A Critical Review of the A Critical Review of the “Regime Shift-Junk Food” “Regime Shift-Junk Food”

Hypothesis for the Steller Sea Hypothesis for the Steller Sea Lion DeclineLion Decline

Lowell Fritz and Sarah HinckleyLowell Fritz and Sarah Hinckley

Alaska Fisheries Science CenterAlaska Fisheries Science Center

National Marine Fisheries ServiceNational Marine Fisheries Service

Regime Shift/Junk Food Regime Shift/Junk Food HypothesisHypothesis• 1976/77 regime shift changed the fish 1976/77 regime shift changed the fish

community of the North Pacific Ocean community of the North Pacific Ocean from one “dominated” by clupeids-from one “dominated” by clupeids-osmerids to gadid-flatfishosmerids to gadid-flatfish

• Sea lions ate more gadid and less Sea lions ate more gadid and less clupeids-osmerids after the regime shiftclupeids-osmerids after the regime shift

• Gadids are low quality food (“junk”)Gadids are low quality food (“junk”)

• Sea lion vital rates (survival, fecundity) Sea lion vital rates (survival, fecundity) were reducedwere reduced

Things that should have been Things that should have been observedobserved(if this hypothesis is true)(if this hypothesis is true)

• Within the Fish Community:Within the Fish Community:– Gadids low before the late ‘70s and high sinceGadids low before the late ‘70s and high since– Clupeids and Osmerids (C&O) high before the late ‘70s Clupeids and Osmerids (C&O) high before the late ‘70s

and low sinceand low since

• In Steller Sea Lion Food HabitsIn Steller Sea Lion Food Habits– Less gadid consumption prior to the late 1970sLess gadid consumption prior to the late 1970s– More C&O consumption after the late 1970sMore C&O consumption after the late 1970s

• Negative consequences to sea lions/otariids when Negative consequences to sea lions/otariids when they eat a lot of gadids they eat a lot of gadids

Central and Western

Alaska

020406080

100120140160180

1970 1980 1990 2000

Thousands

0

2

4

6

8

10

12

14

16

1970 1980 1990 2000

Thousands

SE AK

BC

OR & CA

Western Stock Eastern Stock

Non-Pup Index

Steller Sea Lion Rookeries, Stock Structure and Population Trends

Eastern Bering Sea Pollock Catch Eastern Bering Sea Pollock Catch and the Regimesand the Regimes

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96

Year

Pollock Catch (millions of mt)

Aleutians

EBS Shelf

Regime 2Regime 1 Regime 3

EBS Pollock Recruitment 1964-EBS Pollock Recruitment 1964-19981998

0%

20%

40%

60%

1964-76 1977-88 1989-98

Freq. of Large YC

0%

10%

20%

30%

40%

1964-76 1977-88 1989-98

Freq. of Small YC

GOA Pollock Recruitment 1968-GOA Pollock Recruitment 1968-20002000

0%

20%

40%

60%

1968-76 1977-88 1989-00

Freq. of Large YC

0%

10%

20%

30%

40%

1968-76 1977-88 1989-00

Freq. of Small YC

EBS Pacific codEBS Pacific cod

0

500

1000

1500

2000

2500

3000

1950 1960 1970 1980 1990 2000 2010

Surveys

Stock Assessment 2001

Possible Scenario (Bakkala 1993)

Regime 1 Regime 2 Regime 3

HerringHerring

Eastern Bering Sea HerringEastern Bering Sea Herring

-5

-4

-3

-2

-1

0

1

2

3

1969 1972 1975 1978 1981 1984 1987 1990 1993

Norton Sound

Togiak

Warm RegimeCold Regime

Residuals from ln-transformed mean recruitment; Williams and Quinn 2000

EBS Pollock and Herring Age 3+ EBS Pollock and Herring Age 3+ BiomassBiomass

0

2000

4000

6000

8000

10000

12000

14000

16000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

1997 Pollock Assessment2002 Pollock AssessmentPacific herring

1,000s of mt; Wespestad 1991, 1997; Ianelli et al. 2002

Gulf of Alaska Herring Gulf of Alaska Herring StocksStocks

-5

-4

-3

-2

-1

0

1

2

3

1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990

Kamishak/Kodiak

Prince William Sound

Warm RegimeCool RegimeWarm Regime

Residuals from ln-transformed mean recruitment; Williams and Quinn 2000

Historical Historical PerspectivePerspective• Alexander, A. B. Seal Schooner Observations. 1894-95

• David Starr Jordan, L. Stejneger, et al. 1896, 1898.Pollock and codPollock and cod were were plentifulplentiful and formed “by far” the and formed “by far” the most importantmost important part of part of

the fur seals and sea lions diet.the fur seals and sea lions diet.

