Introduction: Climate, people, fisheries and aquatic ecosystems

122 Pages·2008·1.07 MB·English

(cid:1)
1 Introduction: Climate, people, fisheries and aquatic ecosystems
robert engelman, daniel pauly, dirk zeller, ronald g. prinn,
john k. pinnegar and nicholas v.c. polunin
INTRODUCTION TO THE BOOK
conservation. The extent to which wilderness areas
Evidence of human damage to natural resources and the everywherewerecontaminatedorotherwiseinfluencedby
environmentislong-standingeveninthesea,butsome50 human agency was beginning to be generally recognized,
years ago awareness of human degradation of natural andsomepeoplepredictedtheseimpactswouldonlygrow
environments around the globe grew substantially. This in future. But few predicted the extent and number of
concern was expressed above all in the creation of pro- globalenvironmentalchangesthatarenowoccurring.The
tectedareas,organizationsandagenciesfocusedonnature limitstogrowthoftheworld’seconomies, individuallyor
AquaticEcosystems,ed.N.V.C.Polunin.PublishedbyCambridgeUniversityPress.ªFoundationforEnvironmentalConservation2008.
1
2 R. ENGELMAN ET AL.
collectively, were little questioned in ecological contexts. horizonsufficientlyfarinthefuturetoprovokethoughtful
Uncertainties surrounding how economics and ecology and imaginative projections across all the ecosystems, but
might relate to each other were little explored, and ques- within a time-frame for which some detailed scenarios
tions such as ‘At what points will economies become such as of human population growth and global ambient
constrained by the decline and loss of natural ecological temperatures existed. The year 2025 was chosen as an
goods andservices?’ persisttothisday. appropriate compromise between those two constraints.
Waterisincreasinglyseenasaconstraintonsustainable Thisbookaimstoassembletheviewsofexpertecologistson
humandevelopmentandfocusofpotentialhumanconflict. thestatusofallecosystemsacrosstheaquaticrealm,review
Nevertheless,ithasbeenrarefortheprovisionofthisgood, contemporarychangesandtheirdrivers,andconsiderlikely
andrelatedecologicalservicessuchasfishproductionand outcomes at the 2025 time horizon. Major drivers con-
wastedisposal,tobeviewedholisticallyinthecontextofthe sideredareclimatechangeandthedirectimpactsofhuman
natural environment. Also, there have been no compre- populationgrowthandeconomicdevelopment.
hensive reviews of status and trends encompassing all Climateisusefullydefinedastheaverageoftheweather
aquaticenvironments(Clarketal.2006),fromthefreshand experienced over a 10–20-year period. Temperature and
terrestrialsalinetothoseofthedeepestseas.Certainfresh rainfallchangesaretypicalmeasuresofchangethatcanbe
waters and saline lakes have been radically altered by expressedatlocal,regional,nationalorglobalscales.Global
humans, but the extent and nature of these impacts vary warmingorcoolingcanbedrivenbyanyimbalancebetween
amongecosystemtypesandgeographicallocations.Theseas the solar energy the Earth receives from the Sun and the
andoceansretainagreatercomplementofresource-devel- energy itradiates back tospace as invisibleinfrared light.
opmentfrontiersthandoestheland,forexampleinmining Thegreenhouseeffectisawarminginfluencecausedbythe
andfisheries(e.g.Berkesetal.2006);theirwildernessvalue presenceofgasesandcloudsintheatmosphere,whichare
remainssubstantial.Clearly,theextentofhumandisturb- veryefficientabsorbersandradiatorsofthisinfraredlight.
anceisincreasingacrossenvironmenttypesandlocations, The greenhouse effect is opposed by substances at the
yet there is little comprehensive scientific appraisal of the Earth’ssurface(suchassnow anddesertsand)andinthe
magnitudeandnatureofthispermeation. atmosphere (such as clouds and white aerosols) that effi-
It is important at this time to consider what is hap- cientlyreflectsunlightbackintospace(albedo)andarethusa
pening ecologically to the world’s aquatic environments, coolinginfluence.Globalclimatechangesandtheirpossible
and where possible project these forward to an appro- consequences are and will remain a major area of debate
priatetimehorizonatanappropriateecologicalscale.The withinandamongmostnations.Internationalnegotiations
terminology surrounding ecological units is large and intheFrameworkConventiononClimateChangeandits
application can be problematic especially where, as here, Kyoto Protocol are contentious in particular because the
freshwater and marine environments are to be bridged. componentsoftheproblemaremany,thescienceisuncer-
Thus the term ‘biome’ is discerning of terrestrial envir- tainandthewholeissuehasamajorbearingonotherglobal
onments but not with respect to those of the sea, while problemssuchaspoverty,inequalityandeconomicdevel-
‘ecoregions’(e.g.Bailey1998)omitthecontinentalshelves. opment. Another aim of this introductory chapter is to
It was important in the design of this book to focus on consider uncertainties in climate predictions and review
a number of natural environments that would be com- warming, sea-level rise and related trends as they might
prehensive yet feasible in terms of relevant data and affecttheworld’saquaticenvironments.
