Growth & Survival of Salmon at Sea in Response to Competition & Climate Change Greg Ruggerone (NRC), Jennifer Nielsen (USGS), Bev Agler (ADFG) Funding: USGS Global Change Program Moore Foundation AYK SSI
Does competition in the Ocean occur among or between salmon species? Growth? Survival? Few survival studies; complicated because high abundance infers high survival; difficult to conduct experiment. Google Earth
Hatchery Premise: No Competition 5 billion per year Asia & NA releases into ocean Updated from Mahnken et al. 1998
Wild v. Hatchery Chum Abundance: Competition? Wild pink and sockeye salmon increased after mid-1970s Why not wild chum salmon?
Competition Controversy Shuntov, Laevastu studies: Many prey in ocean Salmon consume <2% of prey eaten by all nekton All nekton consume <10% of total prey production Salmon do not shoal beyond coastal waters Competition not likely important Correlation & modeling growth studies Multiple species & regions suggest competition Density-dependent growth (adults & juveniles) Few survival studies Effects of reduced size on future production?
Bristol Bay Sockeye Salmon Competition with Asian pink salmon Growth Survival Mechanism for AK sockeye salmon increase after 1977 ocean regime shift Increase growth early marine life? Competition?
Eastern Kamchatka Pink Salmon Runs, 1952-2006 Natural Experimental Control E Kamchatka pink run (Z) 3 Even-numbered years 2 Odd-numbered years 1 0-1 Odd-yr mean ± 1 SD = 52 ± 26 million pink salmon -2 1950 1960 1970 1980 1990 2000 2010 Y e a r 100 million Odd-year pink salmon 39x more abundant in Bering Sea (Davis et al. 2005)
Overlap of E Kamchatka Pink & Bristol Bay Sockeye salmon Tag Data (K. Myers)
Sockeye & Pink Salmon Diet Overlap in Bering Sea, 1991-2000 (Davis et al. 2005) Stomach content of sockeye & pink salmon declined 36% & 24%, respectively, in oddyears. Pink Salmon Key prey (squid & fish) declined 27% in sockeye, 7% in pinks. Pink CPUE was 58x greater than sockeye.
Salmon Scales Record Growth Across Time & Broad Regions of Ocean
Bristol Bay sockeye growth reduced during odd years at sea (2nd & 3rd yrs) Normalized growth (Z) 3 2 1 0-1 -2-3 3rd year at sea mean = 612 ± 54 µ Odd-numbered year Even-numbered year 53 57 61 65 69 73 77 81 85 89 93 97 Year at sea Pinks increase after mid-1970s Ruggerone et al. 2003
Smolt to Adult Survival, 1977-1997 Survival at sea (%) 25 20-45% -26% 15 10 5 Odd 2nd y r Even 2nd y r Odd 2nd y r Even 2nd yr 0 Age 1. Age 2. Freshwater age Ruggerone et al. 2003
91 Million Fewer Sockeye, 1977-1997 15 ($482 million loss) Adult sockeye salmon (millions) 10 5 Odd 2nd yr Even 2nd yr 22% loss 0 Egegik Kvichak Naknek Ugashik Nushagak Sockeye salmon stock Ruggerone & Nielsen 2004
Abundance of AK sockeye salmon doubled after 1977 Mechanism? Sockeye salmon run (millions) 125 Western AK North America 100 World 75 50 25 0 50 55 60 65 70 75 80 85 90 95 00 05 Y e a r
Hypothesis: 1976/77 climate shift led to greater growth at sea & greater survival & abundance. Problems: Few long-term data on salmon prey abundance. Adult size (all species) has declined over time & densitydependence. How do we know if salmon prey increased if adult size has decreased?
Test Hypothesis: 1976/77 climate shift led to greater growth at sea & greater survival & abundance. Bristol Bay & Chignik sockeye salmon scale growth 1955-2001.
Bristol Bay & Chignik Sockeye Broadly distributed in Bering Sea and North Pacific
Bristol Bay & Chignik Sockeye Growth: Regime Shift Effect on prey & salmon growth Sockeye scale growth (Z) 1.5 0.5-0.5-1.5 1.5 0.5-0.5 Years 1 & 2 1989 Shift Regime shift Year 3 & migration -1.5 52 57 62 67 72 77 82 87 92 97 02 Year at sea Bristol Bay & Chignik correlated Ruggerone et al. 2007
Sockeye Run Size vs. Growth at Sea, 1955-2001 Alaska sockeye run size (millions) 80 60 40 20 0-1.5-1.0-0.5 0.0 0.5 1.0 1.5 80 60 40 20 (A) (B) Sockeye growth at sea (Z): years 1 & 2 0-1.5-1.0-0.5 0.0 0.5 1.0 1.5 Sockeye growth at sea (Z): year 3 & SWPL y = 2.46 + 17.88(SW1&2) - 11.78(SW3&SWPL) - 13.91(pink index) + 12.18(SST), R 2 = 0.56 Ruggerone et al. 2007
Climate, Competition & Sockeye Length-at-Age L = 550.9 -.178(sockeye) -.144(pinks), r 2 =.40 Model residual (mm) 10 5 0-5 (B) 1976/77 Shift 1989 Shift -10 58 63 68 73 78 83 88 93 98 03 Y e a r Ruggerone et al. 2007
Sockeye Length vs Sockeye & Pink Abundance, 1958-2003 555 550 545 Sockeye length (mm) 540 535 530 0 20 40 60 555 550 545 540 535 Bristol Bay sockeye run (millions) 530 0 20 40 60 80 Eastern Kamchatka pink salmon catch (mt) L (mm) = 550.0 -.275(sockeye) -.170(pink) + 10.3(period: 77-88) + 4.4(period: 89-03) Ruggerone et al. 2007
Conclusions Climate and prey availability are key to salmon survival. Increasing evidence: competition at sea can affect salmon growth & possibly survival. Prey patches & large prey (squid, fishes) may be key to salmon growth.