Aspectsof the Biologyof the NorthernQuahog, Mercenaria mereenaria, with Emphasison Growth and Survival during Early Life History

V. MONICA BRICELJ Marine Sciences Research Center StateUniversity of New York Stony Brook, NY 11794

Abstract.Key features of thebiology of Mercenaria mercenaria are reviewed with emphasis onearly life historyprocesses. Predatory mortality during juvenile stages of thenorthern quahog is identifr ed as a primaryfactor controlling recrui tment of natural populations. Predation rates are shown to be strongly modulatedboth by substrate preference and prey-size selectivity of majorpredators crabs and carnivorous gastropods!.Smaller xanthid crabs prefer heterogeneous substrates gravel and shell bottoms!, and consumequahogs ata higherrate in thesesubstrates, whereas larger, portuni d crabsprefer and forage mostelectively in homogeneoussubstrates. In contrast topredictions ofoptimal foraging theory, even largercrabs preferentially consume smaller quahogs, when a widerange of prey sizes is available, thus increasingpredation pressure on smallerquahog size classes. Underfield conditions, atnear-optimum temperatures, j uvenile M. rnercenaria exhibit mean shell growthrates of 0.8 mm week- t maximum= 1 mmwk ~!. Native populations along the east coast exhibit comparativelylowerand higher than average lifetime growth rates at the species' northern Prince Edward Island,Canada! and southern Florida! distributional limits, respectively. These extremes correlate with thelength of the gro~ing season, which is strong Ly temperature-dependent. Thus,the time to attain Legal market-sizeranges from 1.9 to ! 6yearsand averages three to four yearsin themid-portion of the northernquahog 'slatitudinal ranges Massachusetts toVirginia!. Up to a two-to three-fold variation in growthrates is typicallyobserved within a singleestuary, Three toxic/noxious algal species are identifr ed aspotentially harmful to M. mercenariaunder bloom conditions: the chrysophyte Aureococcus anophagefferens,thechlorophyte Nannochloris atomus, and the dinoflageLLate Alexandrium fundyense. Managementimplications and suggested fruitful directions for future research are discussed throughout

the text.

Introduction The biology of northernquahogs, Mercenaria stocks.Processes operating during early life mercenaria,has been the subjectof severalearlier history stages Figure 1! are emphasized, e,g,Belding, 1931! and more recent literature becauserecruitment successinto the fishery reviews Pmtt et al., 1992;Rice and Pechenik, appearsto be largely predeterminedduring the 1992!.Therefore this paperdoes not attemptan clams'first one to two yearsof life Malinowski, exhaustivereview, but rather,will highlight 1985;Wallace, 1991!.Poorly understoodaspects somesalient features of this species'life history of thespecies' biology will alsobe stressed, in which areof significancein managingwild orderto suggestavenues for futureresearch. Fecundity,as determined by repeated spawninginduction of matureindividuals in the laboratory, is positively correlated with body size,but highly variableamong individuals of the saine size Table 1!. M. tttercenaria shows no evidenceof reproductivesenility, or declinein reproductiveoutput or gameteviability with agelsize Bricelj andMalouf, 1980!,since older clamsproduce gametes at a levelpredicted by the powercurve relating gonadmass to body sizein youngerindividuals isometricgrowth! Peterson,1986!. Bricelj and Malouf 980! showedthat matureeggs spawned at one time by Figure 1. Schematicdiagram of major factors a singlefemale are characterized by a bimodal controlling MercenariamercerLaria recruitment to a size size-frequencydistribution, with modalpeaks at shel'Ilength of 20-25 mm! whenhard clams attai n size 67 and 81 panin diameter range= ca.50 to 97 refugefrom many of their commonpredators. See text pm!, This was confirmedby Gallagerand Mann for discussion. 986!, who found that quahog eggs separated Reproduction into thee distinct bands following density Mercenaria mercenaria is a relatively slow- gradientcentrifugation. The significanceof this growing, long-lived, dioeciousbivalve, wide rangein egg sizeshas not beendetermined. characterizedby iteroparity multiple Sinceegg sizein M mercenanais known to be reproductionsover its lifespan!, high fecundities, positivelycorrelated with egglipid content productionof planktotrophiclarvae that typically Gallager and Mann, 1986!, eggs of different remainin the planktonfor one to two weeks sizesmay be characterizedby different Camker, 1961!,and high juvenile relative to developmenttimes Clarke, 1982!or differential adult survival Malinowski and Whitlach, 1988!. viability. Thus Kraeuteret al. 982! found that Importantlife history characteristicsof this sinallereggs < 35 pm! had significantly lower speciesare summarizedin Table 1. Agmg survival than eggs > 44 pm. techniquesrely on the presenceof annualgrowth Spawningof quahogpopulations is less checks in the shell, which are typically produced synchronousand startsearlier in the yearwith during the winter in the northernand central decreasing latitude Table 3.3 in Eversole, 1989!. portion of the northernquahog's geographic The length of' the spawningseason and the range,and in the summerand early fall in frequencyof peakspawning periods also tendto southeasternstates North Carolina, Georgia, increase with decreasinglatitude. A single, and Florida! Fritz and Haven, 1983; Grizzle and annualspawning peak, occurring in the summer, Lutz, 1988; and references therein!. Longevity is characteristic of northern and rnid-Atlantic estimatesfor thespecies range widely between waters e.g. Connecticut, New York, and 23 and46 yearsbecause of the difficulty in aging Delaware!, whereas two spawning peaks in the older specimens,which show crowding of spring and fall! occur in North and South growth rings and numerousspurious growth Carolina reviewed by Eversole, 1989!, and a checks. Maxiinum size ranges between 110-111 third winter spawningmay occur in Georgia inm in shell length Rice et al., 1989;Jones et Heffernan et al., 1989! and in Florida al., 1989! and 135 mm Walker and Tenore, Hesselman et aL, 1989!. Quahogs may retain a 1984!.A long lifespan,and the coexistenceof relatively high condition index after spawning multiple year classes,will tend to buffer hard Ansell et ai., 1964; Keck et al., 1975!, and clam populationsfrom suddenpopulation crashes consequently do not experience the large causedby sporadic recruitment failure. fluctuations in meat quality and marketability associatedwith changesin the reproductivecycle chemicallymediated Keck et al., 1974;Ahn, which aretypically observedin oysters, 1990!.In the field, larval settlementand/or Crassostreaspp. e.g. Purdueet al., 1981!. retentionof postlarvaemay be enhanced in shell- Settlementof quahoglarvae is highly coveredsediment, which could providea suitable gregarious,and is stimulatedby the presenceof attachment substrateand/or refuge from predators conspecifics e,g. 3 mmjuveniles! or otherclam Carriker, 1961!,but this effect hasnot been speciessuch as Gemmagemma, which often rigorously testedunder field or laboratory ocul at high densitiesin Mercenariahabitat conditions. Flume studies show that selection Ahn, 1990!.This attractionappears to be capabihtiesof quahoglarvae for a suitable

31 settlement substrate i.e. preference for sand vs. Natural Mortality: Predation mud! areaffected by flow conditions Butmanet Predation is often considered the most al., 1988!, but the relevance of this finding to significantsource of naturalmortality, and field conditions has not been demonstrated. therebythe dominant factor controlling Studies of settlement successand post-settlement recruitment successof naturally occurring survivalof quahogshave been hindered primarily bivalves,including Mercenariamercenaria e,g. by the difficulty in efficiently segregating Virnstein, 1977; Malinowski, 1985!. postlarvaefrom sediinentgrains of comparable Vulnerability to predationis known to be size. Differential settlement was successfully strongly size-dependent,with smallestquahogs usedby Ahn 990! in small-scaleexperiments, < ca. 20 rum in shell length! suffering greatest but may not be practicalfor large-scalesampling mortalities MacKenzie, 1977; Malinowski, of a patchynatural environment. 1985!.Furthermore, modeling efforts by Interactions between adult, benthic Malinowski and Whitlach 988! demonstrated populations,through suspension-feeding activity that populationgrowth ratesof quahogswere or reworking and destabilizationof sediinents, two to four ordersof magnitudemore sensitiveto andquahog larvae are poorly understood. changesin juvenile survivorship,than to thosein Kurkowski 981! demonstratedthat adult adult survival or fecundity. These authors quahogscan readily consumeyoung veliger therefore suggestedthat stock enhancement larvae< 120 elmin laboratoryexperiments, and measures would be most effective when directed that larvaedo not surviveentrapment in towards enhancing juvenile survival e.g. pseudofeces.A negativeinteraction between throughpredator control!. In this context, adult Mercenaria stocks and settlement was also Peterson990! recentlyargued convincingly for suggestedby Rice et al. 989!, who the needto apply experimentaldata on size documentedmuch higher densities of juvenile selectivityand habitat preference of bivalve quahogsin areasof NarragansettBay, Rhode predatorsto fishery managementand resource Island, with low adult densities. enhancement efforts, Successful metamorphosis and post- settlement recruitment of hatchery-produced Effect of Prey Size quahoglarvae is known to be influencedby egg Newly settled clams are expected to be highly andlarval quality, asmeasured by their lipid vulnerable to predation becausethey are content Gallageret al., 1986;Gallager and asiphonateand must feed at the sediment-water Marin, 1986!. These authors found that survival interface.Information on predationof early post- of quahogand oysterlarvae to the pediveliger settlement stagesis extremely liinited, however, stagewas invariably poor whenegg lipid levels andlargely qualitative reviewedby Gibbonsand were low < 18% of the ash-free dry weight!, but Blogoslawski, 1989!. Losses during later, that high egg lipid contentcould resultin both juvenile stagesare betterdocumented, but have high andlow survival. A similar relationshipwas rarely been determined by sampling of natural described between larva1lipid content and populations becausequahogs < 20 mm in length survival through metamorphosis Gallager et aL, are inefficiently captured by most commonly 1986!. These results indicate that lipid content used sampling gear, e.g. quahog shell buckets. aloneis not alwaysa reliablepredictor of gamete MacKenzie 977!, however, was able to quality and larval survival. It also remainsto be providestrong evidence of high predatory determinedwhether naturally occurring egg and mortalitiesat smallersizes in GreatSouth Bay, larval populationscommonly experience lipid New York and Horseshoe Cove, New Jersey, by levels below the minimum threshold which was determiningthe relativeproportion of deadand establishedas prerequisitefor larval survival in live quahogscollected with a diver-operated the laboratory. hydraulic suction dredge. He also used

