IMEP # 140 The Round Clam Beds Of Madison CT 1940's to 1960's

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IMEP #140: The Round Clam Beds of Madison, CT 1940's to 1950's
The Cultivation of Marine Soils – Introduction and Comments
"Understanding Science Through History"
Tim Visel – Updated November 2018
Viewpoint of Tim Visel only no other agency or organization
This is a delayed report – February 2023
This report is a re-issue of a Hydraulic Clam Harvest presentation at the Madison, CT Surf Club – August 1990
Tim Visel retired from The Sound School on June 30, 2022

A Note from Tim Visel

It was Frank Dolan who invited me out in the small oyster boat Teal, in 1974 and again the winter of 1975. Some may remember it was a treat for those who liked to see the traditional oyster boats all tied up in Guilford Harbor.  The Dolans (Frank and Joe) often had three in Guilford Harbor over the winter—the Columbia, Teal and Alice A.  The winter had locked them in ice and the photo credit goes to Brian Sullivan, a longtime friend who frequently joined our Madison fishing and oystering trips.

I was working with the Madison Shellfish Commission since 1973 on a shellfish (mostly oysters) management plan and the first hydraulic dredge trip was in 1974 with Mr. Dolan. We worked a section of ground known as the "Evarts Blakeman grounds" between West Wharf and Tuxis Island. It was hard bottom, sandy, some mud but littered with large crumbling old quahaug shells. When you picked them up, they were thick but loaded with holes. The remaining live clams were like this, very thick heavy shells. To Frank Dolan this was the end of the great set that had happened here two to three years after the 1938 Great New England Hurricane, except it was not great for those few oyster companies still operating in Connecticut.   The waves rolled oysters off production beds, some were completely buried, many beds were ruined and crops lost for years, including silting of the seed beds according to Mr. Dolan.

The 1938 hurricane sunk vessels, damaged wharfs and broke seawalls along the shore. Oysters themselves were rolled off culture beds by waves and currents hard bottom into soft, market beds buried in "new sand" and seed oyster beds buried by inches of silt carried off land suffocating small oysters, by the tens of millions. According to Mr. Dolan it was a financial blow to the growers from which the oyster industry would never really recover. But the storm had done something else, it had as a natural outcome mixed shells, sand and organics violently which loosened these hard-packed marine soils.

Quahogs can live to be a century, but only set in the deep water here two or three times in a century – according to Mr. Dolan. The "spawn' was in the water column more often than that except the soil was too hard or acid from organics, the soft or "sticky" bottoms. It took a storm to cultivate the soil – (It was Frank Dolan and John Hammond who both gave me several terrestrial soil/garden examples) without this cultivation sets (or the great sets) did not happen over time these soils failed – a type of habitat succession.  Mr. Dolan said the weight of water was part of the problem, it packed it down- (the soil) and he gave me the example of the steam roller over a garden soil, packed hard and throw some corn seeds on top and see how much corn you will get – It was a good point, as the hurricane was incredibly destructive, with loss of human lives, equipment and shore property it did change predator/prey relationships and cultivate large areas that in time set heavy with "hard" clams.  These would in time be known as the great sets of quahogs.

According to Mr. Dolan and some accounts from the Town of Madison officials, there was post-1938 a huge deep-water clam bed of quahogs at Madison Reef but because of the depth and strong tides, few people tonged them, and that most hard rakes "bullrakers" were never used here because of the tides. Mr. Dolan was often stronger in his verbal description, but "they let them die" works here (Town Officials) had prevented shellfishers who had tried to harvest them, but it involved "power dredging", and it was felt that those deep water beds contributed to clams in the shallows, so it was never approved.  He estimated the loss at tens of thousands of bushels.  Mr. Dolan could dredge this lot because his company secured written or deed access to these private beds, he could cultivate his own acres. It was the waste of clams that bothered him, and while working this bed was a donation of large clams for the recreational fishery for the town of Madison. While about 120 bushels of clams were harvested for recreational use, only a few dozen clams were cherries (cherry stones) and no small clams.  He had thought that if more Madison residents could benefit, they would support the remaining shellfishers.  He did not mind the expense believing that this type of relationship was "cooperative" and educational as he hoped the town (Madison) would be more accepting of harvesting food.  This effort was "to break open the ground," loosen the soil, raise the pH, and facilitate a set.

