control of oyster drills, eupleura caudata

CONTROL OF OYSTER DRILLS, EUPLEURA CAUDATA ANDUROSALPINX CINEREA, WITH THE CHEMICAL POLYSTREAM

BY CLYDE L. MACKENZIE, JR., FISHERY BIOWGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORYMILFORD, CONN. 06460

ABSTRACT

Five experimental and 10 commercial treatments ofoyster bed. In four States were made with Polystream.On a typical bed, where water currents were lessthan 2.7 lan. per hour, Polystresm killed about 85percent of the thick-lipped drill, Eupleura caudata,and 66 percent of the Atlantic oyster drill, Urosalp;nscinerea. A sltnificantly hither percentate of oysterdrills was kllled by treatments made in late April andearly May rather than later in the summer. Oyster

Boring gastropods, known as oyster drills, andstarfish, Asteria.s forbesi, are the most serious pred­ators of oysters in Long Island Sound. The drillsprey haavily on oysters, Ora88ostrea virginica,along the entire Atlantic Coast, from Canada toFlorida, and in certain areas of the Pacific Coast.Where they are extremely numerous, oyster drillsdeStroy nearly all oysters on commercial ·beds. InLong Island Sound, however, drills usually reducethe number of oysters to such a level that mostbeds are of marginal value commercially.

This article summarizes laboratory and fieldexperiments made during the development of acontrol method of oyster drills for use on com­mercial oyster beds in southern New England andNew York; it includes the rc..c;ults of 15 treatmentsduring 1961-67.

HISTORY OF DEVELOPMENT OF METHOD

All early phases of work on the development.of a method of control of oyster drills by use ofPolystream, including the initial testing of chem­ica.ls, was done by the biological laboratory atMilford, Conn. Field tests and commercial appli­cations of Polystream were made under theinspection of the author in the States of Connecti­cut, New York, Rhode Island, and Massachusetts.Additional independent laboratory and field stud­ies were later made in Virginia.

Published May 1970.

FISHERY BULLETIN: VOL. 68, NO.2

drills that survived did not feed for several month••The number of drills remained low for at least 2 years.Polystream treatments killed only sman percentatee offish, small clams, Mercenorlo merCImIJrlo. crabs, andother Invertebrates. After a treatment, oysters, CraslO8­trea virginica. clams, and other orpnlams had smanresidues of Polystream In their tluuee but AfBduaUylost these residues. Growth of oysters was normal ontreated beds.

EXPERIMENTAL WORK AT MILFORD

In 1946, the Fish and Wildlife S~rvice biologi­cal laboratory, Milford, Conn., began a programof screening organic chemicals with the goal ofeventually developing a method to control oysterdrills (Loosanoff, 1960). A method was soughtthat would kill oyster drills, but would not harmoysters, clams, Mercenaria mercenaria, and otherorganisms on a shellfish bed, and ailso would notlea.ve residues in tissues of shellfish that would beharmful to man. Tests were made in the laboratoryand the field.

Laboratory Tests

Loosano:ff, MacKen.zie, and Sh~r (1960a,1960b) reported that chlorinated benzenes, such asmonochlorobenzene, orthodichlorobenzene, para­dichlorobenzene, trichlorobenzene, tetrachloro­benzene, and their mixtures, are toxic to severalspecies of marine gastropods, including the thick­lipped drill, E'Upleura caudata, and the Atlanticoyster drill, Ur08alpi'fl1lJ cinerea. These chemica.lswere. selected for further tests because they weretoxic to snails, virtually insoluble in sea water,and of sufficient density to settle to the bottom ofthe Sound. The last two characteristics reducedthe chance of damage to any but bottom-dwellingorganisms whose soft parts contact the chemicalsdirectly. Small quantities of Sevin (l-naphthyl-

285

N-methylcarba.mate) -were added to the chlorin­ated benzenes to increase their killing effect on thesnails. In laboratory experiments, orthodichloro­benzene mixed with dry sand in the ratio of 1 to 19,by volume, and then spread over shallow panskilled most oyster drills; and when used to form '&

ba.rrier in small troughs it prevented them fromcrossing the barrier for several months.

Loosanoff, MacKenzie, and Davis 1 stated thatfor 14 months small barriers consisting of ortho­dichlorobenzene and sand continued to affect oys­ter drills on contact but were not toxic to larvaeand juveniles of sea squirts, Molg'lila'11Wlnhattemis,common shipworms, Teredo 'sp., Atlantic oysterdrills, eastern white slippers, Orepidula plana,and mud blister worms, Polydora sp., which setand grew within '2.5 em. (1.0 inch) of the barriers.These observations showed that orthodichloroben­zene was only a contact poison. In large outdoortroughs siltation reduced the effectiveness of chlo­rinated benzenes by forming a covering layer thatkept the oyster drills from touching the chemicals.

Field Testa

Loosanoff (1961) reported that oyster drills canbe greatly reduced in numbers by spreading chem­ically treated sand over shellfish beds. The combi­nation that gave good results consisted of 95percent dry sand and 5 percent orthodichloroben­zene conta.ining 1 to 3 percent, by weight, of Sevin.The chemicals were mixed with the sand in largecommercial cement trucks., The treated sand,loaded on the deck of a boat,' was then spread overthe oyster bed by lL high-pressure stream of water.

Davis, Loosanoff, and MacKenzie 2 reported theresults of treatments of severa' small oyster beds.They emphasized the effects of chemical treat­ments on organisms other tha.n oysters and clams.On July 16, 1961, a bed of about 1:6 ha. (4 acres)in Great South Bay, Long Island, N.Y., wastreated with 9.5 kl. per hectare (5 yardlll,per acre)of sand mixed with 1.9 hI. (50 gallons) of ortho­dichlorobenzene containing 6 kg. (13 pounds), (2percent by weigh:t)-·.of ,Sevi.n~ .As ,~he sand-de-

I LoosaDolf, V. L., C; L. KacKeDzle, Jr.', aDd H. C. Davis.1960. Progress report OD chemical methods. or coDtrol of molluscanenemies. Bur. Commer. FIsh. BioI. Lab., 'MIlfOrd, ConL, BuU. lK(8).20 pp.

• Davis, H. C., V; ,L. Loosanolf,. and C. L.' 'MacKenzie, Jr.1961. FIeld tefltB of a chemical methOd for the cODtrol of marlDegastropods. Bur. Commer. Fish. BioI. Lab., Milford, CoDn.,"Bull.25 (3),9 pp. . '

286

scended, several small fish were killed and commonjellyfish were carried to the bottom. Shortly afterthe sand reached the bottom, sea squirts werefound partially contracted; oyster drills wd othersnails were greatly swollen; and a number ofhermit crabs, PagU1'U1J sp., and mud crabs, Neo­pOl1W'pe teaJana, were dead. They did not determinewhether this experimental trea.tment eventuallykilled the oyster drills. Another bed, which was offthe east end of Long Island in 9 m. of water, wastreated in like manner. Because of strong watercurrents over the area., little sand actually reachedthe bottom that was to be treated and, as a result,the treatment was not effective. This failure indi­cated that in an area with strong currents it wasvery difficult to control oyster drills with sandtreated with a chlorinated benzene.

