Linkages between climate, growth, competition at sea, and production of sockeye salmon populations in Bristol Bay,
Alaska, 1955-2000
J. Nielsen (USGS) & G. Ruggerone (NRC)
North Pacific Ocean – a Highly Productive Ecosystem2002 U.S. North Pacific exvessel harvest value = $1.13 billion
Pacific Rim Salmon Runs, 1951-2001
0
200
400
600
800
Salm
on
ru
n (
million
s)
50 60 70 80 90 100
Year
Coho
ChinookChum
SockeyePink
Climate Change and North Pacific Salmonid Species Abundance Shifts
-4
-3
-2
-1
0
1
2
3
PD
O I
nd
ex
51 56 61 66 71 76 81 86 91 96 01
Year
1997/98El Nino
1976/77Oceanregimeshift
Regime Shift Impacts on Marine PopulationsCompiled by D. L. Alverson (NRC)
Eastern North Pacific Winter Sea Surface Temperature
-3
-2
-1
0
1
2
No
rmali
zed
SS
T(
Z)
65 70 75 80 85 90 95 00
Year
Oceanregimeshift
Bristol Bay Sockeye Salmon Run, 1951-2002
0
20
40
60
80
So
ckeye r
un
(m
illi
on
s)
51 56 61 66 71 76 81 86 91 96 01
Year
1997/98El Nino
1976/77Oceanregimeshift
Key Question
What biological and physical climatic feedback mechanisms have influenced
historic and current abundance patterns in Bristol Bay sockeye salmon?
New Use for an Old Tool: Salmon Scales
Focus
FW1
FW2
FWPL
SW1
SW2
SWPL
Salmon Size Related to Scale Radius
100
200
300
400
500
600
Scale
rad
ius (
µ)
30 40 50 60 70 80 90 100 110
Sockeye length (mm)
r2 = 0.96
Davis et al. 1990; Zimmerman 1991
Sockeye salmon growth using salmon scale annuli & circuli measurements
Ocean Carrying Capacity Hypotheses Greater salmon abundance is related to greater early marine growth
in coastal waters.
Greater salmon abundance is associated with reduced growth during older life stages (density-dependence).
Competition during freshwater & marine life-stages can reduce growth and survival.
Highly migratory salmon may compete with conspecifics
originating from distant natal rivers.
Peterman 1984; Ishida et al 1993; Rogers & Ruggerone 1993; Welch & Parsons 1993; McKinnell 1995; Pyper & Peterman 1999; Pearcy et al. 1999
Kvichak Sockeye Growth During First Two Years at Sea
-2
-1
0
1
2
Norm
alize
d g
row
th (
Z)
52 57 62 67 72 77 82 87 92 97
Year at sea
Climate shift
Salmon Abundance Linked to Early Ocean Growth, 1955-2000
0
20
40
60
80
Weste
rn A
K s
ockeye (
million
s)
1.4 1.5 1.6 1.7 1.8 1.9
Kvichak SW1&2 scale growth (mm)
Kvichak Sockeye Growth During Third Year at Sea:Density-dependent
-2
-1
0
1
2
3
Norm
alize
d g
row
th (
Z)
52 56 60 64 68 72 76 80 84 88 92 96
Year at sea
Climate shift
• Asian pink salmon are highly abundant during odd numbered years.
• Bristol Bay sockeye salmon overlap with Asian pink salmon during their 2nd and 3rd years at sea.
• Pink and sockeye salmon have similar diets on high seas.
• Food consumption of both species declines in odd yrs.
• Sockeye diet changes more than pink diet in odd-yrs.
• Few wild or hatchery pink salmon originate from Bristol Bay.
Facts Supporting Competition Hypothesis
Eastern Kamchatka Pink Salmon Runs, 1957-2002
0
25
50
75
100
Ru
n (
million
s)
57 61 65 69 73 77 81 85 89 93 97 01
Year
Hatchery Pink Salmon Release
0
500
1000
1500
Pin
k sa
lmon r
ele
ase
(m
illio
ns)
50 60 70 80 90
Release year
Overlap of Asian pink & Bristol Bay Sockeye salmon
Sockeye growth reduced during odd years at sea (2nd & 3rd yrs)
-3
-2
-1
0
1
2
3
Norm
alize
d g
row
th (
Z)
53 57 61 65 69 73 77 81 85 89 93 97
Year at sea
Even-numbered year
Odd-numbered year3rd year at seamean = 612 ± 54 µ
Asian Pink Salmon Affect Adult Sockeye Length, 1958-2000
540
550
560
570S
ock
eye l
en
gth
(m
m)
0 20 40 60 80
Bristol Bay sockeye run (millions)
1977-2000
1958-1976
540
550
560
570
So
ckeye l
en
gth
(m
m)
0 50 100 150 200 250 300 350
Asian Pink salmon run (millions)
Smolt to Adult Survival, 1977-1997
-45% -26%
0
5
10
15
20
25S
urv
ival at
sea (
%)
Age 1. Age 2.
Freshwater age
Odd 2ndyr
Even 2ndyr
Even 2nd yr
Odd 2ndyr
59 Million Fewer Sockeye, 1977-1997(>$310 million)
0
3
6
9
12
Ad
ult
sockeye s
alm
on
(m
illion
s)
Egegik Naknek Ugashik Nushagak
Sockeye stock
Even 2nd yr
Odd 2nd yr
Implications of Feedback between Global Change & Competition Effect on Salmon Survival
• Climate feedback processes can impact salmon production on multiple scales.
• Climate change influence on local production of salmon may have unintended impacts on distant stocks.
• Natural and anthropogenic fluctuations in salmon production and shifts in food web dynamics may impact ESA protected salmon species throughout the North Pacific Ocean.
• These findings provide evidence of the need for “salmonid ecosystem management” looking at both freshwater and marine feedback patterns in salmon.
Acknowledgements: E. Farley, P. Hagen, B. Agler,J. Meka, D. Rogers, K. Myers, S. Ignell, M. Zimmerman