32 distinctiveshell markingsto attributedeaths to for quahogsthat aretypically two to threeorders specific predatorgroups variousgastropods, of magnitudelower than thoseof crabs[e.g. g 1 crabs,and starfish!. This approach,when used quahogweek 1 forwhelks and moon snails in commerciaHyexploited areas, is obviously Carriker, 1951; Greene, 1978!]. Whelks only reliableto determinenatural mortality rates pieferentiallyfeed on largerquahogs ! 40 mm!, of quahogsbelow legal harvestablesize. It also and both whelks and moon snails show tends to underestimate the number of dead preferencefor thin-shelledbivalves, when quahogs,because crabs often breaksheHs, alternateprey is available Cairiker, 1951!. especiallyof smallerprey, to irretrievable Nevertheless,whelks areknown to be major fragments.Evidence of greaterpredation predatorsof adultMercenaria in North Carolina pressureon smallersizes is thereforemostly Peterson, 1982; Irlandi and Peterson, 1991!, generatedfrom field plantingsof quahogsof andcan accountfor up to 13 percentannual varying sizes e.g. Malinowski, 1985;Flagg and lossesof the quahogpopulation in GreatSouth Malouf, 1983; Peterson, 1990!. Bay, New York Greene,1978!. Starfishcan Crabs,carnivorous gastropods, and starfish onlyprey on largequahogs in aggregation are the threemost importantgroups of predators Doering, 1981!,and aremore effective of quahogs,although finfish e.g. rays! are piedatorsof epifaunalthan infaunal bivalves known to be significant predatorssouth of e.g. oysters,mussels, and scallops!. DelawareBay Kraeuterand Castagna, 1980!. Due to their motility, high predationrates, M. niercenariaattains complete size refuge from andhigh relativeabundance, crabs are deemed oysterdrills, and most crabs,including spider the inost seriouspredators of smallerquahogs. crabs,rock crabs,green crabs, and mud crabs They are generallyable to consumequahogs of Dyspanopeussayi j at a shelllength p 30 mm shell lengthsup to 30 percentof their CW, Figure1!. Qoahogs 40 mmremain vulnerable althoughPanopeus herbstii, which feedson to two of the larger crabsspecies, the mud crab quahogsup to 65 percentof its CW, providesan Panoepusherbstii andblue crab,CalDnecres exceptionto this rule of thumb MacKenzie, sapidus,which attain maximumsizes of ca. 62 1977; Whetstone and Eversole, 1981; Gibbons mm and227 mm in carapacewidth CW! and Blogoslawski,1989!. The high vulnerability respectively Williams, 1984!.Susceptibility to to piedationof quahogs<20-25 mm in length is predationis inverselyrelated to quahogsize aggravatedby the fact that evenlarger crabs,that becauseboth the number of potential predators arenot mechanicaHyconstrained to feedon small Figure 2!, and the numberof prey consumedby prey, selectsmaHer quahogs when a widesize any given predatorsize class e.g. Peterson, rangeis available.For example,large blue crabs 1990!decline with increasingprey size. > 125mrn in CW! prefetentiaUyprey on 10-25 Burrowing, predatorygastropods such as min M. mercenaria, when offered quahogs whelks and moon snails are the most important rangingin sizefrom 5 to 35 mm, both in the predatorsof adult quahogs> 40 rnm in shell presenceand absence of sediment Peterson, length Figure 1!. Gastropods including oyster 1990!.Their consumptionrates numberof prey drills! arehigMy specializedpredators that feed eatenper unit time! for 30-35mm quahogsare 5 almostexclusively on bivalves,and leave distinct timeslower thanthose for 10-15mm quahogs.A markings on their shells. However, they are similar preferencefor smaHerquahogs was relativelyslow moving andthus cannot rapidly shownfor the largemud crab,Panopeus herbstii invadean areafollowing natural e.g. salinity Whetstone and Eversole, 1981!, although disturbance!or man-inducederadication. Wide energyintake tissueweight of quahogs dispersalis further limited by thelack of a free- consumedper unit time!, was maximizedat swimmingearly developmentalstage, except in larger sizes. the caseof moonsnails. Gastropods also exhibit Selectionfor smallerprey appearsto be a long prey handling times,and consumption rates general phenomenonamong crustaceans

33 Figure2. Maximumsize shell lengthin mmj of hardclams consumed by twelvecommon predators of Mercenaria metceuaria in east coast esfuanes. Sources: P. longicarpus hermit crab! Gibbons, 1984 Libinia sp. spidercrab! Gibbons h Blogoslawski, 1989 D. Neoism~! sayi mud crab! Carriker, 1961; Gibbons, 1984 C. uT0rates rock crab! MacKenzie, 1977 O. occllatus caMo crab! Gibbons 4 Blogoslawski,1989 C. maes' greencrab! MacPhail et al. 1955 k Taxiarchis, 1955 in Gibbons d Blogoslawski,1989 P. berbstii mud crab! Whetstone k Eversole, 1981 C. sapidus blue crab! Arnold, 1984 Eupleuracaudata k Umsalpinx ctuerea oysterdrills! MacKenzie, 1977 P. duplicatus moon snail! Carriker, 1951, Greene, 1978 Busyconcanaticulatum whelk! Carriker, 1951, Greene, 1978 Asterias forbesi Doering, 1981

primarily crabs!feeding on hard-shelled theory,which predictspreference for prey that mollusks, and occurs even when larger prey are maximizethe predators'net energygain, may be moreprofitable in termsof energyyield per unit relatedto greaterclaw damageand Qtness costs time Juanes,1992!. This discrepancybetween associatedwith handlingaf largerprey Juanes einpiricaldata and classical optimal foraging and Hartwick, 1990!.

34 Effect of Substrate Type especially in areasthat ee at the limit of their Characterization of the predator assemblageat distributional range, than that of mud crabs, a givensite, and an understandingof the effects which form less mobile, gregarious populations of environmental factors e.g. temperature and that persist from year to year. substratetype! on feedingrates of key predator Mud crabs are often the numerically dominant speciesare important in explainingand predicting crabsin eastcoast estuaries. Dyspanopeus sayi is site-specificdifferences in populationabundance most abundant north of Delaware Bay, attaining of quahogs,and in implementingresource densitiesof upto 100crabs m 2 WAPORA, enhancementmanagement strategies e.g. 1981!, whereasFttrypanopetts depresstts and habitatmanipulation!. The effectsof sediment Panopertsherbstii are prevalent in Chesapeake type on quahogpredatory mortalities have only Bay and the Carolinasrespectively Day, 1987!. beenstudied in the laboratory or smaH-scale Field surveys reveal that the three speciesaa: field trials; their outcome dependsto a large found at highest densities in heterogeneous extenton the speciescomposition, abundance, substrates gravel, or bottoms with shell, size structure, and substratepreference of eelgrass or Spartr'ttacover! WAPORA, 1981; existing predators. Seagrasseswere shownto enhancesurvival of infaunal prey that can burro~ beneath the root- rhyzomemat, suchas quahogs,by reducingthe foragingeffectiveness of whelks Peterson, 1982!.Whelks are alsogenerally absent from shell-covered bottoms, which inhibit their burrowing activity WAPORA, 1981!. Crabs typically show highestpredation rates in their preferred substrates.This generalization will be illustratedbelow for two major groupsof quahog predators,the large swimmingcrabs Portunidae!, such as blue crabs Callirtectes sapidus!and calico crabs Ovalipesocellatus!, and for the smaller mud crabs Xanthidae!. The former prefer homogeneous substrates sand or mud/sand combinations! to crushed shell or gravel0 to 50 inm in diameter! Figure 3A!. Given an equal density of quahogs among substrates,they also prey mostheavily in their preferredsubstrate Figure 3B!. Reduced foraging efficiency of 0. oceQatus in gravelwas related to increasedsearching time andhandling of non-preyitems in this substrate Sponaugle and Lawton, 1990!. This behavioral Figure 3. A! Results of blue crab Callinectes responseprovides the basisfor the recommended sapidus!substrate preference rests, in which the location use of gravel or crushed stone aggregatein of a crab with respectto sedunenttype wasdetermined in a series of laboratory paired -choice! comparisons quahoggrowout sitesin southeasternstates such drawnPorn Arnold, l984!. as Virginia, whereblue crabsare prevalent Castagnaand Kraeuter,1977!. Abundance and B! Predationrate mean~ standarderror! of bluecrabs thereforepredation intensity by large,highly and calico crabs on Merceiiaria mercetiaria in various substrates, determined in the laboratory drawn from mobile portunid crabs e.g, blue crabs! is Sponaugle 8 Lawton, 1990! see sourcesfor further expected to be temporally much more variable, derails!.

35 Day andLawton, 1988!.In agreementwith field maintainingthe low densitiescharacteristic of data,and in contrastto the largerportunid crabs, quahogpopulations. laboratorytrials show that mud crabs D. sayi, E. Low densitymay thus provide infaunalprey depressusand P. herbsriQprefer heterogeneous populationswith a mechanismfor persistence substrates,especially crushed shell, to sandor evenwhen subjectto intensepredation mud Day, 1987!. Predationrates of D. sayi on Egglestonet al., 1992!. Sponaugleand Lawton juvenile quahogswere found to be significantly 990! suggestedthat juvenile quahogsachieve a greaterin smail <17 mm diameter!or large 0 relativerefuge from predationby calico crabsat mm! gravelthan in sand Day, 1987!,thereby low densities,in heterogeneous sand/shell! lendingsupport to the observationthat substrate substrate, but not in sand. In contrast, Peterson preferenceand predation pressure are positively 982! found no low densityrefuge, over the correlated,and illustrating that habitat structural rangeseven to 28 quahogs m 2,for adult complexityis not alwaysassociated with a quahogspreyed upon by whelks.Thus refuge reductionin foragingefficiency. Flagg and valueat low densitiesmay be predator-and Malouf 983! alsofound that survivalof field- habitat-specific. plantedjuvenile quahogsin areaswhere mud crabswere abundant,was inversely correlated Growth with gravelsize ranging between 6 and32 mm The time requiredfor seedclams to achieve in diameter. sizerefuge from most predatorswill be Thispreference for substrateswith a complex effectively determined by their growth rate. topographyappears to be relatedto the mud Growth datafor clams < oneyear old, sampled crabs' small adult size e,g. D. sayi attains only from naturalpopulations, may be biasedby size- 28 mrn in CW!, andthus requirementfor refuge selectivepredation or samplingefficiency, and from top predators bottom-feedingfish!. are thusmore readily derivedfrom land-based Consumptionof juvenile quahogsby D. sayi, culturesystems or field enclosuresthat exclude for example,is strongly inhibitedby increased predators.Growth ratesof seedclams reared in predatoryrisk in the presenceof toadfish, the laboratoryunder optimal temperatureand Opsanustau Day, 1987!.Introduction of food conditionsaverage about 0.58 mm week this fish specieshas therefore been suggested Table 2.12 in Malouf and Bricelj, 1989!.Even asa methodof biological controlof predation highergrowth rates, of up to one rnm wk-1 can in quahoggrowout sites Gibbonsand be ieahzed with natural sestonat near-optimum Castagna,1985!. temperatures7 to 28oC! Table 2!. However, lowervalues e,g. 0.45 to 0.62 rnm week 1 are Effect of Prey Density typicallyobtained when averaged over the entire A strong,predator-mediated, negative growing season e.g. Eldridge et al., 1979!. correlationbetween population density and Table 3 lists some of the factors which have survivorshipof M mercenariahas been beenshown to significantly influencegrowth of demonstratedduring juvenile but not adult stages quahogs seeRice and Pechenik,1992 for a Malinowski, 1985!. Average seasonal moreextensive review!. Temperatureand survivorshipin easternLong Island was four sedimenttype are two of the environmental timesgreater at a densityof 100juvenile quahogs variablesmost frequently correlated with growth m 2than at 1200quahogs m 2.In thisstudy, of M. mercenaria.Growth is generallygreater in quahogdensity had a greatereffect in explaining coarse-grained sand or silty sand!than in fine- juvenile survival at two siteswhere crustaceans grainedsediments. However, the effectsof were the dominantpredators, than all other substratetype per se cannotbe readily decoupled combinedvariables tested quahogsize, time of from the effects of flow velocity, and the quality year,and location!. Predationduring juvenile andquantity of the overlying seston.Growth rate stageswas thus attributeda dominantrole in is consistently reduced at high suspended

36 Table 2

Growth rates of juvenile Mercenaria rnercenaria exposed to natural seston Lo and Lf = initial and final shell length in mm!. Maximum subtidal and density-independent! growth rates were selected where several conditions were tested. Growth rates were determined in enclosures in the natural environment unless otherwise noted.

Site;Period Shell Length Ye inp. Growth Source Lo - Lg! oC! Rate rnmlwit!

NapeagueHarbor, 10.3 - 14.2 22- 28 0.96 Bricelj 4 NY; July-Aug. Borrero,unpubl.

Great South Bay, 10.5 - 15.4 27 0.54 Bricelj,unpubl. NY; Oct.-Nov. raceways!

Fishers Island, 4.6 - 5.7 22 1.05 Appelmans,1989 NY; Aug. land-based upwellers!

Shinnecock Bays, 7.9 - 15.4 0.62 Flagg k NY; July-Oct. Malouf, 1983

Folly River, SC; Hadley & Manzi, Feb.-Aug. 3.9 - 16.9 8-32 0.48 1984 May 21-26 1 lla raceways!

Clark Sound,~ SC; 13.0 - 26.9 0.45 Eldridge et May-Dec. aL, 1979

Wassaw Sound~, GA 6.1 - 28.3 1.08 Walker, 1984 intertidal!

