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Gulf of Alaska - Fish & Fish Habitat
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A Model for Early Life History
Survival for Pacific Herring in
Prince William Sound
Brenda Norcross, Seanbob Kelly,
Peter-John Hulson, Terry Quinn
School of Fisheries and Ocean Sciences
University of Alaska Fairbanks
Herring – An Important Species
Forage fish
Commercial fishery
Prince William Sound
http://marine.alaskapacific.edu/octopus/pws-map.php
Recent History of Herring
Fishery closed in March 1989 following
the Exxon Valdez oil spill
Stock collapsed 1993 due to (VHSV)
Species has not recovered to pre-oil
spill abundance
Spawning and Larvae
Herring spawn
onshore in April
Larvae herring are
advected counterclockwise through
open water
Years 1 and 2
June-August metamorphosis
Nursery habitats at heads of bays
In nursery bays for 2 winters
Leave bays and join adult schools
Early Life History to Age-1
4 stages - eggs, larvae, fall juveniles,
winter juveniles
Know mortality changes as life stage
changes
Determine which life stage is most
influential
Early Life History Model
Life-stage specific survival to age-1
Builds on an earlier range-based study
(Norcross & Brown 2001)
Statistical distributions of survival to
account for uncertainty
Data input from published estimates
Standard Year-Class Model
(Quinn and Deriso 1999)
Cumulative mortality - z for each stage
multiplied by number of days per stage
Total mortality - combines mortalities
of sequential life stages to age-1
,
Delta Method
(Seber 1982)
Converts standard error of survival to that
of mortality
Assumed normal distribution
Allows determination of 95% confidence
intervals
.
Egg Stage - first 21 days
(Haegele 1993)
Subsurface oophagy - crabs, sea
anemones, and snails
(Rooper et al. 1999)
Duration of air exposure - exposure
abiotic forces, and avian predation
Larval Stage - next 92 days
(McGurk et al. 1993)
Larval mortality caused by advection,
predation, and inability to feed
Data from Auke Bay, Southeast Alaska
Comparable to estimates from British
Columbia
Fall Juvenile Stage - next 92 days
(Stokesbury et al. 2002)
Greatest mortality due to predation
Averaged over four bays and two years
Winter Juvenile Stage - next 135 days
(Patrick 2000)
Energy reserves (WBEC) and water
temperature affect survival
Age-0 winter mortality due to starvation
Averaged over 12 bays
Egg Stage
>Age-3
spawn
Larval Stage
hatch
next 92 days
mortality 0.07 d-1
first 21 days
mortality 0.07 d-1
drift
Winter Juvenile Stage
Fall Juvenile Stage
nursery bay
Age-1
next 135 days
mortality 0.004 d-1
next 92 days
mortality 0.01 d-1
Results
Total survival through age-1
118 herring out of 1 million eggs
Compare to range-based – 1-6,500
Consistent with the results of agestructured assessment (ASA)
Distribution of total
mortality
ASA (age-3)
0.4
ELH (age-1)
Frequency
0.35
0.3
0.25
ASA
ELH
0.2
0.15
0.1
0.05
0
4
5
6
7
8
9
10
11
12
13
14
Total mortality
Total Mortality (Z)
Average ELH mortality is lower than ASA mortality
ASA incorporates mortality ages-0 through -3
Greater uncertainty in the distribution of ELH mortality
Single-Stage Sensitivity Analysis
Altered mortality of each life stage by 10%
Total survival was most affected by the
larval stage
Length of stage (92 days) and mortality
level (* 0.07 d-1) is cause
Other life stages had an order of
magnitude less effect
Conclusions
Life stages did not contribute equally
to mortality and survival
Larval stage has the largest influence
on total survival
This model shows that there is high
uncertainty in the early life history
Acknowledgments
Exxon Valdez Oil Spill Trustee Council
Jeep Rice
Mark Carls
Daily Survival and Daily Mortality
.
10% Increase of Mortality
Base ELH Model
10% Decrease of Mortality
0.00025
Total Survival (S)
0.0002
0.00015
0.0001
0.00005
0
Invert Pred & Air Exp
Larval
Egg
Drift
Autumn
Winter
Juvenile
Results of single-stage sensitivity analysis. Both of the textured series
are the results from increasing (left) or decreasing (right) daily
mortality (zi) while the black series is the total survival estimated from
the base early life history (ELH) model
Interaction Sensitivity Analysis
Determined all possible paired
combinations of life stages
Altered each pair of mortality estimates by
10%
Larval stage combined with any other life
stage contributed the most to total survival
Total survival maximized by decreasing
mortality for larval and egg stages