Six years later, Mr. Dolan called me at the Cape Cod Cooperative Extension Service (1982) office with a simple message "It's time."  I asked time for what? He said time for you to learn. That weekend after his call, I was on board his dredge vessel off Madison working the same area six years before – the bed was loaded with little necks – the cultivation had worked. But he was harvesting as fast as he could as "blackfish" were eating the clams (somewhere in the dredge) and conch and starfish were also on the increase. It now became a race to see who got what- but the lesson had worked, the hydraulic dredge had cultivated the soil, as powerful storms- only it could be monitored. His full comments can be found in a 1990 paper/presentation titled The Cultivation of Marine Soils, and excerpts found later in a 2011 report by the NOAA Milford Laboratory.   NOAA Technical Memorandum NMFS – NE 220 2011 Mercaldo-Allen and Goldberg – Review of the Ecological Effects of Dredging in the Cultivation and Harvest of Molluscan Shellfish.

Footnote-
One of the aspects of this cultivation lesson was in 1977. Mr. Dolan had found small clams on the bed and had taken four loads of "black shell" out of the East River and put them over the clams to help sweeten the soil and improve growth. Oyster growers had noticed that thin layers of oyster shell always held significant quahaug sets below them in saline waters at the edge of oyster production beds.  He had planted this shell but without his knowledge it had set with oysters, so in 1979 he arranged with George McNeil to plant his small bed which was just below the closures line in Clinton Harbor. The planting of shell hard yielded about two thousand bushels of healthy seed oysters, but were being attacked by oysters drills in larger numbers- starfish had also come into the area.

He moved the seed oysters to save them, and in the process noticed the heavy quahog set below. When he later harvested these oysters from the Hammonasset River (McNeil beds), he did harvest about 5 or 6 bushels of adult bay scallops thought to be the result of transplanting 20,000 seed scallops obtained from Milford Shellfish Laboratory in 1978 and were planted with Brian Sullivan from my 16'Brockway skiff in the fall of 1978. Aboard the skiff was Edwin Rhodes of NMFS, and John Baker, Aquaculture (Dept. of Aquaculture, Division) and Dr. Lance Stewart, then my boss at the Sea Grant Marine Fishery Program – University of Connecticut.

The set of quahogs was under these seed oysters, but had attracted predators, only the beds cultivated caught a clam set, areas to the east and west were like the beds in we found 1974, and 1977-78 only a few old adults and the remains of dead quahog shell.  The soil difference was very easy to see – and research after I left Cape Cod should be reviewed on the positive aspects of soil cultivation and the Cation Exchange Capacity or CEC trials conducted by H. Karl Rask in the late 1980s. John C. Hammond's information was that the great sets did come after storm events a natural marine soil cultivation process – in cycles and possible cultivation recommended by the much smaller hydraulic dredge in seed beds.  He had observed these "new sets" after the storms that cut into the Chatham shore including Monomoy that had washed "new sands."

Hydraulic hard shell clammers of the 1960's first experienced the impact of soil cultivation – it was perhaps the first use of a marine plow to till subtidal soils lay the foundation of refreshed soil cultivation – has the reason and title of the presentation in 1990- see, The Hydraulic Cultivation of Marine Soils.  The oyster and clam fishers found that soil type and condition could alter the impact growth.  Those soils that were soft and sticky were poor while sandy/mud soils much better.

Tim Visel
December, 2023

Introduction/References Timothy C. Visel, The Sound School

"The Hydraulic Cultivation of Marine Soils to Enhance Clam Production" has been one of the most requested reports from our Adult Education and Outreach program directory.  The report is actually a combination of 3 individual papers/slide presentations from 1985-1990 while I was employed by The Connecticut Sea Grant Marine Advisory Program at the University of Connecticut, Avery Point campus.  The concept of a habitat history or habitat successional properties were introduced to me by John C. Hammond a retired oyster grower on Cape Cod in the early 1980's.  (While this presentation was developed as an employee of the Connecticut Sea Grant Program, it is not an official Sea Grant publication.)

