Table Of ContentSCALLOPFISHERIES !NSOUTHERN AUSTRALIA:
MANAGINGFOR STOCK RECOVERY
WILLZACHARIN
Zachann, W. 1994 08 10: Scallop fisheries in .southern Australia: managing for stock
recovery. Memoirs ofthe Queensland Museum 36(2); 241-246. Brisbane. ISSN 0079
8835.
ScallopfisheriesinsouthernAustraliaare showingsignsofslockrecoveryafteraperiodof
lowabundance.Therecoveryhasbeensporadicandslowalthoughlargeareasofthefishing
groundshavebeensubjecttolittleornofishingforupto5years.Newmanagementstrategies
designed toencourage stock recovery and promotesustainableharvestsin the futurearc in
place. Managementstrategiesand fishery monitoringprogramsarepresented.
WillZacharin,SeaFisheriesDivision, Departmentof'HnmorvIndustryandFisheries, GPO
Box6l9F. Hoban, Tasmania 7001,Auumita: 15April 1994
Thereare5 distinctcommercialscallopFishing that management decisions can be based on a
zonesinsouthern Australia Port PhillipBayami soundunderstandingofbiologicalandoperation-
:
Lakes Entrance in Victoria; the greater area of al characteristics of the fishery; 4, to allow an
Bass Strait (known as the Central Zone), the 20 effective level of recruitment to the fishery by
nautical milezonearound the north coastofTas- prohibitingthetaking ofscallopsof<80mmwith
mania called the Tasmanian Zone, and the east a view to allowing adult stocks to complete at
coast ofTasmania (Fig.l). They are geographi- leasttwo majorspawningsbeforeharvest;and 5,
callydistinctin termsoftheirhistoricalcatchand to allow participants to maximise their return
fleetdynamics. Managementisunderthecontrol fromharvestingthescallopresource. (BassStrait
of3 separate authorities; the Victorian and Tas- ScallopManagementPlan 1992,Commonwealth
manian Slate Governments and the Common- Fisheries Act 1991 j.
wealth Government (Australian Fish Man- The resultant management strategy combines
agementAuthority) Threedifferentmanagement inputandoutputcontrolstorestrictthenumberof
strategies are operating. fishers;toprohibitthetakingofsmallscallops;to
The Bass Strait ScallopConsultative Commit- control scallop landingsandto provide level of
fl
tee(BSSCC)formedin 1991 todeveloparational profitability to the fleet.
management plan for scallop fisheries across
Ba.vN Strait. This was the second time in the CONTROLS ON FISHING
fisheries' history that such a process had been
attempted(Zacharin,1990. 1991) Anearlierplan In the past, both the States and the Common-
developed by the B3ss Strait Task Force which wealth restricted fishing activities by imposing
recommended that the fisheries* jurisdiction be inputcontrols,suchasclosed seasons,sizelimits
split between Victoria and Tasmania was not and dredge restrictions. Over the past 4 years
effectively implemented (Zacharin,1990). there has been a shift towards output controls as
Fishermen and managers recognised that future theyareperceivedtobemoreeffectiveinmanag-
harvesting strategies needed to be based on cur- ing catch and controlling quality, provided that
rent biological knowledge of the species (in the necessary level of monitoring and enforce-
regard to reproductive maturity and growth ment is present A size limit of80mm at widest
rates), fleetdynamics andthe need foreconomic diameter, however, still exists. The two main
efficiency.Thecommitteedraftedamanagement strategies of the new management plan for the
planwith 5 mainobjectives: I, tocontrolfishing CentralZoneofBassStraitarethe ' 20%trashing
effort to a level which is consistent with the rate' requiremeni and the 'two-spawnings'
currentstateofknowledgeofscallopstocks;2.to criterion.The20% trashing rate wasdesignedas
encourage investigation and modification ofthe ayieldoptimisationstrategy,throughlimitingthe
most appropriate fishing equipment and fishing captureof,andminimisingincidentalmortalityto
practicesto improvecatchefficiency andtomin- small (<S0mm at widest diameter) scallops. The
imise damage to the scallop beds; 3, to allow 'two spawning' criterion is a parallel manage-
furtherscientificandotherdatatobecollectedso mentrequirementdesignedtoallow scallopstwo
242 MEMOIRS OFTHEQUEENSLANDMUSEUM
FIG.L Southern Australian scallop fishery divided into 5 distinct zones. Port Phillip Bay (1), Lakes Entrance
(2), BassStrait(3), northernTasmania(4),andeasternTasmania(5).
