Impact of 21st Century Climate Change on Baltic Sea Fish ... - BALTEX

<strong>Impact</strong> <strong>of</strong> <strong>21st</strong> <strong>Century</strong> <strong>Climate</strong> <strong>Change</strong>on Baltic Sea Fish and FisheriesNordic Marine Academy course<strong>Impact</strong>s <strong>of</strong> <strong>Climate</strong> <strong>Change</strong>on the Baltic Sea- From Science to PolicyJuly 27 – August 5, 2009Brian R. MacKenzieTechnical University <strong>of</strong> Denmark and University <strong>of</strong> AarhusNational Institute for Aquatic ResourcesDK-2920 CharlottenlundDenmarkbrm@aqua.dtu.dkArtwork: G. Gorick

Outline1. General fish population dynamics-trends <strong>of</strong> fish abundances and landings-fishing trends and impacts on populations and communities2. Consequences <strong>of</strong> climate variability for fish - general3. What has happened already – oceanographic and fish examples4. What could happen in future-future and historical perspectives5. Foodwebs and cascading effects+ 3 Exercises to be completed by 3 pm.

Variations in Spawner Biomass <strong>of</strong>3 Fish Species in the Baltic SeaSpawner Biomass (1000s t)200015001000500CodSpratHerring01968 1976 1984 1992 2000 2008ICES 2008

Millennial Scale Variations in Fish BiomassBaumgartner et al. 1992

Trends in Exploitation and Adult Biomass in27 European Demersal PopulationsOverall long-term significant-increase in fishing mortality(F = ca. 2-3 x nat. mortality)-decline in adult biomass (SSB)-large number <strong>of</strong> stocks in EUwaters overexploited (EEA)Sparholt, Bertelsen, Lassen 2007ICES J. Mar. Sci.

Fishing Down Marine Food Webs-fishing has removed big species and big individuals-cascading effects on food webs and lower trophic levelsnow becoming evident, also in Baltic SeaPauly et al. 1998, SciencePauly 2000, Ambio; Myers et al. 2007; Casini et al. 2009

Effects <strong>of</strong> Fishing on Fish PopulationsThe obvious…death <strong>of</strong> fish, regulation/reduction <strong>of</strong> population sizeThe less obvious…changes in size/age composition <strong>of</strong> populations-size/age structures become truncated inheavily exploited populations-can affect reproductive successExploited spp.-exploited populations more variable thanunexploited populationsNonexploited spp.-more vulnerable to fishing, climatevariability and human impacts.Hsieh et al. 2006; Cal. CurrentNature

Recovering Marine Food Webs andPopulationsPauly et al. 1998, SciencePauly 2000, Ambio-recoveries are slow, maybe impossible-will become more difficult if climate change and otherhuman activities reduce productivity <strong>of</strong> surviving populations.

Baltic Sea – hydrographic gradientsaffect species distributions and biology-permanenthalocline,seasonalthermocline-few speciesSalinity Temperature-fish biomass dominatedby 3 species (sprat,herring and cod)Salinity-salinity restrictsreproduction by FW andmarine species(e. g., cod)

Baltic Sea Fish Biodiversity-relatively few species, compared with otherregional seas <strong>of</strong> similar size (North, BlackSeas):Number <strong>of</strong> marine fish species250No. species200150100500EEA 2002Baltic SeaBlack SeaNorth Sea

Spawner Biomass <strong>of</strong> 3 Key Fish SpeciesSpawner Biomass (1000s t)200015001000500CodSpratHerring01968 1976 1984 1992 2000 2008ICES 2008

Species Interactions amongBaltic Fish and ZooplanktonArtwork: G. Gorick

Species Interactions: Cod & Clupeids in the Baltic-predator-prey spatial distributions, stomach analysescannibalism on juvenilespredationon spratpredation onjuvenile herringAll interactions being modelled in ICES stockassessment.Köster, Uzars, Plikshs, Möllmann, Neuenfeldt et al.

Species Interactions: Cod & Clupeids in the Balticpredation on sprat & cod eggscannibalismon eggsfood competitionfor zooplanktonKöster, Uzars, Plikshs, Möllmann, Neuenfeldt, Feldman, Viitasalo, Aro, Flinkman, Hansson et al.

Estimating Effects <strong>of</strong><strong>Climate</strong> <strong>Change</strong> on Fish??How to do it?-understand processes affecting ecology and lifehistories-identify historical relationships in nature-(possible precedents for future?)-estimate or find out what the hydrographic conditions will be infuture-expect surprises (nonlinear effects, threshold responses,species invasions, etc.)