expertise.Oneaimofthischapteristoconsideralternative The human population is approaching the 7 billion
comprehensive categorizations of aquatic environments as mark, increasing by c.1.2% per year. Mapping and pho-
abasisfor thisbook. tography of the Earth’s night lights (Weier 2000) show
Naturalprocessesandecologicalservicesrelyonnotions howunevenlyhumanbeingsaresettled(Deichmannetal.
of system functioning that have long been integral to the 2001). Especially dense populations characterize northern
concept of the ‘ecosystem’. Otherrecognizedtypes ofeco- SouthAsia,EastAsia,Europe,easternNorthAmericaand
logical unit such as the biotope exist, but the term ‘eco- south-western Africa. More than half of the world’s
system’ is the most relevant, and most widely used and populationliveswithin60kmofthecoast,andthisfigure
recognized, and is thus the unit of choice for this book. could reach 75% by the year 2020 (Roberts & Hawkins
Whatwasalsoneededinthedesignofthisbookwasatime 1999).Inaddition,humaneconomicwealthandoutputare
Introduction 3
often concentrated close to major rivers or estuaries, 100%andnitrousoxide(N O)byabout15%.Thesegases
2
especially in the temperate regions of the northern hemi- are now at higher concentrations than at any time in the
sphere (Cohen 1997; Nicholls & Small 2002). Various past160000years(IPCC1996).Thecombustionoffossil
humaninteractionswithcritical natural resources andthe fuelsand,toalesserextent,changesinlanduseaccountfor
environmentillustratethatthehumanpopulationoverthe anthropogenic CO emissions. Agriculture is responsible
2
past several decades has reached levels that significantly for nearly 50% of human-generated CH emissions and
4
modify aquatic ecosystems. While some of this change is about70%ofanthropogenic N Oemissions.
2
economically and socially beneficial, some is ecologically Whentheconcentrationofaparticulargreenhousegas
detrimental(e.g.biodiversityloss;seebelow).Athirdaim increases, it tends to lower the flow of infrared energy to
of this chapter is to introduce a human backdrop for spaceandincreasestheflowofinfraredenergydowntoward
assessingglobalchangesinaquaticecosystems;thiswillbe thesurface.TheEarthisthenreceivingmoreenergythanit
doneinparticularbyreviewingsomeoftheconsequences radiatestospace.This‘radiativeforcing’warmsthesurface
of human population growth for water, water supply and and the lower atmosphere; however, the rate of surface
itsnatural sources. warmingisslowedbyuptakeofheatbytheworld’soceans.
Fisheries have been recognized as a major driver of Thegreenhouseeffectasquantifiedbythisradiativeforcing
change in the aquatic realm. They constitute a major isrealandthephysicsrelativelywellunderstood.Whatis
impactattheinterfacesamonghumanpopulationgrowth, more uncertain, and the cause of much of the scientific
economic development and environmental changes, both debate,istheresponseoftheglobalsystemthatdetermines
anthropogenic and natural. Modern industrial fisheries climatetothisradiativeforcing.Feedbacksinthesystemcan
resultedfromtheeconomicandtechnologicaldevelopment eitheramplifyordampentheresponseinwaysthatarestill
of Europe, North America and Japan over a century ago. onlypartiallyunderstood.
Frontiers in the development of global fishery resources The IPCC was jointly established by the World
persistintheuseofSouthernOceananddeep-seaorreef Meteorological Organization and the United Nations
resources. What are the current trends in global fisheries, Environment Programme (UNEP) in 1988, in order to
andhowdotheserelatetowhatishappeningintheaquatic (1)assessavailablescientificinformationonclimatechange,
ecosystems involved?Theintention inthischapterisalso (2)assessthe environmentaland socioeconomic impacts of
to introduce marine fisheries as an important example of climate change, and (3) formulate response strategies. The
humanintrusionintotheoceansandseas;thisisfollowed IntegratedGlobalSystemModel(IGSM)isonemeansthat
byanoverviewofglobaltrendsinaquaticbiodiversityand theIPCChasatitsdisposaltoanalysecarefullythescientific
specificextinctions. and economic implications of proposed mitigation policies
(Fig. 1.1). The IGSM consists of a set of coupled sub-
modelsofeconomicdevelopmentandassociatedemissions,
COMPLEXITIES OF CLIMATE CHANGE
natural biogeochemical cycles, climate and natural ecosys-
AND ITS CONSEQUENCES
tems (Prinn et al. 1999; MIT [Massachusetts Institute of
Globalclimatehasremainedrelativelystable(temperature Technology]2003).Itattemptstoincludeeachofthemajor
changes of <1(cid:2)C over a century) during the last 10000 areasinthenaturalandsocialsciencesthatareamenableto
years.However,societynowfacespotentiallyrapidchanges quantitativeanalysisandarerelevanttotheissueofclimate
because human activities have altered the atmosphere’s change(Schneider1992;Prinn&Hartley1992;IPCC2001a,
composition and changed the Earth’s radiation balance b, c). Amajorchallengeinherentinglobalclimatemodel-
(IPCC[IntergovernmentalPanelonClimateChange]1996). lingistodecidewhatisimportantandwhatisunimportant.