major spawnings prior to their being fished, commercial operations. Ifmore than 20% ofthe
without regard to size. Thus scallops need both catch landedon the sortingtray is being returned
to have spawned twice and have less than 20% to the water, fishermen are required to cease
of the catch smaller than 80mm at widest fishing in the area until scallop size increases.
diameterpriortotheirbeing fished. ThisisnotdifficultforthemajorityofBassStrait
The trashing rate is the proportion of small scallopbeds as theyare usuallyoftheonesizeor
scallops discarded over a fishing ground during age class. However, in the event of two age
SCALLOPSTOCK RECOVERY,SOUTHERN AUSTRALIA 243
classesbeing mixed in theonearea,a20%trash- yearand closes in late December. This summer
ing rate is considered acceptable, having regard closure protects juveniles from dredge damage
forincreasingmortalityintheolderageclass,and andstopsscallopswithpoormeatconditionbeing
the potential ofpredators (o significantly reduce landed. In most years, post spawning meat and
theremainingscallopsonafished bed. gonad condition does not improve until March,
Failureoffishermentoleavetheareacanresult Scalloplandingsaresubjectto'quota*,setpertrip
in a 3 month closure to the whole fishery. This or fortnightly. At present the quota is 150 units
closure can be implemented by the management per fortnight: aunit beingablackpolypropylene
committeeundera specificprovisionin the BASS onion bag measuring 900mm x 580mm and
Strait scallop managementplan. having a volume of0.08 m3 This measure owes
.
Application of trashing rates are not new in iLs derivation to the past availability and suit-
shellfish management. A trashing rate of not ability ofonion bags forlanding scallops.
more than 30% of landed catch was introduced Whilethefortnightlyquotadoesreducefishing
into the eastern U.S offshore clam fishery in effort to someextent, this is not its primary pur-
1983. The reason was loprevent wastage due lo pose. It isamarketingtool whichprovidesforthe
excessive discarding and to meet minimum size landing ofquality scaJlopsand prevents wastage
requirements (Murawski & Serchuk, 1989). due to time delays in landing and processing
Twomajorspawningsfromadults,priortotheir largervolumes. Itpreventsa 'goldrush' event,as
beingfished,areconsideredessentialifsufficient occurswhenthereisacompetitivetotalallowable
reproductiveoutput fromthefishery is to occut. catch. The catch quota was agreed through
CommercialscaJlopsinBassStraithavetheirfirst negotiationbetweenGovernment,fishermenand
major spawning in their second year (1+ age the processing sector. Ifcosts offishingrise and
class).However,fecundityisrelativelylowatthis landed price falls or even remains steady, it is
age(R. McLouglin pcrs. comm.) and therefore possible fortheindustry tore-negotiatethe catch
delaying the fishing until the scallops' second quota at any time. Profitability ofthe fleet is a
majorspawningisdesirabletoincreasethe prob- main objectiveofthe management plan.
ability of some recruitment from that particular Catch is also controlled in the Victorian and
age class of adult spawners. Restricting fishing Tasmanian Zones. In Victoria a weekly catch
operationsevenfurtheruntilathirdmajorspawn- limit iscurrentlyoperating, while inTasmania,a
ing has occurred cannot be defended, as natural 'per trip' limit will continue to operate when
mortality is thought to be high in Bass Strait fishing recommences in the future.
