Kahekili Herbivore Fishery Management

KahekiliHerbivoreFisheryManagementArea—InterimMonitoringResults
Background.Inresponsetoconcernsaboutthelong‐termdeclineoflocalcoral
reefs,thestateofHawaiicreatedtheKahekiliHerbivoreFisheryManagementArea
(KHFMA)alonganapproximately2‐milestretchofcoastlineinKa’anapali,West
Maui(seepictureright).TheKHFMA,whichwasestablishedinJuly2009,involvesa
formofmanagementthatisuniquewithinHawaii,namelyprotectionofcoralreef
herbivores(i.e.,surgeonfishes,parrotfishes,chubs,andseaurchins),whichmaynot
bekilled,injured,orharvestedwithintheFMAboundaries.ThegoaloftheKHFMA
istorestorenaturalgrazingprocessesandultimately,therefore,toincreasethe
localreef’sabilitytoresistandrecoverfromexcessivealgalgrowththatis
detrimentaltocorals.TheKHFMAdoesnotinanywayrestrictfishingofothertypes
offinfishorinvertebrates.Tofurtherpromotegrazingbylocalfishstocks,feedingof
fishes,otherthanforlegalfishing,isalsobannedwithintheKHFMA.
IntheyearsimmediatelyleadinguptothecreationoftheKHFMA,summertime bloomsoftheinvasiveredalga
Acanthophoraspicifera,hadbecomeregularoccurrencesontheKahekilireef(seepicturesbelow).Large‐scale
seasonalbloomsofotheralgalspecies,suchasthegreenalgaCladophorasericea,hadalsobeendocumentedin
precedingyears,includingin1999and2001,andapparentlyalsoatothertimessinceatleastthemid‐1980s.Of
particularconcernwasthedeclineincoralcoverevidentinlong‐termmonitoringdatafromtransectsinfrontof
KahekiliBeachPark:from~55%in1994,whenmonitoringbegan,to~30%intheyearspriortothe
establishmentoftheKHFMA.Thedeclineincoralcovercoincidedwiththeperiodbeginningin1999during
whichsummertimemacroalgalbloomswerecommonlyobserved(seefigurebelow).Althoughthecausesand
consequencesofthosealgalbloomsarecomplex,itisreasonabletoexpectthatprotectionofreefherbivorescan
reducetheseverityandfrequencyofalgalbloomsand,therefore,canhelptocheckandpotentiallyreversethe
downwardtrendinconditionofKahekilireefs.
Pictures show examples of algal blooms at Kahekili in (left) 2005 and (right) 2001. Photos R. Sparks, J. Smith Figure at right shows trends in coral and macroalgal cover prior to creation of the KHFMA. Note that decline in coral cover coincides with the period in which summer algal blooms were regular occurrences. CoralreefmonitoringwithintheKHFMA.Becauseitis
highlydesirabletohavebaselinedatabeforea
managementactionisimplemented,theHawai’iDAR
(HDAR)inpartnershipwiththeUniversityofHawai’i
beganacomprehensivemonitoringprogramatKahekiliin
January2008.Thatprogramhasbeenmaintainedusing
consistentmethodsandsurveydesign,butithasbeen
implementedbyHDARandNOAAPacificIslandsFisheries
ScienceCenterpersonnelsince2010.Monitoringinvolves
1–2“rounds”peryear,generallyspringandlatesummer,
witheachroundcomprisingco‐locatedsurveysoffishes,
urchins,andbenthos(e.g.,coralsandalgae)at~80–100
haphazardlylocatedsites.Thefiguretotheleftshowsdata
fromApril2012:eachbubblerepresentsasurveysite,and
sizeofbubblecorrespondstoeitherbiomassorcover(%).
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PIFSC Internal Report IR‐13‐008 Issued 22 February 2013 BulletheadParrotfish(Chlorurusspilurus)initialphase
(upperphoto)andterminalphase(lowerphoto).
PhotosJ.E.Randall.Figuretotherightshowssteady
increaseincontibutionoflargeindividualstototal
speciesbiomass.
Interimmonitoringresults.Monitoringdataweregatheredbetween
January2008andSeptember2012,i.e.,upto~3yearsaftercreationof
theKHFMA.Itisimportanttonotethatlong‐termstudiesofcoralreef
closureshavetendedtoshowthatfullrecoveryofmostgroupscantake
manyyears.Surgeonfishesappeartohaveparticularlylongtrajectories
ofrecovery,possiblyrelatedtotheirlongevity.Becausesome
surgeonfishescanlivefor>40years,pristinestocksincludebiomass
accumulatedovermultipledecades.Parrotfishes,whichhaveshorter
lifespans,seemtoreachpeakbiomasssooner,but,eventhen,itmaytake
adecadeormore.Herearethemainmonitoringresultstodate:
‐ Noclearoveralltrendinbiomassofsurgeonfishes(<‐upperfigure)
‐ Consistentupwardtrendinbiomassofparrotfishes(<‐lowerfigure),
whichmorethandoubledbetween2009and2012(3.3±0.8gm‐2
[mean±SE]to6.8±0.7gm‐2).
‐ Increasesinparrotfishbiomasshavenotbeendistributedevenly
acrosstheKHFMA,and,inparticular,therehasbeenlittleorno
recoveryofparrotfishbiomassintheshallow,nearshorereefareas
adjacenttoKahekiliBeachPark.
BulletheadParrotfishsizetrends. The
numberoflargeindivdualsofthis
species,whichisthemostabundant
parrotfishrecordedduringmonitoring
surveys,hassteadilyincreasedsincethe
KHFMAwasestablished.Itsmaxsizeis
~40cm,butin2008–09,fishes>30cm
wererarelyrecorded.By2011and
particularly2012,largeindividuals
(≥30–35cm)havebecomerelatively
common(seefig<‐).Thispatternis
consistentwithaprotectioneffect,i.e.,
reducedmortalityratesthatmeanthat
morefishesarereachingolderand
largerlifestages.Recoveryoflarge
parrotfishesispotentiallysignificant
ecologically,too,asthedeepexcavating
bitesmadebythoselargefishesare
believedtobeespeciallyimportantin
promotionoftheconditionsthatallow
coralstothrive.
Lookingahead.Themechanismsbywhichprotection of herbivores
couldincreasereefresilienceandcoralrecoveryinvolve(i)
promotionofbenignalgalformsthattendtodominateinheavily
grazedenvironments(e.g.,crustosecorallinealgae[CCA],whichare
importantforcoralsettlement),and(ii)reductionofalgaethatcan
overgrow,smother,orotherwisenegativelyaffectcorals(generally
uprightmacroalgaeanddenseturfs).Asdescribedabove,fulleffects
oftheKHFMAonfishesandonrelativelyslow‐growingcoralswill
onlybecomeevidentoveraperiodmuchlongerthanthreeyears.
However,therearealreadyindicationsthatsustainedincreasesin
parrotfishbiomasswillleadtoincreasedCCAcover.Specifically,
surveyresultsshowastrongpositiverelationshipbetweentotal
parrotfishbiomassandtotalCCAcover(seefig‐>;eachpoint
representsaverageparrotfishbiomassandCCAcoverinonesurvey
round).