In treatments along the Connecticut shore theeffects of the chemicals on animals inhabiting thebottom varied somewhat depending on location ofthe bed. In open waters, divers noticed only a smalleffeet on: fish, hermit crabs, mud crabs, and anne­lids. In areas where waters were shallower andcurrents slower, however," the effect was greater.In all tests, fish, hermit crabs, and mud crabs fedand moved normally in an area within a few daysafter a. treatment. Fish, perhaps attracted by theexposed white feet of swollen gastropods, weremore numerous after a treatment. Most pelagiccommon shrimp that we~ in the immediate areaat the time the treated sand was spread were ap­parently killed. Once the chemicals were on the1;x>ttom, however, shrimp moved in again and re­mained uninjured. Oysters and mussels, Mytilused'lilis, when present, were pumping normally with­in an hour of the treatment. Starfish, Asterias for­beBi, were irritated by treated sand falling on theiraboral surface, and small .sores soon appeared. Ina number of treated areas starfish consumed swol­len oyster drills and northern moon shells, Poli­nices sp. Davis et a1.3 also reported tha.t the treat­ment did not reduce the intensity of setting ofoyster and starfish larvae in the area.

.Polystream4 (trademaJ:'k of Hooker ChemicalCorporation for a mixture of polychlorinated ben­zenes Containing a minimum of 95 percent total ofactive trichlorobenzene, tetrachlorobenzene, and

• See footnote 2.t Trade Dames referred to In this publlcatioD do DOt lJDp1:r

eDdorBement of commercial products.

U.S. FISH AND WILDLIFE SERVICE

pentachlorobenzene, and having a last crystal pointof 18° C. + 3° C.), a less expensive product thanorthodichlorobenzene, was used for the first time onexperimental beds in New Haven Harbor, Conn.,in the summer of 1961. I made field tests to com­pare the effectiveness of Olihodichlorobenzene. andPolystream and to determine the minimum quan­tity of chemically treated sand needed to controloyster drills. Sevin was added to both types ofpolychlorinated benzenes at the rate of 2 percentby weight, and a total of 1.9 hI. of either ortho­dichlorobenzene or Polystream was mixed withench 9.5 k1. of sand. The two chemical-sand mix­tures were spread over eight OA-ha. beds at ratesof 1.9, 5.1, 9.5, and 19 kl. per hectare. Drill trapswere used to estimate the effects of treatments onpopulations of oyster drills and mud crabs.

SCUBA divers studied the effects of thesetreatments. Their observations indicated thattreatments of 9.5 and 19.0 kl. per hectare of eitherorthodichlorobenzene and Sevin or Polystream andSevin caused all visible gastropods, includingthick-lipped drills, northern moon shells, knobbedwhelks, Busycon cmictt, channeled whelks, BU8Y­

eon cOllUlHmtlat'urn, and New England nassas, N0.8­

8aJ'>iU8 t1'iv-ittatus, to become swollen (snails listedin order of importance as shellfish predators; theNew England nassa is not a predator). Appar­ently, the latter three species of predators werecompelled to emerge from their usual positionburied in the bottom. A number of pipefish,Syngnathus lusam, mud crabs, and shrimp wereeither partially paralyzed or behaved abnormally.Small flounders, Pseudopleu1'onectes americanus,however, swam around apparently unharmed.Three days later theseefl'ects ,vere more evident;all visible gastropods were either swollen and beingeaten' alive by starfish or they had already died.The pipefish, mud crabs, and shrimp, nevertheless,had either recovered 01' had been replaced by othersfrom surrounding areas. Subsequent observationsrevealed that starfish were gradually consumingthe remaining swollen gastropod~. Thus, the areawas left with a large number of empty gastropodshells which gradually disappeared; a lot with 42shells of the northern moon shell per 50 m.2 ofbottom on July 3, for example, had none by July18. Presumably, the shells had been oceupied byhermit crabs and carried away.

Catches of oyster drills on traps indicated that

CONTROL OF OYSTER DRILLS WITH POI.YSTREAl\I

417-060 0 - 71 - 8

applications of 9.5 and 19.0 kl. of treated sandper hectare had killed nearly all drills and thatthe mixture of Polystream and Sevin was moreeffective than the mixture of orthodichlorobenzeneand Sevin. The numbers of mud crabs on trapsbefore and after treatments indicated that theywere not harmed by the treatments. As a result,we thereafter used Polystream exclusively, aban­doned orthodichlorobenzene, and standardized thetreatment rate a.t 9.5 k1. per hectare.

Increased catches of drills, along the borders oflots several weeks a.:fter the treatment, indicatedthat drills were migrating into the lots from sur­rounding areas. This observation suggested thatto ensure protection of an oyster bed from oysterdrills, a zone perhaps 25 or more meters wide out­side the bed, as well as the bed itself, should betreated, and that treatment of a single large bedwould be more efficient than treatment of a numberof small beds.

Polystream was used to treat beds inhabited byoysters and clams that are later consumed byhumans. It was necessary, therefore, to determinewhether these shellfish retained any residues of thischemical. In practice, however, only those bedswith seed oysters on them are treated with Poly­stream. T,hese oysters are t.ransplanted to untreatedbeds at least 4 months before harvest. It was alsodesirable to know whether other organisms inhab­iting treated beds, particularly those that mightbe taken by sport or commercial fishermen, retainresidues of Polystream.

To determine whether oysters, clams, or otheranimals or plants accumula.ted and tJlen lost resi­dues of Polystream, I studied specimens that werecoHected from treated beds by divers or by dredg­ing. I also studied northern lobsters, H O'lna:rus

americanus, in cages to determine whether residueswould be lost after a period of time in water freeof Polystream. The U.S. Testing Company ofHoboken, N.J., determined the quantity of Poly­stream in tissues of the plants and animals throughuse of a technique developed by Schwartz, Gaffney,Sehmutzer, and Stefano (1963).

In 1961 and 1962, I determined the quantities ofPolyst.ream in oysters and clams from a 0.4-ha.lot,treated with 1.9 hI. of this chemical. In oysters theresidue was 1.8 p.p.m. (parts per million) 8 daysafter the treatment. It diminished slowly untilnone 'Was detected 119 days later. Residues in clams

287

TABLE I.-Residues of Polystream in oysters and clams ona O.4-hectare bed in New Haven Harbor, Conn., after itwas treated with Polystream-sand, June 27-29,1966

TABLE 2.-Residues of Polys/ream in olJsters collected atvarious distances from lot 42, Norwalk, Conn. Lot wastreated on August 24, 1966

Time after treatmentResidues

In Oysters In clamsDistance Crom lot '2

Date oC collection (1966)

Sept. 1 Oct. 13 Dec. 8

were at similar levels and were lost at similar rates(table 1).