The most important greenhouse gas is water vapour, In the IGSM, the coupled atmospheric chemistry and
whichtypicallyremainsforaweekorsointheatmosphere. climate model (Fig. 1.1) is driven by a combination of
Concerns about global warming, however, revolve around anthropogenic and natural emissions. The essential com-
much longer-lived greenhouse gases, especially carbon ponentsofthismodelarechemistry,atmosphericcirculation
dioxide but also other long-lived gases (methane, nitrous andoceancirculation,eachofwhich,byitself,canrequire
oxide, chlorofluorocarbons), concentrations of which have enormouscomputerresources.Theatmosphericchemistry
increasedsubstantiallysincec.1750.Carbondioxide(CO ) is modelled in sufficient detail to capture its sensitivity to
2
has risen by about 30%, methane (CH ) by more than climateanddifferentmixesofemissions,andtoaddressthe
4
4 R. ENGELMAN ET AL.
HUMAN ACTIVITY
land use agricultural
change national and/or regional production
economic development,
emissions, and land use
CO , CH , N O, NO , SO ,
2 4 2 X X
CO, CFCs, HFCs, PFCs, SF ,
6
NH , VOCs, BC, etc.
3
CH
4
NATURAL N O
2
EMISSIONS 2D COUPLED sea
ATMOSPHERIC level
CHEMISTRY
ocean
AND
CO
2
uptake CLIMATE land
PROCESSES CO
soil C 2
uptake
soil N
coupled ocean,
temperature,
atmosphere,
rainfall
and land
land
nutrients, temperature,
vegetation
pollutants rainfall, clouds, CO2 change
DYNAMIC TERRESTRIAL
ECOSYSTEMS PROCESSES
NPP, vegetative C,
soil C, soil N
Fig.1.1. SchematicillustrationoftheframeworkandprocessesoftheMITIntegratedGlobalSystemModel(IGSM).Feedbacks
betweenthecomponentmodelsthatarecurrentlyincludedorproposedforinclusioninthenextgenerationareshownassolid
anddashedlinesrespectively(Prinnetal.1999;MIT2003).
relationship among policies proposed for control of emis- driveaterrestrialecosystemsmodelthatpredictsvegetation
sionsrelatedtoairpollution,aerosolsandgreenhousegases changes,landCO fluxesandsoilcomposition(Xiaoetal.
2
(Wang et al. 1998). But linking complex models together 1998),andthesefeedbacktotheclimatemodel,chemistry
leadstomanychallenges,illustratedbythefailureofcoupled modelandnaturalemissionsmodel.Theeffectsofchanges
ocean–atmospheremodels(includingIGSM)toaccurately inlandcoverandsurfacealbedoonclimate,andtheeffects
simulate current climate without arbitrary adjustments. of changes in climate and ecosystems on agriculture and
The IGSM coupled chemistry–climate model outputs anthropogenicemissionsarealsoincluded.
Introduction 5
Hundreds of runs of the IGSM have been used to 1.6
quantitatively assess uncertainty in climate projections 1.4 2050 Policy (a)
(Webster et al. 2002, 2003). One study shows a global
y 1.2
median surface temperature rise from 1990 to 2100 of sit 2050 No Policy
2.4(cid:2)C, with a 95% confidence interval of 1.0–4.9(cid:2)C Den 1.0
y 0.8
(Webster et al. 2003). For comparison, IPCC (2001a) bilit 2100 Policy
reported a range for the global mean surface temperature a 0.6
b
rise by2100 of 1.4–5.8(cid:2)C, but did not provide likelihood Pro 0.4 2100 No Policy
estimates for this key finding although it did do so for
0.2
others. The implications of the projected level of climate
0.0
warming for the aquatic realm are unclear, but will vary
0 1 2 3 4 5 6 7
with type of ecosystem. For example, small surface Global Mean Temperature Change from 1990 (°C)
freshwater bodies will typically vary readily with climate,
12
whileintheopenocean,ambienttemperaturewilllagthat
(b)
oftheatmospherebydecades ormore. 10 2050 Policy
globWalhseunrtfhaceeptreombapbeirlaittyurdeisatrnidbusteiao-nlefvuenlcitniocnresafsoerstbheetmweeeann ensity 8
D
1990and2100arecomparedbetweenno-policyandapplied- y 6 2050 No Policy
policy scenarios (designed to simulate strict regulations abilit 2100 Policy
leadingtostabilizationofatmosphericCO concentrationsat b 4
2 o
abouttwicepre-industriallevels),amedianofonly1.6(cid:2)C Pr 2100 No Policy
and 95% range of only 0.8–3.2(cid:2)C is forecast (Fig. 1.2). 2
Thereisa50%chanceofwarmingexceeding2.4(cid:2)Cinthe 0