Alligator Harbor, 5.4 - 9.0 17- 26 0.84 Menzel, 1963 FL; April

Mean= 0.83 Magnum seasonal growth rate Clams rown in substrate. sedimentloads Q 23to 44mg dry weight 1-1!, regime, food concentrations, and structure of whether these result from bioturbation Murphy, subtnergedaquatic vegetation. Positive effects 1985!,or physicaldisturbance wave action! have been attributed to increased near-bottom Turner and Miller, 1991!. food supplyto the benthosthrough enhanced Studies of the effects of seagrasshabitat particlesettlement Petersonet al., 1984!,and relativeto unvegetatedsubstrate on growth of resuspensionor in situ productionof benthicor Mercenaria mercenaria reviewed in Table 3! epiphytic algae within the seagrassbed Judge et haveyielded conflicting resultswhich may be al., in press!,reduced siphon nipping activity by telated to site-specific differences in the flow finfish Coen and Heck, 1991!, enhanced

37 Table 3.

Factors influencing growth of Mercellria Ntercerraria TOM = total organic maatte; Lo and Lf = initial and final shell length!. Positive or negative effects on growth are indicated, as well as the magnitude of growth inhibition, where appropriate.

Variable Effect Magnitude Source

Sediment type Sand ! Mud 24% ! % silt-clay Sand ! Mud ~36% ! or TOM! Sand ! Mud <8% !

Suspended -! 16%at 44 mgDW1-1 ! Sediments -! 38%at 23 mgDWl-l S! -! 38%at 193mgDW 1 1 !

Seston Flux Max, growth at intermediate ,7! 1eveis

Phytoplankton +! Diatoms5 pm ! Concentration +! Chlorophylla 8!

Presence of -! 9,12! Seagrass +! 0,11,12! no effect 2!

Biological 3! disturbance: 1! siphonnipping

Temperature Rangefor +! growth = 9-31oC ,14,15! Optimum= 20-25oC

Population 18% 80clams m-2. 2! Density Lo 5.8 crn! 22% 90 clamsm 2; 6! Lf-6.2ctn! g19% 159 clams m 7! Lo -1.3cm Lf=4.6-5.7ctn! 33% 027 clamsm-2 8! Lo= 1.7,Lf=3.3cm!

Sources:! Prau, 1953; ! Pratt k Campbell, 1956; ! Grizzle k. Morin, 1989; ! Bricelj et al., 1984a; ! Murphy, 1985; ! Turner k Miller, ! Grizzle & Lutz, 1989; 8! Evjen, 1985; 9! Kerswill, 1949; 0! Petersonet al., 1984; 1! Irlandi k Peterson, 1991; 2! Petersonk Beal, 1989; 3! Coen k Heck, 1991; 4! Ansell, 1968; 5! Laing et al., 1987; 6! Rice et al., 1989; 7! Eldridge et al., 1979; 8! Walker,1984,

~ Population density parameters indude average length data.

38 sediment stability and reduced sediment and Georgiagrow at comparablerates, typicaHy resuspension postulated by Irlandi and requiring 3.0 to 4.4 yearsto attain marketsize Peterson,1991!.Adverse effects may result from g able 4!. Differences in growth rate among sites a reductionin horizontalseston flux the product within an estuaryare often greaterthan those of sestonconcentration and current velocity! amonglatitudes over a broadergeographic scale dueto baffling of currentswithin the seagrass [e.g. two-fold variation in Great SouthBay canopy lrlandi and Peterson,1991 and Greene, 1978!, three-fold variation in Cape references in Table 3!. Lookout, North Carolina Peterson and Beal, Differencesin growth rateof M. merceiiaria 1989!, and 1.7- to two-fold variation in the m alongthe eastcoast of North Americawere parameterin the Indian River, Florida Arnold et describedby Ansell 968!, who found no clear aL, 1991! and NarragansettBay, RhodeIsland latitudinalpattern or coiielation of growth rates Jones et al., 1989! respectively]. with temperaturein comparingpopulations Populationdensity of quahogsis generally between Massachusetts and Florida. Reduced not a significantfactor influencinggrowth rates growth occurs,however, near the species' of natural populations e.g. Malinowski, 1985!. northern distributional limit Prince Edward Density-dependentgrowth inhibition, generally bland, Canada!,where lower temperaturesresult only occursduring growout of cultured clams in a shortergrowing season,and quahogsrequire plantedat densitiestwo to threeorders of six yearsor moreto attainlegal marketsize. The magnitudegreater than those found in nature highestgrowth rates time to marketsize = 2.2 Table 3!. Stuntingof adult clams was found, years!have been recently reported for however, in uncertified waters in Greenwich populationsin Florida, wherethey areattributed Cove, NarragansettBay, at unusuallyhigh to continuedgrowth during the winter, and thus naturaldensities of 190clams m 2 Riceet al., lengtheningof the annualgrowing seasonat this 1989!.Similarly, reductionin the condition index latitude Jones et aL, 1990!. These results were of adultclams occurred at experimentaldensities substantiatedby Arnold et aL 991! who noted of 203clams m-2 Malinowski,1985!. that the meanm growthparameter the productof Bulk measuresof food quantity or k andasymptotic size in the von Bertalanffy phytoplanktonbiomass chlorophyHa growth equation!was twice as high in the Indian concentration! may not necessarily provide a River, FlOrid, than in NarraganSettBay, RhOde good predictorof bivalve growth, exceptunder Island. Therefore M, mercenaria can achieve conditions of food limitation, which are not growthrates approaching those of fastergrowing typically encounteredin shallow,eutrophic clam speciessuch as Spisulasolidissima surf estuaries.Thus, during virtually monospecific clams!and Mya arenaria softsheHclams! Fig. bloomsof noxious unpalatable,toxic, or 2.5 in Malouf and Bricelj, 1989! only in the indigestible!algae, bivalve populationsmay southernportion of its geographicrange. exhibit severegrowth depressionwhich may not Table4 comparesgrowth ratesof M. be reflected in low or abnormal chlorophyll levels mercenariapopulations, as reflected in the time e.g. Cosperet al., 1987! Correlationsbetween requiredto attainlegal marketsize. Ansell's food availability andgrowth can be improvedby 968! dataare extended or replacedwhere inore incorporatingrelevant measures of food current information is available, Minimum legal quality e.g.biomass of phytoplanktonspecies size is here assumed to be 25.4 mm in shell known to supportbivalve growth! Pratt and thickness, the New York state limit!, Campbell, 1956!. correspondingto a shelllength of 48 mm based on morphometricsof quahogpopulations in Effect of Noxious Algal Blooms Great SouthBay Greene,1978!, although the Algal specieswhich mayadversely affect ratio of lengthto thicknessmay vary somewhat quahogpopulations under bloom conditions betweenlocations. Populations between Maine include:the chlorophyteNannochloris atones,

39 Table 4.

Average time in years! to attain legal market size [= 48 mm in shell Length see text!! of Mercenariu mercennria natural populationsalong the species'latitudinal range, from north to south. Range is shown between brackets; unless indicated, time to market size is calculated from fitted von Bertalanffy, Gompertz or Logarlthjnic growth equations.

Time Location Source yrs.!

6.0 Prince Edward Island, Fig. 5 in Ansell, 1968 Canada 4.4 Maine Fig. 5 in Ansell, 1968

3.2 Monotnoy Point, Fig. 5 in Ansell, 1968 Massachusetts

4.0 Narragansett Bay, 'Jones et al., 1989 .0 - 4.8! Rhode Island

3.5 Great South Bay, Appendix 4 in Buckner, .0 - 4.0! New York 1984 .5 - 5.0! Greene, 1978 3.0 Barnegat Bay, lKennish and Loveland, 1980 4.3 New Jersey From Table 5 in Kennish, ,8 - 4.6! 1980 4.4 York River, Virginia From Fig. 3 in Loeschand Haven, 1973 2.4 Core Sound, NC >Petersonet al., 1983

3.0- 4.0 WassawSound, Georgia Walker andTenore, 1984 intertidal!

2.0 Kings Bay, southernGA 3Joneset al., 1990

2.2 - 2.3 Indian River, Atlantic 3Joneset al., 1990 2.1 coast of Florida Arnold et al., 1991 .9 - 2.5!

2.6 Gulf Coast, Florida Fig. 5 in Ansell, 1968

1. Shell height H! converted to length using an H/L ratio = 0.933; 2, Assumingthat agein years= numberof annualbands; 3. Using a H/L conversionfactor = 0.91, thechrysophyte Aureococcus anophagefferens, becauseblooms of highly toxic forms of this andthe dinoflageHateAlexandrium fundyense, dinoflagellateelicit feedingdepression and shell the causativeagents of "green," "brown," and closurein this species Twarog andYainaguchi, "red" tidesrespectively, The first two speciesare 1974!.Laboratory toxification experiments picoplanktonicalgae circa 2 pm in diameter!, show, however, that M. mercenaria is capable of which, due to their small size, are expected to be acquiringhigh levels of PSPtoxins to 3 orders poorly retainedby the clams'feeding apparatus. of magnitudeabove the regulatory level for [Particle retention efficiency in M mercenaria sheOfish closures!, when exposed to a Long decreasessteeply with decreasingparticle size Island, low-toxicity strain of A. fundyense,or a below a size of about four mm Riisgkrd, 1988!]. New England,high-toxicity dinoflagellatestrain Summer blooms of N. atomus were in coinbinationwith non-toxic phytoplankton documentedin Long Island'ssouthern bays in Bricelj et aL, 1991!.In conclusion,although the the 1950's reviewed by Ryther, 1989!. effects of blooms of these three algal specieson Laboratorystudies subsequently demonstrated naturallyoccurring quahog populations have not that monospecificcultus of this algado not yet beendetermine, the experimentalevidence supportgrowth of quahogsin either larval Tiu et indicates that they are at least capable of causing al., 1989!or juvenile stages Basset al., 1990!, severegrowth reduction,and could potentially andcause growth inhibition when combinedwith causeinortalities of some life history stages otheralgae of high nutritionalvalue. Lack of under prolonged exposure. growth on a monospecificdiet of N. atomuswas attributedto the quahogs'short gut retentionand References low absorptionefficiency of ingestedorganics Ahn, I-Y. 1990.Effects of the gem clam, for this alga Bricelj et al., 1984b!. Gemmagemma, on thesettlement and the Aureococcusanophagegerens first occurred earlypost-settlement migration, growth and in NarragansettBay Sieburthet al., 1988!and in survivalof the hard clam,Mercenaria easternand southernLong Island baysin 1985 mercenaria. Ph.D. dissertation, Marine Cosperet aL, 1987!,and has reappearedin New SciencesResearch Center, State University York watersin pastyears. This alga causes of New York, Stony Brook, 131 pp. severeinhibition of quahogfiltration rates Ansell, A.D. 1967. Egg production of Tracey,1988!, and inhibition of ciliary beatin Mercenariamercenaria LimnoL Oceanogr. gill tissueexcised from quahogs Gaineyand 12: 172-176. Shumway,1991!. The mechanismof this alga's Ansell, A.D. 1968. The rate of growth of the toxigenicaction is not yet clearly understood. hard clam Mercenaria mercenaria L! Preliminarydata suggest that althoughquahogs throughoutthe geographicalrange. J. Cons. are less sensitive to the effects of A. Perm. Int. Ecplor. Mer. 31: 364-409. anophagefferensthan mussels,Mytilus edulis, Ansell, A.D., F.A. Loosmore and K.F. Lander. they may still experiencegrowth reduction at 1964. Studies on the hardshell clam, Venus even moderate field concentrations of A. mercenaria,in British waters.J. Applied anophagefferens.1 x 108to 3.2x 10 cells Ecology 1: 83-95. liter 1! Briceljand Borrero, unpublished data!. Appelmans,N.L. 1989.Effects of variations in Finally, Alexandriutnfundyense and related chlorophylla andtemperature on growth of speciesate responsiblefor the accumulationof hard clams, Mercenaria mercenaria, L in an paralyticshellfish poisoning PSP! neurotoxins upflow culture system.M.S. thesis,Marine in suspension-feedingbivalves. Mercenaria SciencesResearch Center, State University mercenaria was found to accumulate low levels of New York, Stony Brook, 91 pp. of PSPtoxins during New Englandred tide Arnold, W.S. 1984. The effects of prey size, outbreaks in 1972, when other similarly exposed predatorsize, and sedimentcomposition on bivalve speciesbecame highly toxic, presumably the rateof predationof the blue crab,

