Comparing walleye pollock dynamics across the Bering Sea and adjacent areas

Comparing walleye pollock dynamics across the Bering Sea and adjacent areas Franz J. Mueter 1, Mikhail A. Stepanenko 2 Anatoly V. Smirnov 2, and Orio Yamamura 3 1 School of Fisheries and Ocean Sciences, Juneau Center, University of Alaska Fairbanks, USA, fmueter@alaska.edu 2 Pacific Research Institute of Fisheries and Oceanography (TINRO- Center), Vladivostok, Russia 3 Hokkaido National Fisheries Research Institute, Kushiro, Japan

Goal Review of stock structure and recruitment dynamics of walleye pollock in North Pacific Comparisons across systems Major drivers Resilience

The Bering Sea Russia Karaginsky Bay Cape Navarin Olyutorsky Bay Anadyr Bay Russia U.S. Alaska < 50 m 50-100 m 100-200 m Aleutian Basin Base map from Aydin et al. (2002)

Other walleye pollock stocks Japan Sea Sea of Okhotsk Japan Pacific stock Bering Sea Gulf of Alaska BEST/BSIERP region

EBS pollock recruitment dynamics Warm year, no ice (2004) Summer SST as proxy for feeding conditions Small zooplankton species (Lack of large Calanus) Low %fat High predation Poor survival High % fat Good survival Large zooplankton (Calanus) Based on Hunt et al. (2011) Cold year, late ice (2008) Feb Apr Jun Aug Oct Dec (Profiles: Phyllis Stabeno, PMEL, NOAA) Feb Apr Jun Aug Oct

Recruitment & late summer SST SST (Jul-Sep) 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 log(recruitment) 8 9 10 11 Recruitment estimates From Ianelli et al (2009) 8.0 8.5 9.0 9.5 10.0 Summer SST

Projecting pollock dynamics 1. SST projections, downscaled to Eastern Bering Sea, 2010-2050 SST ( o C) 2010 2020 2030 2040 2050 2. Cannibalism / Predation Probability density 0e+00 3e-05 5e-05 Projected recruits 2040-50 "Observed" recruits 1977-2008 0 10000 30000 50000 70000 Recruitment

Projecting pollock dynamics 1. SST projections, downscaled to Eastern Bering Sea, 2010-2050 SST ( o C) 2010 2020 2030 2040 2050 2. Cannibalism / Predation Probability density 0.0000 0.0006 0.0012 Spawning biomass Projected 2040-50 1000 2000 3000 4000 Spawning biomass Observed 1980-2008

Cautions Proposed mechanism reflects processes in middle domain of southeastern shelf Recently, observations of large concentrations of age-0 pollock in deeper slope waters during cold years, rather than over the shelf (see Parker-Stetter et al. presentation) Change in spawning distribution or transport? Large concentrations of age-0 larvae & juveniles on northwestern Bering Sea shelf during warm years Possible losses due to emigration into northern Bering Sea

Distribution of age-0 pollock in late summer, 2004/2005 Moss et al. 2009

2004/2005 year classes 2007 estimated biomass from Echo-integration trawl survey Age composition of catch in Russian fall fishery % 40 2005 2007 30 20 10 Pink: < 30 cm Blue: > 30 cm Moss et al. 2009 % 40 30 20 10 1 2 3 4 5 6 7 8 9 10 2005 2004 2008 From Honkalehto et al (2008) 1 2 3 4 5 6 7 8 9 10 Total catch ~ 590,000 t in both 2007 & 2008

Navarin region vs. EBS Navarin region Survey biomass & VPA model fit 900 800 700 600 500 400 300 200 100 0 3500 3000 2500 2000 1500 1000 500 0 Navarin (Russia) 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Survey biomass (1000 t) Biomass (1,000 t) 14000 12000 10000 8000 6000 4000 2000 Eastern Bering Sea (U.S.) 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Biomass (1,000 t) Eastern Bering Sea Model estimates (Ianelli et al. 2010)

Other Bering Sea stocks Bogoslof / Aleutian Basin Aleutian Islands Western Bering Sea

Bogoslof Survey biomass (1,000 t) 3000 2500 2000 1500 1000 500 0 Bogoslof Total Biomass (acoustic survey) Bogoslof Survey area

Bogoslof Survey biomass (1,000 t) 3000 2500 2000 1500 1000 500 Ianelli et al 2006 Bogoslof Total Biomass (acoustic survey) Recruitment dynamics Sustained by large year classes originating in late 1970s / early 1980s Incoming year classes coincide with large year classes in EBS Strong connection to EBS stock 0 Bogoslof Survey area

Aleutian Islands 2000 1800 1600 1400 1200 1000 800 600 400 200 0 200 miles 1600 1400 1200 1000 800 600 400 200 0 St. Paul 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009 Recruitment (millions) Survey biomass (1,000 t) Estimates from Barbeaux et al. (2010) Recruits Biomass

Aleutian Islands Recruitment Dynamics Dynamics dominated by 1978 year class Several moderate year classes since then, some of which coincide with strong year-classes in EBS Modeled drift patterns suggest that advective losses may be high (importance of retention areas?) Observed & modeled drifters suggest that larvae can drift onto EBS shelf St. Paul 200 miles

