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acific herring spawning ground surveys for Prince William Sound, 1988, with historic overview. Regional Information Report 2C88-07. Alaska Department of Fish and Game, Juneau, Alaska.

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Abstract

A herring spawn deposition survey program employing underwater techniques,similar to the survey program in Southeast Alaska (Blankenbeckler,1987), was re-implemented in Prince William Sound in 1988. Surveys of this kind had not been conducted in the Sound since 1983 and 1984, when feasibility studies had been completed. The program was re-initiated due to an increase in funding and a need for an increase in accuracy of herring biomass forecasting in Prince William Sound. The Sound was divided into four areas (Figure1) and biomass estimates were calculated for each area. Survey transects were randomly selected from mapped spawning areas derived from aerial surveys. Quadrants of l/10th square meter within each transect were haphazardly sampled for egg density every 5 meters along the transect; the contents of 38 quadrants were collected for determination of diver estimate correction factors or divercalibration. It was discovered from the Prince William Sound data and from Southeast Alaska data (Funk,1988) that diver error is not a constant and is affected by substrate type and egg density; a model was derived to employ a diver error correction that takes into account substrate, year, diver, and density effects. Fecundities were determined from 315 weighed females over a range of 10mm lengths in order to provide egg numbers per female, as a parameter in the biomass estimate model. AWL samples representative of the timing of spawn for each area examined were selected to obtain average fish weight and sex ratio; the numbers were then employed for back-calculation of spawner biomass. In addition, a skiff survey was conducted in two of the four areas to examine the accuracy of mapping from aerial surveys and major discrepancies were discovered. In 1988, a total of 166.3 miles of spawn was mapped, with an average spawner density of .56 million pounds of spawners per mile. The resulting spawner biomass estimate for the Sound was 43,581 tonnes or 48,047 short tons. With the commercial catch of 11,731 short tons, the total herring pre-spawning biomass was estimated at 59,778 short tons which is 17,778 tons over the Prince William Sound stock threshold of 42,000 tons. The resulting exploitation rate for 1988 was approximately 19.6% KEYWORDS: Pacific herring, Clupea harengus pallasi, spawn deposition surveys, biomass, diver calibrations, fecundity, aerial survey.
ABSTRACT
A
herring
spawn
deposition
survey
program
employing
underwater
techniques,
similar
to
the
survey
program
in
Southeast
Alaska
(Blankenbeckler
,
1987),
was
reimplemented
in
Prince
William
Sound
in
1988.
Surveys
of
this
kind
had
not
been
conducted
in
the
Sound
since
1983
and
1984,
when
feasibility
studies
had
been
completed.
The
program
was
reinitiated
due
to
an
increase
in
funding
and
a
need
for
an
increase
in
accuracy
of
herring
biomass
forecasting
in
Prince
William
Sound.
The
Sound
was
divided
into
four
areas
(Figure
1)
and
biomass
estimates
were
calculated
for
each
area.
Survey
transects
were
randomly
selected
from
mapped
spawning
areas
derived
from
aerial
surveys.
Quadrants
of
l/lOth
m2
within
each
transect
were
haphazardly
sampled
for
egg
density
every
5
meters
along
the
transect;
the
contents
of
38
quadrants
were
collected
for
determination
of
diver
estimate
correction
factors
or
diver
calibration.
It
was
discovered
from
the
Prince
William
Sound
data
and
from
Southeast
Alaska
data
(Funk,
1988)
that
diver
error
is
not
a
constant
and
is
affected
by
substrate
type
and
egg
density;
a
model
was
derived
to
employ
as
diver
error
correction
that
takes
into
account
substrate,
year,
diver,
and
density
effects.
Fecundities
were
determined
from
315
weighed
females
over
a
range
of
10
mm
lengths
in
order
to
provide
egg
numbers
per
female
as
a
parameter
in
the
biomass
estimate
model.
A-W-L
samples
representative
of
the
timing
of
spawn
for
each
area
examined
were
selected
to
obtain
average
fish
weight
and
sex
ratio;
the
numbers
were
then
employed
for
back-calculation
of
spawner
biomass.
In
addition,
a
skiff
survey
was
conducted
in
two
of
the
four
areas
to
examine
the
accuracy
of
mapping
from
aerial
surveys
and
maj
or
In
1988,
a
total
of
166.3
miles
of
spawn
was
mapped,
with
an
average
spawner
density
of
.56
million
pounds
of
spawners
per
mile.
The
resulting
spawner
biomass
estimate
for
the
Sound
was
43,581
tonnes
or
48,047
short
tons.
With
the
commercial
catch
of
11,731
short
tons,
the
total
herring
pre-
spawning
biomass
was
estimated
at
59,778
short
tons
which
is
17,778
tons
over
the
Prince
William
Sound
stock
threshold
of
42,000
tons.
The
resulting
exploitation
rate
for
1988
was
approximately
19.6%~
KEY
WORDS:
Pacific
herring,
Clupea
harengus
pallasi,
spawn
deposition
surveys,
biomass,
diver
calibrations,
fecundity,
aerial
survey
ix
... Estimates of the number of eggs deposited are often used by management agencies to calculate the total spawning biomass of Pacific herring (Haegele et al. 1981;Biggs and Funk 1988). Egg numbers are typically estimated by scuba surveys of the spawning beds. ...
... Because these surveys occur from several days to a couple weeks after spawning, egg loss may reduce the biomass estimate, making a correction necessary to estimate egg biomass. A correction factor of 10% has previously been applied to Prince William Sound, Alaska, stocks (Biggs and Funk 1988). Recent herring research in Alaska and British Columbia suggests that egg loss is higher than previously thought and variable across years and sites (Blankenbeckler and Larson 1987;Biggs-Brown and Baker 1993;J. ...
... For spawn-deposition surveys, divers visually estimated the number of eggs in 0.1-m 2 quadrats every 5 m along each transect, which extended perpendicularly from the beach. The methods for Prince William Sound spawn-deposition surveys are detailed in Biggs and Funk (1988). Visual estimates of egg numbers were calibrated for each diver before data analysis was undertaken (Biggs-Brown and Baker 1993). ...
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