no-policy case and a 1-in-7 chance in the policy case. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Implementingthepolicythereforelowerstheprobabilityof Sea Level Rise due to Thermal Expansion (m)
largeamountsofwarmingtoasubstantialdegree. Fig.1.2. Probabilitydensityfunction(PDF)forthechange
Tobetterappreciatetherisksoftheno-policyscenario, inglobalmean:(a)surfacetemperatureand(b)sea-level
itisimportanttoexaminethelatitudinaldistributionofthe risefrom1990to2100estimatedasabestfitto250
projectedwarming.Incommonwithotherclimatemodels, simulationsusinglatinhypercubesamplingfrominputPDFs
the computed temperature increases in polar regions are foruncertainvariables.ThesolidlineshowsthePDF
resultingfromnoexplicitemissionsrestrictionsandthe
much greater than those in equatorial regions (no-policy
dashedlineisthePDFunderhypotheticalemissionspolicy
case:Fig.1.3).Polarregionscontainvulnerableecosystems
leadingtosteadylevelsofatmosphericCO ofabouttwice
with large carbon storage (e.g. Chapter 8), and the 2
pre-industrialvalues(Websteretal.2003).TheIPCC
Greenland and Antarctic ice sheets with large water stor-
(2001a,b,c)upperestimateisbeyondthe95%confidence
age(e.g.Chapter21).Releaseofsomeofthisstoredcarbon
limit.Basedonthisdistributionthereisa12%chancethat
and water is of significant concern. A 1-in-40 chance of thetemperaturechangein2100wouldbelessthantheIPCC
warmingby8–12(cid:2)Corgreaterinpolarregionsfortheno- lowerestimate.
policycase(Fig.1.3)isparticularlyworrisome.Thepolicy
scenario lowers the polar warming in the 1-in-40 calcula- uncertaintyforkeyprojections,withanexplicitdescription
tionto5–7(cid:2)C(Webster etal.2003). ofthemethodsused(Allenetal.2001;Reillyetal.2001).
Similarsignificantreductionsintheprobabilityoflarge
andriskyamountsofsea-levelriseduetothehypothetical
Sea-level rise
policyarealsoevident(Fig.1.2).Emissionsreductionsare
predictedtolowerthechanceofexceedinganextremecli- Globalmeansealevelhasrisenby10–25cmoverthelast100
mate outcome but not to eliminate the risk entirely, and years,andalthoughtherehasbeennodetectablechangein
analysisofthereductioninprobabilityisanimportantpolicy therateofsea-level riseoverthecourseofthecentury,it
consideration. Future climate assessments would better wouldappearthatthishasbeensignificantlyhigherthanthe
serve the policy process by including formal analysis of rate averaged over the last several thousand years (IPCC
6 R. ENGELMAN ET AL.
14
e Lakes, streams and wetlands
g
an 12
h Inland aquatic ecosystems are expected to be greatly influ-
C
perature °100 (C)108 No Policy eflO¨noqcwuedisrtebgyeitmcaleilms.aa1tn9ed9c6hw).aanWtgeerattlehervr-oeleulsvgeh(lea.dglte.ecKrleinadecwszmamtaearreyktebmeetpsaeelrv.aet1ru9er9ei6sn;,
m2
e– 6 lakesandstreamsindryevaporativedrainagesandinbasins
T0
ean 199 4 withsmallcatchments,whilstthedistributionofwetlandsis
M Policy likelytoshiftwithchangesintemperatureandprecipitation
nal 2 (IPCC 2001a; Chapters 2–10). Wetlands temporarily store
o
Z 0 runoff water, thereby reducing floodwater peaks and
–80 –60 –40 –20 0 20 40 60 80 protectingdownstreamareas,consequentlyareductionof
Latitude wetlandareaduetoclimatechangecouldseverelyhamper
Fig.1.3. Zonalmeantemperaturechangeinsurfacewarming flood-controleffortsinsomeregions(e.g.Kaczmareketal.
bylatitudebandbetween1990and2100inthecaseassuming 1996;O¨quistetal.1996;Chapters 9and10).
noexplicitpolicyinFig.1.2.Thereisa1-in-40chanceof
beingaboveorbelowtheupperandlowercurvesanda1-in-2
Coastal systems and small islands
chanceofbeingaboveorbelowthemiddlecurverespectively
(Websteretal.2003). Coastal systems are economically and ecologically
important.Climatewarming,sea-levelriseandincreasesin
2001a,b).Itislikelythattheriseinsealevelhasbeenlargely storms and storm-surge frequencies may result in erosion
duetotheincreaseinglobaltemperatureoverthelast100 of shores and associated habitats, altered tidal ranges in
years.Thepossiblefactorsincludethermalexpansionofthe rivers and bays, changes in sediment and nutrient trans-
oceans and melting of glaciers, ice caps and ice sheets. port, and increased coastal flooding (see Bijlsma et al.
