thefoodchainareknownasareasof highproductivity.
So what makes some areas of the ocean more
productive than others? Firstly, phytoplankton need
sunlightto providetheenergyto photosynthesise,but
because sunlight disappears rapidly as it enters the
ocean,phytoplankton needto benear the surfaceto
survive,evenin deepoceans.Toreproduceandgrow,
phytoplankton also need nutrients such as dissolved
iron, phosphorous and nitrogen. These nutrients are
typically brought to surface ocean waters through
either deep-water upwelling, eddies mixing cold and
warmwaters,riverinputsor rainfall.FISH NEEDOXYGENTOO
While phytoplankton require sunlight and nutrients
togrow,theanimalshigherin thefoodchainrequire
notonlyphytoplanktonto eat(orsomethingthateats
phytoplankton),butalsooxygen.Fishneedto breathe
dissolvedoxygenin thewaterto survive.
Oxygen enters the water either through the
photosynthesisprocessgeneratedby thephytoplankton,
or through wind and wave action dissolving oxygen
from the atmosphere. Cold water can hold more
oxygenthanwarmwater.
A lackof oxygenin anaquaticenvironmentcanhave
catastrophiceffects,andthisis oftenthecauseof fish
die offsin inshore andinland waters,although such
extreme reactions are very rare in the open ocean
environment.AUSTRALIA’SCONTINENTALSHELF
The continental shelf is generally considered to be
thewatersshallowerthan200m.Manyof theworld’s
most productivebottom fisheries(demersal species)occuronthecontinentalshelfand
associated continental slope. By
worldstandards,most ofAustralia
hasa relativelynarrowcontinental
shelf. New Zealand by contrast
has a much larger portion of its
waters on the continental shelf
andslope,andthereforehasmuch
largerfisheriesforspecieslikeblue
grenadier(alsoknownashoki)and
lingthanAustraliadoes.
Australia’s narrow continental
shelfhastheadvantageof bringing
largeoceanicgamefishcloseto the
coastandwithinrangeof modest-
sized boats. The famous narrow
shelf at Bermagui means even
trailerboats have easy accessto some of Australia’s
most iconic game fishing grounds. In fact, the
proximityof thesedeepwatersto a suitableportsaw
thebirthof Australia’sgamefishingindustry.
Australia’s narrow continental shelf also means
commercial tuna boats typically fish closer to shore
than most otherplaces in the world,enabling them
to land fresh,unfrozenproduct andfly it directly to
Japan,givingthema uniquemarketadvantage.MANAGEMENT FOR
A LIMITED RESOURCE
Fisheries managers needtounderstand andaccount
forproductivitywhenmakingmanagementdecisions.
The Australian Fisheries Management Authority
(AFMA) takes this into account when setting catch
limits andputting in placemeasuresto ensure they
are adhered to. Because of the low productivity of
the waters surrounding Australia, it is unlikely that
AFMAwilldevelopthelarge-scale,highlymechanised
fishing operationsseenoff SouthAmerica, Alaskaor
theNorthSea.Forthisreason,Australia’scommercial
fishingindustrylargelyfocusesonsellinghigh-quality
product in relatively lowvolumesto export markets
primarilyin Asia.
FortunatelyforAustralia’sanglers, therelatively low
productivity of the country’s surrounding waters has
notimpactedthequalityof gamefishingopportunities.
Black marlin have long been known to spawn off
CairnsandfollowtheEasternAustralianCurrentdown
the coastastheygrow.Theusuallytropicalandsub-
tropicalstripedmarlinalso followthewarm watersof
thiscurrentsouthto becommonlycaughtoffBermagui
and Merimbula, with global warming now extending
somemarlindownasfarsouthasTasmania.RESEARCHFORTHEFUTURE
AFMA, along with the Fisheries Research and
DevelopmentCorporation,CSIROandtheNewSouth
Wales Fishing Trust, are all investing in research to
better understand how tuna and billfish respond to
oceanographicconditionsandproductivityevents.It is
hopedthatin comingyears,AFMAandotherswillbe
ableto reportthefindingsfromthisresearchin future
issuesofBlueWater.“Australia’s
narrow
continental
shelf has the
advantage
of bringing
large oceanic
gamefish
close to the
coast.”
Australia is an old and dry continent, with its
sparse southern rivers delivering little water
flow and few nutrients to feed growth in the
ocean. Consequently, Australia is regarded as
having low productivity along its continental
shelf waters.Black marlin are
known to spawn
off Cairns, with
the juveniles
subsequently
following the Eastern
Australian Current
south as they grow.70 facebook.com/BlueWatermagazine
AFMA: Australia’s ocean productivity