populations after scallops reach an age of four
years. High levels of predation by starfish on QUOTA MONITORING ANDCATCH DATA
commercial scallop beds have been observed on
a numberofoccasions. Each unit ur bag landed must have a plastic
Delaying the time offirst capture till alter the colour-coded lag attached Tags are issued each
second spawning hasa numberofotherbenefits. monthinadvancebytheAustralianFishManage-
Scallops have another year's growth, which ment Authority Unused tags are returned as a
results in the majority ofthe population reaching costsavingmeasureandarcre-issuedthefollow-
a shell height 70mm (shell width 80mm), In- ing year but in a different month. Numerical
dividual yields increase c.30%, and the landed coding also changes each month and yeat to
value ofthe fishery should rise. There is an as- ensureunusedtagswillnotbeheldoverfromyear
sumptionthatthereisnorapidincreaseinnatural toyear. The tagsystem allowsefficient monitor-
mortality.Ayieldoptimisationmodelneedslobe ing and enforcement Ofthequota, and in provid-
completed tosupport this assumption. ing a validation system for scallop landings
The crux of the management plan is, ii the through the processing sector.
trashingrateisbelow20%,thenitcanbeassumed A new logbook introduced in 1992 is based on
that the bed should be fished until it is no longer a 7 x 7 nautical mile grid. Returns are filled out
economically viable to continue. After fishing for each trip and data entered on a central com-
scallops will still remain in the area but at a low puterdatahase in Hobart. The system willgive a
density. betterassessmentoffleet dynamics exploitation
rates and total landed catch from the Central
CATCH RESTRICTIONS Zone. In the past the fleet has provided catch
returns without meaningful spatial data to the
TheBussStrait fisheryopenson 1 Aprilofeach Slate authoritv in which the vessel was based,
-
244 MEMOIRSOFTHEQUEENSLAND MUSEUM
Consequently, nocomprehensiveanalysis ofthe testedunderrigorousfishingoperationsduetothe
fishery has been possible. Victorian and Tas- low level of commercial fishing operations.
mania* fisherymanagerscontinuetocollatetheir Mechanisms suchas at-sea monitoring andshore
own catch returns from the inshore 20 nautical based market measurers will provide for a quick
mile zones. response to any problems that arise with regard
to scallop size. The Victorian fishery has been
LICENSING operating under a tag system for two years and
the scallop industry seems pleased with the
AH 3 jurisdictional /.ones are limited entry progressofthinsystem
fisheries and no new licences will be issued. Anymanagementplan forthesouthern scallop
There are 165 vessels licensed to fish in the fishery should be complementary between Vic-
Central Zone. Ofthese73 arebased inTasmania torian and Tasmanian authorities The new plan
and92inVictoria. LicencesinVictoriaaretrans- for the Central Zone goes a long way towards
ferable and have been for the better part of the achieving this, however, further gains may be
30-year history of the fishery Jn Tasmania, difficult because of the differences in fleet
limitedentry was not introduced until 1986 with dynamics between the two Stales.
transferability following in 1992 (Zacharin, The Victorian scallop fishery has a single
1990), Central Zone licences are still non-trans- licensed fleet that isheavily depreciated and lar-
ferable pending the development of options for gelyrelianton annual scallop fishingseasons. In
reducingthenumberofparticipantsLnthefishery. Tasmania the multi-purpose fishing fleet has
It is desirable that the issue of transferability be evolved with the majority of scallop licences
resolved,asCentralZone licencescannotbesplit being on vessels with rock lobster entitlements.
from State scallop licences, which are trans- Other Tasmanian scallop vessels are licensed to
ferable. It would be highly undesirable to create drop-line, trawl or take shark during a closed
a 'third' scallop fleet in the Central ZoneofBass scallop season. These differences in dynamics
Strait. An important objective of ihc licensing betweenthe VictorianandTasmanianfleetshave
policyistohavealltheCentralZonelicencesheld resulted in each having different economic con-
by the Stale scallop fleets, as (he inshore scallop straints. The zoning of the Bass Strait scallop
fishing grounds have historically provided the fishery needs to be retained to enable the subtle
bulk ofthe scallop catch, with the Centtal Zone differences in management priorities tooperate,
providinggoodcatches intermittently. as appropriate foreach State's fishing industry.
