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Hollowed, A.B., and Wooster, W.S. 1995.
Decadal-scale variations in the eastern
subarctic Pacific: II. Response of northeast
Pacific fish stocks. Can. Spec. Publ. Fish.
Aquat. Sci. 121: 373-385.
Mantua, N. J., Hare, S.R., Zhang, Y., Wallace,
J.M., and Francis, R.C. 1997. A Pacific
interdecadal climate oscillation with impacts
on salmon production. ,Bull. Am. Meteorol.
Soc. 78: 1069-1079.
Ware, D. M. 1992. Climate, predators and prey:
behaviour of a linked oscillating system. In
Kawasaki T., Tanaka S., Yoahiaki T., and
Taniguchi A. (eds). Long-term variability of
pelagic fish populations and their
environment. Pergamon Press, Sendai, Japan,
pp. 279-291.
Zebdi, A., and Collie, J. S. 1995. Effect of
climate on herring (Clupea pallasi) population
dynamics in the northeast Pacific Ocean. Can.
Spec. Publ. Fish. Aquat. Sci. 121: 277-290.
Herring size-at-age variation in the North Pacific
Jake Schweigert1, Fritz Funk2, Ken Oda and Tom Moore3
1 Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, BC, Canada. V9R 5K6 E-mail:
schweigertj@pac.dfo-mpo.gc.ca
2 Alaska Department of Fish and Game, P.O. Box 25526, Juneau, AK 99802-5526, U.S.A. E-mail:
fritz_funk@fishgame.state.ak.us
3 California Department of Fish and Game, Belmont and Bodega Bay, California, U.S.A.
Introduction
Herring have been one of the more important
components of the marine fisheries on the west
coast of North America over the past century.
Dramatic population fluctuations are common in
all stocks of herring but virtually all populations
from Alaska to California declined dramatically
and synchronously in the late 1960s and all have
subsequently recovered. Despite the impacts of a
significant harvest in most of these stocks, large
scale environmental forcing appears to have been
a significant factor in the observed population
fluctuations. However, it is unclear what
mechanisms were involved in affecting survival
over such a broad geographical scale. Long time
series of stock abundance estimates are not
available for most of these populations. Instead,
we investigated the available data on fish size and
growth, reviewing trends in weight-at-age,
condition factor, and growth increments of Pacific
herring from Alaska to California in relation to
environmental conditions or food supply to assess
whether these factors may have affected herring
survival in the North Pacific.
Methods
Pacific herring weight-at-age data were collated
for a number of stocks in the North Pacific (Fig.
30) ranging from the Bering Sea [Togiak] through
the Gulf of Alaska (Kodiak], Prince William
Sound [PWS]), SE Alaska [Sitka], British
Columbia (Queen Charlotte Islands [QCI], Prince
Rupert [PRD], Central Coast [CC], Strait of
Georgia [GS], west coast of Vancouver Island
[WCVI]), and California (San Francisco Bay
[SFB], Tomales Bay [TB]). Unfortunately, the
available data is sparse in many cases and
generally available for only limited time periods
restricting the type and extent of statistical
analyses possible. The time period investigated
for this study ranges from 1940-2000. For some
populations both length and weight at age data are
available and for those we examined changes in
condition factor. For all populations trends in
weight at age 4 were examined as well as trends in
the annual growth increment at age over time.
The condition factor was also calculated annually
for each age-class in each stock following Tesch
(1988), as:
3
at
at
tLength
Weight
CF =
47
Spratt (1987) has previously used similar methods
to examine growth variation in San Francisco Bay
herring following the strong 1982-83 El Niño.
The indices of environmental forcing that were
examined included the Pacific decadal oscillation
(PDO), atmospheric forcing index (AFI), the
Aleutian low pressure index (ALPI), the Pacific
circulation index (PCI) and the ENSO southern
oscillation index (SOI). All but the last index are
available from http://www.pac.dfo-mpo.gc.ca/sci/
sa-mfpd/english/clm_indx1.htm. The SOI index
was obtained from ftp://ftp.ncep.noaa.gov/pub/
cpc/wd52dg/data/indices/soi. Information on
plankton biomass is difficult to obtain since there
have been few long-term efforts to collect these
data. Recently, Hare and Mantua (2000) have
consolidated a large number of data series for the
period 1965-1997 and we have used their results
in this study.