41 Callinectessapi dus Rathbun, on the hard Busyconand other predators.Ecology 32: clam, Mercenaria mercenaria Linne!. J. Exp. 73-83. Mar. Biol. Ecol. 80: 207-219. Camker, M,R, 1961. Interrelation of functional Arnold, W.S., D.C. Marelli, T.M. Bert, D.S. morphology,behavior, and autoecologyin Jones and I,R. Quitmyer. 1991. Habitat- early stagesof the bivalveMercenaria specificgrowth of hardclams, Mercenaria mercenaria. J. of the Elisha Mitchell mercenaria L.! from the Indian River, Scientific Soc.77: 168-241. Florida J. Exp. Mar. Biol. EcoL 147: 245- Castagna, M. and J.N. Kraeuter. 1977. 265. Mercenaria culture using stone aggregatefor Bass. A.E., R.E. Malouf and S.E. Shumway. predatorprotection. Proc. Nat. Shellfish. 1990. Growth of northern quahogs Assoc. 67: 1-6, Mercenaria mercenaria Linnaeus, 1758!! Clarke,A. 1982.Temperature and embryonic fed on picoplankton,J. ShellfishRes. 9: developmentin polar marineinvertebrates, 299-307. lnt. J. InvertebrateReproduction 5: 71-82. Belding, D.L. 1931. The quahog fishery of Coen, L.D. and K.L. Heck. 1991. The Massachusetts.Mass. Dept. Conserv.,Div. interacting effects of siphon nipping and Fish. Game, Mar. Fish. Serv. 2, 4lpp. habitat on bivalve Mercenaria mercenaria Bricelj, V.M. and R.E. Malouf, 1980.Aspects L.!! growth in a subtropical seagrass of reproduction of hard clams Mercenaria Halodule wrightii Aschers! meadow. J rnercenaria! in Great South Bay, New York. Exp. Mar. Biol. Ecol. 145: 1-13 Proc. Nat. Shellfish.Assoc. 70: 216-229. Cosper,E.M., W.C, Dennison,E.J. Carpenter, Bricelj, V.M., R.E. Malouf andC, de Quillfeldt. V.M. Bricelj, S.H. Kueiistner,D. Colflesh 1984a.Growth of juvenile Mercenaria and M. Dewey. 1987.Recurrent and mercenariaand the effect of resuspended persistentbrown tide bloomsperturb coastal bottom sediments. Mar. BioL 84: 167-173. marineecosystem. Estuaries 10: 284-290. Bricelj, V.M., A.E. Bass and G.R. Lopez. Davis, H.C. and P.E. Chanley. 1956. Spawning 1984b.Absorption and gut passagetime of and egg productionof oystersand clams. microalgaein a suspensionfeeder: an Biol. BulL 110: 117-128. evaluationof the 5~Cr:14C twin tracer Day, E.A. 1987.Substrate type and predatory technique.Mar. Ecol. Prog. Ser. 17: 57-63, risk. sects of mud crabpredation on Bricelj, V.M., J.H. Lee and A.D. Cembella. j uvenile hard clams.M.S. thesis,Marine 1991.Influence of dinoflagellatecell SciencesResearch Center, State University toxicity on uptakeand loss of paralytic of New York, Stony Brook, 112 pp. shellfish toxins in the northern quahog Day, E.A. and P. Lawton. 1988. Mud crab Mercenaria mercenaria. Mar. EcoL Prog. Crustacea:Brachyura: Xanthidae! substrate Ser. 74: 33-46. preferenceand activity. J. ShellfishRes. 7: Buckner,S.C. 1984.Aspects of thepopulation 421-426. dynamicsof the hard clam, Mercenaria Doering, P.H. 1981. Observations on the mercenaria L, in Great South Bay, New behaviorof Asteriasforbesi feeding York. Ph.D. dissertation, Marine Sciences on Mercenariamercenaria. Ophetia ResearchCenter, State University of New 20: 169-177. York at Stony Brook, 217 pp. Eggleston,D.B., R.N. Lipcius and A.H. Hines. Butman, C.A., J.P. Grassle and C.M. Webb. 1992.Density-dependent predation by blue 1988. Substratechoices made by marine crabs upon infaunal clam specieswith larvae settling in still water and in flume contrastingdistribution and abundance flow. Nature 333: 771-773. patterns.Mar. Ecol. Prog. Ser. 85: 55-68. Carriker, M.R. 1951. Observations on the Eldridge, P.J., A.G. Eversole and J.M. penetration of tightly closing bivalves by Whetstone 1979. Comparative survival and growthrates of hardclams Mercenaria Center,State University of New York, Stony mercenaria,planted in trayssubtidaliy and Brook, 102 pp. intertidally at varying densitiesin a South Gibbons, M.C. and W.J. Blogoslawski. 1989. Carolina estuary.Proc. Nat. Shellfish. Predators,pests, parasites aad diseases.In: Assoc. 69: 30-39. Cajun mariculture in North America, J.J. Eversole,A.G. 1989.Gamtogeaesis aad Maazi and M. Castagna eds.!,Dev. in spawningin North Americanclara Aquacultureand FisheriesScience 19, populations:iraplications for culture.Chapter Elsevier, New York, pp, 167-200. 3 In: Clam rnariculture in North America, J.J Gibbons, M.C. and M. Castagna.1985. Manzi aad M. Castagna eds !, Elsevier, Biological control of predationby crabsin New York. bottom cultures of hard clams using a Eversole, A.G. W.K. Michener and P.J. combination of crushed stone aggregate, Eldridge. 1980.Reproductive cycle of toadfish, and cages.Aquaculture 47: Mercenaria mercenaria in a South Camlina 101-104. estuary.Proc. Nat. Shellfish.Assoc. 70: 22- Greene, G.T. 1978. Population structure, 30. growth and mortality of hard clamsat Evjen, A.J. 1985.Above bottom bivalve growth selected locations in Great South Bay, ¹w in Long 1slandSound and theinfluence of York. M.S. thesis, Marine Sciences Research resuspendedsediment. M.S. thesis,Marine Center, State University of New York, Stony SciencesResearch Center, State University Brook, 199 pp. of New York, Stony Brook, 83 pp. Grizzle, R.E. and R.A. Lutz. 1988. Descriptions Flagg, P.J. and R.E. Malouf. 1983. of macroscopicbanding patterns in sectianed Experimeatalplantings of juvenilesof the polishedshells of Mercenariamercenaria hard clam Mercenaria mercenaria Linae! in from southern New Jersey. J, Shellfish Res. the waters of Long Island, New York. J. 7: 367-370. Shellfish Res.3: 19-27. Grizzle, R.E. and R.A. Lutz. 1989. A statistical Fritz, L.W. and D.S. Haven. 1983. Hard clam, model relatinghorizontal seston fluxes aad Mercenaria mercenaria. shell growth patterns bottom sediment characteristics to growth in ChesapeakeBay. Fish. BulL 81: 697-708. of Mercenaria mercenaria Mar. Biol. 102: Gaiaey,L.F. aad S.E. Shumway. 1991.The 95-105. physiologicaleffect of Aureococcus Grizzle, R.E. and P.J. Moria. 1989. Effect of anophagegerens "browa tide"! on the lateral tidal currents, seston, and bottom sediments cilia of bivalve molluscs. Biol. BulL 181: on growthof Mercenariamercenaria: results 298-306. of a field experiment.Mar. Biol. 102. 85-93. Gallager,S.M. and R. Mana. 1986.Growth and Hadley, N.H. and J.J. Manzi. 1984.Growth of survival of larvae of Mercenart'a mercenana seedclams, Mercenaria mercenaria, at L,! aad Crassostrea vi rgini ca Gmelin! various densities in a commercial scale relative to broodstock conditioning and lipid nurserysystem. Aquaculture 36: 369-378. contentof eggs.Aquaculture 56: 105-121. Heffernan, P.B., R.I.. Walker aad J.L. Carr. Gallager,S.M. R. Mann and G.C. Sasaki.1986. 1989.Gametogenic cycles of threebivalves Lipid as an index of growth and viability in in WassawSound, Georgia: L Mercenaria threespecies of bivalve larvae.Aquaculture mercenaria Lianaeus, 1758!. J Shellfish 56: 81-103. Res. 8: 51-60. Gibbons,M.C. 1984.Aspects of predation by Hesselmaa, D,M., B.J, Barber and N.J. Blake. the crabsNeopanope sayi, Ovalipes 1989.The reproductivecycle of adult ocellatus, and Pagurus longicarpus on hardclams, Mer cenaria spp. in the Indian juvenile hard clamsMercenaria mercenaria. River Lagoon, Florida. J. ShellfishRes. 8: Ph.D. dissertation, Marine Sciences Research 43-49.