Western Bering Sea VPA model estimates Biomass Biomass (tons) Abundance Abundance (1000s) Heavy fishing led to drastic decline in early 1990s Fishery closed 2002-06 Rapid response in biomass

Western Bering Sea Recruitment Dynamics Very high macro-zooplankton biomass (> 3.5 mm): 834 1848 mg/m 3 (Volkov 2008) No evidence of reduced food intake even at lowest observed zooplankton abundances (Shuntov et al 2007) Cannibalism lower than EBS (separation of juveniles & adults)

Other regions Gulf of Alaska Sea of Okhotsk Northern Japan Sea Pacific Coast of Japan

Gulf of Alaska Recruitment Dynamics Important role of advection to suitable nursery areas Switch from bottom-up control to top-down control (arrowtooth fl.) Some strong year classes shared with adjacent regions 4000 3500 3000 2500 2000 1500 1000 500 0 4500 4000 3500 3000 2500 2000 1500 1000 500 0 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 2008 Recruitment (millions) Recruits Estimates from Dorn et al. (2010) Biomass Biomass (1,000 t)

Sea of Okhotsk Spawning locations Kamchatka Recruitment trends Strong 1978/79 year classes Strong recruitment in 80s, low in 90s Kurils Moderately strong: 2000, '02, '04, '05 Survey Spawning biomass (W. Kamchatka) Stock synthesis estimates VPA estimates

Sea of Okhotsk Recruitment Dynamics Highest juvenile survival in years with: High abundance of zooplankton (especially copepods) Strong northward advection of (warm) Pacific waters Strong year classes during both warm and cold years!

Northern Japan Sea After Funamoto (2011) Sea of Okhotsk Funamoto (2011) Hokkaido Island

After Funamoto (2011) Northern Japan Sea Funamoto (2011) Hokkaido Island Effect on recruitment Recruitment dynamics Advective losses to Sea of Okhotsk Reduced survival at high SST

Japan Pacific stock Recruitment (millions) 6000 1600 5000 1400 1200 4000 1000 3000 800 2000 600 400 1000 200 0 0 See Orio Yamamura's (S6) presentation tomorrow 11:30am 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 Biomass (1,000 t) Recruitment Dynamics Important role of advection (egg/larval transport into Funka Bay) Heavy cannibalism & predation by Kamchatka flounder & Pacific cod

Recruitment series Spearman rank correlations EBS Bogoslof Aleutian Islands Gulf of Alaska Japan - Pacific EBS Bogoslof 0.480 P < 0.05 AI 0.310 0.680 GoA 0.240 0.490 0.540 Japan - Pacific -0.010 0.210 0.350 0.270

Recruitment-based clustering Bogoslof Aleutians Similarity Japan-Pacific EBS GoA

Summary Stock Eastern Bering Sea Bogoslof / Basin Aleutian Islands Western Bering Sea Gulf of Alaska Sea of Okhotsk N. Japan Sea Japan Pacific Bottom-up controls Temp.-mediated prey availability Top-down controls Predation strong in warm years Resilience Moderate? (immigration)? Low (retention?)? Moderate? Strong High Advection Strong Moderate Advection Prey availability Advection SST Advection Weak Weak Strong (Cannib + predation) High Low Moderate Outlook (short / long)?????

Summary Stock Eastern Bering Sea Bogoslof / Basin Aleutian Islands Western Bering Sea Gulf of Alaska Sea of Okhotsk N. Japan Sea Japan Pacific Bottom-up controls Temp.-mediated prey availability Top-down controls Predation strong in warm years Resilience Moderate? (immigration)? Low (retention?)? Moderate? Strong High Advection Strong Moderate Advection Prey availability Advection SST Advection Weak Weak Strong (Cannib + predation) High Low Moderate Outlook (short / long)?????

Conclusions Walleye pollock in the North Pacific form a number of loosely connected meta-populations (e.g. Bailey et al 1989) Strong year classes typically every 4-6 years Synchronous strong recruitment through much of North Pacific in the late 1970s (1978) Little evidence of basin-wide synchrony since then Moderate to strong synchrony within NE Pacific Pattern of declining strength of large year classes Largest populations in areas with broad shelf and moderate currents Eastern Bering Sea & Sea of Okhotsk

Conclusions (cont'd) Advective processes critical to recruitment success in most regions Retention / Transport to suitable nursery areas Evidence of prey limitation (low copepod abundances) in some years Eastern Bering Sea & Sea of Okhotsk Strong potential for top-down limitation e.g. Gulf of Alaska, Japan and possibly others Recent warming associated with reduced recruitment in several regions Japan Sea, Eastern Bering Sea

Proposed hypothesis Major perturbation of the 1976/77 regime shift allowed an "outburst" of walleye pollock throughout the North Pacific following one or several "super-abundant" year classes As communities adapted to the new regime, pollock have been subjected to more efficient predation and the magnitude of subsequent recruitment peaks has diminished over time and may continue to diminish in some systems

Acknowlegements Funding: North Pacific Research Board BEST/BSIERP investigators