FISHING GEAR RESEARCH ANDDEVELOPMENT
REQUIREMENTS
The southern scallop fishery uses tooth-bar
steel box dredges 2-4.5m wide. Protruding teeth Six future research needs, identified for the
on the bars range from 2.5-15cm, depending on soulhern scallop fishery by Ihe Bass Strait
the type ofbottom sediment and the individual Management Committee, are listed in order of
operator. Thesedredgescan cause high levelsof priority; 1, confirmation that BassStraitscallops
incidentaldamageandalternativedesignsarestill consist of a single stock; 2, development of an
being investigated. Evidence from dredge trials efficient and reliable recruitment monitoring
shows that up to 50% of scallops in the dredge's technique to provide an index ofannual spatial!:
pa(h may be damaged, depending on the type of 3. development of statistically reliable survey
bottom, length of toothbar. density of scallops techniques for assessing biomass on individual
and fishing practices. Dredge efficiency can be beds; 4, assessment of the overall impact of
l%ow, having beenexperimentally measured at 10 predationbystarfish{Coscinasteriassp.)onscal-
(McLougliitetui,1991). Geartechnology im- lop populations; 5* investigation of recruitment
provements are important tn this fishery as any enhancement/sea ranching ofscallops as per the
reduction in incidentalmortality and increases in New Zealand model; and 6» investigation ofdif-
efficiency will reduce costs and increase yields. ferences in growth rates and fecundity schedules
for scallops in different regions of Bass Strait
EFFECTIVENESS OFMANAGEMENT (Bass Strait Scallop Management Committee
STRATEGIES lW2,mimeo).
\
The second priority is importantinprovidinga
The new planfortheCentralZonehasyel tobe measure of success of the management plan.
SCALLOPSTOCKRECOVERY. SOUTHERN AUSTRALIA 245
specifically the two-spawning criterion. A environmental variables on successful spawning
recruitment indexalsoprovidesearlywarningof events, settlement and subsequent recruitment
recruitment failure or 'above-average' recruit- Stock/recnul relationships of P. fumatus in
mentsuccess. southern Australia appear to be extremely noisy
The impact of predatory starfish was iftheyexistatall.Theseobservationssupportthe
demonstratedtobeofconsiderableimportancein new strategy of allowing two major spawnings
1992. An identified scallop bed east of Deal Is- before harvesting, particularly in the offshore
land in Bass Strait was decimated by starfish fisheries where retention of spat over scallop
duringadelaytofishing,inanattempttoconform grounds will be more variable than in the
(o thetwo-spawning criterion and improve scal- enclosedenvironsofPortPhillipBay.
lop yields. Further investigation of these Tt is important to remember that the scallop
predators is necessary to prevent such an occur- fleets of Victoria and Tasmania are different in
rence happening again terms of their level ofcapital investment, vessel
specifications, fishing patterns and reliance on
PROGNOSIS FOR 1993 AND BEYOND the scallop resouice forincome. Nohardand fast
management planacrossthe threeexistingzones
Therehasbeenasignificantrecoveryofscallop will be successful in meeting both States' ad-
stock(s) in both Port Phillip Bay and off Lakes ministrative and economic requirements. Com-
Entrance in Victoria.Alargesettlementoccurred plementary management plans ihat take account
inthespringof1990withsubsequentrecruitment Of ihese differences ;ire preferable to continued
to the fisheries in t992. Further settlement has friction between the two State based fleets. One
beenobservedineachofthefollowingyears and needstobeawarethatthe majority ofthehistori-
the fisheries arc showing good prospects for the calcatchhascomefromthestate20 nauticalmile
nextonetotwoyears(Zacharin - pers. obs). It is zones, the Central Zone resource being one of
ironic that the beds off Lakes Entrance (which sporadic opportunity.