The first is a fisheries history of hydraulic shellfish harvesting and slide presentation made possible by the cooperation of Mr. Francis (Frank) Dolan of Guilford CT and earlier information obtained from George McNeil of Clinton, CT.  This information accompanied a slide show which was completed in 1985 for the National Research Council (See IMEP #129, posted October 8, 2023, The Blue Crab ForumTM) and reshown twice four years later on August 27, 1990 at the University of Rhode Island Shellfish Conference and September 20, 1990 at the Madison Town Hall – Madison, CT.  The August 27, 1990 presentation was titled "Shellfish Management and Restoration Programs in Connecticut."  This presentation included slides of the Oyster Pond River in Chatham Mass.

The second is a section discussion regarding several environmental issues attributed to hydraulic shellfish harvesting – Appendix 1 is a literature search (references) for biological/environmental and fisheries technology (methods) as it relates to hydraulic or power clam dredging.   This literature search was first conducted for the Madison Shellfish Commission and updated in October 1997 for the Rhode Island Legislative Commission for Aquaculture.   It was rekeyed for Rhode Island Aquaculture Taskforce during a program organized by the Rhode Island Seafood Council visit to the Sound School in February of 1999.

The third section is a resource allocation/management study also in the town of Madison. This component details shellfish access issues following enormous sets of both oysters and clams on natural beds located within that community and harvesting from the 1950 to 1980's.  That was included to document jurisdiction and management – access conflicts and waste of adult shellfish – food and the comments by Frank Dolan and letter from John Walston, a shellfisherman from Guilford, Connecticut.

It was part of the Rhode Island Discussion on free and common fisheries a discussion for University of Rhode Island Aquaculture Committee looking to enhance aquaculture industries in Rhode Island.

After several years of providing hard copies of these reports, it was suggested that they become available as part of our publications/directory.  In 2005, all three sections were combined into one and put on our Adult Education and Outreach directory as Paper #25.

Of the three sections, the one most referenced is the oral history of Mr. Dolan and his comments on the "marine soil" from which he harvested hard shell clams.  His comments about "sour" or acid bottoms (pages 6 to 9) reference a widely observed habitat shift in many small coves and estuaries.  Many small boat/inshore fishermen during this period observed the impacts of lowering pH and increased organics on bay bottoms and they were very concerned about it. Although Mr. Dolan's method of determining bottom pH may have been what could be described as "unscientific" he had learned what was for him a good way to do a "soil test."  He urged municipal shellfish commissions consider clamming an aquaculture activity clearly dependent upon good soil conditions for shellfish sets that required work (energy) to prepare soils low in clay for shellfish sets.  He also told me of hard shell clams that had an off taste and at times loose (watery meats) of Green Harbor New London.  Once relayed to Guilford waters this off taste flavor ended.  This off flavor is now associated with marine soils with high sulfur – sulfide levels.  In the presence of sulfide shellfish do not eat property (Frank Dolan comments to Tim Visel).

Finally, although these reports were compiled in the 1980's while employed by the University of Connecticut Sea Grant program they are not official UCONN Sea Grant publications and do not have a Sea Grant publication number.  Hard copies are only available from The Sound School Adult Education program contact person Susan Weber, The Sound School 17 Sea Street, New Haven, CT 06519.

Individuals or groups interested in soil conditions suitable for the soft shell clam Mya should review papers written for the Long Island Sound Study Habitat Restoration Initiative titled "Softshell Clam Habitat Creation and Associated Population Expansion Follows significant Marine Soil Cultivation/ Disturbances" also found on the Sound School Adult Education and Outreach Directory as Paper # 23. 

Tim Visel



The Hydraulic Cultivation of Marine Soil to Enhance Clam Production
Compiled by Timothy C. Visel

Oral Histories: Dolan Shellfish Company Experiences with the Hydraulic Hard clam dredges, comments from George McNeil soft shell production from New Haven Harbor.  Industry comments on the benefits of marine soil cultivation.

The Hydraulic Harvesting of the hard shell clam, Madison Presentation, September 20, 1990.
Environmental concerns raised by shoreline residents – Madison – The Hard Shell Clam Fishery – newspaper and press reports.
Resource Allocation issues and shellfish resource waste as raised by commercial shell fishermen in Madison waters – a review of comments and written records.

Key words: hard shell clam, soft shell clam, increased shellfish productivity, marine soil cultivation practices, hydraulic and mechanical clam dredges, renewable natural resources, water quality issues, industry practices, shellfish management concepts.