Togiak Bay
Ko d ia k Pri nc e
William
Sound
Sitka
Queen
Charlotte
Islands
Pri nc e Rup e rt
Central
W. C . Va n c o u ve r Is .
Georgia
St ra i t
Berin g
Se a
Alaska
British
Columbia
California
Sa n Fra n c i sc o
Ba y
Tomales
Ba y
EBSZOO
CPZOO
EPZOO
CCZOO
Fig. 30 Map of the study area illustrating the
location of data sets for the analysis.
Results and discussion
Pacific herring generally exhibit a cline in size-at-
age from south to north, with fish in the Bering
Sea being far larger than fish from California.
Herring also mature at later ages as one progresses
from south to north. Therefore, comparison of
size, condition, and growth increment becomes
complicated as fish trade off growth for
reproduction once they are mature. Consequently,
we chose to examine trends in the average weight
of fish at age 4 throughout the study area
(Fig. 31). However, this is of limited utility as an
index of growing conditions because it represents
an integration by the fish of growing and feeding
conditions over the preceding four years. Fish
from the Bering Sea are much larger and
demonstrate greater fluctuation in size at age 4
than herring from any of the other areas. Sitka and
PWS indicate a long term decline in size since the
1940s. It should be noted that the pre-1970 data
from all areas represent fall reduction fisheries
whereas recent data are from spring roe fisheries
and so may reflect some loss of weight by fish
over the winter period. British Columbia stocks
and those from Sitka show a marked increase in
size at the time of the stock collapses in the early
1960s with a subsequent decline in the 1970s
which may reflect a density-dependent response
as the populations rebuilt. California stocks do
not show evidence of any trends except for
reductions in size during the 1982-83 and 1997-98
El Niño events.
The condition factor at age is presented in Figures
32 and 33. It represents an index of growing
conditions for herring the previous year.
However, it is possible that herring compensate
for reduced food availability by growing more
slowly in length while maintaining an average
condition. Thus, it may not be a good indicator of
growing conditions in the ocean except under
extreme circumstances such as a severe El Niño
which disrupted normal feeding patterns. British
Columbia herring stocks do not show any marked
trends in condition over time although the QCI,
CC, and WCVI suggest a slight increase in
condition from the 1950s through the 1990s.
48
1940 1950 1960 1970 1980 1990 2000
100 120 140 160 180 200
Weight at Age 4
100 120 140 160 180 200
TOGIAK
KODIAK
1940 1950 1960 1970 1980 1990 2000
60 80 100 120 140
Weight at Age 4
60 80 100 120 140
PWS
SITKA
1940 1950 1960 1970 1980 1990 2000
60 80 100 120 140
Weight at Age 4
60 80 100 120 140
QCI
PRD
CC
1940 1950 1960 1970 1980 1990 2000
60 80 100 120 140
Weight at Age 4
60 80 100 120 140
GS
WCVI
1940 1950 1960 1970 1980 1990 2000
60 80 100 120 140
Weight at Age 4
60 80 100 120 140
SF Bay
Tomales Bay
Fig. 31 Trends in weight-at-age 4 in Pacific herring from 1940-2000.
49
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
QCI
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
PRD
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
CC
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
GS
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
WC
Age 3
Age 4
Age 5
Age 6
Fig. 32 Condition factor at age for British Columbia herring from 1940-2000.
50
1940 1950 1960 1970 1980 1990 2000
1.1 1.3 1.5 1.7
1.1 1.3 1.5 1.7
Condition at Age
PWS
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.2 1.4 1.6 1.8
1.2 1.4 1.6 1.8
Condition at Age
SITKA
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
1.2 1.4 1.6 1.8
1.2 1.4 1.6 1.8
Condition at Age
SFB
Age 3
Age 4
Age 5
Age 6
1.2 1.4 1.6 1.8
1.2 1.4 1.6 1.8
Condition at Age
TB
Age 3
Age 4
Age 5
Age 6
Fig. 33 Condition factor at age for Alaska and California herring from 1940-2000.
