the role of egg predation in pacific herring populations of puget sound
TRANSCRIPT
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
growth rate without preda.on
mortality due to preda.on
+
-‐
0 rate N
a$er Sinclair et al. 1998 Cons Bio
Puget Sound herring are declining in some locations
The problem
Siple and Francis, in press, Oecologia
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
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1970 1980 1990 2000 2010 2020
Quartermaster Harbor
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1970 1980 1990 2000 2010 2020
Port Madison
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1970 1980 1990 2000 2010 2020
Quilcene Bay
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1970 1980 1990 2000 2010 2020
Holmes Harbor
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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