Abstract:

In the late 1950's and early 1960's, the hydraulic "wet dredge" hard clam harvesting equipment was introduced into Connecticut.  This was a period of reduced oyster harvest and several large oyster companies, reequipped starfish mop vessels and some production vessels for hydraulic harvesting of the hard shell clam (Quahog) Mercenaria/mercenaria on leased and granted shellfish grounds.  Shellfish operators soon noticed the differences in clam growth and clam setting when combined with light plantings of oyster shell cultch.  This paper is the result of a presentation made in support of hydraulic clam harvesting when environmental concerns were raised about its continued use.  The concern was hydraulic clamming would increase bacterial contamination and close swimming beaches.  Resource allocation/use questions were also discussed as part of the presentation.

This paper reviews observations that hydraulic or mechanical manipulation of the soil changes chemical, circulation and grain/pore sizes.  Increases in pH seem to indicate increase growth and cultivation of suitable bottom types (soil) indicates increased hard clam sets.  A review of the available literature highlighting these industry observations are found in Appendix #1 which was updated in 2005.


The Hydraulic Cultivation of Marine Soils to Enhance Clam Production
September 20, 1990 Special Meeting Madison Town Hall, Madison CT

Timothy C. Visel
Environmental Fisheries History - Frank Dolan of Dolan Brothers*
Company 1974-1986 (Slide show)
Madison and Cape Cod Hydraulic Harvesting

The Sea Grant/Cooperative Extension Service – National Research Council Presentation 1985
University of Connecticut at Avery Point September 1990 Reprinted by The Sound School Regional Vocational Aquaculture Center, September, 2006

*Mr. Frank Dolan who co-owned a shellfish company with his brother, Joseph out of Guilford, Connecticut.   

On several occasions, I was able to accompany Mr. Frank Dolan oystering on the "Teal" "Laura and Ellen J." three   oyster boats owned by Frank and Joseph Dolan.  Shellfish experiences included cultch planting, bottom       cultivation, hydraulic clamming, relaying and oystering.

This article concerns the hydraulic harvesting of hard shell clams and is being submitted in support of written and oral testimony about the effects of hydraulic clam dredging.   Madison has a rich shellfishing history that includes clamming for hard shells or round clams from its 6,000 acres of shellfish area.  Recent experiments also have been conducted for determining the extent of subtidal soft shell clams in town waters.  This was the J. Milton Jeffrey shellfish internship program with Daniel Hand High School.

Hydraulic Dredging – Fisheries History Soft Shell Clam Harvesting

From what I have been able to learn, the clam dredge was preceded by the oyster dredge and early  beam trawls. Beam trawls were mentioned in 1372 as England was recording complaints by its oystermen over planted oysters being taken by such means.  Often beam trawls were weighted by chain to scrape the bottom to catch clams.  One practice that was utilized in Bridgeport and New Haven was to plow tidal populations of soft shell clams with a horse/oxen team and then at high tide drag a beam trawl over the clam beds.  This is still done in southern waters as "clam kicking." They caught tremendous amounts of soft shell clams, but  the breakage was high, thus the term "soft shell." Since these clams were used in the offshore longline fishery as bait broken shell was of little concern.  The modern day version of this modified bream trawl/shellfish drag still can be found in commercial offshore scallop dredges and oyster dredges which use a combination of medieval chain mail and mesh netting.  Previous to this point, most "steamers" were called "long clams" in Connecticut. We also know that clam plows were being used to cultivate tidal flats in Massachusetts and Connecticut for aquacultural purposes. In the 1870's, one direct reference (pg. 590 History and Methods of the Fisheries Vol. II GPO 1887, The Fisheries and Fishery Industries of the United States, George Brown Goode, editor) describes this early practice.

"After many trials of all sorts of plows and cultivators, surface and subsoil and providing them unadapted to the turning of the dense, wet, heavy mixture of sand and mud, Mr. Wheeler Hawley (of Bridgeport, CT) succeeded in inventing a light plow, having a thin, narrow, steel mold- board, which did the work satisfactory after seeding the comments regarded the clams being shoulder to shoulder and growing slowly." 

At one point, the US Fish Commission considered locating its first shellfish station in    Clinton, Connecticut because of the tremendous softshell clam population in Clinton Harbor.  Milford, Connecticut was selected instead and a focus upon oysters.

According to George McNeil, an oyster grower from New Haven, the plowing of clam bar flats and light clam dredging continued until about 1910.  It was at this time salted clam necks were use as cod fish bait in winter months when fresh cut bait was hard to find.