51
1940 1950 1960 1970 1980 1990 2000
-50 0 50 100
-50 0 50 100
TOGIAK
Growth Inc at Age
Age 5
Age 6
Age 7
Age 8
1940 1950 1960 1970 1980 1990 2000
0204060
0204060
KODIAK
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
0204060
0204060
PWS
Growth Inc at Age
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40 60
-20 0 20 40 60
SITKA
Growth Inc at Age
Fig. 34 Trends in the growth increment at age for Alaska herring stocks from 1940-2000.
52
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
QCI
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
PRD
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
CC
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
Fig. 35 Trends in growth increment at age for northern BC herring stocks from 1940-2000.
53
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
GS
Growth Inc at Age
Age 4
Age 5
Age 6
Age 7
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
WCVI
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
SFB
Growth Inc at Age
Age 2
Age 3
Age 4
Age 5
1940 1950 1960 1970 1980 1990 2000
-20 0 20 40
-20 0 20 40
TB
Growth Inc at Age
Age 3
Age 4
Age 5
Age 6
Fig. 36 Trends in the growth increment at age for southern BC and California herring stocks from
1940-2000.
54
1940 1950 1960 1970 1980 1990 2000
-3 -2 -1 0 1 2 3
Winter PDO
-3 -2 -1 0 1 2 3
1940 1950 1960 1970 1980 1990 2000
-3 -2 -1 0 1 2 3
AFI
-3 -2 -1 0 1 2 3
1940 1950 1960 1970 1980 1990 2000
-4-202468
ALPI
-4-202468
1940 1950 1960 1970 1980 1990 2000
-200 -100 0 100 200
PCI
-200 -100 0 100 200
1940 1950 1960 1970 1980 1990 2000
-2 -1 0 1 2
SOI
-2 -1 0 1 2
Fig. 37 Environmental indices for the North Pacific from 1940-2000.
55
All stocks also indicate a small decline in
condition in the mid- to late 1980s and again in the
late 1990s following the two strong ENSO events.
Results for Alaska and California are quite
variable with Sitka and PWS suggesting a marked
increase in condition from the 1940s through the
1960s although this may be a function of changes
in sampling locations. Both California stocks
suggest a very slight increase in condition factor
over time with sharp declines associated with the
1982-83 and 1997-98 ENSO events. Spratt (1987)
has previously reported the strong negative effects
of the 1982-83 El Niño on San Francisco Bay
herring condition factor and growth.
The growth increments at age for Pacific herring
stocks are presented in Figures 34-36 and are
perhaps the best indicator of growing conditions in
the previous year in each area. Togiak fish show
the largest growth increment coastwide which
includes a marked increase in the early 1990s
followed by a recent decline. PWS and Sitka
stocks do not demonstrate any long term trends in
growth increment although there are declines in
the mid-1980s and late 1990s which may
correspond to El Niño effects. British Columbia
stocks all show a decline in growth increment
from the early 1970s through the late 1990s. They
all show a marked decrease in 1997 and some in
the mid-1980s. The California stocks do not
indicate any clear trend in growth increment over
time but both show the effects of the 1982-83 El
Niño and SFB also the 1997-98 El Niño.
The environmental indices are presented in Figure
37 and demonstrate broadly similar patterns in
winter PDO, AFI, and ALPI based on a lowess
smoothed trend line. The PCI may be inversely
related to these indices but at a different frequency
since they are not quite in phase. The SOI index
appears to be inversely related to the first three
indices. A comparison of these indices with
herring weight at age 4, condition factor, and
growth increment does not indicate any strong
correlation but there is the suggestion of a loose
association between the trend in PDO and weight
at age 4, condition, and perhaps growth increment
since 1970.
Figure A9 from Hare and Mantua (2000) presents
the available zooplankton data for the North
Pacific and indicated a generally decreasing trend
in zooplankton biomass since the 1977 regime
shift (see Fig. A9 in their paper). This observation
is consistent with the observed declining trend in
herring growth increment in British Columbia but
surprisingly not in California. It is also consistent
with the trend of declining size at age 4 in British
Columbia and parts of Alaska. Although not
explicit in the plankton data, it is possible that
changes in species composition during El Niño
events are responsible for the marked decline in
growth observed during these time periods so that
overall plankton biomass remains relatively stable
but the preferred prey items for herring decline
markedly or are completely absent from the
normal feeding areas.