43 Irlandi, E,A. and C.H. Peterson. 1991. Knaub, R.S. and A.G. Eversole. 1988. Modificationof animalhabitat by largeplants: Reproductionof different stocksof mechanismsby which seagrassesinfluence Mercenariamercenaria. J. ShellfishRes. 3: clam growth. Oecologia87: 307-318. 371-376. Jones,D.S., I.R. Quitmeyer,W.S. Arnold and Kraeuter,J.N. and M. Castagna.1980. Effects D.C. Marelli. 1990. Annual shell banding, of large predatorson the field cultureof the age,and growth rateof hardclams hard clam, Mercenaria mercenaria Fishery Mercenariaspp.! from Florida,L Shellfish BulL 78: 538-541. Res. 9: 215-225, Kraeuter,J.N., M. Castagnaand R. van Dessel. Jones,D.S. M.A. Arthur and D.J. Allard. 1989. 1982. Egg size and larval survival of Sclerochronologicalrecords of temperature Mercenaria mercenaria L.! and Argopecten andgrowth from shellsof Mercenaria irradians Lamarck!. J. &p. Mar. Biol. Ecol. mercenariafrom NarragansettBay, Rhode 56: 3-8. Island. Mar. Biol. 102: 225-234. Kurkowski, K.P. 1981.sects of fr ltration by Juanes,R. 1992.Why do decapodcrustaceans adult Mercenaria mercenaria upon its own prefer small-sizedmolluscan prey? Mar. larvae. M.S. thesis, Marine Sciences EcoL Prog. Ser. 87: 239-249. Research Center, State University of New Juanes, F. and E,B. Hartwick, 1990. Prey size York, Stony Brook, 73 pp. selectionin dungenesscrabs: the effect of Laing, I., S.D. Utting and R.W.S. Kilada. claw damage.Ecology 7: 744-758. 1987. Interactive effect of diet and Judge,M.L., L.D. Coen and K.L. Heck. Does temperatureon the growth of juvenile clams. Mercenaria mercenaria encounter elevated J. Exp. Mar, Biol Ecol. 113: 23-38. food levelsin seagrassbeds?: results from a Loesch, J.G. and D S. Haven. 1973, Estimated novel techniqueto collect suspendedfood growthfunctions and size-age relationships resources.Mar. Ecol. Prog. Ser., in press. of the hard clam, Mercenaria mercenaria, in Keck, R., D, Maurer and R. Malouf. 1974. the York River, VirginiL Veliger 16: 76-81. Factorsinfluencing the settingbehavior of Lutz, R.A. and H.H. Haskin. 1985. Some larval hard clams, Mercenaria mercenaria observationson the longevity of the hard Proc. Nat. Shellfish. Assoc.64: 59-67. darn Mercenaria mercenaria Linne!. J Keck, R.T., D. Maurer and H. Lind. 1975. A Shellfish Res.5: 39 abstract!. comparativestudy of the hardclam gonad MacKenzie, C.L. Jr. 1977. Predation on hard developmentalcycle. Biol. Bull 148: 243- clam Mercenaria mercenaria! populations. 258. Trans. Am. Fish. Soc. 106: 530-537. Kennish, M.J. 1980. The use of shell Malinowski, S.M. 1985.The population ecology microgrowthpatterns in agedeterminations of the hard clam, Mercenariamercenaria, in of the hard clam, Mercenaria mercenaria easternLong Island. Ph.D. dissertation, Linne!. Chapter7 In. Skeletalgrowth of University of Connecticut,Storrs, CT, 101 aquaticorganisms: biological records of pp- environmental change, C. Rhoads and R.A. Malinowski, S. and R.B. Whitlatch. 1988. A Lutz eds.!, Plenum Press, New York. theoretical evaluation of shellfish resource Kennish, M.J. and R.E. Loveland. 1980. management.J, ShellfishRes. 7: 95-100. Growth models of the northern quahog, Malouf, R.E. andV.M. Bricelj.1989. Mercenaria mercenaria Linne!. Proc. Nat. Comparativebiology of clams:environmental Shellfish. Assoc,70: 230-239, tolerances,feeding and growth. Chapter2 In: Kerswill, C,J. 1949.Effects of water circulation Clam mariculture in North America, J.J. on the growth af quahaugsand oysters.J. Manzi and M. Castagna eds.!, Elsevier, Fish. Res. Bd Can. 7: 545-551. New York. Menzel, R.W. 1963.Seasonal growth of the Pratt, D.M. and D.A. CampbelL 1956. northernquahog, Mercenaria mercenaria and Environmental factors affectIng growth in the southernquahog, Mercenaria Venusmercenaria. Limnol. Oceanogr. campechiensis,in Alligator Harbor,Florida. 1: 2-17. Proc. Nat. Shellfish.Assoc. 52: 37-47. Pratt, S.D., A.R. Ganz and M.A. Rice. 1992. Murphy, R.C. 1985.Factors affecting the A speciespro/le of the quahogin Rhode distribution of the introduced bivalve, Island. Rhode Island Sea Grant Publ. RIU- Mercenaria mercenaria, in a California T-92-001 P-1272!, 117 pp. lagoon-theimportance of bioturbation.J. Purdue, J.A., J.H. Beattie and K,K. Chew. Mar. Res. 43: 673-692. 1981.Some relationships between Peterson,C.H. 1982.Clam predationby whelks gametogeniccycle andsummer mortality Busyconspp.!: experitnentaltests of the phenoinenonin the Pacific oyster importanceof prey size,prey density,and Crassostreagigas! in WashingtonState. J. seagrasscover. Mar. Biol. 66: 159-170. Shelijtsh Res. 1: 9-16. Peterson, C.H. 1986. Quantitative allometry of Rice, M.A. and J.A. Pechenik. 1992. A review gameteproduction by Mercenariamercenaria of factorsinfluencing the growth of northern into old age.Mar. Ecol. Prog. Ser.29: quahog,Mercenaria mercenaria Linne, 93-97. 1758!. J. Shellfish Res. 11: 279-287. Peterson, C.H. 1990. On the role of ecological Rice, M.A., C. Hickox and I. Zehra. 1989. experimentationin resourcemanagement. Effectsof intensivefishing effort on the Managingfisheries through mechanistic populationstructure of quahogs,Mercenaria understandingof predatorfeeding behaviour. mercenaria Linn;mus 1758!, in Narragansett In: Behaviouralmechant'sms of food Bay. J. Shel/fishRes. 8: 345-354. selection, R.N. Hughes ed.!, NATO Riisg&d, H.U. 1988.Efficiency of particle ASI seriesVol. G20, Springer-Verlag,pp. retentionand filtration rate in 6 speciesof 821-846. Northeast American bivalves. Mar. Ecol. Peterson, C.H. and B.F. Beal. 1989. Bivalve Prog. Ser. 45: 217-223. growth and higher orderinteractions: Ryther, J.H. 1989 Historical perspectiveof importanceof density,site, andtime. phytoplanktonblooms on LongIsland and Ecology 70: 1390-1404. thegreen tides of the 1950's.In: Novel Peterson, C.H., H,C, Summerson and P,B, phytoplanktonblooms. Causes and impacts Duncan. 1984. 'The influence of seagrass of recurrentbrown tidesand other unusual cover on populationstructure and individual blooms.E.M. Cosper,V.M. Bricelj and E.J. growth rate of a suspension-feedingbivalve, Carpenter eds.!Coastal and Estuarine Mer cenaria mercenaria J. Mar. Res. 42: Studies35, Springer-Verlag,New York, pp. 123-138. 375-382. Peterson, C.H., P.B. Duncan, H.C. Summerson Sieburth, J McN., P.W. Johnson and P.E. and G.W. Safrit, Jr. 1983. A mark-recapture Hargraves.1988. Ultrastructure and ecology testof the annualperiodicity of internal of Aureoccocusanophagegerens gen. et sp. growth banddeposition in shellsof hard nov. Chrysophyceae!:the dominant clams, Mercenaria mercenaria, from a picoplankterduring a bloomin Narragansett populationalong the southeasternUnited Bay, RhodeIsland, surntner1985. J. States. Fish. Bull. 81: 765-779. Phycol. 24: 416-425. Pratt, D.M. 1953. Abundance and growth of Sponaugle,S. and P. Lawton. 1990.Portunid Venus mercenaria and Callocardia morrhuana crabpredation on juvenile hardclams: effects in relation to the character of bottom of substrate type aud prey density, Mar. sediments. J. Mar. Res. 12: 60-74. Ecol. Prog. Ser. 67: 43-53

45 Tiu, A.T., D. Vaughan,T. Chiles and K. Bird. Whetstoiie, J.M, and A.G. Eversole. 1981. 1989.Food value of eurytopicmicroalgae to Effectsof size andtemperature on mud crab, bivalve larvae of Cyrtopleura costata Panopeusherbstii, predationon hardclams, Linnaeus, 1758!, Crassostrea vir ginica Mercenaria mercenaria. Estuaries 4: 153-156. Ginelin, 1791! and Mercenaria mercenaria Williams, A.B. 1984.Shrimps, lobsters, and Linnaeus, 1758!. X Shellfish Res. 8: crabsof theAtlantic coastof the eastern 399-405. United States,Maine to Florida. Smithsonian Tracey,G.A. 1988.Feeding reduction, Institution Press,Washington, D.C., 550 pp. reproductivefailure, and mortality in Mytilus edult'sduring the 1985'brown tide' in Questions and Aaswers NarragansettBay, RhodeIsland. Mar. EcoL Q. Mr. GeorgeDeBlois, shellfisherman!Have Prog. Ser. 50: 73-81. there beenany studiesto show how many Turner, E.J. and D.C. Miller. 1991. Behavior spawnersare neededto electively repopulatean andgrowth of Mercenariamercenaria area, given predation, fishing, and other during simulatedstorm events.Mar. Biol. factors? 111: 55-64. A. Dr. Monica Bricelj, SUNY-Stony Brook! Twarog, B.M. and H. Yamaguchi. 1974, Therehas been some interest in trying to Resistanceof paralyticshellfish toxins in determine the minimum amount of stock bivalve molluscs. In: Proc. First int. Conf. necessaryto sustainrecruitment into the fishery. on toxic dinoflagellateblooms, V.R. I know that therewas a planto do this kind of LoCicero ed.!, Mass. Science and study in New Jersey,but I don't know if the plan TechnologyFund, Wakefield, was actuallycarried out. There is no published Massachusetts, pp. 382-393. information at this time about minimum required Virnstein, R.W. 1977. The importance of broodstock, but there is some indirect evidence predationby crabsand fisheson benthic that rrught be considered, In the Great South Bay infaunain ChesapeakeBay, Ecology 58: of Long Island,there has been a steadydecline of 1199-1217, the adult population,In spite of this, therehas Walker, R.L. 1984. Effects of density and been no noticeable effect on the abundance of samplingtime on the growth of the hard sublegal-sizedclams new recruits! between clam,Mercenart'a mercenaria, planted in 1986 and 1989 in eastern Great South Bay, predator-freecages in coastalGeorgia. wheresurvey data are available.Fishing has not Nautilus 98: 114-119. appearedto lower the adult populationbelow the Walker, R.L. and K,R. Tenore. 1984. The critical minimumrequited to sustainrecruitment. distributionand production of the hardclam, A decreasein the number of sublegal clams has Mercenaria mercenaria, in Wassaw Sound, been observed, however, in the last few years Georgia, Estuaries 7: 19-27. 990 through 1992!. Wallace,H.V.E. 1991.A comparisonof hard In termsof quahoggrowth, most studies clampopulation characteristics between high have shown that the density of quahogs is not too and low densityregions within Great South importantin hmiting growth. In most areas, Bay. M.S. thesis, Marine Sciences Research densities are somewhere between two to 15 Center,State University of New York, Stony animah per squaremeter. Generally it is rather Brook, 67 pp, rare to find naturalpopulations of quahogsin WAPORA, Inc. 1981. Estuarine impact densities of hundreds per square meter. assessment shell+h resources!for the GreenwichCove is oneof the exceptionalareas Nassau-Suffolk streamfiow augmentation with very high adult densities.In thesevery high alternatives, draft report on existing densities,lower growth or stunting hasbeen conditions. U.S. Env Protection Agency, shown,Density may havea majoraffect on New York, 114 pp. iecruitment, but this needs further study. Q. DeBlois! I have read that cherrystones on a variety of scales to show just where it is producemany more eggsthan the smaller effective. Eradication measuresmay be mote littlenecks Is there any evidence of a cessation effective at controlling moon snails or whelks, of egg production as quahogs age? becausethey move slowly into an area If you A. Bricelj! Thereis no evidencefor this have highly motile predators such as blue crabs, reproductive senecencein quahogs. Scallops are it is doubtful that any eradication measureswould the only groupof bivalvesthat I am awareof that work becausethey can come into an area so havea reductionof gameteproduction with age. quickly. In brief, I think thatany kind of Thereis oneimportant thing to be awareof. The eradication program must addresspredator type studies which have shown that chowder quahogs and scale. are the most fecund are based upon laboratory examination of the number of garnetesproduced Q. Mr. John Finneran, shellfisherman! Is there during inducedspawning. We do not know how any evuknceshowing that somesediments are this reflects what is going on in the real world, in more conducive to larval seolement than others? the sensethat "How often do chowders spawn in In other words, are there sediments that have a nature?" But from the laboratory spawning "betterflavor" to settling kuvae? experiments,there is no differencein the viability A. Bricelj! Yes, there have been some of eggsfrom littlenecksor chowders. laboratorystudies on this. Keck and co-workers showed that if you treat sediment with "clam Q. Prof. Dennis ¹xon, URI! One of our juice," you will get an attractantresponse and objectivesis increasingthe stock,and my increased larval settlement. This is a similar result questionis aboutpredator controLAbout a to the data I presented which showed that hundredyears ago thereused to be a statutein juvenile clams exhibit an attractant response.It Rhode Island that set a bounty on starftsh, must be a chemosensoryresponse, because becauseof their recognizedimpact on sheliftsh sediments that were "pretreated" by placement of populations.Do you believethat attemptsat clams that were subsequently removed, also predator control in an openfi shery such asin enhancedsettlement. Physical factors may also NarragansettBay coukfbe of any value? play a role,since additions of gravel or clean A. Bricelj! Well, Clyde MacKenzieof the clamshell to the sediment also increased National Marine Fisheries Service has suggested settlementin this study. just this in the past,but peoplehave balked at programsthat would clear largeareas such as the Q. Finneran! Are there any inorganics that GreatSouth Bay of predators.Economically it is mightact asan attractant?I havenoted that there not a veryfeasible solution. Perhaps in the are often large quahog assemblagesin sediments context of smaller-scale areas, enhancement that are high in coal ash. programsmight work. Sometype of habitat A. Bricelj! No, but one of the possible manipulationmight be undertakenwhen we explanationsfor areasof high abundancein Great know which predatoris most troublesomeand South Bay, might be the presenceof shell what features of the substrate or other fragmentsthat modify the bottomtopography characteristicsate important,Predator control is making the area better for larval settlement and certainly important in nursery and growout survival of juveniles. There has been no testing phasesof aquaculture.Predator control in open of this though. This is very difficult work. With fisheries has not been tested except for oysters it is relatively easy, becausethey settle on MacKenzie's work back in the mid-1970s. He hard surfaces like shells. Postset quahogs are in did somepredator eradication in relativelysmall the size range of sediment particles, so nobody plots and showed that there was a positive really wants to do this kind of tedious work. This response,but therehas been little further testing kind of work is not intractable though, just of this in the field. Eradication needs to be tested difficult. One of the key thingsI want to

47 emphasizeis thatwe need many more studies on theearly life historystages of quahogsrather thanadults. Year-class strength is being determinedby post-larvaland juvenile survival. Thesestages need more tcsearch attention.