He attributed the decline from a lessening demand for salted softshell clams to be used as bait in the long line industry (codfish).  This early clam dredge (from early terms  dredge meaning "oyster net" and dredge "to draw") is the antecedent of the oyster dredge.  Clam cultivation by use of plows was to continue for another 25 years here in CT and on the Cape but proved to be uneconomical as the vast percentage of softshell of clams were used for bait and   pig fodder and not for human food.  However, Mr. McNeil estimated that catches of soft shell clams in New Haven was once in the tens of thousands of bushels each year.  A similar method of catching clams with nets has continued until modern times in the Carolinas.  It is called "clam kicking." In 1986 and 1987, the Madison Shellfish Commission used a Bourne/Yarmouth wand a hydraulic, single stream 5 hp pump sampling device to survey soft shell clams below the low tide line.  Substantial/subtidal soft clam populations were found at Circle Beach, the flats off Fence Creek and the end of Hotchkiss Lane at Webster Point.

Hard Shell Quahog Dredges Fisheries History and Hard Clam Cultivation Practices

The concept would return in a different way a century later to harvest the hard shell or round clam. Earlier methods included hard tine weighted pole rakes made by the Quinnipiac Indians and other tribes. Long poles enabled them to rake deep water, hard shell clams from salt ponds and coves such as the Niantic River between East Lyme and Waterford. Thus, the first references to early clam dredges call them "drag rakes" and not dredges.  The first clam dredges were attributed to Dutch oyster farmers of New York City who noticed quahogs or hard shell clams living under oyster shells that were harvested for the production of lime and street surfaces. Laws soon were enacted to end this practice as it was deemed to be harmful to the lucrative oyster business (page 518, George Brown Goode).

The demand for seafood in a growing New York City soon caused clam dredging as a direct off-shoot of oyster shell dredging and, by 1870, emerges as a distinct "fishery."  An early account describes the clam dredge as being thrown overboard and when it has sunk into the sand it is "drawn" along the bottom, and taken up about once a minute, when the clams are extracted from the sand, washed and thrown into the vessel.  This is, the account continues, "exceedingly laborious work and four to five hours of it in one day is sufficient to use up the "stoutest scrapper" (US Fish Commission Report, 1887).

Modern Clam Dredges

The literature review I was able to undertake, including the clam fisheries prior to World War II attribute the dry dredge to have originated in New Bedford, Massachusetts. Apparently, some of the first powered fishing vessels experimented with a heavy dredge called the New Bedford rocking chair dredge.  The concept was that vessels lacked sufficient power to cut through the bottom, so the boat was put into a fast forward, slow forward motion as to rock  the dredge, causing it to chop into the bottom one bite at a time.   
It was slow and hard work-the cutting blade that cut into the bottom would often hit a boulder or rock causing the boat to lurch, and the great weight of the dredge was necessary to keep it from jumping off the sea floor (which I am told it often did). After World War II, the shortage of fish greatly expanded the clam markets. More powerful engines were being installed resulting in less rocking and more direct sea bottom contact in a steady cutting motion.  This new method caught more clams but greatly increased  breakage.  Sometimes up to 40% of the clams were now being broken or crushed. This was caused by the fact that the cutting bar now was acting like a knife and striking the clam in the middle tended to cut the clam in half according to Mr. Dolan.  Frank said that few Connecticut oyster growers would clam this way.  It was punishing to the wood frame oyster boats, and George McNeil thought they would "rattle the boats apart."  George also stated that the oyster business was far more valuable than clams and that Rhode Island had pretty much taken over the clam market by the 1940's.  That would change dramatically in 1958.

The First "Wet Dredges" for Hard Shell Clams

The hydraulic effects of pumped water into soil were well known in the mining industry.   First applications were used to wash over burdens off silver and gold deposits and    flume the flows for densities – the heavy constituents being the metals.  In 1954, two researchers looked at reducing the clam mortalities with clam harvesting both soft and hard clams and taking the land-based hydraulics application pumped water to fluidize the bottom in front of the clam dredge.  The first experiment was conducted in Massachusetts with a hydraulic manifold followed by traditional rakes for the collection of subtidal soft shell clams.  This method allowed harvesting of never exposed subtidal population not that dissimilar to the horse and oxen plowing and beam trawls almost a century before. The early experiments with this manifold of water jets was quickly communicated to other New England states, and by 1956, manifolds were being welded to the dry rocking chair dredges with immediate implications; catches improved, the horse power required to tow the dredges decreased, and mortalities dropped to under 8% and many times between 2% or less.  According to Mr. Dolan, news soon spread to Connecticut with Massachusetts and Rhode Island fishermen quickly converting their dry to "wet" dredges.   