Changesinsurfacewaterandgroundwaterstorage(related 1996). Some coastal ecosystems are particularly at risk,
to changes in human activities and changes to drainage namelysaltmarshes,mangroves,coralreefsandatolls,and
basins)mayalsohaveaffectedsealevel. river deltas (Chapters 11–13 and 16). Changes in these
Model simulations have predicted 2–7 cm of the ecosystemsarelikelytonegativelyaffecttourism,fisheries
reported sea-level rise over the last 100 years (10–25 cm) and biodiversity (IPCC 2001b). Many small island coun-
and attributed it to thermal expansion of the oceans, yet tries could lose asignificant part of their land area with a
many of the world’s mountain glaciers have retreated sea-levelriseof0.5–1m,theMaldivesforinstancehaving
substantiallyoverthistimeperiodandmayhaveaccounted averagealtitudes ofonly1–1.5m(Bijlsma etal.1996).
for2–5cmoftheobservedrise.However,mostofthenon-
oceanic water onEarth residesingreat icesheets, namely
Oceans
those of Antarctica and Greenland, and most of their
volume lies on land above sea level. Loss of only a small Climatechangecouldleadtoalteredoceancirculation(e.g.
fraction of this volume could have a significant effect on weakening of the Atlantic thermohaline circulation) and
sealevel(Warricketal.1996).InAntarctica,dischargesof wave climates, and reductions in sea-ice cover (IPCC
enormous icebergs and recent break-ups of Antarctic 2001a, b, c; ACIA [Arctic Climate Impact Assessment]
Peninsulaiceshelveshavefocusedpublicattentiononthe 2004). As a result, nutrient availability, biological prod-
possibilityof‘collapse’ofthisicereservoirwithinthenext uctivity,thestructureandfunctionsofmarineecosystems,
century,withmajorpotential impactsonsealevel. andheatandcarbonstoragecapacitymaybeaffectedwith
According to the IPCC (2001a, b) ‘best estimate’ cli- important feedbacks to the global climate system (see
matechangescenario,globalsealevelisprojectedtoriseby Ittekkot et al. 1996). These changes would have implica-
20cmbytheyear2050(withinarangeofuncertaintyof7– tionsforcoastalregions,fisheries,tourismandrecreation,
39 cm) and by 49 cm by 2100 (within a range of uncer- transportandoffshore structures.
taintyof20–86cm);morethanhalfofthisisattributedto Most CO released into the atmosphere as a result of
2
oceanic thermalexpansion. burning fossil fuels will eventually be absorbed by the
Introduction 7
ocean.AstheamountofCO intheatmosphererises,more Table 1.1. World population byyear and UN projection
2
ofthegasreactswithseawatertoproducebicarbonateand variant
hydrogenionsthatincreasetheacidityofthesurfacelayer.
Ocean pH was around 8.3 after the last ice age and 8.2 Low-variant Medium-variant High-variant
beforeCO emissionstookoffintheindustrialera.Ocean Year projection projection projection
2
pHisnow8.1andifatmosphericCO exceeds1900ppm
2 2010 6843645000 6906558000 6967407000
bytheyear2300,pHattheoceansurfacecouldfallto7.4
2025 7568539000 8010509000 8450822000
(Caldeira&Wickett2003).Thereislimitedunderstanding
2050 7791545000 9191287000 10756366000
oftheeffectincreasedaciditymighthaveonmarinebiota,
but coral reefs, calcareous plankton and other organisms,
Source: UNPD (2006).
skeletonsorshellsofwhichcontaincalciumcarbonate,may
besubstantiallyaffected.
all but the most remote and best-protected areas, there is
constant pressure on water resources. By hydrological
PEOPLE AND WATER
benchmarks of water stress (c.1000–1700 m3 per person
Perhaps the best-documented human interaction with per year) and scarcity (<1000 m3 per person per year)
aquatic ecosystems involves the use of fresh water (Falkenmark & Widstrand 1992; Engelman & LeRoy
(Engelman&LeRoy1993;Engelmanetal.2000).Precious 1993), the numbers of human beings living in these two
little of the world’s water is salt-free, and only a small high-risk categories is growing much faster than popula-
proportion of this fresh water is accessible to human tion growth generally. One-third of humanity lives in
beings.Waterusehasincreasedformanycenturies,butin countriesexperiencingmoderatetohighwaterstress(WRI
manymajorwatersheds(thekeygeographicunitofinterest [World Resources Institute] 1998), and a billion people
forfreshwateruse),onlyinthepastfewcenturieshasthe couldfacesevere watershortages by2025 (Potts 2000).