48 Overview of Quahog Management Studies in Narragansett Bay, 1946 to 19921

MICHAEL A. RICE Defertmentof Fisheries,Animal, and Veterinary Science University of RhodeIsland Kingston, Rl 02881

Abstract.There have been a considerablenumber of studieson quahogpopulations in NarragansettBay thathave provided valuable informatt'on for fisheries managers. Addi'tionaNy, there have been a fewsocio- economicstudies that havecharacterized the laborforce in the quahogfisheryand haveprovided informationpertinent to levelsoffishing effort. Most ecological studies have focused on thepopulation structureand standing crop densities of quahogsin NarragansettBay. 1he age and growth rates of quahogsin diferentparts of Narragansett Bay are well known, but there is a dearthof information about thepatterns of quahogrecruitment. As with most fisheries that require little capital requirements, the levels offishing effort in NarragansettBay are known to increase or decreasewith relative ease as conditions in thefishery or thegeneral economy change. It is recommendedthatavailable socioeconomic data about thefishery be updated, and that studies be undertaken toassess the relative impacts of currentlyused fishing gear.

Introduction It hasbeen recognized by fisheries managersthat a numberof factorsdescribing a fishery stock mustbe determinedbefore one can beginto makeany rationalpredictions aboutwhat levels of fishing effort are desirable for maintenance of a sustainable fishery e.g. Royce, 1984!. In simple terms, the inputsto a fisherystock are the recruitment of new individualsinto the fishery andgrowth Figure1. Thefour keyfactors that determinequahog of individualspreviously recruited into the stock size, fishery Figure 1!. Likewise, the factors which tend to reduce the size of fishery stocks Onekey aspectthat distinguishes arenatural mortality of the stocksand the assessmentof bivalve fisheries, such as the fishing mortality a combinationof the quahogfishery of NarragansettBay, from fishing catchplus associatedmortality dueto assessmentof finfisheries is that one is dealing damageby gearetc. Thesebasic principles of with a sessilepopu1ation of juveniles and dynamicfishery stockmodels have been most adults.Additionally, quahogsand other frequentlyused for the managementof finfish bivalvesare highly fecund,so that parental stocks,but with carecan be appliedto bivalve stock sizeis consideredless important for molluscan fisheries Caddy, 1989!, recruitmentthan is availablespace, suitable

49 conditions for settlement, and postsettlement predationloss prior to recruitmentinto the fishery Hancock, l 973; Kassnerand Malouf, 1982; Malinowski and Whitlatch 1988; Malinowski, this volume!. The end result of the variousphysical and biological factors determiningquahog distribution is that fishery recruits are found in patches or clumps e.g. Kassner et al., 1991.!.As a consequenceof the patchinessin distributionof quahogs,special caremust be takento designappropriate samplingprotocols that utilize appropriate statisticalmethods e,g. Sailaand Gaucher, 1966;Gardefors and Orrhage,1968; Ludwig and Reynolds,1988; Murawski and Serchuk, 1989!.Techniques that may be appropriatefor the samplingof quahogsin NarragansettBay includetransect or quadratmethodologies in covesand inlets e.g. Rice et al,, 1989!or stratifiedrandom sampling methods over wider areas e.g, Russell, 1972;Murawski and Serchuk, 1989!. Recognizingthat the samplingand statisticalmethods f' or quahogsmay be different from those used for finfish stock Figure 2. Locations of stationsin ¹rragansett Bay assessments,it is the aim of this paper to from which quahogsvere sampledfor studiesof growth outlinekey studiesrelated to shellfishstock rate. Triangles:Pratt and Campbell956!; Squares: assessment that have been carried out in Joneset al. 989!; Circles: Rice et aL 989!, NarragansettBay over the last 45 years,and to provide someinsights into the at@aswhere andCampbell 956! wereable to collect very datais lacking. It shouldbe notedthat a recent detailedinformation aboutthe growth of reporthas been prepared that outlinesin quahogsfrom a numberof locationsaround greaterdetail many of the studiescovered in NarragansettBay Figure 2!, this paper Pratt et al., 1992!. More recent studies have used the technique of sclerochronology the assessmentof ageby quantificationof periodicincrements in the Quahog Age and Growth shell! for determiningthe ageof quahogs e.g. One of the key factorsof interestin Rhoads and Panella, 1970; Kennish, 1980!. quahogstock assessmentis the rateat which Use of sclerochronologyallows for the quahogsgrow. There havebeen a numberof identification of individual year classes,which studies since the 1950s that have investigated is otherwise difficult becausequahogs are the growth rate of quahogs.Pratt 953! spawningthroughout the summerand estimated the growth of quahogs by individual growth ratesate highly variable. measuringchanges in the length-frequency By quantifying annualgrowth rings of distributionsof experimentalpopulations quahogsfrom 10 stationsin NarragansettBay quahogsplanted into bottomenclosures! over Figure 3!, Joneset al. 989! wereable to time, Using a protocolof markingquahogs at give a verydetailed description of quahog variousstations arotmd Narragansett Bay and growth as relatedto averageannual water ineasuringtheir growth after recapture,Pratt temperatures.One of their main findings is

50 minimum legal size 5.4 mrn, 1 inch wide! by the end of its third growing season,and remains in the littleneck size category 5.4 to 38 mm wide! for four years after recruitment into the fishery. A recent comparison of growth data collected by Pratt and Campbell 956! and the data of Jones et al. 989! showed that although the methods were different and the studies were 33 years apart, the averagegrowth ratesof quahogsin NarragansettBay werequite similar Pratt et al., 1992!. Additionally, a study done in North Carolina has validated the annual periodicity of bandsin quahogsby useof a mark-and-recapture study Peterson et al.. 1983!. Rice et al. 989! also used sclerochronologyto determinethe growth ratesof quahogsin denseadult assemblagesin Greenwich Cove and West Passage Figure 2!, They found that quahogsin very dense assemblagesgrow at considerably lower rates thanquahogs in lessdense assemblages typified by the other growth studies.See Rice and Pechenik 992! for a review of factors Figure 3. Growth curvesfor quahogsfrom NarraganseaBay basedon 100 individualsPom l0 that may affect the growth of quahogs. stations. The top graph representsaverage size-at-age measurements~ I SDfor eachyear of growth.?ate Spawning and Recruitment bottomgraph representsmodeled growth basedon the The spawningof quahogsis known to be von Bertalanfry equation.Curve fittingfolloeed hvo temperaturedependent, and appearsto be trig- approaches a! faringone curve to theaveraged shelhu- age measurementson the top graph, and b! fitting a geredas watertemperatures approach 20o C separatecurve to eachof the No quahogsand averaging Loosanoff, 1937!. Details of quahog the resultantvon Bertalang growth parameters Jones fecundityand spawningare provided by et al. J989!. Bricelj this volume!. A study basedon planktonnet tows in NarragansettBay from that quahoggrowth is bestdescribed by the 1950-1952 showed that the maximum von Bertalanffy negative exponential growth numbers of quahog larvae in the water column function Figure 3!. Joneset al. 989! used were found during the summermonths June shell height SH! umbo to ventral valve to August Landers,1954!. Since the larval marginmeasurement as their standard period of quahogscan last approximatelytwo measurement.%heir averagevon Bertalanffy weeks Loosanoff et al., 1951!, it is most growthparameters from the 10 Narragansett probable that tidal currents and wind- Bay stations were: generatedsurface waves can effectively SH = 73.32mm valve height! disperse quahog larvae throughout lt = 0.21 Narragansett Bay Wood and Hargis, 1971; and t p = 4.57 Andrews, 1983!. Thus, there need not be a Althoughthere are differencesin the growth necessityfor a closeproximity of broodstock ratesof quahogsfrom varioussites in to increase the level larval settlement and NarragansettBay, the averagequahog reaches subsequentrecruitment into the fishery.

51 Successfulrecruitment of quahogsis Assessmentsof Standing Stocks of highlydependent on postsettlementsurvival of Quahog juveniles ratherthan absolute numbers of There have been a number of' studies in the spawnersproducing gametes Hancock, 1973; last 40 yearsaimed at mappingthe locationof Malinowski and Whitlatch, 1988; quahogstocks and providing estimatesof Malinowski, this volume!. Kassner and standingstock densities,but most have been Malouf 982! evaluatedthe practiceof confined to coves, inlets, and small portions augmentingthe numbersof broodstockin the of NarragansettBay. A survey by Pratt 953! GreatSouth Bay, Long Islandand found that carried out in 1949-1950 included 123 stations therewas no significantincrease in quahog in NarragansettBay, but the datawere not recruitment. Indeed, MacKenzie 979! urged mapped.The first NarragansettBay-wide that the most effective meansfor increasing study that mappedthe distribution of quahogs quahogrecruitment is to protectjuvenile was basedon a dredgesurvey between 1956 quahogsfrom predationlosses. and 1957,undertaken in responseto calls for There have been few studies carried out theconstruction of mid-Bay hurricanebarriers in NarragansettBay in which the ratesof Stringer,1959!. In this study,nearly 2,800 quahogrecruitment have been determined. sampleswere taken on a 900-footgrid. Juvenilequahogs have been quantified in Although the datafrom this study Figure 4! somebenthic surveys e.g. Pratt, 1977!,but werecollected 35 yearsago, the quahog thesestudies were not fonowed up to distributionsroughly approximatethe general determinethe ratesat which postsetjuveniles position of known stockstoday. The last reachlegally fishablesize. There have been NarragansettBay-wide study of quahog two studiesaimed at investigatingthe effects distributionswas conducted jointly by the of fishing gearon the recruitmentof U.S. Environmental Protection Agency and quahogs.We first of thesestudies compared the R.I. Division of Fish and Wildlife 974!. the relativeimpact of powerdredging versus Mapsof shellfishdistribution were made,but bullrakingon the recruitmentof quahogs therewas no informationprovided as to stock Glude arid Landers,1953!. In the study area abundance.The reason why large-scale chosen for this study, there was little surveysof quahogpopulations have been settlementor recruitment in control and test carriedout only on an occasionalbasis is that areas.Likewise, in a recent study by Sparsis thesestudies tend to be quite expensive. and DeAlteris details in this volume! Most quahogpopulation studies have designedto testthe effectsof bottom focused on coves or other subsections of cultivation on the settlement and recruitment NarragansettBay. Quahog population studies of quahogs,little settlementor recruitmentof werecarried out by grabsampling in quahogswas noted in theirtest or control GreenwichBay from 1951-1957 by the U.S. plots,The failure to find settlementand Fish and Wildlife Service and the R.I. recruitmentof quahogsin thesestudies Division of Fish andGame Stickney and during 1949-1950and 1990-1991suggests Stringer,1957!. At that time, maximum that theremay be somepaucity of quahog densitiesof quahogswere found in mixed recruitmeiit in some areasof Narragansett sand and silt bottoms near the mouth of Bay.In anotherarea of NarragansettBay- Greenwich Cove and near Mary's Creek GreenwichBay, which is known to be one of Figure 5!. For a comparison,divers in 1988 the most productiveareas for the quahog usingquadrat sampling methods found an fishery benthic studiessuggest that thereis averagedensity of 190quahogs/m2 atthe annualrecruitment af quahogs Stickneyand mouth of Greenwich Cove Rice et al., 1989!. Stringer,1957; Rice et al., 1989!. Quantitativestock surveys have been carTied Pigare4, Distributionof quaItogsin NarragansettBay from a quantitativesurvey 1955-l956 Stringer,1959!. out in the closed areas of Providence River In comparisonto the numerouspublished and the Upper Bay in 1956, 1965,1976, and studies which have focused on stocks in areas 1985 Stringer, 1959; Campbell,n.d.; closedto shellfishing,there have been Canario and Kovach, 1965a; Saila et al., relatively few publishedstudies on shellfish 1967; Sisson, 1977; Pratt et aL, 1987!. In stocks in the areasof Narragansett Bay open eachof thesestudies, the populationof to shellfishing.In addition to the previously quahogsin theseareas was dominatedby the cited Narragansett Bay-wide studies, Russell presenceof large adults,which typifies the 972! surveyedquahog populations in the populationstructure of quahogsin areasthat West Passageof NarragansettBay using havebeen closed to shellfishingfor a long dredgesampling techniques. A numberof time Figure 6!. R.I. Department of Environmental

53 Figure 5. Distribution of quahogsover 25 mm long Figure 7. Quahogswere collected by diversfrom 30 in GreenwichBay during l952. Data weregathered from quadrats.25 m2>ineach of threesites in Narragansea 226stations using a 0.46m2 grab sampler and a 12mm Bay, Thesites are: A! GreenwichCove, B'l Greenwich meshsieve Stickneyand Stringer, 1957!. Bay, and C! SouthFerry, WestPassage. Histograms representtotal numbersof quahogsin sizeclasses of 3 nimincrements. The indicated valve lengthsare sizeclass midpoints.The dashed line representsthe Rhodeisland legalsize limit for quahogsthat is a one-inchhinge width, which correspondsto a 48 nun valve length Rice et al., 1989!

