Salmon Phishing in the Gulf of Alaska an Archaeological Dig in the North Pacific Survey Data (1956-1964)

Salmon pHishing in the Gulf of Alaska An archaeological dig in the North Pacific Survey data (1956-1964)

Skip McKinnell, PICES James C. Christian, Fisheries & Oceans Canada Nancy D. Davis, University of Washington David 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 ?

sockeye humpback coho

chinook chum

Predominantly planktivorous

Pacific salmon (encircled) Aragonite saturation depths

Source: Feely et al. (2004) FRBC North Pacific Survey

Fisheries 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

Salmon growth is density-dependent

Ocean entry First autumn (5 mo.) Maturity (14 mo.)

4 cm 13 cm 45-50 cm Gulf of Alaska salmon diets 1956-1964

Chum Coho

Humpback Sockeye

Data source: Fisheries Research Board of Canada Limacina in salmon diets (1956-1964)

0.15 Humpback Chum •Highest fractions (~15%) of Sockeye Limacina in diets occurred in 0.10 humpback salmon in April, diminishing to 8% by August. •Sockeye & chum salmon diets have little (~1%) Limacina in April, 0.05 increasing (~3%) through the Proportion of food growing season. •Not found in winter sampling

0.00 2 4 6 8 10 Month

Data source: Fisheries Research Board of Canada Seasonal Cycles at Station P

• 1956-64 (640 tows) • Copepods are 100.0 dominant in the plankton 3 10.0 • Pteropod biomass

mg / m peak is 1 mo. earlier 1.0 than copepod peak Pteropoda Copepoda • Pteropod abundance 0.1 1 2 3 4 5 6 7 8 9 10 11 12 persists in surface Month waters

Data source: McKinnell & Mackas 2003 Humpback Salmon diets Northwest Pacific 1950-2000 Chum • Percent pteropods (purple) – Infrequent in sockeye and humpback salmon – >25% of chum salmon diet + increasing trend Sockeye – Limacina eaten when higher quality foods not available

Source: Karpenko (2007) NPAFC Bulletin 4 Dateline (180º) transect salmon diets 1994-1999

2.0 2.0 2.0 Sockeye Sockeye Sockeye Humpback Humpback Humpback 1.5 Chum 1.5 Chum 1.5 Chum Coho Coho Coho

1.0 1.0 1.0

0.5

Cumulative proportion Cumulative 0.5 0.5

Cumulative proportion

0.0 0.0 0.0 Fish Squid Fish Fish Squid Squid CopepodaDecapoda Pteropoda Amphipoda Euphausiid Unidentified CopepodaDecapoda Pteropoda CopepodaDecapoda Pteropoda Amphipoda Euphausiid Unidentified Amphipoda Euphausiid Unidentified 2.0 Prey 2.0 Prey 2.0 Prey Sockeye Sockeye Sockeye Humpback Humpback Humpback 1.5 Chum 1.5 Chum 1.5 Chum Coho Coho Coho

1.0 1.0 1.0

0.5

0.5 0.5 proportion Cumulative

Cumulative proportion Cumulative Cumulative proportion

0.0 0.0 0.0 Fish Fish Fish Squid Squid Squid CopepodaDecapoda Pteropoda CopepodaDecapoda Pteropoda CopepodaDecapoda Pteropoda Amphipoda Euphausiid Unidentified Amphipoda Euphausiid Unidentified Amphipoda Euphausiid Unidentified Prey Data Source: MasahidePrey Kaeriyama, Hokkaido Prey University Prince William Sound

Juvenile humpback salmon Prince William Sound hatcheries

50 8-9%

• Pink salmon grew faster in 40 2002, 2004 3% • Marine survival higher for 30 releases in 2002, 2004 than in 2001, 2003

WEIGHT 20 • Diets in August in 2002, 2004 YEAR had greater fractions of 2001 (pteropods+Oikopleura) 10 2002 • But diets in 2001 had high 2003 2004 fractions of pteropods but low 0 survival (next slide) 6 7 8 9 10 MONTH

Data source: Cross et al. 2008 Gulf of Alaska Shelf Juvenile humpback salmon diets 1999-04

Interannual Diet Comparison: August GAK 1-6 n=36 n=28 n=80 n=52 n=82 n=50 100%

Other* 80% Insects Fish 60% Larvaceans Pteropods (Limacina) Crab/Shrimp 40% Hyperiid Amphipods Diet as %Prey WT Euphausiids 20% Large Copepods Small Copepods 0% 1999 2000 2001 2002 2003 2004 Year

Source: US GLOBEC Present Day Commercial Catch

1100 1000 900 800 700 600

Tonnes (x (x Tonnes 1000) 500 Data: 400 NPAFC 300 1955 1965 1975 1985 1995 2005 2015 Year Summary

1. 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