Consequences <strong>of</strong> <strong>Climate</strong> <strong>Change</strong> on Fish1. Direct effects on fish physiology, phenology and lifehistory-growth, survival, reproduction, migration are all sensitiveto temperature & salinityGT, S2. Indirect effects on fish ecology (”food web effects”)-changes in abundance <strong>of</strong> food-interactions with predators, competitors,pathogens (new relative spatial – temporal distributions)

Data Sources: Ocean Monitoring-compiled and analyseddaily SST measurements fromlightships, lighthouses and harbour sampling-data were collected daily by pr<strong>of</strong>essionaltechnicians and meteorologists with calibratedInstruments-started 1860s-1880sSkagen LightvesselPainting: Carl Locher 1892Source: Skagens Kunstmuseum

Measuring Sites and Areas* *-Christiansø, Denmark 1880-1979-Skagen, Denmark 1880-1998-Torungen, Norway 1867-2003-Marsdiep, Netherlands 1861-2007+*** = SST measured daily= Hadley Centre (opportunistic data)

Long-term Temperature Variability inBaltic and North SeasSummer (JAS) SST 1880-2003Summer SST, So. Baltic191817161514131880 1900 1920 1940 1960 1980 2000MacKenzie & Schiedek 2007Global <strong>Change</strong> Biol.-temperatures during 1990s-2000s are warmest sincemeasurements began in 1860s-1880s-same pattern with winter, summer, annually averaged data

Comparison with Global & RegionalWarming Expectation in 21 st <strong>Century</strong>-expectation: ca. 3º C/100 years = 0.03º C/yr (Kerr 2004; BACC 2007)Rate <strong>of</strong> change <strong>of</strong> SST ( 0 C yr -1 ;+ 2 SE)0.090.060.030.00MacKenzie & Schiedek 2007Global <strong>Change</strong> Biol.B B A B Bquarter vs avg. increaseJFM AMJ JAS OND Ann.Season-annual rate <strong>of</strong> warming similarto expectation-summers have warmed 2-3x fasterthan expected-seasonal differences in warming willhave important consequencesfor ecological processes(e. g., timing <strong>of</strong> events, probability <strong>of</strong>completion <strong>of</strong> lifehistories, trophiclinkages, …)

Extreme YearsSST, Q319Torungen1817161514131860 1880 1900 1920 1940 1960 1980 2000Year-define extreme yearsfrom frequencydistribution <strong>of</strong> observations…No. Observations30252015105Lower 10 th%ile“cold” yearUpper 10 th%ile“warm” year-repeat for each sitefor each quarter012.0 12.8 13.6 14.4 15.2 16.0 16.8 17.6 18.4 19.2 20.0Sea surface temperature (Q3; Torungen)MacKenzie & Schiedek 2007Global <strong>Change</strong> Biol.

Decadal Probability <strong>of</strong> Extremely Cold andWarm Years0.30.20.11860s1870s1880s1890s1900s1910s1920s1930s1940s1950s1960s1970s1980s1990s2000s0.0Annual1860s1870s1880s1890s1900s1910s1920s1930s1940s1950s1960s1970s1980s1990s2000sProbability (T < 10th percentile)Decade0.80.60.40.20.0AnnualProbability (T > 90th percentile)Decade-extreme cold years becoming rarer -extreme warm years becoming commonMacKenzie & Schiedek 2007Global <strong>Change</strong> Biol.

Effects <strong>of</strong> Past Oceanographic Variability onFish and Food WebExamples

Sprat in the Baltic SeaPhoto: Muus and Nielsen 1999-small clupeid (max. BL = 10-12 cm)Baltic Sea-zooplanktivore-prey for juvenile and adult cod, but also predator<strong>of</strong> cod eggs-important commercial species (100s kt/yr since 1974)

Sprat Recruitment and SpawnerBiomass Trends320Spawner Biomass(1000s t)16001200800400Rec.S.B.24016080Recruitment(age 1; 10 9 )01974 1980 1986 1992 19980ICES 2001Spawner biomass and recruitmentnot related (ICES 2001).