Bay and West Passage Figure 7! Rice et al., 1989!.

Estimates of Natural Mortality The first of the factors which remove individuals from quahogstocks is natural mortality. Natural mortality includeslosses Figure 6. Overall length-frequencydistribution of due to predation and diseases.It is known that quahogsin the ProvidenceRiver and Mount Hope pre-recruitjuvenile quahogsare, high1y Bay.Both areasare closedto shellftshing.Quahogs susceptible to predation losses. However, were collected November 1985 Pratt et al., 1987!. oncequahog reach the size at which they Management R,I,D.E,M.!-sponsored studies recruit into the fishery,they am relatively are documented in the R.I. Division of Fish resistantto most predators e.g..Whetstone and Wildlife Leaflet Series. These R.I.D.E.M, and Eversole, 1978; MacKenzie, 1979; surveys include the northern portion of Boulding and Hay, 1984!. Greenwich Bay Campbell, 1959a!; the Caddy 989! outlines a method for Potowomut River Campbell, 19S9b!; the estimating the natural mortality of bivalves Kickamuit River Campbell 1959c; Canario, by successivelysampling the numberof 1963!; and the East Passage Canario and dead shells paired valves! present in closed Kovach, 1965b!. In general, the population areas in relation to the number of live structureof quahogsin actively fishedareas of animals present. In the various studies of NarragansettBay differs from closed areas in stock abundance in closed areas of that the fishedareas have a predominanceof Narragansett Bay, there has been no younger, smaller quahogs. This distinction is quantitative data collected as the levels of best illustrated in a comparisoti study between naturalmortality in thoseareas. It is likely actively fished and closed areasin Greenwich that naturalmortality is relativelyhigher in

54 quahogsin excessof 8S rnm valve length Estimates of Fishing Effort and becauseof their reduced ability to reburrow Fishing Intensity Rice et al., 1989!. 'Dere may be periodic The number of fishermen in the quahog increasesin natural mortality of quahogs fishery and the averagecatch per fisherman correspondingwith cyclic fluctuationsof are importantdata which can be usefulfor starfish Asteriasforbesir'! populationsin estimatingfishing effort. Me National NarragansettBay Pratt et al., 1992!. Marine Fisheries Service NMFS! makes annual estimates of the numbers of shellfrshermen in Rhode Island. Based on Estimates of Mortality Caused by the number of licenses issued and the Fishing numberof boatsregistered to Estimatesof the mortality of quahogs shelifishermen, NMFS estimates there to be causedby fishing can be madeby using between 1,000 and 1,300 full-time estimatesof standingcrop abundancesof shellfishermenin recentyears. This estimate quahogsand the numberof quahogscaught. is considerablyhigher thanthe estimateof This methodof estimatingfishing mortality 700-800 full-time sheilfishermen currently is highly dependentupon knowledge of the used by Rhode Island Department of selectivityof the harvestgear. Using a Environmental Management fisheries "rocking chair" dredge,with catch scientists see Pratt et al., 1992 for efficiencies known for various substrate discussion of estimation methods!. types,Russell 972! estimatedthe fishing There have been two surveys of mortality of quahogs in the West Passage shellfishermento gatherdata about the levels during one seasonof the commercialdredge of fishing effort among shellfishermen. fishery. During the dredge season,the Holmsen 966! and Holmsen and Horsley standingcrop of quahogsin his study area 981! conducted mail surveys of all shellfish declined from 18,148 2 5,704 bu to 7,23S 4 license holders and made estimates of the 2,167 bu bu = approximately 80 pounds numbers of those deriving different or 31.5 kg!. Breakage is important to proportionsof their incomefrom quahogging consider as it may be a source of bias in Table 1!. fishing mortality estimatesif catchalone is the sole basis of these estimates. One study in NarragansettBay comparedthe effectsof harvestinggear and handlingon the breakageof quahogs Glude and Landers, 1953!.Broken quahogs caught in a "rocking chair" dredgeranged from 0.7% to 1.2%of the total catch.In rocky sediments,2.9% of the remainingquahogs were found broken on the bottom, but in sand/silt areas, 1.0% of the remaining quahogs were found to be broken. There was no evidence of breakage of quahogs<60 mrn valve lengthby the dredge,and there was no evidencethat the dredgesmothered quahogs by covering them with sediments. There was essentially no damageto quahogsdirectly by bullrakm, but handlingof quahogsby bullrakers aboard the boat caused some breakage 0,1% to 0.3% of the total landed.

55 The proportionof fishermenobtaining at least75% of their incomefrom quahogging increased from 21% to 36% in these two surveys.Holmsen 966! also found an increase in full-time fishermen from the mid- 1950sto 1961,indicating a trendof professionalizationduring periods of inclining aswell asdecreasing landings. One key conclusion of Holmsen's surveys is that one of the main characteristics of the Rhode Island quahogfishery is therelative ease of increasingor decreasingfishing effort as conditionschange in the fishery or the generaleconomy. At present,the three commercial methods of quahoggingin RhodeIsland watersare with the useof tongs,bullrakes, and by Figure S. Location of tong and bullrake fi shennenin commercialdiving. Commercialdiving has NarragansettBay recorded between Septeniber 1959 and increasedin importanceas a methodof August 1960 Campbell, 1961!. quahogharvesting since the 1981study of Holmsenand Horsley, so thereis little information about the amount of fishing effort attributableto divers.Boyd 991! provides an excellenthistorical overview of tongingand bullrakingin NarragansettBay. Over the years sincethe late 1940s,there has been a gradual shift in the useof gearfrom a predominance of tongsto a predominanceof bullrakes. The locationof tong and bullrakefishing effort wasmapped intermittently between June 1955and August 1960 Campbelland Dalpe 1960;Campbell, 1961!. Maps generatedby thisproject Figure8! showedthat the major fishingeffort was confined to themiddle and upperNarragansett Bay, with tongfishermen confined to the shallower near-shore areas. By useof a mail-surveyquestionnaire, Hoimsenand Horsley 981! showed similarly that most of the fishing effort was confined to the middle and upper Narragansett Bay Figure 9!. Thereis little published information about the location of fishing effort by shellfish divers.

Relative Gear Efficiencies and Environmental Impacts Figure9, Percentof quahoggingeffort in selected Therehas been only one study in areasof ¹rragansett Bay Hobnsenand Horsley, NarragansettBay that comparesthe reiative l981!.

56 impactsand efficiencies of differentgear types orderto updatethe fishing effort information. Glude and Landers,1953!. In this study Additionally, giventhe currentmix of harvest carriedout in 3-acreplots, the efficiencyratios technologies,a studyof the relativeharvest for the bullrakeand dredgewere determined. efficienciesof tongs,builrakes, and hand The bullrakes used were able to most collectingby commercialdivers is efficiently retainquahogs greater than 55 rnm iecommended. In conclusion, there is a great valve length,but somequahogs 35 to 5S inm wealth af information available to fisheries in valve lengthwere ableto be retained.The inanagersabout quahogs in NarragansettBay. dredgewas ableto mostefficiently retain It is hopedthat this review will providea quahogsabove 70 mm in valve length.There startingpoint for the assessmentof wherewe wereno significantdifferences in the physical have been in terms of the fisheries or biologicalcomposition of rakedor dredged managementstudies, and that it will beuseful bottoms,but both had fewer living forms than in planningmanagement strategies for Rhode the unfished control area. These authors Island'smost importantfishery resource. concludedthat therewas no biological basis for prohibitingeither bullraking or dredging. References A recentstudy on the environmental Andrews,J.D. 983!. Transportof bivalve impactof bottomcultivation and removal of larvaein JamesRiver, Virginia. Journal of adult quahogson the setand recruitmentof ShellfishResearch 3:29-40. quahogswas recently concluded Sparsiset Boulding, E.G. and T.K. Hay. 984!. Crab al., this volume!. They found that after three responseto prey densitycan result in monthsthere were no significantdifferences density-dependentinortality in clams. in thephysical, chemical, and biological CanadianJournal of Fisheriesand Aquatic parametersbetween fished, cultivated, and Sciences 41:521-525. control plots becauseof high environmental Boyd,J.R. 991!. The NarragansettBay variability. shellfishindustry: a historicalperspective andan overviewof problemsof the Conclusions and Recommendations 1990s.Pp. 2-10. In: M.A. Rice, M. There have been a considerable number of Grady and M.L. Schwartz eds.!, studiessince 1946focusing on the biology Proceedingsof the First RhodeIsland and fishery of quahogsin NarragansettBay. ShellfisheriesConference. Report No. The informationbase about the growth rates RIU-W-90-003, Rhode Island Sea Grant, of quahogsm NarragansettBay seems to be University of RhodeIsland, Narragansett. quitegood. There appears to be a shortageof Caddy,J.F. 989!. Recentdevelopments in informationabout quahog recruitinent. Some researchand management for wild stocks studiesappear to indicatethat thereis a paucity of bivalves and gastropods.pp. 665-700. of recruitment into some areas,yet there In: J.F.Caddy ed.! Marine Invertebrate appearsto be annualrecruitment into other Fisheries: Their Assessment and areas,particularly Greenwich Bay andupper Management.Wiley Interscience,New NarragansettBay. A systematicstudy of York, 752pp. quahogrecruitment patterns throughout Campbell,R. no date!.An inventory of the NarragansettBay is warranted.Estimates of quahogpopulation of the Providence fishing effort and fishing mortality in areas River and Mount Hope Bay. Rhode throughoutNarragansett Bay are lacking, and Island Division of Fish and Game. much of the information that is available is unnumbered leaflet. now 10 yearsout-of-date. It is recommended Campbell,R. 959a!. Quahoginvestigations: that a socio-economicstudy similar to that of Nausauket 8uttonwoods, 19S5-1958- Holmsenand Horsley 981! beundertaken in 1959. Rhode Island Division of Fish and

