Salmon pHishing in the Gulf of AlaskaAn archaeological dig in the North Pacific Survey data
(1956-1964)
Skip McKinnell, PICESJames C. Christian, Fisheries & Oceans Canada
Nancy D. Davis, University of WashingtonDavid L. Mackas, Fisheries & Oceans Canada
Motivation• Pacific humans eat Pacific salmon.
• Pacific salmon eat shelled pteropods.
• Measurable CO2 increases are causing measurable pH declines in the North Pacific.
• Pteropod shells dissolve in low pH water.
• So what ?
chum
humpbacksockeye
coho
chinook
Pacific salmon (encircled)Predominantly planktivorous
Aragonite saturation depths
Source: Feely et al. (2004)
FRBC North Pacific SurveyFisheries Research Board of Canada (1956-1964)• Deployed 4 ocean-going salmon fishing vessels
– Salmon age, sex, length, weight (n≈2000 per year)– Zooplankton (vertical net tows from 150m to surface)– Sea surface temperature and salinity
• >10 000 salmon stomachs examined for prey types.• One naval vessel geared for oceanography.
– Bottle casts– Bathythermograph traces– pH measured in fall/winter of 1956/57– Nutrients– Plankton
• Before 2-3 billion salmon (annually) released from hatcheries.
Humpback salmon – growth at sea
Ocean entry
4 cm
Maturity (14 mo.)
45-50 cm
First autumn (5 mo.)
13 cm
Salmon growth is density-dependent
Gulf of Alaskasalmon diets 1956-1964
Chum Coho
Humpback Sockeye
Data source: Fisheries Research Board of Canada
Limacina in salmon diets (1956-1964)
2 4 6 8 10Month
0.00
0.05
0.10
0.15
Pro
po
rtio
n o
f fo
od
SockeyeChumHumpback
•Highest fractions (~15%) of Limacina in diets occurred in humpback salmon in April, diminishing to 8% by August.
•Sockeye & chum salmon diets have little (~1%) Limacina in April, increasing (~3%) through the growing season.
•Not found in winter sampling
Data source: Fisheries Research Board of Canada
Seasonal Cycles at Station P
• 1956-64 (640 tows)• Copepods are
dominant in the plankton
• Pteropod biomass peak is 1 mo. earlier than copepod peak
• Pteropod abundance persists in surface waters
1 2 3 4 5 6 7 8 9 10 11 12Month
0.1
1.0
10.0
100.0
mg
/ m3
CopepodaPteropoda
Data source: McKinnell & Mackas 2003
Salmon dietsNorthwest Pacific
1950-2000
• Percent pteropods (purple)– Infrequent in sockeye and
humpback salmon– >25% of chum salmon diet +
increasing trend– Limacina eaten when higher
quality foods not available
Source: Karpenko (2007) NPAFC Bulletin 4
Humpback
Chum
Sockeye
Dateline (180º) transectsalmon diets 1994-1999
Data Source: Masahide Kaeriyama, Hokkaido University
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Amphipoda
Copepoda
Decapoda
Euphausiid Fish
PteropodaSquid
Unidentified
Prey
0.0
0.5
1.0
1.5
2.0
Cum
ulat
ive
prop
ortio
n CohoChumHumpbackSockeye
Prince William Sound
Juvenile humpback salmon Prince William Sound hatcheries
• Pink salmon grew faster in 2002, 2004
• Marine survival higher for releases in 2002, 2004 than in 2001, 2003
• Diets in August in 2002, 2004 had greater fractions of (pteropods+Oikopleura)
• But diets in 2001 had high fractions of pteropods but low survival (next slide) 6 7 8 9 10
MONTH
0
10
20
30
40
50
WEI
GH
T
2004200320022001
YEAR
Data source: Cross et al. 2008
8-9%
3%
Gulf of Alaska ShelfJuvenile humpback salmon diets 1999-04
Interannual Diet Comparison: August GAK 1-6
0%
20%
40%
60%
80%
100%
1999 2000 2001 2002 2003 2004
Year
Die
t as
%P
rey
WT
Other*
Insects
Fish
Larvaceans
Pteropods (Limacina)
Crab/Shrimp
Hyperiid Amphipods
Euphausiids
Large Copepods
Small Copepods
n=36 n=28 n=80 n=52 n=82 n=50
Source: US GLOBEC
1955 1965 1975 1985 1995 2005 2015
Year
300
400
500
600
700
800
900
1000
1100
Ton
ne
s (
x 1
00
0)
Present Day Commercial Catch
Data: NPAFC
Summary1. Pacific salmon and pteropods share ocean
habitats that are among the most threatened by ocean acidification.
2. They have lived together in this habitat for millennia
3. Pacific salmon, augmented by hatchery releases, are currently very abundant.
4. The exception is the California Current upwelling system, but here salmon survival is worse when upwelling is diminished.
Review of ideas and data• In general, the pelagic Pacific salmon have varied diets.• The presence of pteropods (primarily Limacina) in their diet varies
• among species• by life history (developmental) stage of salmon• by season and by year• by region
• Chum salmon in the NW Pacific have >25% Limacina in their diets and the trend was increasing over 5 decades.
• Limacina and Oikopleura are said to be critical to growth and survival of juvenile humpback salmon in Prince William Sound
• Humpback salmon generally eat what their environment provides, but occasionally not; in the Gulf of Alaska pteropods formed 15% of the diets in April during the late 1950s and 1960s.
• At this point in history, the abundance of hatchery-reared salmon has had a greater effect on Limacina abundance than OA.
“Salmon is of vital importance to the Indians; we need only cut them off from their salmon fisheries to have them completely at our mercy.” John Keast Lord (1866)
This 150 year old opinion reflects the importance of Pacific salmon to Pacific culture and should form at least part of the basis for concern about the effects of an increasingly acidic ocean. Neglect is unacceptable.
What to do? Multi-national science program on NPacOA
• Coastal/shelf and basin components where the basin component has a sampling frequency greater than once/century.
• Improve technology for monitoring oceanic carbonate system.• Improve knowledge of life histories and ecological roles of the
key players in the OA issue.• When and where do corrosive waters create corroded pteropods?• Genomics component.
• Extend/focus salmon diet studies on OA issue• Trophodynamic models embedded in carbonate-parameterised
global ocean/atmosphere models.• Communication – OA as a “sleeper issue” of global change
• pH is a scientific scale; use a metric and language that resonates with the public
• Ecological Dow-Jones
Pteropod abundance in BC• Coastal pteropod
abundance varies logarithmically from year to year
• Lowest observed values in ~30 years occurred in 2007
Source: D.L. Mackas, Institute of Ocean Sciences