Baltic Sprat Egg Survival andTemperature (Lab Studies)% Survival to Hatch(mean + sd)8060402001 3 5 7 9 11 13 15TemperatureNissling 2004-egg survival is higher in warmer water (> 5 C)

Zooplankton ConcentrationsHigher in Warm SpringsZooplankton Conc.(no./litre; May)1612840'80'82'83'73'72'74 '75'76'87'71'85 '86'63'66 '62 '64'77'81 '67 '65 '61 '88'78'69'60'700 1 2 3 4 5 6 7'89 '90 Temperature (May; 56-65 m)Temperature (May; 56-65 m)Zooplankton Conc.(No./litre; May)604530150'790 1 2 3 4 5Temperature (May; 56-65 m)'80'81'82'83Zooplankton Conc.(no./litre; May)2520151050'86'90'92'74 '75'59 '61'83 '88'73 '89'65'72'78 '64'82'66 '80 '62 '60 '84 '76'91 '71'79'77'81'70 '68'67'87'85'63'58'56 '690 1 2 3 4 5 6 7MacKenzie et al. 1996

Variability in Prey Abundance forLarval Sprat-preferred prey <strong>of</strong> larval sprat is Acartia naupliiand copepodites (Voss et al. 2003)-spring Acartia abundance has been high in 1990s(Möllmann et al 2000):Abundance anomaly3210-1-2-3Acartia spp.1960 1965 1970 1975 1980 1985 1990 199543210-1-2-3-4Temp. anomalyMöllmann et al. 2000

Long-term Temperature VariabilitySpring T at 45-65 m;1955-2003Summer (JAS) SST1880-2003May Temperature(45-65 m; Bornholm Basin)654321Summer SST, So. Baltic1918171615141301952 1960 1968 1976 1984 1992 2000 2008MacKenzie & Köster 2004:Ecology1880 1900 1920 1940 1960 1980 2000MacKenzie & Schiedek 2007:Global <strong>Change</strong> Biol.-warm conditions during 1990s-2000s

Temperature – Recruitment Relationship forBaltic Sprat 1973-2004( )Ln recruitment131211R 2 = 26%adj.P = 0.00178694103829180968476 81781019383887597951029973 92100 988910474901079858777MacKenzie & Köster 2004 EcologyMacKenzie et al. 2008 CJFAS91 2 3 4 5 6May Temperature (45-65 m; Bornholm Basin)-warm temperature promotes growth and survival<strong>of</strong> eggs and larvae, partly via zooplankton community

<strong>Climate</strong>-Hydrography-RecruitmentLinks in the Baltic Sea 1955-2004Winter climate (NAO)---Ice coverage---Spring temperaturesMartin Visbeckhttp://www.ldeo.columbia.edu/NAOGRAS AS,http://www.gras.ku.dkMacKenzie & Köster 2004Ecology 85: 784-794+++Sprat recruitmentAll links P < 0.01

Temperature-Recruitment RelationshipGeographic considerations:Muus & Nielsen 1999MacKenzie & Köster 2004Ecology 85: 785-794Ln Ln Recruitment33221100-1-1-2-2-3-3Baltic Sea(spring-summer Baltic Sea spawners)(spring-summer spawners)Black Sea(winter spawners)0 2 4 6 8 10 120 2 4 6 8Water Temperature10 12Water Temperature

Management Application:Risk <strong>of</strong> Stock Collapse under Different Fand <strong>Climate</strong> ScenariosProbability (Spawner Biomass < B PA )2015T = 2.4; F = 1.2*F SQ= F PAT = 2.4; F = F SQT = 3.7; F = F SQ10502000 2002 2004 2006 2008 2010Mean T - SD,FpaMean T - SD,FsqMean T, FsqMacKenzie & Köster 2004EcologyRisk <strong>of</strong> a stock decline increases in cold climateeven at precautionary fishing levels (F PA ).

Baltic Sprat in a Future Warmer <strong>Climate</strong>?Sprat RecruitmentTemperatureIn 2100, spring SST likelyca. 3 o warmer (Meier 2006).

Survival <strong>of</strong> Baltic Salmon and Temperature-highest survival at intermediate temperatures (1972-1999)-lower survival in future, warmer Baltic?Jutila et al. 2005

Effects <strong>of</strong> Temperature Warming onFish Phenology: Migration TimingGarfish (Belone belone; hornhecht) enterthe Baltic in spring to spawn and feed.Emigrate in fall to North Sea.Compare arrival and departure timesin different years with SST.Jacobsen, MacKenzie, Richardson in prep.

Timing <strong>of</strong> Garfish MigrationDepends on SST 1986-2003Arrival to BalticDeparture from Baltic214820869846938688Week Number191817161587 94 9296 95 103 101 88919397 89 99 100 901023 4 5 6 7 8 9Week Number4442403887 98 94 9792 90 91 96 95 100102 10310189999 10 11 12 13 14Average Temperature ( o C ) March-May-4 week variation in arrival times amongyears-garfish arrive earlier in warmyearsAverage Temperature ( o C ) September-November-7 week variation in departure timesamong year-garfish depart earlier in warmyearsJacobsen, MacKenzie, Richardson in prep.