scale reached the point where natural variations in water Apart from fisheries, which are considered below,
supply have begun to collide with growing human use. several other interactions between human population and
This is most evident in western Asia and eastern and the environment are especially salient for aquatic ecosys-
southern Africa, but to varying degrees such problems of tems.Interms offoodsecurity, much ismade ofagricul-
availabilityarealsopresentelsewhere.Humansalreadyuse tural intensification as the antidote to forest loss. When
morethanhalfoftherenewablefreshwaterthatisreadily morefoodcanbeproducedonthesameland,thereisless
accessible (Postel et al. 1996), and human population needtoconvertrelativelywildlandtofarmland.Thiscan,
growthiscurrently thedominant factorintheincrease of of course, benefit wetlands, which historically have been
waterwithdrawals worldwide. lost to farmland more frequently than to settlement,
The world’s urban population is currently growing at although this ratio is changing as coasts and river valleys
four times the rate of the rural population. Between 1990 becomemore denselypopulated (Chapters9–13).
and 2025, the number of people living in urban areas is Water is the greatest transportation network for
projected to double to more than 5 billion out of a total chemicalwastesofalltypes.Humanitynowexceedsnature
8billion(Table1.1).Anestimated90%oftheincreasewill as a fixer and producer of nitrogen compounds (Smil
occurindevelopingcountriesandatthecurrentpace,over 1997),andstudiesofrivershaveshownthatnitrogenloads
60millionpeopleareaddedtourbanpopulationseachyear, arehighlycorrelatedwithhumanpopulationdensityalong
placinggreatstrainonlocalgovernmentstoprovideeventhe river banks (Cole et al. 1993). Intensive farming can also
mostbasicservices.Ofallurbaninhabitantsindeveloping exacerbatesoilerosioniffarmersdonothavetheresources
countries,25–50%liveinimpoverishedslumsandsquatter tomanagetheirsoilproperly,andtheworld’sriversoffload
settlements, with little or no access to adequate water, muchoftheresultingsiltontothecontinentalshelvesand
sanitationorrefusecollection(UN[UnitedNations]1997). beyond.Conversionofforesttofarmlandisanothersource
Human water demand for agricultural irrigation (an of soil erosion, also closely correlated with population
increasing proportion of food production comes from densityandgrowth.
irrigated cropland), industrial and household uses almost Introduction of alien species is an indirect result of
invariably takes precedence over environmental needs. In humanpopulationgrowthandeconomicandtechnological
8 R. ENGELMAN ET AL.
development, because human beings uniquely face few world’s countries, couples are only just replacing them-
barrierstotheirmovementovertheEarth’ssurface.From selvesinthepopulation,ortheyarehavingfewerthanthe
Nileperchtozebramussels,thelistofintroducedaquatic c.2.1childrenneededfornetreplacement(UNPD[United
species altering aquatic ecosystems is lengthening. In Nations Population Division] 2002). Contrary to public
addition, marine life is at growing risk from a range of impressions,thisdoesnotmeanthatthesepopulationsare
diseases, the spread of which is being hastened by global nowstableordeclining.Thelargeproportionofpeopleof
warming, global transport and pollution (Harvell et al. childbearingageinpopulationsthatupuntilrecentlywere
1999, 2002). Well-documented cases include crab-eater growing fairly rapidly guarantees that more births than
seals in Antarctica infected with distemper by sled-dogs, deathswilloccurforessentiallyanaveragehumanlifetime
sardines in Australia infected with herpes virus caught after replacement fertility is reached. Also, high levels of
from imported frozen pilchards, and sea-fans in the migration mean that most nations experiencing low fer-
Caribbeankilledbyasoil-borne fungus. tility rates will continue to grow (International Organiza-
The further interaction between human populations tionforMigration 2000;UNPD2002).
and economics offers an additional obstacle to the con-
servation orrestoration of aquatic ecosystems. When eco-
GLOBAL TRENDS: THE CASE OF
systemsaredegraded,acommonactionoflastresortisto
GLOBAL MARINE FISHERIES
attempt some sort of protection, where human use and
accessarerestricted.Buttheprocessofsettinglandand/or Given the means and opportunity, fishers like hunters
fishing space aside becomes more difficult as population beforethemultimatelydepletetheresourcesthattheytarget
density increases. People may bid up the price of land to (e.g.ClovisofNorthAmerica:Alroy2001).Understanding
the point where conservation efforts become financially this analogy is important, as it provides a framework for
impossible(Cincotta&Engelman2000).Landconservation understandingtheseveredepletionofsmallerandmid-size
organizationshaveincreasinglyfocusedonwetlands,coasts mammals in Africa (‘bushmeat’: Bowen-Jones 1998) and
and other aquatic ecosystems, knowing they are in a race large fishes in the world’s oceans. The recent marine fish
with time to buy key parcels of land or convince govern- biomassdeclines(e.g.Christensenetal.2003fortheNorth
ments to protect them. Too rarely, however, do conser- Atlantic) are primarily attributable, not to scientific
vationists acknowledge that continued population growth incompetence in monitoring (Malakoff 2002), nor shifts in
limitstheirprospectsforlong-termsuccess,simplybecause distribution (Bigot 2002), nor regime shifts (Steele 1998),
land will become too valuable to serve environmental buttooverfishing(Jacksonetal.2001).
