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