• Jordan, D.S. and B.W. Evermann 1902.““Alaskan Alaskan pollock … ispollock … is excessively abundantexcessively abundant throughout the Bering Sea, swimming throughout the Bering Sea, swimming near the surface and furnishing the great part of the food of the fur seal. It near the surface and furnishing the great part of the food of the fur seal. It reaches a length of 3 feet and is doubtless a good food-fish.”reaches a length of 3 feet and is doubtless a good food-fish.”

• Kenyon and Wilke 1952 “ “Evidence from the food remains on the Pribilof rookeries is that fur seals Evidence from the food remains on the Pribilof rookeries is that fur seals

depend to a large degree on the…family Gadidaedepend to a large degree on the…family Gadidae during their stay in the during their stay in the Bering Sea.”Bering Sea.”

• Fiscus, Baines and Wilke 1962““Theragra, Mallotus and squidTheragra, Mallotus and squid have consistently been the have consistently been the principal foodprincipal food of seals of seals

in the Bering Sea” since observations began in the 19in the Bering Sea” since observations began in the 19thth century (N=thousands) century (N=thousands)

Steller sea lion food habits: Steller sea lion food habits: Western Stock Pre vs Post Regime Western Stock Pre vs Post Regime

ShiftShift

1946-75 1976-79 1980s 1990s winter 1990s summerCephalopods Capelin Herring Atka mackerel Atka mackerelGreenlings Cephalopods Octopus Pacific cod Cephalopods

Pollock Pollock Pacific cod Pollock HerringRockfish Rockfish Pollock Salmon Pollock

Sand Lance Sand lance Squid Sculpins SalmonSmelts Unid fish

# Studies 6 2 5 1 1Samples Stomachs Stomachs Stomachs Scat ScatAge/Sex Many adult males Mixed Mixed Mixed Mixed

Principal Prey (alphabetical order)

0

0.5

1

1.5

2

2.5

3

3.5

PollockHerringCapelin

Atka Mackerel

EulachonSand LanceP. Sandfish

SquidP. CodP. HakeO. mordax

FlatfishSalmon

kcal/g (wet weight)

sRange in Energy Density of Various

Fish eaten by Steller sea lions

Seasonality of CollectionSeasonality of Collection

• Energy density directly affected by reproductive Energy density directly affected by reproductive cyclecycle

• Most species have lowest energy density Most species have lowest energy density immediately after spawningimmediately after spawning

• Energy content increases during the summer feeding Energy content increases during the summer feeding season, stored as lipid either in liver (pollock) or flesh season, stored as lipid either in liver (pollock) or flesh (herring)(herring)

• As gonads develop, energy transferred from As gonads develop, energy transferred from liver/flesh to gonadsliver/flesh to gonads

• Energy lost at spawningEnergy lost at spawning

Range in Energy DensityRange in Energy Density

Captive feeding studies – Captive feeding studies – what do they show?what do they show?

• Single species diets not naturalSingle species diets not natural

• Short durationShort duration

• Many sources of variation not controlled forMany sources of variation not controlled for

(age, season, reproductive status, etc)(age, season, reproductive status, etc)

• Control of appetite in captive animals not simpleControl of appetite in captive animals not simple

(Issues of palatibility, acclimation, feeding (Issues of palatibility, acclimation, feeding rhythms, manner of presentation of food, training)rhythms, manner of presentation of food, training)

• Byproducts of improper storage (e.g. Byproducts of improper storage (e.g. formaldehyde) may be present in fish – cause of formaldehyde) may be present in fish – cause of “gadoid anemia”“gadoid anemia”

Other pinnipeds and gadidsOther pinnipeds and gadids

Species Gadid % FO Pop. Status

CA Sea LionCA Sea Lion 28-98% 28-98% IncreasingIncreasing

StellersStellers

SE AKSE AK 55-90% 55-90% IncreasingIncreasing

Pac NWPac NW 62-100% 62-100% IncreasingIncreasing

Harbor sealsHarbor seals

NW AtlanticNW Atlantic 71% 71% IncreasingIncreasing

Brit. ColumbiaBrit. Columbia 62% 62% IncreasingIncreasing

FO = Frequency of occurrence in scat or spewing samples

ConclusionsConclusions• Gadids and herring had peaks in abundance both before Gadids and herring had peaks in abundance both before

and after 1976-77 regime shiftand after 1976-77 regime shift

• Data are insufficient to conclude that Steller sea lion diets Data are insufficient to conclude that Steller sea lion diets have changed significantlyhave changed significantly

• No single species is “junk” because of No single species is “junk” because of seasonal/ontogenetic variation and need for “balanced seasonal/ontogenetic variation and need for “balanced diet” diet”

• Gadids are common in the diets of pinniped populations Gadids are common in the diets of pinniped populations around the world, many of which are increasingaround the world, many of which are increasing