ratherthan economicinterests. When fishing starts in a new area, the large fishes go
Market forces and global economics can also greatly first,astheyarerelativelyeasiertocatchthansmallfishes
influence theneed for anddevelopment ofportand ship- (e.g. with harpoons or lines) and tend to provide a better
pingfacilities.Historically,estuariesandsaltmarsheshave return on investment (Pauly et al. 2002). Large fish, with
provided cheap sources of land for development. As theirlownaturalmortalitiesandrelativelyhighageatfirst
commodities continue to be traded onglobal markets and maturity (Pauly 1980; Froese & Binohlan 2000), cannot
shipsbecomeeverbigger,thedemandforcoastallandfor sustain substantial fishing pressure and rapidly decline
development will increase and much of it will become (Denneyetal.2002),forcingthefisherseithertomoveon
degraded(Pinnegar etal.2006). to smaller fishes, and/or to other, previously unexploited
While these interactions between human population areas.Aslargerfishtendtohavehighertrophiclevelsthan
andaquaticecosystemspaintableakpicture,therearealso smallerfish–indeed,thelatterareusuallythepreyofthe
reasons for hope. One of the most positive trends is that former – this process, now called ‘fishing down marine
the human population is seen by most demographers as food webs’, leads to declining trends in the mean trophic
unlikely to double again. One way to explain this is that level of fisheries landings (Pauly et al. 1998; though see
women all over the world are having fewer children than Caddyetal.1998).
everbefore,andseeminglywanttohaveevenfewerinthe The ‘fishing down’ process has occurred around the
future. Average family size has shrunk from five children world (Table 1.2) and the broad pattern is that fishing
per woman in the early 1960s to a bit more than 2.5 targets a succession of species until the residual species
childrenperwomantoday.Inmorethantwo-fifthsofthe mix ceases to support a fishing economy. This implies a
Introduction 9
Table 1.2. Occurrence of ‘fishing down’ using local/detailed data sets, following the original presentation of this
phenomenon by Pauly etal.(1998), basedon the global FAOcatch dataset
Country/areaa Years Decline Source and remarks
Iceland 1900–1999 1918–1999 ValtssonandPauly(2003),basedoncomprehensivecatch
databaseof Valtsson(2001)
CelticSea 1945–1998 1946–2000 Pinnegar et al.(2002), based ontrophic levels estimated
fromstableisotopes of nitrogen
GulfofThailand 1963–1982; 1965–1982; Christensen (1998); Pauly andChuenpagdee (2003)
1963–1997 1965–1997
Eastern Canada 1950–1997 1957–1997 Pauly et al.(2001), based ondata submitted toFAOby
theCanadian Department ofFisheries and Oceans
Western Canada 1873–1996 1910–1996 Pauly et al.(2001), based oncomprehensive dataset
assembled byS.Wallace
Cuban EEZ 1960–1995 1960–1995 Pauly et al.(1998) and Baisre(2000)
EastCoast, USA 1950–2000 all R. Chuenpagdee et al.unpublished data;emphasis on
Chesapeake Bay
Chinese EEZ 1950–1998 1970–1998 Pang and Pauly (2001)
West Central 1950–2000; 1950–2000; D.Pauly andM.L. Palomaresunpublished data, based
Atlantic 1950–2000 1950–2000 onFAOdata (Area 41),disaggregated into USA
(North)and other countries (South)
World,tuna and 1950–2000 1950–2000 D.Pauly andM.L. Palomaresunpublished data, based
billfishes onFAOdata (ISSCAAP [International Standard
Statistical Classification ofAquatic Animals and
Plants]group 36 only)
World,all fishes 1950–2000 1950–2000 Pauly and Watson (2003), based onspatially
disaggregated data
aEEZ,Exclusive Economic Zone.