Oysters removed from a treated bed and re­planted on an untreated area lost any ~idue ofPolystream within a week. Nevertheless, the firstfew times oysters that had once grown on a treatedbed were to be harvested, they were analyzed forany possible residue of Polystream before clear­ance for marketing. None of these oysters hadresidues.

In 1966, I determined the rates of loss of Poly­stream in oysters at several distances from lot 42,Norwalk, which was treated on August 24, 1966,and where strong currents had washed many gran­ules off the lot. After 8 days, residues were as highas 0.3 p.p.m. in oysters 150 m. from the lot andwere higher in oysters closer to the lot. On October13, however, only those oysters 15 m. or closer tothe lot showed any residue. At this distance thelevel had dropped from 1.7 p.p.m. in Septemberto 0.2 p.p.m. On December 8, 106 days after thetreatment, no residues were detected in any oystersoutside the treated lot (table 2).

To determine the quantity of Polystream in tis­sues of other organisms inhabiting an oyster bp,d,

I made periodic collections from treated beds. Allspecies of animals or plants collected within a yearhad accumulated a small quantity of Polystream.Residues of Polystream eventually diminished inthose species, namely, the bay scallop, Pecten il"J'a­dlaruJ, hermit crab, and sea lettuce, Uz'va sp., wherecomparisons between time intervals were made(tn,ble 3) .. By holding northern lobsters in a cage for a

week in the center of a bed 45 days after it wastreated, I found that they do accumulate a smallresidue of Polystream (1.4 p.p.m.) when retainedin a treated area. A group of lobsters held on thetreated lot for a week and then held on an un­treated area for another week did not have anyresidue. Thus, lobsters may accumulate a smallquantity of Polystream while they inhabit atreated bed, but they lose it soon after they leavethe bed.

To determine mortality rates of oysters becauseof possible predation by oyster drills on treatedbeds, divers collected oysters periodically on sev­eral beds. The divers either swam across the centerof beds for a distance of perhaps 150 m., gatheringabout 30 clusters of oysters randomly, or they col­lected oysters and all other material from withina metal ring enclosing either 1 or 1.5 m.2 of bottomfrom 10 different sections.

Del/'8 • . . -- - ----. --- - -. -- -.-l' .__ . . -. _28 • - •••_----. --- --- -- --- . - ---116 •• • _77. • ._. -- - - -- - - -- -- --. - --.119 • • __336 • -. _--- - ----- -- -- ---'55 . _

P.p.m.1.82.30.20.30.7

<0.1<0.1

0.1

P.p.m.1.11.70.60.30.7

<0.1<0.1

0.1

M.15 . __ . ---.30 . • •• __75 • •• __ • _160 •• __ •• -_ --- - -.-

P.p.lIl.1.70.'0.20.3

P.p.m.O.:!<.1<.1<.1

P.p.m.<0.1<.1<.1<.1

TABLE a.-Residues of Polystreall~ in animals and plants inhabiting oyster beds in Conn. and N.Y. treated with Polystream

Northern pulI'er (SpluNrofd"maeulatu.)----- .. ----.------- .. -- •.. ---- New Hllven (State spawning bed)--. . _Sea robin (PrlonoCUI coroUnu,)-- ._. . . ... New Hllven (State spawning bed) .. . __

i~~~~~~~;r~~~~~ ~~ ~~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~~ ~ ~ ~ ~ ~~ ~ ~:~~Ef ~~1:lff~~ ~~ ~ ~ ~ ~ ~~ ~~ ~ ~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~ ~ ~ ~ ~ ~ ~~ ~Northern moon shells (Pollnle" sp.)- .. •••• •__ North~rt (lot 1)--------- . _. " • _

~=:~t(~~~~~~:~::::::::::::::::::::::::::::::::::::::::::::_~~~ _. ~~_~~_t.~~~: :::::::::::::::::::::::::::::::::::Mud crab (N,ofJ/DUl1l'lluana)- _. • •.. . _••• • New Haven (lot 162).-. _.. . _. . __ . •Red sponge (Mlcroelono proliltra) __ ... _. .. New Haven (lot 13)-- • • • • •S~hettl grass (Codlum fragtle) •. _. . Sag Harbor (lot S) ..... .. _=~::=_~~_~~:)_::::::::::::::::::::::::::::::::::::::::::::::::: ~:.:w~b:~d~tJ~~::::::::::: :::::::::::::::::::::::::

Animal or plant Location Time alter Residuetreatment

Dal/' P.p.m.31 6.925 8.,8 6.0

30 1.86 13. 6

260 0.9I hour 60.0

1 12.325 2.2

1 2D.626 2.3

250 0.11 8.96 0.8

288 U.S. FISH AND WILDLIFE SERVICE

EXPERIMENTAL RESULTS ,IN OTHER AREAS

Wood and Roberts (1963) reported that in thelaboratory Polystream alone killed 50 to 78 percentof large Atlantic oyster drills from the Easternshore of Virginia and that a mixture of Poly­stream and Sevin killed 66 to 77 percent. Thus,they felt that Sevin was not needed. They also in­dicated that if oyster drills are in poor condition,they are more easily killed by Polyst,ream. There­fore, they recommended that treatments should bemade in the early spring when oyster drills areemerging from winter dormancy.

Haven, Castagna, Chanley; Wa.ss, and Whit­comb (1966) reported the results of a field test inHog Island Bay, Va. A 0.4-ha. section of bottomwas treated with 9.5 k1. of sand mixed with Poly­stream containing 2 percent of Sevin. The oysterdrills were not killed by the treatment, they depos­ited egg cases at a normal rate, and they destroyedas many oysters on the treated plots as on un­treated control plots. I believe the renson for theineffectiveness was that the treated sand soon sankas deep as 4 em. into a layer of silt on the bed; thus,the drills couM move over the bottom withoutcontacting significant quantities of the chemicals.Haven et a1. (1966) also reported that the Poly­stream-Sevin treatment had a deleterious effect onother living organisms and that growth of oystersand clams was apparently retarded.

RESULTS OF COMMERCIALTREATMENTS

I used several methods to evaluate the effective­ness of treatments in killing oyster drills and theireffects on organisms inhabiting oyster beds. Tencommercial treatments of oyster beds are described.

METHODS USED IN EVALUATION

Oyster companies used a standard rate of 1.9 hI.of Polystream per hectare (50 gallons per acre) ofoyster bed. In early treatments, they mixed Sevinwith Polystream at the rate of 2,percent by weight.The Polystrea.m was mixed with either dry sand ora granula.r clay [the mixture is termed Polystrea.m(Granular)] which carried it to the bottom anddispersed it.