<strong>Climate</strong> <strong>Change</strong> & Anchovy inBelt Sea-Kattegat 1994-2005North Sea SST (JAS)17161514131860 1890 1920 1950 1980 2010Proportion <strong>of</strong> stations with anchovyin Kattegat-Belt Sea0.50.40.30.20.10.0R 2 = 0.39P = 0.021998199620002005200420011994199520021999 1997200315.0 15.5 16.0 16.5 17.0 17.52003MacKenzie, Nielsen,Lassen in prep.Summer SST in North Sea ( 0 C)

Anchovy Spawning in Kattegat-ichthyoplankton samples for Kattegat lightshipNo. Anchovy Eggs/haul10864201928 1930 1932 1934 1936 1938 1940 1942Summer SST, So. Baltic191817161514131880 1900 1920 1940 1960 1980 2000Heegard 1947MacKenzie and Schiedek 2007-are probably spawning in Kattegat again.

“Southern” Species in the Western BalticSwordfish Xiphias gladius, 66 kgLittle BeltSeptember, 2006Bornholm, July 2008P. Møller, Uni. Cop.Bullet tuna Auxis rocheiLubeck Bay, western BalticJuly 2008

Will Warm Invaders Reproducein the Baltic?-in 2100, can we expect afish community likee. g., Bay <strong>of</strong> Biscay in thecentral Baltic?-anchovy, giltheadseabream, red mullet,swordfish…?Depends on salinity tolerances and adaptation <strong>of</strong>individual species and populations…Artwork: G. Gorick-cod as case study

Cod Spawning Areas in the Baltic Sea-in deep basins (ichthyoplankton surveys; spawning adults)-salinity must be highenough to allow eggsto float-in shallow and northern areaseggs, salinity is too low. Eggssink to bottom and donot survive or cannot befertilized successfully(Nissling, Vallin, Westin papers)

Cod Spawner Biomass and RecruitmentSome good news!:-SSB increasing for first time in > 10 years8001000Spawner Biomass (1000s t)600400200SSBRecruits800600400200Recruits; millions <strong>of</strong> age 2ICES 200901968 1976 1984 1992 2000 20080

Cod Spawner Biomass and Fishing MortalityFishing mortality has decreased:8001.6Spawner Biomass (1000s t)600400200SSBFishingmortality1.41.21.00.80.60.40.2Fishing mortality Fbar01968 1976 1984 1992 2000 20080.0ICES 2009

Cod Recruitment per Spawner4Recruits/Spawner3210ICES 2009 1968 1976 1984 1992 2000 2008-record high R/S in recent years (average or above – average)

Parent – Offspring Relationships(Spawner-recruit)Exercise 1:Does cod recruitment depend on biomass <strong>of</strong> cod adults?Is the relationship stable (similar) over time?Check with latest ICES data (2009).

Exercise Results:Cod Spawner Biomass – Recruitmentrec9000008000007000006000005000004000003000002000001000000y = 0.5145x + 140413R 2 = 0.28280 200000 400000 600000 800000ssbrecruitment residuals600000y = 360.17x 2 - 1E+06x + 1E+09500000R 2 = 0.27024000003000002000001000000-1000001960 1970 1980 1990 2000 2010-200000-300000ssbSignificant time trendin residuals:Mostly positive pre-1980and mostly negative1981-present.

Period-Specific Relationships1966-1980 1981-2007rec9000008000007000006000005000004000003000002000001000000y = 0.832x + 195216R 2 = 0.47710 200000 400000 600000 800000ssbrec9000008000007000006000005000004000003000002000001000000y = 0.3027x + 108355R 2 = 0.45980 200000 400000 600000 800000ssb-differences in slopes indicate differences in recruit prodn. per spawner-different levels <strong>of</strong> productivity-implies that vulnerabililty to exploitation varies over time (F consideredsustainable in some time periods may not be sustainable under otherless productive periods)

Exercise 1: ConclusionsAbundance <strong>of</strong> fish populations vary over time.Their dynamics and productivities vary over time.These variations have implications for how they should beexploited.