transition fromfisheries targeting largefish (e.g.northern Exports have become a major issue in fisheries, with
cod) to those targeting smaller fishes (e.g. capelin) or marine products being amongst the most heavily traded
invertebrates(e.g.northernshrimpandsnowcrab).Inthe commodities (Pauly et al. 2002). The general trend is for
north-east Atlantic, fish species that mature later, grow developed countries to increasingly to compensate for the
more slowly and have lower rates of potential population shortfall of products from traditional fishing grounds in
increase, have exhibited greater long-term declines in their exclusive economic zones (EEZs) by fishing in
abundance than closely related species which are smaller, developing countries (Pauly et al. 2005). Given the debts
grow faster and are more fecund (Jennings et al. 1998, thatmostdevelopingcountrieshaverunupwithrespectto
1999; Dulvy et al. 2000). In sharks, rays and skates, large international lenders, this implies that marine resources,
sizecombinedwithlowfecunditymakesthemparticularly and their underlying ecosystems, suffer from increased
vulnerable to overexploitation; many populations have pressure to make up shortfalls. Examples include the
beenrapidlydeclining(Dulvyetal.2000)andarelikelyto countries of West Africa, whose dependence on financial
be rendered extinct in the coming decades (Dulvy et al. support from the European Union forces them to sign
2003). In some cases, depletion of keystone species may fisheriesagreementsprovidingaccessforEuropeanfishing
haveimportantindirecteffectsoncommunityandhabitat fleets under terms that appear unfair to these countries
structure (e.g.Dulvyetal.2004). (Kaczynski & Fluharty 2002). In Argentina, demersal
10 R. ENGELMAN ET AL.
Table 1.3. Marine fishthat are unlikely to survive,given continuation of presentfisheries trends
Majorfeatures Representative groups
Large- tomoderate-sized, predaceous, territorial reef Snappers, seabasses, emperors, rockfishes, seabreams
fishesand rockfishes with late age atmaturity, very
lownatural mortality ratesand lowrecruitment rates
versus adultstock size
Large- tomoderate-sized shelf dwelling, softbottom Cods, flounders, soles, rockfishes, croakers, skates
predators susceptible tobottom trawling
Large- tomoderate-sized schoolingmidwater fishes Hakes,rockfishes, armorheads, rougheyes
susceptible tomidwater trawling
Large- tomoderate-sized shelf dwelling, schooling, Bonitos,sierras, capelin, eulachon, salmon, sharks
pelagicfishes
Anyspecies withexceptionally high monetary value Bluefintuna, redsnappers, halibuts, medicinalfishes,
aquariumfishes,groupers,salmon,redmullets,billfishes
Source: Adapted fromParrish (1995, 1998) and Pauly (2000).
resourceswhichintheearly1980swereamongthefewthat now derives from aquaculture. However, as currently
were both large and underexploited have now collapsed practised, aquaculture also causes environmental damage,
underthepressureofbothnationalandinternationalfleets, raising questions about how to meet food demands and
licensed for their ability to generate foreign exchange preserve environmental quality (WRI 1998). Aquaculture
(Sa´nchez 2002). infactexistsintwofundamentallydifferentforms.Oneis
Given present trends and pressures, present target devoted to the farming of bivalves (e.g. oysters, mussels)
speciesarenotexpectedtosurviveandsmallnon-palatable and/orfreshwaterfish(e.g.carp,tilapia)andreliesmainly
non-schooling species will be those that will fare best onplantmattertogenerateanetadditiontothefishfood
(Table1.3).Inextremecases,finfishmaybeprogressively supply available to consumers. This is based predomin-
replacedbyconsumerspeciessuchasjellyfish,whichhave antlyindevelopingcountries(mainlyinChina,butalsoin
few predators and may impede any finfish recovery (e.g. countries such as the Philippines and Bangladesh), and
northern Benguela,Namibia: Lynametal.2006). supplies cheap animal protein where it is needed (New
The fishing industry on its own is incapable of 2002).Bycontrast,theotherformofaquacultureinvolves
reversing the fishing down of food webs. There are other thefarmingofcarnivorousfishsuchassalmonorseabass,
socialforces,whichcanandwillplayanincreasingrolein andincreasingly,thefatteningofwild-caughtbluefintuna.
the international debates on fisheries. Foremost is the In nature, salmon, sea bass and bluefin tuna have high
communityofnon-governmentalorganizationsdevotedto trophic levels, hence it is impossible to feed them only
maintainingorre-establishing‘healthy’marineecosystems, on vegetable matter. This implies that as this form of
and striving for ecosystem-based fisheries management. aquaculture increases, there will be fewer cheap fish (e.g.
Publicdebateaboutfisherieswasunheardof20yearsago, sardine, herring, mackerel and anchovies) available for
andmanyconservationbiologistsfeeltheyneedtodebunk humanstobuyandeat.Itisthusnotaddingtoglobalfish
those who deny the need for action (e.g. Lomborg 2001). supply, and instead increases the pressure on wild fish
Globalcatchesaredeclining(Watson&Pauly2001;Pauly stocks(Nayloretal.2000).
et al. 2002) but catches can and usually do remain high This second type of aquaculture predominates, and it
when stocks collapse. Thus the cod off eastern Canada hasledtomassiveimportsbydevelopedcountriesofmeal
yielded good catches until the fishery had to be closed fromfishescaughtandgroundupindevelopingcountries,
becausetherewereliterallynofishleft(Myersetal.1997). exacerbating fishing pressures in these regions. Coastal
Some suggest that aquaculture could help compensate pollution and diseases emanating from the uneaten food
for overfishing, and a quarter of human fish consumption andfaecesofthesemarinefeed-lotoperationsarealsoseen