A Critical Review of the “Regime Shift-Junk Food” Hypothesis for the Steller Sea Lion Decline Lowell Fritz and Sarah Hinckley Alaska Fisheries Science Center National Marine Fisheries Service

Regime Shift/Junk Food Hypothesis 1976/77 regime shift changed the fish community of the North Pacific Ocean from one “dominated” by clupeids-osmerids to gadid- flatfish 1976/77 regime shift changed the fish community of the North Pacific Ocean from one “dominated” by clupeids-osmerids to gadid- flatfish Sea lions ate more gadid and less clupeids- osmerids after the regime shift Sea lions ate more gadid and less clupeids- osmerids after the regime shift Gadids are low quality food (“junk”) Gadids are low quality food (“junk”) Sea lion vital rates (survival, fecundity) were reduced Sea lion vital rates (survival, fecundity) were reduced

Things that should have been observed (if this hypothesis is true) Within the Fish Community: Within the Fish Community: –Gadids low before the late ‘70s and high since –Clupeids and Osmerids (C&O) high before the late ‘70s and low since In Steller Sea Lion Food Habits In Steller Sea Lion Food Habits –Less gadid consumption prior to the late 1970s –More C&O consumption after the late 1970s Negative consequences to sea lions/otariids when they eat a lot of gadids Negative consequences to sea lions/otariids when they eat a lot of gadids

Western StockEastern Stock Non-Pup Index Steller Sea Lion Rookeries, Stock Structure and Population Trends

Eastern Bering Sea Pollock Catch and the Regimes

EBS Pollock Recruitment

GOA Pollock Recruitment

EBS Pacific cod

Herring

Eastern Bering Sea Herring Residuals from ln-transformed mean recruitment; Williams and Quinn 2000

EBS Pollock and Herring Age 3+ Biomass 1,000s of mt; Wespestad 1991, 1997; Ianelli et al. 2002

Gulf of Alaska Herring Stocks Residuals from ln-transformed mean recruitment; Williams and Quinn 2000

Historical Perspective Alexander, A. B. Seal Schooner Observations David Starr Jordan, L. Stejneger, et al. 1896, Pollock and cod were plentiful and formed “by far” the most important part of the fur seals and sea lions diet. Jordan, D.S. and B.W. Evermann “Alaskan pollock … is excessively abundant throughout the Bering Sea, swimming 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.” Kenyon and Wilke 1952 “Evidence from the food remains on the Pribilof rookeries is that fur seals depend to a large degree on the…family Gadidae during their stay in the Bering Sea.” “Evidence from the food remains on the Pribilof rookeries is that fur seals depend to a large degree on the…family Gadidae during their stay in the Bering Sea.” Fiscus, Baines and Wilke 1962 “Theragra, Mallotus and squid have consistently been the principal food of seals in the Bering Sea” since observations began in the 19 th century (N=thousands)

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

s Range in Energy Density of Various Fish eaten by Steller sea lions

Seasonality of Collection Energy density directly affected by reproductive cycle Energy density directly affected by reproductive cycle Most species have lowest energy density immediately after spawning Most species have lowest energy density immediately after spawning Energy content increases during the summer feeding season, stored as lipid either in liver (pollock) or flesh (herring) Energy content increases during the summer feeding season, stored as lipid either in liver (pollock) or flesh (herring) As gonads develop, energy transferred from liver/flesh to gonads As gonads develop, energy transferred from liver/flesh to gonads Energy lost at spawning Energy lost at spawning

Range in Energy Density

Captive feeding studies – what do they show? Single species diets not natural Single species diets not natural Short duration Short duration Many sources of variation not controlled for Many sources of variation not controlled for (age, season, reproductive status, etc) (age, season, reproductive status, etc) Control of appetite in captive animals not simple Control of appetite in captive animals not simple (Issues of palatibility, acclimation, feeding rhythms, manner of presentation of food, training) Byproducts of improper storage (e.g. formaldehyde) may be present in fish – cause of “gadoid anemia” Byproducts of improper storage (e.g. formaldehyde) may be present in fish – cause of “gadoid anemia”

Other pinnipeds and gadids SpeciesGadid % FOPop. Status CA Sea Lion 28-98% Increasing Stellers SE AK 55-90% Increasing Pac NW % Increasing Harbor seals NW Atlantic 71% Increasing Brit. Columbia 62% Increasing Brit. Columbia 62% Increasing FO = Frequency of occurrence in scat or spewing samples

Conclusions Gadids and herring had peaks in abundance both before and after regime shift Gadids and herring had peaks in abundance both before and after regime shift Data are insufficient to conclude that Steller sea lion diets have changed significantly Data are insufficient to conclude that Steller sea lion diets have changed significantly No single species is “junk” because of seasonal/ontogenetic variation and need for “balanced diet” No single species is “junk” because of seasonal/ontogenetic variation and need for “balanced diet” Gadids are common in the diets of pinniped populations around the world, many of which are increasing Gadids are common in the diets of pinniped populations around the world, many of which are increasing