57 Game. Leaflet no 1. Holmsen, A.A. and S. Horsley. 981!. Campbell,R. 959b!. Quahoginvestigations: Characteristics of the labor force in Potowomut River. Rhode Island Division quahoghandraking, Rhode Island Sea of Fish and Game. Leaflet no. 2. Grant Marine Memorandum No. 66, Campbell,R. 959c!. Quahog University of RhodeIsland, Narragansett. investigations Kickamuit River.Rhode Jones,D.S., M.A. Arthur, and D.J. Allard. Island Division of Fish and Game. Leaflet 989! Schlerochronologicalrecords of no. 3. temperatureand growth from shellsof Campbell,R, 961!. A summaryreport on Mercenaria rnercenaria from Narragansett the fleet plotting programin Narragansett Bay, RhodeIsland. Marine Biology Bay.Rhode Island Division of Fishand 102:225-234. Game. Leaflet no. 7. Kassner, J and R.E. Malouf, 982!. An Campbell,R. andP. Dalpe.960!. A evaluationof "spawnertransplants" as a preliminaryreport on the fleet plotting managementtool in LongIsland's hard programin NarragansettBay, Rhode clam fishery.Journal of Shellj7sh bland Division of Fish and Game. Leaflet Research 2:165-172. no. 4. Kassner, J., R. Cerrato, and T. Carrano. Canario,M.T. 963!. Shellfish survey of the 991!. Toward understandingand Kickamuit River, Rhode Island Division improving the abundanceof quahogs of Fish and Game. Leaflet no. 12. Mercenaria mercenart'a!in the eastern Canario,M.T. and K.A.M. Kovach. 965a!. Great South Bay, New York. pp. 69-78. Shellfish surveyof the ProvidenceRiver. In; M.A. Rice, M. Grady and M.L. Rhode Island Division of Conservation Schwartz eds.!,Proceedings of the First Leaflet no. 17. RhodeIsland ShellfisheriesConference. Canario,M.T, and K,A.M. Kovach. 965b!. Report No. RIU-%-90-003, Rhode Shellfishsurvey of the EastPassage Island SeaGrant, University of Rhode Channel. Rhode Island Division of Island, Narragansett. Conservation leaflet no. 16. Kennish,M.J. 980!. Shell microgrowth Gardefors,D. and L. Orrhage.968!. analysis:Mercenaria mercenaria as a type Patchiness in some marine bottom examplefor researchon population animals:a tnethodologicalstudy. Oikos dynamics.pp. 255-294.In: D.C. Rhoads 19:311-321. and R.A. Lutz eds.!, Skeletal Growth Glude, J.B. and W.S Landers 953!. of Aquatic Organisms.Plenum Press, Biological effectsof bullraking vs. power New York. dredgingon a populationof hardshell Landers, W.S. 954!. Seasonalabundance clams, Venusntercenaria. National of clam larvae in Rhode Island waters ShellfisheriesAssociation Convention 1950-1952.U.S. Fish and Wildlife Addr esses 1951:47-69. ServiceSpecial Science Reports in Hancock, D.A. 973!. The relationship Fisheries 117. 1-29. betweenstock and recruitment in exploited Loosanoff, V.L. 937!. Spawningof Venus invertebrates. Rapports et Proces- tnercenaria L. Fcolog y 18:506-515. Verbeaux des Reunions Conseil Loosanoff, V.L., W.S. Miller, and P.B. Internationalpour 1'&ploration de la Mer Smith. 951!. Growth and settingof 164: 113-131. larvae of Venus mercenaria in relation to Holmsen,A.A. 966!. The RhodeIsland temperature.Journal of Marine Research quahogindustry some economic 10:59-81, aspects.URI AgriculturalExperitnent Ludwig, J.A. and J.F. Reynolds. 988!. Station Bulletin No. 386. StatisticalEcolog y. Wiley Interscience,

58 MacKenzie,C.L. 979!. Managementfor Rhode Island, Narragansett. 117pp. increasingclam abundance.Marine Rhoads, D.C. and G, Panella. 970!. The Fisheries Review 410!:10-22. use of inolluscan shell growth patterns Malinowski, S. and R.B. Whitlatch. 988!. in ecologyand paleoecology. Lethaia A theoretical evaluation of shellfish 3: 143-161. resourcemanagement. Journal of Shellfish Rice, M.A. and J.A. Pechenik. 992!. A Research 7:95-100, review of the factors influencing the Murawski, S,A. and F.M. Serchuk. 989!. growth of the northernquahog Mechanized shellfish harvesting and its Mercenaria mercenaria Linnaeus, management:The offshoreclam fishery of 1758!.Journal of ShellfishResearch 11: the easternUnited States.pp. 479-506.In: 279-287. J.F. Caddy ed.! Marine Invertebrate Rice, M.A., C. Hickox, and I. Zehra. Fisheries: Their Assessment and 989!. Effects of intensive fishing Management.Wiley Interscience,New effort on the populationstructure of York. 752pp. quahogs,Mercenaria mercenaria, in Peterson, C.H., P.B. Duncan, H.C. NarragansettBay. Journal of'Shellfish Summerson, and G.W. Safrit Jr. 983!. Research 8:345-354. A mark-recapturetest of annualperiodicity Royce,W.F. 984!. Introduction to the of internal growth banddeposition in Practiceof FisheryScience. Academic shells of hard clains, Mercenaria Press, New York, 428pp. mercenaria.Fishery Bulktin of the US Russell, H.J, Jr. 972!. Use of a Fish and Wi7dlifeService 81:765-779. commercialdredge to estimatehard-shell Pratt, D.M. 953!. Abundance and growth of clam populationby stratifiedrandom Venus rnercenaria and Callocardia sampling.Journal of the Fisheries morrhuana in relation to the character of ResearchBoard of Canada29: bottom sediments.Journal of Marine 1731-1735. Research 12:60-74. Saila, S.B. and T.A. Gaucher 966!. Pratt, D.M. and D.A. Campbell.956!. Estimationof the samplingdistribution Environmentalfactors affecting growth in and numerical abundance of some Venusmercenaria. Limnology and mollusks in a Rhode Island salt pond. Oceanography1:2-17. Proceedingsof theNational Pratt, S.D. 977!. Benthic biology of areas ShellfisheriesAssociation 56:73-80. adjacentto the Quonset/Davisvillebase. Saila, S.B., J.M. Flowers, and M.T. Appendix 2. The redevelopmentof Canario.967!. Factorsaffecting the Quonset/Davisville;an environmental relative abundance of Mercenaria assessment.Marine Tech. Rept. 55, Coastal mercenaria in the Providence River, Resources Center, University of Rhode Rhode Island. Proceedings of the Island, Narragansett. National Shellfisheries Association Pratt, S.D., B.K. Martin, and S.B. Saila. 57: 83-89. 987!. Statusof the hardclam, Mercenaria Sisson, R.T. 977!, Hard clam resource mercenaria, in the Providence River and assessmentstudy in upper Narragansett Mount Hope Bay. Reportno. NBP-88-08, Bay and the ProvidenceRiver. Rhode NarragansettBay Project,U.S. Island Division of Fish and Wildlife EnvironmentalProtection Agency. 38pp. Leaflet no. 49. Pratt, S.D., A.R. Ganz, and M.A. Rice. Stickney, A.P. and L.D. Stringer. 957!. A 992!. A SpeciesProfile of the Quahogin study of the invertebratebottom fauna of RhodeIsland. Report no. RIU- T-92-001, Greeiiwich Bay, RhodeIsland. Ecology RhodeIsland SeaGrant, University of 38: 11 1-122. Stringer,L.D. 959!. The population Q. Mr. GeorgeDeBlois, shellfisherman! abundance and effect of sediinent on the I'ou mentioned the Kassner and Malouf hard clam. In: Hurricane Damage l982! spawnertransplant study in Great Control,Narragansett Bay and Vicinity, SouthBay. Whatwas the timeframe of that Rhode Island and Massachusetts study? AppendixE. A detailedreport on fishery A. Rice! Jeff Kassner,one of thepeople resources. U.S. Fish and Wildlife who did that work is in the audience. Service, 17pp. Perhapshe could answer that for you . V.S. EPA and R.I. Division of Fish and A. Mr. Jeffrey Kassner,Brookhaven, Wildlife. 974!. Stateof RhodeIsland New York! What that study did was to look ShellfishAtlas. 6 figs, andkey. at the spawningcycle of hardclams in the Whetstone,J.M and A.G. Eversole978!. Great SouthBay that was performedover a Predation on hard clams, Mercenaria two-yearspawning period. The underlying mercenariaby inud crabs,Panopeus principal behindthe spawnertransplant was herbstii. Proceedingsof theNational that braodstockwere broughtin from more ShellfisheriesAssociation 68:42-48. northern, colder waters and had a retarded Wood, L. and W.J. Hargis Jr. 971!. gametogeniccycle. The idea was to exploit Transportof bivalvelarvae in a tidal the retardedcycle to extendthe spawning estuary.Proceedings of the European period after the nativestock had ceased Marine Biology Symposia4:29-44. spawning.What we found is that the natural spawningvariability was so high that Questions and Answers bringing in clainsdid nat affectthe Q. {'Mr. JohnFinneran, shellfi sherman!In recruitment.Additionally, bringing in 400 to the Gludeand Landersstudy, were divers 500 bushels did not make much difference usedto determinewhat was left and what whencompared to thenatural spawning was broken on the bottom? stocks.Now the idea of spawnertransplants A. Dr. Michael Rice, URI! No, the Glude evolved into the idea of spawner andLanders 953! study useda largegrab sanctuaries.If you thenknow the likely samplerthat brought up intact sediinents and hydrographiclarval dispersalpatterns, yau quahogsafter the dredging or bullraking can strategicailyplace your spawnerstack treatments.Grab samplingcan be used for settlementin preselectedareas. effectivelyfor samplingbecause everything is broughtup juveniles, adults,etc. One Q. Mr. EdgarThompson! Are thereany possibleproblem with grabmnpling is that recentstudies on the sects of pollution on care must be taken to avoid biases in quahogs?An examplemight be theeffects breakageestimates, because some breakage of heavymetals on quahogs.There are a will occur as the sampler hits bottom. numberof organizationssuch as SaveThe Subsamplesfram thecenter of thegrab Bay that are committedto cleaningup the sampleare representative of intact Bay, and I want to know if there has been sediments.Grab samplingwas usedduring some headway. the surveysof the 19%s andthe Sailaet al. A. Rice! Thereare a considerablenumber 965! study. More recentstudies have used of studies on this. In the first quahog diversfor sampling.Diving appearsto be conference we held in 1990, Ms. Katrina bestfor samplingjuveniles and determining Kipp of theEnvironmental Protection populationstructure without gear bias. Agencyand the NarragansettBay Project Indeed,the bestway to calibratesampling gavea veryexcellent review of studiesof gearsuch as dredges, tongs, and rakes is by NarragansettBay in whichquahogs were diver sampling, analyzedfor heavymetals, various organic pollutants,and pesticides. She outlined the risk overflow systemare a positivestep forward. assessmentprogram in which the healthrisk to Shellfishopenings albeit not all the time! in peopleeating Narragansett Bay quahogswas the conditional areassuggest some comparedto othercornrnon health risks. In improvement.Tlm next thing in line, general,Narragansett Bay quahogscarried a however,is the nonpointsource pollution rather low-risk value to the consuming public. problem.This is a muchmore expensive Sheldon Pratt from here at GSO had one study problem,and technically a hardernut to that lookedat quahogpopulations in the crack. Providence River, and the adults are alive and well. One interestingstudy that cameout of the Q. Mr, David Borden, DEM! Youhave National Marine Fisheries Service shellfish lab in summarizedwhere thereis knowledgeand Milford, Connecticut showed that heavy metal wherethere is needfor more work Can you pollutantsare much more toxic to bivalve larvae give me somesense of priority on what thanthey areto adults.It is possiblethat studiesyou think are mostimportant? shellfisheriesin pollutedareas might be damaged A. Rice! As it so happens,we have a full by reducingrecnutment rather thart by the paneldiscussion this afternoon,with your outright killing of adults. queslionas our topic So, pleasestay tuned.

Q. Johnson!In a nutshell,do you believe that we are movingforward or backward. A. Rice! Well, I think we're probably IThisstudy was funded in partby RhodeIsland Sea Grant moving forward, Improvementsin upper Marine Advisory Serviceand RhodeIsland Cooperative NarragansettBay water quality due to the Extension.This is publication number 2779 of the Rhode irnprovernentsby theNarragansett Bay Island Agricultural ExperitnentStation, College of Commission to the combined sewer ResourceDevelopment, University of RhodeIsland.

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