Pacific herring populations in the eastern Pacific
have experienced significant synchronous
fluctuations in abundance that appear to be related
to environmental forcing. We examined
biological characteristics associated with changes
in growth as a proxy for herring survival over the
available data record. Results indicate a complex
interaction between density dependent effects,
food supply, and environmental variation. During
the collapse of herring stocks throughout the
Pacific in the late 1960s growth of herring
increased dramatically, declining again as stock
rebuilt. During the period from 1977 to present
growth characteristics of many stocks in British
Columbia and Alaska have shown a decline which
is apparently a result of declining food availability.
Plankton availability is most probably driven by
changing environmental conditions that have at
least recently not been favourable for herring
growth in British Columbia and southern Alaska.
Superimposed on these relationships are the recent
strong ENSO episodes which have negatively
impacted herring growth through the area of their
effect. Overall, there appear to be threshold
effects related to population density, ocean
production and plankton availability, and sea
surface temperature mediated by ENSO that affect
the growth parameters of herring populations
throughout the North Pacific. Future studies
should be directed at defining the thresholds and
their effects on long-term herring production.
56
References
Hare, S.R., and Mantua, N.J. 2000. Empirical
evidence for North Pacific regime shifts in
1977 and 1989. Prog. Oceanography 47: 103-
145.
Spratt, J.D. 1987. Variation in the growth rate of
Pacific herring from San Francisco Bay,
California. Calif. Fish and Game 73: 132-138.
Tesch, F.W. 1988. Age and Growth. In W.E.
Ricker [ed.] Methods of assessment of fish
production in fresh waters’. IBP Handbook
No. 3. Blackwell Scientific Publications,
Oxford, pp. 93-123.
Implications of variation in euphausiid productivity for the growth,
production and resilience of Pacific herring (Clupea pallasi) from the
southwest coast of Vancouver Island
Ron W. Tanasichuk
Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, B.C. Canada. V9R 5K6. E-mail:
tanasichukr@pac.dfo-mpo.gc.ca
This presentation includes the results of a number
of studies which collectively suggest that the
recent order of magnitude reduction in euphausiid
production along the southwest coast of
Vancouver Island depressed the productivity and
resilience of the West Coast Vancouver Island
(WCVI) herring (Clupea pallasi) population.
We have been studying the oceanography of the
southwest coast of Vancouver Island since 1985 to
learn how the ocean affects fish productivity there.
Results of diet analyses show that euphausiids are
the dominant prey of the more abundant pelagic
fish species and that herring feed on them
exclusively. We have also been monitoring the
species and size composition of prey. Tanasichuk
(1999) showed that Pacific hake (Merluccius
productus), the dominant planktivore, selects
larger (>17 mm) euphausiids of one species
(Thysanoessa spinifera) regardless of how
euphausiid biomass varies. WCVI herring select
the same prey. Euphausiid population biology and
productivity along the WCVI have been monitored
since 1991 (Tanasichuk 1998). Figure 38 shows
that herring and hake prey biomass has varied by
an order of magnitude over the last 10 years. The
same degree of prey variation has also occurred
for coho salmon (Oncorhynchus kisutch).
The effect on herring productivity and resilience
appears to operate through influencing growth.
Tanasichuk (1997) examined the effect of
variations in year-class strength and
oceanographic conditions on the size of recruit
herring and the growth rates of adult fish. At that
time, data were available to 1996 only. He
suggested that the 1993 year-class was an outlier
because this year-class was the first to be
subjected to low T. spinifera biomass over its first
three years of life. All subsequent year-classes
have been outliers, over a period when T. spinifera
biomass remained depressed (Fig. 39). This
dataset suggests that the compensatory population-
0
100
200
300
400
0
1000
2000
3000
Year
1991 1992 1993 1994 1995 1996 19981997 1999 2000
>17 mm
9-12 mm
Median T. spinifera biomass (mg dry mass.mg -2 )
Fig. 38 Median biomass (mg dry mass/mg2) of
key prey for Pacific herring and Pacific hake (>17
mm T. spinifera) and coho salmon (9-12 mm T.
spinifera) over the summer feeding period.
57