Several techniques were used to evaluate theeffects of treating commercial oyster beds with

CONTROL OF OY~TI!JB DRILLS WITH POLYSTREAM

Polystream and Sevin. On numerous occasionsSCUBA divers examined each bed carefully for20 to 30 minlJ,tes to determine the gross effects ofthe chemicals on all visible living animals andplants. Often they made the first examinationwithin an hour of a treatment and followed it bymany subsequent periodic examinations during thenext 2 to 3 years. They examined certain beds oncea month during collections to determine survivalrates of oysters.

In 1961-63, drill traps were used to estimate theeffectiveness of treatments in controlling oysterdrills. Because mud crabs enter drill traps in largenumbers, I estimated the effect of treatments onthese populations.

From 1964-67 I made quantitative determina­tions of the number of drills per unit area with ahydraulic sampler, which pumps through a. meshbag all bottom material from within a ring enclos­ing areas o'f 1 or 1.5 m.2 All coarse material isretained within the bag, carried to the surface, andsorted. This sampling method, whi6h is carried outby divers, provides an aceul'8lte measure of thedensity of oyster drills and other mollusks on ashellfish bed if enough samples are taken. I tookabout 25 random samples on beds 2 to 6 'ha. in sizea few days before and again about a month aftera. treatment. I determined the percentage of oysterdrills killed by comparing their densities beforeand after treatments. Actually, the Atlantic oysterdrills on many beds were too few in number forme to determine the precise percentage of thisspecies killed.

EFFECTS OF TREATMENTS IN DIFFERENT AREAS

Ten commercial treatments in four States weremade with Polystream. Each treatment will bedescribed separately by areas.

Area 1: Lewis Gut. Bridgeport. Conn•• 1962

Lewis Gut is a long narrow arm of BridgeportHarbor. The water is about 1 to 3 m. deep at lowtide, and maximum currents run at about 4.5 km.per hour (2.5 knots). On June 27 and 29, 1962,an oyster company treated 12 ha.. of this area. witha mixture of Polystream-Sevin and sand.

Effect on gaatropoda.-Divers observed thatwithin an hour after the treatment nearly all thick­lipped drills, Atlantic oyster drills, northern moonshells, and both knobbed and channeled whelks

289

were swollen; a few weeks later most of these gas­tropods, as well as mud snails, were dead.

To evaluate the number of oyster drills killed,I used drill tra.ps. The catch per trap per week fellfrom 16 drills before the treatment to 0.4 drillafterwa.rds. One year later the average catch ofoyster drills increased, primarily by recruitmentof young drills, to about two per trap per week.In 1964, th~ average catch rose to about 5 per trapper week, again as a result of recruitment by youngoyster drills; by July 1965 it rose to 13 per trapper week (fig. 1).

Effect on. associated animals.-During 1961,divers observed that only a small number of fish­primarily sea robins, Prionotus carolinus,' pipe­fish; flounders; nllunmichogs, Fmullulus heterocli­tUB,' and eels, A.1tfJ'Uirla rostrata-were present inLewis Gut before or after the treatment. Immedi­ately after the application of chemicals only thepipefish appeared· to be affected, i.e., more slug­gish than usual. A few hours later, however, mum­michogs were dying along the shore as some of thefiner sand coated with Polystream was churned upin the water by wave action.

This treatment had a slight effect on several

20

organisms. Hermit crabs were affected to somedegree. A number of them had no shells; appar­ently, 0. small quantity of treated sand entered theshell and caused enough irritation to compel themto leave. The abdomens of 0. number of these c.rabshad been bitten off. Most mud crabs were unaf­fected, but between 5 and 10 percent were twitch­ing abnormally immediately after the treatment.The treatment also compelled many nereids andnemertea.ns to emerge from their burrows. A fewweeks later all animals not killed by the initialt.l'eatment appeared to be normal.

Catches on drill traps indicated that the treat­ment did not reduce the population of mud crabs.The weekly catch of these crabs on drill traps fol­lowed the same pattern each year: Each trapca.ught an average of about 15 crabs per week inMay, June, and July; about 10 crabs during Au­gust; and (because of recruitment of young crabs)18 to 23 crabs in the fall (fill. 2).

Effect on predation.-In midsummer of 1962 anoyster company planted 3,500 hI. (10,000 bushels)of seed oysters in Lewis Gut. Periodic examinationof the oysters through ea.r1y winter showed littleloss from preda.tion by oyster drills.

A-

~ 16l­ao:wA-I/)

:! 12ao:a....oao:w

; 8:;)

Z

I­Zw~

!<w

'"I-110

o J

oI---L-:--J::::=:i:;:::;;;::~~::::::::::t::::~~~-L._J-/ 1,...-'---'JUNE JULY AUG. SEPT. OCT. JUNE JULY JULY AUG. JULY

1962 . . 1963 1964 1965

FIGURE 1.-Catches of oyster drills on traps in treated a~a of Lewis Gut, Bridgeport, Conn.·

290 U.S. FISH AND WILDLIFE SERVICE

25

a..

~....ffi 20a..II)..,.«IX

u 15.0;:)

~....offi 10..,.~Z

5

...zw:l!!:(w

'"l-I'.

a

o MAY JUNE JULY AUG. SEPT. OCT. NOV.

1962MAY JUNE JULY AUG.SEPT.OCT.

1963JULY AUG. SEPT. OCT.

1964

ll'IGURE 2.-eatclleB of mud crabs on traps in treated area of Lewis Gut, Bridgeport, Conn.

Area 2: Northport Harbor, N.Y., 1963

Northport Harbor on the north shore of LongIsland is about 6.5 km. long. The oyster beds are inwater 4.5 to 7.5 m. deep at low tide, and water cur­rents rarely exceed 1.8 km. per hour.

On May 21 and 28, 1963, I made a series of COIn­

parative treatments. The purpose was to determinewhether Drillex (a mixture of Polystream and 2percent by weight of Sevin) is more lethal to oysterdrills than Polystream alone. The experiment hadfour 2-ha. lots. Two lot.s received an applicationof 11.5 kl. of treated sand per hectare. They weredesignated as 1 (for Polystream) and 1 x (forDrillex). The remaining two lots which receivedW.O kl. of treated sand per hectare were desig­nated as 2 and 2 x.

Effect on, gastropods.-The treatments had avery deleterious effect on gastropods. A few hoursafter the trelttments, divers observed that nearlyevery visible gastropod on all four lots wasswollen; on lots treated with Drillex, however, thedrills expanded faster and sooner. Ten days afterthe treatments, most thick-lipped drills weredrawn deeply into their shells but some were still

CONTROL OJi' ()¥WfJjJR DRILLS WITH FOLYSTREAM

swollen. Northern moon shells were observed inthree conditions-:-partially expanded, dormantwith their operculum flush with their aperture,and dead. Twenty-three days after the treatmentsdivers noted that all visible thick-lipped drillswere dead on lots 2 and 2 x, and only a small num­ber were alive on lots 1 and 1 x. No northern moonshells were observed either dead or alive; eventheir shells were gone. Hermit crabs had probablycarried them off the bed.