Why Does R/S Vary?-consider ecosystem processes affecting survival andgrowth <strong>of</strong> early lifehistory stages-eggs, larvae, young juveniles

Cod Spawning Areas in the Baltic Sea-in deep basins (ichthyoplankton surveys; spawning adults)-salinity must be highenough to allow eggsto float-in shallow and northern areaseggs, salinity is too low. Eggssink to bottom and donot survive or cannot befertilized successfully(Nissling, Vallin, Westin papers)

Cod Reproduction and Baltic Oceanography:010Oxygen content (ml/l)0 2 4 6 8 10Salinity (psu)7 9 11 13 15 17 19Depth (m)2030405060708090SalinityOxygen-low O 2 and salinity limits cod reproductive habitatin the eastern Baltic Sea (Plikshs et al. 1993; Wieland et al. 1994)

Variability in Cod Reproductive VolumeS > 11 pptO 2> 2 ml/lReproductive volume (km3)70060050040030020010001950 1960 1970 1980 1990 2000 2010Reproductive volume (km3)40030020010001950 1960 1970 1980 1990 2000 2010Reproductive volume (km3)1501005001950 1960 1970 1980 1990 2000 2010Plikshs et al. 1993, pers. comm.MacKenzie et al. 2000

Reproductive Volume Depends on Hydrographicand Climatic Processes:-exchange (inflows) with the North Sea60Matthäus and Schinke 1998Inflow intensity (Q)5040302010very strongstrongmoderateweakWorld War IWorld War II01880 1900 1920 1940 1960 1980 2000Year

Salinity, Zooplankton and Larval Cod Preynon-seasonal anomalies <strong>of</strong> biomass (ln mg/m 3 )3210-1-2-3-4-53210-1-2-3-43210-1-2-3Pseudocalanus elongatusTemora longicornisAcartia spp.1960 1965 1970 1975 1980 1985 1990 1995210-1-243210-1-2-3-443210-1-2-3-4nsa salinity (psu)nsa temperature (°C)Pseudocalanusis preferred prey<strong>of</strong> larval cod in BalticSea (Hinrichsen et al.2002)-abundance declineswhen salinity fallsMöllmann et al. 2000

Stock – Recruitment RelationshipsInfluenced by Environmental VariabilityTotal repro. volume (km 3 )7006005004003002001000326 + 147 171 + 921968 1976 1984 1992 2000 2008Recruits (age 2; 10 6 )1000800600400200071727766106 707367746910568103 107 98 91104 9293 99 9796 100 90102 101 94 8887 95 89767578860 200 400 600 80085Spawner biomass (kt)79 8081828384-production rate (R/S) varies over time-different levels <strong>of</strong> production and recoverydepending on regimeJarre-Teichmann et al. 2000 (updated)

Oxygen Depletion Rate Following aMajor Baltic Inflow (Jan. 2003)depth [m]102030405060marchaprilmayjulyaugustsummerspring-processes (rates,O 2 solubility) aretemperaturedependent.7080902 3 4 5 6 7 8 9 10Oxygen concentration (ml x l -1 )-based on grid <strong>of</strong> 20-30 stations(ICES 2004)

Seasonal Variability in Reproductive Volumeand TemperatureReproductive Volume(mean + 2 s.e.; km 3 )20018016014012041 41 45 454541J F M A M J J A S O N DDifference in Reproductive Volume(May - August; km 3 )200150100500-50-100-150-200R 2 = 32%P = 0.0002'67'92'77 '73'65 '72 '88'90'85 '70'58'68 '81'83'61 '71 '75'66'64'78'80 '91 '52'87'54 '55'60'53'56 '69 '57'82'89'62'79'85 '76'86 '63'74'590 1 2 3 4 5 6 7Temperature (May; 56-65 m)MacKenzie et al. 1996

Physical - Biogeochemical ProcessesAffect Reproductive Volume-all processes affectingsalinity and oxygenconcentrationArtwork: G. Gorick-inflows-primary production-sinking <strong>of</strong> POC-decomposition <strong>of</strong> POC-temperature-etc.

Coupled NPZD – 3D hydrographic modelincluding NH 4 and H 2 SOxygenreaerationPhytoplanktonZooplanktonWaterexchangeUptakeNutrientsPrimary production:oxygen releaseDetritusWaterexchangeMineralisation:oxygen demandSettlingSettlingEntrainmentnutrient exchangeWaterexchangeNutrientsMineralisationoxygen demand:DetritusSettlingWaterexchangeSediment

Oceanographic Modeling <strong>of</strong> Sea Circulation,2002SalinityO 2

Modelled (IOW) and Field Estimates <strong>of</strong> CodReproductive VolumeBornholmGdanskModelField obs.GotlandUNCOVER-main variations seem to be in both series in most areas, butsome systematic differences also present and causes need to be identified.