By 1958, oyster growers started to experiment with the so called hydraulic dredges.  Mr. Dolan commented it couldn't have come at a better time.  More people were coming to the shore as tourists, and they were able to market clams they just could not catch easily before. Most of the hard clams were in 15 to 25 feet of water.  Waves and tides in the Sound made tonging and bullraking both difficult and economically unfeasible.  The oyster industry was having a decade of poor oyster sets, and many oyster growers were "just hanging on." It also came during a period when hard shell clams "were everywhere" after the 1940's, and now in the 1950's, clam beds had matured such as the one off Madison. (Mr. Dolan states that the hard clam bed extended from Guilford Harbor to Tuxis Island and out to Madison Reef – some 600 to 800 acres).

This was confirmed by clam surveys of Madison in the mid 1980's).  He was disappointed in the response from Madison to first attempts to harvest these deep water clam beds, and by the late 1960's, most of the clams had died. He said he thought the clam bed off Madison was one of the largest in the country, and it was a shame to waste that much seafood.  It also was frustrating because the waters off Madison were clean and certified for direct shellfishing.  What I have been able to determine is that it was just not only Madison's beds that had dense concentration of hard shell clams but many areas in Connecticut had clam sets.  It is just that Madison's beds were by far the largest. Repeated attempts by fishermen in Guilford who knew the extent of the beds were rejected by the Town of Madison.  (Most of the hard shell clam beds were in Town of Madison waters.)

Mr. Dolan said most of the clamming then was in the Thames River and Norwalk and Milford Harbors.   He said the Thames River held more clams than any other river in New England.  According to Mr. Dolan, by 1975, these offshore beds had "died out" but he could show me "how to bring them back."

In the vessel trips and meetings, Mr. Dolan talked about his clamming experiences and knowledge.  Much of the clamming concerned Thames River private beds, all of them belonging to Larry Malloy who owned leases and deeds to harvest in Montville and Ledyard waters.  It is in these beds that edges and banks could change clam populations – remnants of past populations were in the "dead shells."  It also provided (the bends and banks) to keep soil free of leaves and brought down river but the width of the river allowed waves to developed – much like those in a salt pond.  It is from Larry Malloy that I learned that smelly bottoms (suspect sulfide poisoning) were a bad sign and resulted in an increase in oyster mortality. 

In a January 1990 issue of New England Coastal News interview with my brother Raymond Visel (pg. 23), Mr. Malloy would mention the black shells of dead oysters with sulfide smell and I saw on dredge trips with him, from the article Oysterman, Larry Malloy –

"There's something wrong with the oysters out here [in the Thames River] now.  If I put 500 bushels down, I would get 250 back.  The rest would be empty shell.  Something's terribly wrong out there.  I just know it, but I can't get anyone to listen to me," Mallow says.

Sets of clams occurred more frequently in the Thames River than open shores according to Mr. Dolan.  The open shores set (quahog) only after the most powerful of storms (hurricanes) or under seed oyster beds.  Larry Malloy had noticed an increase of leaves and muds covering oyster beds – while a transition from quahogs (hard shell clams) to Mya soft shell clams off Ledyard.  During a shellfish survey, one soft shell clam bed was estimated to be 100 acres in size.

To the middle 1980's most of these clams had perished and large amounts of loose soft shell shells (being lighter than Quahog) had collected in banks that had an oyster set.  Mr. Malloy felt that many times these loose shells formed the cultch for oysters with currents and waves in winter storms moved these shells down river.  Mr. Dolan experience in more upon waters was different, storms did cultivate the beds – but left the shells mostly in place a natural modification of pH – described as sweet (alkaline) or sour (acid) bottoms.

The next large contribution came from H. Karl Rask work on Cape Cod with Cation Exchange Capacity or CEC.  Here in some hydraulic rake and manifold trials cultivation of Mya beds resulted in lower CEC values which made calcium ions easier for shellfish to obtain and growth differences had a marine soil cultivation focus.  His work is found in reference #8.