Because many flounders were swimming overthe beds and crabs were numerous when the snailswere swollen, these fish had ample opportunity tofeed 011 the paralyzed drills. I observed no snailsbeing consumed, however; instead, they appearedto die directly from the toxic effects of thechemicals.

Examination of the bottom showed that Poly­stream alone killed almost as many oyster drills asDrillex.

Effect on, associated an,imals.-Divers observedthnt during the applications of Drillex-sand asmall number of flounders, many hermit crabs,shrimp, and annelids were killed; however, 10

291

days later tbey saw a large number of healthyflounders (only about 1 percent were still affected)and mud cra~ on the two treated beds.

Polystream was used in all later commercialtreatments because these experiments showed itwas much less toxic than DriIlex to associatedanimals, particularly arthropods.

Effect on predation.-I made no careful quanti.tative determinations; however, periodic observa­tions of the lot indicated that predation by oysterdrills on oysters on the treated lots during 1963was slight. .

Area 3: Northport Harbor, N.Y., 1965

On April 28, 1965, which was 2 years after theinitial treatment, lot 1 was treated again withPolystream-sand.

Effect on gastl'opods.-Eight days after thetreatment divers observed that every snail wasswollen.

The treatment killed 64 percent of the oysterdrills (77.2 percent of the thick-lipped drills and8.6 percent of the Atlantic oyster drills) and re­duced their numbers from 31.5 to 11.4 per m.1I

(table 4).Effect on associated animal&.-Nine days after

the treatment divers found 6 stunned adult floun·ders and one dead juvenile on the bed among about50 healthy flounders of mixed ages. The only her­mit crab they saw was 'healthy.

Before treatment the number of young clams(5-7 mm. long) on the bed was 158 per squaremeter; 28 days after the treatment the number ofclams was 125 per squa.re meter. Thus, apparentlyonly about 20 percent were killed. .

Effect on predation.-I made no quantitative de­terminations. Periodic observations of the lot indi­cated, however, that predation by oyster drillsduring 1965 was slight.

Area 4: NorthPort Harbor, N.Y., 1966

On May 9, 1966, 3 years a.fter the initial treat­ment, lot 2 was treated again, this time with Poly­stream (Granular).

Effect on gastropods.-'fihree days after thetreatment divers found that all thick-lipped drills,Atlantic oyster drills, northern moon shells, andNew England nassas were swollen.

The treatment killed 92 percent of ·the oysterdrills (94.5 percent of the thick-lipped drills and71.7 percent of the Atlantic oyster drills) and re­duced their numbers from 27 to 2.1 per squaremeter (table 4).

Effect on assoc-iated animals.-No observationswere made by divers.

Effect on predation.-I made no ca.reful quan­titative determinations. Several observations ofthe lot indicated, however, that predation by oysterdrills during 1966 was slight.

TABLE 4.-Demity (lj oy.ter drill., bejore and after treatment. with Poly.tream and Band ()f' Poly.tream (Granular), on oy.terIota in N.Y., Conn., R.I., and Ma88., 1966-67 .

Lot no. lIIld area I (bectal'llS)Date oftreat­ment

Formulation

Drills per m.1

Before treatment After treatment

E. call1fata u. elner,. E. caud" U. elRm'CG

Killed I

Bothspecies

combined

23 (3.2) .__ 4PJJI661 (u·a2) • ._._ 4/28/662 (2.0)_. . ._ 1/9/111J2011 (1.8}_.________ _ __ ___ ___ 0/11/&8lSi•••• • . ____ ___ 4/ T/67401•• • . --- . ._ _ 4/29/67

411 1•••• _-.------. - --- -- - -- - ---. - 4/'B/W142(2.8). ._._. . • 1/1/671101••••• _._. •. •• 1/1/6710_••. •• . _._. _. ._ ControlBI(O.8)_•• ._ •• .___ '" 1/67PP (o.oS)••• _•• • __ •_. 6fJJJ/67PP•••••••• - ._._. . _. Control

Number NumberPoly-sand__ .. . 8.3 0. 0Poly-8llnd ... __ 25. 2 8. 3Poly (Gran.)_•• . ._ 24.1 2.0Poly (Gran.)_. ._________ 14.0. ._Pol)' (Gran.)•• . ._ 7.6 0.0Pol)' (Gran.) . .__ 12.0 4. 7Poly (Gran.>- . . __ .__ 5.6 0. 7Poly (Gran.)__________________ 3.0 0.3Poly (Gran.). .___ 12.6 1.3None•••• . ._. .__ 18.S 0. 7Poly (Gran.)_. • • 0.0 8.6Poly (Gran.)._________________ 0.0 40.8None • __ . __ ••• ._._. 0. 0 37.2

NumlJcr NumlJcr PerUlit P,rUllt P,rUllt0.0 0.6 100.0 48.6 88.75.7 6.7 77.2 8.6 64.01.3 0. 8 0&.6 71. 7 92. 3

10.0 • .__ 77.62.4 1.6 ao .___________ 62.0

2.2 1.6 82. 2 68. 7 77. S0. 0 0. 0 84. 6 100. 0 88. 40.0 1.0 68.7._ .•. • 43.61.7 0.6 88.4 511.6 83.6

19.6 1.7 _••• ._••• _. .• ._ ••••0.0 0.0 _._._ ••• • 100.0 100.00.0 2.2 ••• • 94.6 94.60.0 33.2 •••••••••••••• __ •••• __ •••••••••_.

I Lot 26, 0YBterBay, N.Y.; Lota I, 2, Northpm"t. N.Y.; Lots 2011, IS, 40,49,42. 110, and 19, NorWalk,Conn.; BI, Charleatown Pond, B.I.; PP,Presh PondIIIISS.

I Actual number of hectares treated on these beds Is unmown, but I estlmated that lII'elIII treated ralJll8d bet-ween 1.2 and 6.0 hectares.I Both species•• IfC011nt Incl'888ed, no percentage Is glvell ror tbl. SDeo\eJ

292 U.S. FISH AND WILDLIFE SERVICE

Area 5: Sag Harbor, N.Y., 1963

A O.4-ha. lot along the eastel'1l shore of ShelterIsland in Sag Harbor was trea,ted. The water overthis lot is about 3 m. deep at low tide, and mnxi­mum currents are about 2.7 km. per hour.

On September 27,1963, Polystream (Granular)was used for the fil'st time to control oyster drills.

Effect on ga,sf-I'opods.-'Vithin an hour of thet.rentment divers noticed t.hat all visible snails were~tt least partially swollen. A week later divers ob­ser\'ed many affected thick-lipped drills, Atlanticoyst.er drills, northern moon shells, and both knob­bed and channeled whelks.

