)
p(hatch)=Q*exp(-Zh) Q = prob(hatch) in lab Z = egg loss rate
Egg loss and probability of hatching
Egg loss: Bayesian state space modelProcess model ObservaSon model
Probability of hatch: egg loss and lab hatch rates
Egg survival rates are similar across years
Larval Index = SSB * Probability of Hatch
Potential larval production is greater in the absence of large predators