have been sporadically fished) have recovered Change for its own sake can be a destructive
before iM scallop grounds in Tasmania (where policy. The success or otherwise of the current
the fisheryhas been closed forfiveyears). In this management plan operating in thesouthern scal-
instance, total closure ofthe fishery has not lead lopfisheryshouldbeassessedbeforemajorchan-
to any earlier stock recovery than has been ob- ges arc contemplated Feedback op theeffectsof
served in Victorian waters, where fishing con- the trashing rate and twospawning strategy will
tinued. However, there is no certainty that the notbeevidentfortwotothreeyears.Withthenew
factors affecting recruitment off Lakes Entrance logbook providing better spatial information on
applyoveramuchwiderarea,andnoconclusions catch, an integrated catch database system and
c$r be made in terms of management for stock progression towards developing a recruitment
recovery. index or forecasting system, management ofthe
Recentexploratoryexcursions intotheCentral scallop resourcesin southern Australia can only
Zone and the northern Tasmanian Zone have improve.
shown thatjuvenile scallops are present over a The Australian Fish Management Authority
wide area. Ifthesejuveniles successfully recruit will piobably relinquish responsibility for the
intothefisheryin 1993and 1994.aneconomical- BassStraitscallop fishery in 1994andleavejoint
ly viable fishery will again operate in the Tas- management to the Victorian and Tasmanian
manian and Central Zones. agencies. A jurisdictional line would be drawn
for the purpose of monitoring and enforcement
LESSONSTO BELEARNT responsibilities.Theexistenceofremaining Bass
Strait permits forthe CentralZone which are not
Therecoveryofthe Victorian scallopgrounds, attachedtostatescalloplicence*mayimpedethis
throughwhatappearsinPortPhillipBaytohedue proeej-
to an enormous settlement event in 1991, is dif
ffculltoexplain.Theresidualstock inthebaywas ACKNOWLEDGEMENTS
apparentlyatanalltimelowat 19million, butone
of(he largest recorded settlements has occurred. Thanks arc due to the many memhers of the
The estimated abundance is in excess of 800 Bass Strait Scallop Consultative Committee for
million scallops (D. Molloy, pcrs. comm.). This plugging away at a new management plan after
is another example of ihe critical influence of ten years of meetings at all manner of manage-
246 MEMOIRSOFTHEQUEENSLANDMUSEUM
mentcommittees and venues. I wouldalsothank MURAWSKI, S.A. & SERCHUK, F.M. 1989.
twoanonymousrefereesforsuggestingimprove- Mechanized shellfish harvesting and its manage-
mentstothis manuscript. ment: the offshore clam fishery of the eastern
UnitedStates.Pp.479-506. InCaddy,J.F., (ed.),
LITERATURECITED ZACH'AMRaIriNn,eiWnv.eFrte1b9r9a0te.fiSschaelrlieosp*.fisheries manage-
COMMSTORNAWIETASLCTAHLLFOIPSHEMRAINESAGAECMTE1N99T1:PBLAASNS mDernetd:ge,theM.TLa.sCm.a,niZaacnhaerxipne,rieWn.cFe.. &Pp.Jo1ll-,11L..M.I,n
(eds), 'Proceedings of the Australasian Scallop
MCLOP1U9AG9R2L.SILNO,WR,.J,J.YO1U99N1G.,TPh.eC,AuMsAtrRaTlIiaNn,sRc.aBl.lo&p ZACHWmAeoRnrItkNsP,hrionWpt.eFrH:.oHb1oa9br9a1tr.t)S1.9l8o8w'.re(cToavsermyanfioarnBaGsosvSetrrani-t
dredge: estimates ofcatching efficiency and as- scallops. Australian Fisheries 50(1): 28-30.
sociated indirect fishing mortality. Fishery Re-
search 11: 1-24.