Ten drill traps were placed on the treated lot andan adjacl:'nt area before the t.rentment. The trapsin each al'l:'a eo]]ected between 200 and 300 oysterdrills. After ,the treatment, traps were examinedonly once. They collectl.'d only 10 oyster ell'ills onthe treated lU-etl but gat'lwl'ed 127 on the cont.rolarea. I did not count the t.wo species of drillsseparat.ely.

Effect on ({8socir.tff'd a·nhn((ls.-Di\"ers obsCiTedt.hat the treatment did not. affect associated animalsand plants, such as flonnders, bay scallops, mudcrabs, and sea lett.uce.

Effect on l)redati01I.-No determinations weremade.

Area 6: Oyster Bay Harbor, N.Y., 1965

Oyster Bay Harbor on the north shore of LongIsland is nbout 8 km. long. The oyster beds arein wat.er fl'OlU 3.5 to 10 m. deep at low tide andwater cnrrents do ·not exceed 2.7 km. per hour.

On April 30, 1965, lot 2:3, 8.2 ha., was treatedwith Polystream-snnd.

Effect on gastl'opods.-The divers made no ob­se.rvations. The treatment killed 89 percent of theoyst.er drills (100 percent of the thick-lipped drillsand 46.6 percent of the Atlantic oyster drills) andreduced their numbers from 4.2 to 0.5 per squaremeter (table 4).

Effect on associated anim..als.-The divers madeno observations.

Effect on lJl'edation.-Lot 25 was plant.ed withsmall oysters in 1965, 1966, and 1967. Each yearoysters were grown on the bed during their firstsummer of life and thl.'n transplanted to anotherbed the following spring. When first planted inJune, July, August., and early September, the oys­ters were about 5 to 10 mm. long. By late Novem­ber most. of them had grown to 40 to 60 mm.

CONTROI~ OI!' OYSTER DRILLS wrrH POLYSTRE.\.)[

Predation on the oysters was light in each of t.he3 years. On October 1, 1965, examination of thebed showed that less than 5 percent of the oyst.ershad been killed by oyster drills and starfish com­bined. On Jul;y 22, 1966, divers observed tllat nooysters had been drilled. By October 9, 1967, oys­ter drills and starfish had killed 4.3 percent of theoysters on one section of the lot and 8.1 percenton another section. Predation by starfish was re­sponsible for most of the mortality.

Area 7: Norwalk Harbor, Conn., 1966

Norwalk Harbor is interspersed with severalsmall islands that protl.'ct oyster beds in channelsand bays from storms. 'Water over the beds is from2 to 6 m. at low tide, and the strongest currentsrun about 3.5 km. per hour.

I~ot 42 in Norwalk Harbor was treated withPolystream (Granular) on August 24, 1966. Depthof water at mean low tide averages about 3 m.;maximum current is 3.5 km. per hour. Divers re­ported that strong currents carried off the lot a por­tion of the granules.

Effect on gastropods.-Before the treatment,divers counted up to five oyster drills of both spe­cies on each cluster of oysters. "Tithin an hour afterthe treatment all visible thick-lipped drills andAtlantic oyster drills on clusters of oysters wereswelling.

On September 8, 1966, 14 days after the treat­ment, divers observed thut most. oyster drills at­tached to clust.ers of oysters had fallen to the bot­tom. Ina few instances, howe"er, one or two o~Tster

drills that were protected by being attaclled onthe underside of clusters were unaffected and somewere feeding on oysters.

On frequent inspections of the lot divers foundthat most oyster drills remained stunned, in asemiswo]]en condition, until November. A smallnumbl.'r of drills may have recovered before. thewater dropped below 10° C., the temperature atwhich they normally become. dormant.

As fa.r as divers could determine, the h-eatmentof lot 42 on August 24 did not kill many oysterdrills but only immobilized them and preventedthem from feeding. I suspected that a higher per­cent.age would have been killed if the tl-eatmentwith Polystream had been made in late April orearly May.

To determine more precisely the effect of Poly­stl-eam in the sUlnmer, howe,"er, an oJster company

293

treated lot 205, in a more protected area. Tidalcurrents over this lot run at no more than 0.9 km.per hour aml, therefore., did not carry off the Poly­st.ream (Granular). The water is about 2 m. deepat low tide. On September 15, when the lot wastreat.ed, the water temperature was about 21 0 C.

A month later determinations with the hy­draulic sampler showed that the treatment killed78 percent of the oyster drills (no separation ofspecies was made) (table 4) .

Effect o·n associated a:nlllwl.s.-On lot 42, diversreported tha~ a large number of pipefish, juvenilefloundei's; niud crabs, 'and shrimp were stunned bythe chemic:il an hour after the treatment, but theseanimals appeared to be normal later. They madeno observations on lot 205.

Effect O'n preda.ti()'n.-In early May 1966, lot 42was plant.ed with 350 hI. of 1-year-old oysters(5,000-6,000 individuals per bushel). On June 17,7 weeks later, oyster drills had killed 4.3 percentof t.he oysters and had reduced the number of liveoysters per clust.er from 19 to 18.2.

By July 25, 12 weeks after the planting, therate of kill by oyster drills had increased t.remen­dously. For example, 34 percent of the oysters hadbeen killed around the edges of the bed and 26 per­cent in t.he center. Thus, during t.he period of 5,veeks, from June 17 to July 25, the average killwas 4.8 oysters per cluster, or nearly one oyster percluster per week.

On August 24, tlle day the lot was treated, athird sampling was made. In areas around theedges of the lot, where oysters were planted thinly,clusters averaged only two live oysters each. In thecenter of the lot the number of live oysters percluster averaged between 9 and 10. Thus, even inthe main portions of the lot about 50 percent ofthe oysters had been destroyed. Oyster drillscaused almost all the mortality; starfish causedonly a small amount.

The fourth sampling wus made on September 8.In the main portion of the lot, dusters had an av­~rage of ten I-year-old oysters and, in addition,18.3 live spat had attached to each cluster. Bycounting small oyster scars I determined that theoriginal 1966 oyster set had averaged about 30per cluster. Thus, even in the center of the lot,oyster drills had destroyed more than a third ofthe 1966 oyster spat by the time of treatment,August 24.

294

By observing these oysters through the fall ofll>66 and into the spring of 1967, I fOlUld thatvirtually no additional oysters were killed by oys­ter drills. On March 31, 1967, clusters in the mainportion of the lot averaged 9.3 2-year-olds (in 1966they ,vere 1-year-olds) and 21.5 1-year-olds of the1966 oyster set. No careful determinations weremade on lot 205. Later periodic observations indi­cated, however, that predation by oyster drills wasslight.

In the spring of 1967, when these oysters weretransplanted to another lot, their volume had in­creased to 2,100 hL, a sixfold increase during onegrowing season. I did not determine the increasein size of individual oysters.