Inter-annual Variability inCod Reproductive VolumeTotal repro. volume (km 3 )700 326 + 147 171 + 9260050040030020010001968 1976 1984 1992 2000 2008M. Plikshs, pers. comm.Inflow intensity (Q)605040302010very strongstrongmoderateweakWorld War IWorld War II01880 1900 1920 1940 1960 1980 2000YearMatthäus and Schinke 1998

high<strong>Climate</strong> Variability and Fishing Lead to Regime Shiftsin the Baltic EcosystemCoddominatedWhat happens next??Population levellow-wait for more inflows andcold weather?-fish out the clupeid predators<strong>of</strong> cod eggs?-dominance by invasiveJellyfish?timehighSpratdominated-release hatchery-reared cod?Köster et al. 2003Sci. Mar.1970searly1980s1990searly2000s

Future <strong>Climate</strong> <strong>Change</strong> and Baltic Cod

Future Baltic Surface TemperatureWinterSummerDJFJJA-Baltic surface temperature expected to become2-4 C warmer in winter and summerDöscher and Meier 2004BACC 2007

Future Baltic Salinity in 2070-2100Control: 1960-1990Scenario 1: 2070-2100 Scenario 2: 2070-2100Range = 0-30 PSURange <strong>of</strong> decrease= 0 - 6 PSURange <strong>of</strong> decrease= 0 - 0.8 PSUMeier et al. 2006BACC 2007-regional scale projections uncertain but salinityexpected to fall or remain same

<strong>Climate</strong> Variability and Baltic CodReproductive SuccessWarm temperatures affect reproductive volume:-higher rates <strong>of</strong> biological production andoxygen consumption (metabolism)at higher temperatures-reduced oxygen solubility athigher temperaturesLower salinity could reduce reproductive volume-if salinity < 11 PSU

Exercise 2: <strong>Climate</strong> <strong>Impact</strong>s on Baltic Codin <strong>21st</strong> <strong>Century</strong>-calculate 80-year projections <strong>of</strong> cod biomass under differentexploitation and climate scenarios.To address uncertainty in the salinity projections, conductthe runs using different assumptions <strong>of</strong> salinity decline.-no decline, but random variation-25% decline, with random variation-50% decline, with random variation-for 3 combinations <strong>of</strong> F (0.5, 1, 2)

Scenarios for GroupsGroup Salinity F (relative to SQ)all Random variation 0.5, 1, 21 decline by 25%; var = 0.4 0.5, 1, 22 decline by 25%; var = 0.8 0.5, 1, 23 decline by 50%; var = 0.4 0.5, 1, 24 decline by 50%; var = 0.8 0.5, 1, 2

Uncertainty <strong>of</strong> Projected Salinity-assume 50% decline with random variability <strong>of</strong> rate <strong>of</strong>decline-assume past variability = 0.412.010.0Sallinity (z > 100 m)8.0Run 16.0Run 504.0Run 100Run 1502.0 Run 200mean <strong>of</strong> 2000.02000 2020 2040 2060 2080 2100

Uncertainty <strong>of</strong> Projected Spawner Biomass1400000Series1SSB12000001000000800000600000400000Series3Series5-make histogram <strong>of</strong>SSB in 2089 (N = 200estimates)20000002000 2020 2040 2060 2080 21002520Frequency1510501000 10000 100000 1000000 10000000Log spawner biomass (t)

Scenarios for GroupsGroup Salinity F (relative to SQ)all Random variation 0.5, 1, 21 decline by 25%; var = 0.4 0.5, 1, 22 decline by 25%; var = 0.8 0.5, 1, 23 decline by 50%; var = 0.4 0.5, 1, 24 decline by 50%; var = 0.8 0.5, 1, 2

Projected Cod Biomass for Average andDeclining Salinity800000Random varying salinity800000Declining salinity600000F = 0.5 SQF = 1 SQ600000F = 0.5 SQF = 1 SQSSB400000F = 2 SQSSB400000F = 2 SQ20000020000002000 2020 2040 2060 2080 210002000 2020 2040 2060 2080 2100

Projected Effects <strong>of</strong> Salinity and F onBaltic Cod Spawner Biomass800000F = 0.5 SQ800000F = 1 SQSSB600000400000randomdeclineSSB600000400000randomdecline20000020000002000 2020 2040 2060 2080 210002000 2020 2040 2060 2080 2100800000F = 2 SQSSB600000400000randomdecline20000002000 2020 2040 2060 2080 2100

