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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