Area 8: Norwalk Harbor, Conn., 1967

Five lots in Norwalk were treated with Poly­stream (Granular) between April 29 and May 13,1967. Lot 42 was treated again and two lots along­side, lots 40 and 50, were treated for the first. time.Depths of water and current velocities are aboutthe same over these three lots. Lots 18 and 49 wereaIso treated for the first t.ime. The depth of waterover these lots at low tide is about 2.5 m. and cur­rent velocities do not exceed 0.9 km. per hour. LotH), adjacent to lot 18, was not treated and servedn.s a control.

Effect on gastropods.-Divers made no observa­tions during or immediately after these treatments.

On lot 18 the tren.tment killed 52 percent of theoyster drills (68 percent of the thick-lipped drillsand apparently none of the Atlantic oyster drills­again, numbers of Atlantic oyster drills were toolow for significant comparisons) and reduced theirnumbers from 8.4 to 4.0 per square meter (table4).

On lot 40 the treatment kined 78 percent of t.heoyst.er drills (82.2 percent of the thick-lipped drillsand apparently 66.7 percent of the Atlantic oysterdrills-again, numbers of the latter species weretoo low for accurate appraisal) and reduced theirnumbers from 16.7 to 3.8 per square meter (table4).

On lot 42 the treatment killed 44 percent of theoyster drills (66.7 percent of the thick-lipped drillsand apparently no Atlantic oyster drills-numbersof Atlantic oyster drills were too low for reliablecomparisons) and reduced their nllmbers from 3.3to 1.9 per square meter (table 4). Because most

U.S. FISH AND WILDLU'E SERVICE

I Sampling en-ors account Cor slight variation In 'lumbers., Oysl.ers raised in hatcheries In 1967.3 l-yesr.old o)'stcrs.• Mixture oC 1065 and 1966 oyster set (l and 2 years old).

TABL.: 5.-Percentage of oysters killed bll oys'er drills andstarfish in center areas of lots in Norwalk, Conn., 1967

[Accumulated monthly totals ']

Percent18 , __ • ______________ 0.0 0.0 0.0 0.6 0.4 1.0 0.240·_________________ .0 .0 0.0 1.0 0.0 0.0 .542 3_ --- -- -.--.- •• -'- .0 .0 0.9 0.5 1.0 0.0 .549' .•• ______________ .0 .0 0.0 0.0 0.3 1.5 .050'_____________ ••.• .0 .2 1.0 0.0 1.0 0.7 .0

Oysters planted on these lots freshly treatedwith Polystream grew normally. For e,xample, the1-year-old oysters on lot 50 increased in volumefrom an average of less than 1 cc. to nbout 15 cc.each during the 1967 growing season. My determi­nations of growth of oysters planted on untreatedbottoms show that this amount of growth is aboutnormal.

lIIay June July Aug. Sept. Oct. Nov.Lot number

Area 9: Foster's Cove, R.I., 1967

Foster's Cove on t.he south shore of Rhode Is­land, about 4 ha. in a.rea, is a HdaI pond conne~tedto Charlestown Pond by a narrow inlet. Depth ofwate-r over the oJsters rallges from 0 to 2 111. at lowtide. The-re is little exchange of water between thetwo areas; thus, the. principal water currents inthe cove are caused by winds. Examination of threesections of Foster's Cove on November 10, 1966,indicated that oyster drills had killed about 75percent of the oysters.

On May 31, 1967, two areas totaling 0.8 hectarewere treated with Polystream (Granular).

Effect on gastJ'opods.-Divers made no observa­tions during or immediately after treatment. Mylater observations showed that the treatment killedall Atlantic oyster drills (no thick-lipped drillswere present) in both areas nnd reduced theirnumbers fl'om 0.5 and 3.6 to 0.0 per sfluare meter(table 4).

Effeot on a88o"iated antJlUd8.-0n June 8, 8 daysafter the treatment, I examined the areas by walk­'ing along the shores and divers also examinedthem. Along the north shore, perhaps 15 m. fromone of the treatell are.as, there were 4 dead toad­fish, 0P817:1/"/(8 tau.: 50 dead silversides, lIfe-nidiamenidia: 500 to 1,000 dead mummichogs; 4 deadblue crabs, (!allinectc8 8apid1/..9" 50 dead shrimp;

oyster drills were killed on this lot by the secondtreatment and not by the first in 1966, I believethat trentments in early May are much more effec­tive than those made later in the summer.

On lot 49 the treatment killed 86 percent of theoyster drills (84.6 percent of the thick-lippeddrills and apparently all of the Atlantic oysterdrills) and reduced their numbers from 6.3 to 0.9per square meter (table 4).

On lot 50 the treatment killed 84 pe,reent of t.heoyster drills (86.4 percent of the thick-lipped drillsand 55.6 percent of the At.lantic oyster drills) andreduced their numbers from 13.9 to 2.3 per squaremeter (table 4:).

Lot 19, which served as a control, was sampledat the same time as the other lots. The density ofoyster drills per square meter was a:bout the sameon each date; on May 10 it was 19.5, and on June30 it was 21.2 (table4).

Effe£'t on ((.Y8oaialed a-nimal.y.-Divers did not ex­amine these lots closely during or immediatelyafter trea.tment. At intervals during the summerof 1967, however, they observed that healthyflounders, young starfish, mud crabs, and otheranimals were numerous on the beds. They saw noaffected animals. In fact, most animals were morenumerous on treated lots than on areas barren ofoysters ne..'\rby. The divers did not count the youngstarfish on unplanted aren,s, but on October 6 theycounted 8.8 young-of-year starfish per square, meteron lot 18, and 35.3 per square meter on lot 40.

Effect on pl'edatlon.-I carefully recorded mor­talities of oysters on these lots from the time they'were planted through November when oyster drillsbecame dormant. In May 1967, 1- and 2-year-oldoysters were planted on lot 40 and 1-year-oldoysters were planted on lots 42, 49, and 50; andfrom June through early September, 1967-yea.r­dass hatchery-reared seed oysters about 5 mm. inlength were planted on lot 18. Losses of oystersbecause of predation by oyster drills did not ex­ceed 1.5 percent on any of these lots by late Novem­ber (tahle 5). Because enough drills were presenton some lots to cause higher mortalities-lot 40,for instance, had 3.8 oyster drills per squa,re meter,and lot 50 had 2.3 per square meter-most liveoyster drills must have been sufficiently "stunned~'

by the Polystream to prevent their feeding. Thisapparent "stunning" effect was also evident. on lot42 in 1966.

CONTROL OF OYSTER DRILLS WI'l'H POLYSTREAl\I 295

and 10 dead polychaetes. On t.he inspections madealong the shoreline, just inside the other treatedsection, there were only two dead toadfish and onedead blue crab. Undoubt.edly, a high'percentage offish, blue crabs, and shrimp was killed at the timeof treatment. Divers did not see any fish or shrimp,live or dead, either OIl or off treated areas.

Effect on pl'edatiQn.-No determinations weremade.