Exercise 2: Conclusions re. Baltic Cod in<strong>21st</strong> <strong>Century</strong>-abundance will depend on both F and salinity-abundances higher when F lower and salinity higher-sensitive to climate model projections <strong>of</strong> salinity

Future <strong>Climate</strong> <strong>Change</strong> Threatens MarineSpecies in the Baltic and Belt Seas-cod-sprat-plaice-soleMacKenzie et al. 2007Glob. <strong>Change</strong> Biol.Lower salinity (Meier 2006) will shrink marine habitats in the Baltic

<strong>Climate</strong> <strong>Change</strong> and EutrophicationInteractions-are complex-understanding is still limited-some examples <strong>of</strong> the interactions follow…

Cod in a Future Low-Nutrient Baltic?Fewer sprat& herringLess preyReduced carryingcapacity for codReducedeutrophication

Baltic Cod Condition Decreasesat Low Prey Abundance (1983-2002)Condition (Fulton’s K)1,00,90,8P=0,00125-39 cmP=0,001observed Kpredicted K0,70 5 10 15 20 25 301,040-60cmP=0,001P=0,0010,90,80,70 5 10 15 20 25 3070-89 cmP=0,0011,0P=0,0010,90,80,70 5 10 15 20 25 30>80 cm1,00,90,80,70 5 10 15 20 25(SSB Herring + SSB Sprat )/SSB Cod-reduced prey/cod could affect cod growth and reproductionRichter and MacKenzie in prep.

Cod in a Future Low-Nutrient Baltic?ReducedeutrophicationFewer sprat& herringLess preyReduced carryingcapacity for codLess decomp.<strong>of</strong> organic matterBetter O 2 inspawning areasIncreased repro.success & recr.

<strong>Climate</strong> <strong>Change</strong>, Eutrophication,and Cod in the Future Baltic:Increased precipitationand run<strong>of</strong>f loading<strong>of</strong> nutrients; warmer TReduced nutrientloading; more stormsFrequent and longerperiods <strong>of</strong> anoxia?Fewer and shorterperiods <strong>of</strong> anoxia?MacKenzie et al. 2002CJFAS-outcome not clear-requires process modelling

Baltic Sea Management and ConservationPolicy Objectives (BSAP 2007)-reduce nutrient loading-rebuild seal populations-negative consequences for cod??(lowering overall productivity <strong>of</strong> system andincreasing abundance <strong>of</strong> a cod predator)-consider ecosystem <strong>of</strong> the past…look for past evidence<strong>of</strong> abundances and distributions (develop baselines)-archives, paleo data, etc.

Cod Fishing in the Southern Baltic, 1602Exercise 3: Guess how many cod were caught and wherefrom this tax record:132456Source: Maibritt Bager, Univ. So. DK

Cod Fishing in the Southern Baltic, 16023. 100 dried cod(tax rate perhousehold)3121. Skatte torsk-taxcod2. One man44. Fishing village- Snogebæk5. Total driedcod566. 4½ M 300 pieces(4800 cod)Source: Maibritt Bager, Univ. So. DK

Cod Tax Paid to Hammershus, BornholmNumber <strong>of</strong> cod9000800070006000500040003000200010000Tax <strong>of</strong> cod fishing effort Hammershus County1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610Photo: A. MaciejewskaHolm and Bager 2002-cod were abundant incommercially relevant quantities-source <strong>of</strong> revenue to the King

Range Variability <strong>of</strong> Eastern Baltic Cod-contraction and low biomass duringlow salinity periods (infrequentNorth Sea inflows)Aro & Sjöblom 1983; MacKenzie et al. 2000; Köster et al. 2005-expansion and high biomass duringhigher salinity periods (frequentNorth Sea inflows)-improves recruitment-reduces cannibalism and competition.

Annual Cod Exports from Southern Finlandto Sweden 1556-1635Cod exported fromFinland to Sweden (t)25201510501560 1575 1590 1605 1620 1635MacKenzie et al. 2007 Fish. Res.

Annual Cod Exports from Southern Finlandto Sweden 1556-16352525Finnish cod landings (t)49H1 & 49H2201510501975 1976 1977 1978 1979Cod exported fromFinland to Sweden (t)201510501560 1575 1590 1605 1620 1635-landings 400 years ago were higher than during 1976-78-only get cod landings in SW Finland when biomass is highor salinity is high (such periods usually coincide)MacKenzie et al. 2007 Fish. Res.