Area 10: Fresh (Quahoa) Pond, Falmouth, Mass., 1967

Fresh Pond, about 2.0 ha., is a tidal pond on theeast shore of Buzzard's Bay. It is connected withthe Bay by a long, nalTOW creek only about l m.wide and 0.3 m. deep at the entrance of the pond.The area for growing oysters is from 0 to 2 m.deep. 'Vinds generat.e t.he principal currents in t.hepond.

On May 29, 1967, a O.OS-ha. section of the pondwas treated with Polystream (Granular).

Effect 0'/1. gastl'Opods.-Within an hour of thetreatment divers observed that all snails werebeginning t.o swell.

By July 11, the t.reat.ment had killed 95 percentof the Atlantic oyster drills (no thick-lipped drillswere present.) and reduced their numbers from40.8 to 2.2 per square meter (table 4) .

An untreated area in another section of t.he pondthat served as a cont.rol for the treatment had anaverage on May 29 of 37.2 Atlantic oyster drillsper square meter. On July 11 this control plothad 33.2 drills per square meter.

Effect on aJJ80ciated anil1wls.-Because thetreatment extended to the shoreline of the pond, anumber of observations could be made by walkingalong the shore. An hour after the treatment Iobserved 2 flounders (5 em. long), 5 green crabs,Oal'cinus 111,aena8, and 200 shrimp all dying, and100 mummichogs stunned. I also observed threesmall schools of silversides swimming through thearea; all these fish were healthy. New Englandnassas and mud snails, N a8saJ'i1UJ obsolettts, werebeginning t.o swell.

On July 11, 1967, divers examined the areaagain. The only animal affected other than snailswas a tautog which ,veighed about 1.8 kg. All NewEngland nassas and mud snails were dead.

Effect on predatlon.-The area had no oysters.

296

RECOMMENDATIONS FOR USINGPOLYSTREAM

During t.his study I made a number of observa­tions on the use of Polyst.ream (Granular), theform now most commonly used on commercial oys­ter beds to control oyster drills. These observationsare listed below and should be emphasized fort.hose who might wish to use this product:

1. The bed to receive a treatment should have afirm bot.tom, free of silt.

2. Treatment.s should be made in late April orearly May when oyster drills first become act.iveafter a period of winter dormancy.

3. Polystream (Granular) should be spread atslack current.

4. Most successful treatments have been made inwate·r less than 6 m. deep, where currents are lessthan 2.7 km. per hour. Where current.s are strongerthan this, planted oysters appear to prevent thePolystream (Granular) from being carried off abed.

5. Polystream (Granular) treatments are suc­cessful on beds planted with seed oysters.

6. In certain shallow areas, where little or nocurrent flows, II. smaller quantity of Polystream(Granular) may be successful.

SUMMARY

1. Five experimental and 10 commercial treat­ments of oyster beds were made with Polystreamin the States of Connecticut., New York, RhodeIsland, and Massachuset.ts.

2. Immediately after a treatment, oysters, clams,and other organisms accumulated small residuesof Polystream in their tissues. These residues, how­ever, were gradually lost or greedy diminished.For instance, oysters and clams 'lost the residue ofPolystream within 119 days. If they were trans­planted from a treated to an untreated bed, how­ever, they lost the residue within a week.

3. All oyster drills were killed in areas where,vater current velocities were low. On a typicalbed, in an area. where current velocities were be­tween 0.9 and 2.7 km. per hour, however, about85 percent of thick-lipped drms and 66 percent ofAtlantic oyster drills were killed. Apparently, nooyster drills'were killed where current velocitieswere strong.

4. On treated beds where current velocities werelow, significant percentages of fish, small clams,

u.s. FISH AND WILDLIFE SERVICE

and other invert.ebrates were killed. On treatedbeds where current velocities were between 0.9 and2.7 km. per hour, treatments killed only small per­centages of fish, small clams, crabs, and otherinvertehrat.es. A few hours after the treat,ment thearea ltppeared to be nontoxic to these anima.Is.

5. A higher percent~rc of oyster drills waskilled by treatments made in late April and earlyMay than later in the summer.

6. Oyster drills were killed by the toxic actionof Polystream, not by fish or crabs after they be­came swollen. In a small number of instances, how­Pover, they were consumed by starfish.

7. Oyster drills that survived a treatment ap­peared to be affected by the treatment to the extentthat they did not feed significantly for a fewmonths and, ,thus, did not kill many oysters.

8. The number of oyster drills on a bed whereseed oysters were planted and removed each ye.."rremained low for at least 2 years.

9. Oyster drills killed less than 2 percent ofyoung oysters during the first. year on most treatedbeds.

10. Growth of oyst.ers appeared to be normal ontreated beds. For example, on one bed 1-yea.r-oldoysters increased in volume from less than 1 cc.to 15 cc. in one growing season.

ACKNOWLEDGMENTS

Barry Baiardi, Russell Clark, Otis C. Lane,•fohn J. Manzi, and Nicholas Penchuck providedtechnical assistance. Hillard Bloom and the BloomBrothers Oyster Company; J. Richards Nelson

('ON'I:HOL OF OYSTER DRILLS WITH POLYSTREAI\l

and the former F. Mansfield and Sons OysterCompany; Lester Johnson and G. Vanderborgh,Jr., of G. Vanderborgh and Sons Oyster Com­pany; and Arnold Carr, Division of Marine Fish­eries, Mass., also helped me.

LITERATURE CITEDHAVEN, DEXTER, MICHAEL CASTAGNA, PAUL CHANLEY,

MARVIN WASS, and JAMES WHITCOMB.1966. Etfeclls of the treatment of an oyster bed with

Polystream and Sevin. Chesapeake Sci. 7: 179-188.LooSANOFF, VICTOR L.

1960. Some effects of pesticides on marine arthro­pods and mollusks. Biological problems in waterpollution. In Transactions of the 1959 Seminar,pp. 89-93. U.S. Dep. Health Educ. Welf., PublicHealth Servo

1961. Recent advances in the control of shellfishpredators and competitors. Proc. Gulf Carib. Fish.Inst., 13th Annu. Sess., pp. 113-127.

LOOSANOFF, V. L., C. L. MACKENZIE, JR., and L. W.SHEARER.

1960a. Use of chemicals to control shellfish pred­ators. Science (Wash.) 131: 1522-1523.

1960b. Use of chemical barriers to protect shellfishbeds from predators. Fish., Wash. State Dep. Fish.3: 86-00.

SCHWARTZ, N., H. E. GAFFNEY, M. S. SCHMUTZEll, andF. D. STEFANO.

1963. A method for the analysis of chlorinated ben­zenes in clams (.Uerccnaria mcrcenaria) and oys­ters (OrlJ88oBtrca vil'ginica). J. Ass. Off. Agr.Chern. 46: 893-898.

WOOD, LANGLEY, and BEVERLY A. ROBERTS.1963. Differentiation of elfects of two pesticides upon

Uro8alpt'1Ul1 cinerea Say from the Eastern Shore ofVirginia. Proc. Nat. Shellfish. Ass. 54: 75-85.

297