Swedish Cod Fishery 1550s-1750s-conducted short prelim. search <strong>of</strong> Swedisharchives for area near Stockholm-period 1550s-1750sStockholmSödermanland-some data recovered-compare with recent Swedishlandings in same ICES squaresMacKenzie et al. 2007 Fish. Res.

Central-Northern Swedish Cod Landings,1550s-1750s20Cod landings (t)(1998-2005: mean + 2 se)16128401556155715581559mid-1700s1998-2005-Swedish local fishery caught ca. 10 t / year during sametime period as cod was being imported from Finland (twogeographically-separated fisheries <strong>of</strong> similar magnitude atnearly same time)MacKenzie et al. 2007 Fish. Res.

Baltic Ecosystem Status During 1550-1630Contemporary knowledge suggests it couldhave been “cod-hostile” (!):Primary Production(106 t C/yr)Lower 1 º Prodn.Elmgren 198960504030201001900 1980High seal predation & compet.Fish consumed bymarine mammals (kt/yr)3503002502001501005001900 1980Elmgren 1989-but cod biomass was high and widespread in Baltic(supported economically important fisheriesin northern and southern Baltic)MacKenzie et al. 2007 Fish. Res.

Cod in a Hostile Baltic?How could there be important fisheries in the (northern) Balticin an apparently cod-hostile ecosystem?Hypotheses:1. Better salinity and oxygen conditions? (positive effects on recruitmentand spatial distribution)-needs paleo-evidence2. Fishing effort and mortality rates were much lower than now.-allowed cod biomass to remain high, despite potentially lower 1º prodn.and higher predation rates and food competition due to seals-is very likely (simpler technologies, no fishing <strong>of</strong>fshore, etc.)MacKenzie et al. 2007 Fish. Res.

ConclusionsBaltic cod vulnerable to several human impacts and theirinteractions-exploitation, climate change, eutrophication, etc.<strong>Climate</strong> change likely to affect biodiversity <strong>of</strong> fish community-community “fresher, warmer”, esp. if salinity falls by 50%Many uncertainties remain – need process knowledge,observations and models.

Food Webs and Trophic CascadesPauly 2000

Trophic Cascades in Marine Foodwebs-loss <strong>of</strong> large sharks <strong>of</strong>f east coast USA since 1950s:

Trophic Cascades in Marine Foodwebs-led to increase <strong>of</strong> prey (smaller sharks and rays):

Trophic Cascades in Marine Foodwebs-and to decrease <strong>of</strong> prey’s prey…

Trophic Cascade in a Marine FoodwebNBig sharksSmall sharksYearBig sharksNSmall sharksScallopsYearNScallopsScallopsSmall sharksYearMyers et al. 2007Big sharks

Variations in Spawner Biomass <strong>of</strong>3 Fish Species in the Baltic SeaSpawner Biomass (1000s t)200015001000500CodSpratHerring01968 1976 1984 1992 2000 2008ICES 2008

Hydrographic Effects on Trophic Interactionsin the Baltic SeaOxic bottom layer-more cod-cod feeding on benthic inverts.-cod occupying deep layerAnoxic bottom layer-fewer cod-cod feeding on clupeids-no cod in deep layerArtwork: G. Gorick

Cascading Effects in the Baltic SeaPiscivore-zooplanktivoreZooplanktivore - zooplanktonZooplankton-chlorophyllCasini et al. 2008Proc. Roy. Soc. Lond.

Cod Abundance and Cascading EffectsWhen cod abundant,cascading effects absent.When cod rare,cascading effects present.Casini et al. 2009PNAS

Cod Abundance and Cascading Effectsin a Warmer, Fresher Baltic SeaHypothesis:In a (future?) warmer and fresher Baltic:-expect more sprat-expect fewer codcan we expect these cascading effects to strengthen?

Regime shifts in the Baltic ecosystemhighCoddominatedWhat happens next??Population levellow-wait for more inflows andcold weather?-fish out the clupeid predators<strong>of</strong> cod eggs?-dominance by invasiveJellyfish?timehighSpratdominated-release hatchery-reared cod?Köster et al. 2003Sci. Mar.1970searly1980s1990searly2000s

ConclusionsBaltic cod vulnerable to several human impacts and theirinteractions-exploitation, climate change, eutrophication, etc.<strong>Climate</strong> change likely to affect biodiversity <strong>of</strong> fish community-community “fresher, warmer”, esp. if salinity falls by 50%Roles <strong>of</strong> changes in pH and sea level unclearMany uncertainties remain – need process knowledge,observations and models.

Early 20th <strong>Century</strong> Cod BiomassC. Humborg 2009Eero et al. 2008 CJFAS