Looking back, the issue of marine soil cultivation or hydraulic dredging was more about one group of shellfishers trying to eliminate a competing harvest group – especially in the Rhode Island references- my view Tim Visel.

My presentations in the early 1990's about soil cultivation was guided by accounts of massive storm damage John Hammond, the Monomoy Barrier Islands, Larry Malloy the Thames River and Frank Dolan of Long Island Sound and harbor areas.  All mentioned the 1938 hurricane but thanks to my brother Raymond Visel and an article about Larry Malloy January 1990, New England Coastal News page 23, has this account, from oystermen Larry Malloy of the impact of the 1938 hurricane upon oysterman.

"Then came a day in September 1938.  The sky began to darken and the wind came up.  A little yacht washed ashore at Harrison Landing.  Larry Malloy tried to save it "by the time we came back – boy, we know we had something – the water was right over the dock!  In those days nobody knew anything about a hurricane so we weren't prepared for anything.  We were going to take the Emma Francis out (one of Malloy's boats).  We didn't know where, we just knew we had to get her out of there.  The wind was blowing so hard we couldn't do anything under power. She blew right around on the rocks."
Larry Malloy poured another cup of coffee.  He looked out the window at the landing as if he could see the storm still raging and his boats piling up on the rocks.  "We lost everything" he said, his voice seemed to come from some far way place.  "We lost the four boats.  There was nothing left of the oyster shop but the foundation.  We saved the wheels and shafts off the boats and sold them – that's what we ate on."  The only thing we saved as a 16 foot power sharpie."

The 1938 Hurricane was catastrophic for oyster growers but the next two decades would be storm filled and much colder.  This would benefit the hard clam population and lead to a surge in clam landings after 1947.  The hydraulic dredge could operate in deeper waters and by 1958 two decades after the 1938 hurricane the few remaining shellfish companies knew exactly where to catch them.  After years of just shoveling clams overboard (no market price) they now became the "survival crop" as oysters declined until 1970.

Part 2

Clam Research in Town Waters

In the 1980's, I approached Mr. Dolan about surveying a section of Madison Town Waters as part of a shellfish management plan.  He agreed only after the previous clam bed he purchased in 1961 would be finally approved by the Madison Shellfish Commission.  This was done on July 5, 1983.  I was able to accompany him on several occasions from 1975 to 1983 for shellfish surveys.  I had clams (only living ones) aged at the University of Connecticut. I also kept records on age distribution and bottom conditions.
The first survey yielded only a very few living clams, all big "chowders."   

In 1983, they were aged by slicing the shells and examining deposits (similar to counting tree bark rings). They were old – 30 to 40 years with some 50 or more.  Mr. Dolan would work the dredges in circles and sometimes drop a marker buoy. Most of the first day yielded dead clam shells, some still paired but all dead. Frank asked that he be brought a pail of salt water and asked for some dredged shells to be brought to him.

Taking two shells, he rubbed them vigorously together and placed them in the pail of water.  A white cloud occurred and Mr. Dolan than said "what I thought; the bottoms gone sour."  I had heard this comment about bottoms before with inshore trawl fishermen in New York. He then repeated the "test" several times with the same results, a white cloud. The second survey was done in 1978-79, in the same location with mostly the same results – but we washed two boat loads of dead clam shells back on the beds near West Wharf.  Tens of thousands of bushels had died according to Mr. Dolan.  We dredged all day and found less than 30 live clams between Madison Reef and Tuxis Island.  Mr. Dolan said that he believed the 1938 hurricane was responsible for the great widespread clam sets in 1939-41. He felt many of the clam predators were killed, and that areas that had muck accumulations had gone back to clean and sandy bottoms.  He also felt the waves loosened the bottom that could get as hard as "pavement," allowing the clams to "set in" better.  The better bottoms had no such cloud from the shell test.  He would need to bring in a light coating of shell several times to sweeten the   bottom. The shape of the clam also told him a lot.  According to Mr. Dolan, the "points" and "blunts" tasted different   which he attributed to sweet or sour bottoms.  Points (sharps) were faster growing clams that had hard shells.  Sweet meaning those bottoms which were slightly alkaline and sour for bottoms that had no shell cover.  Blunts were often found in muddy or muck covered bottoms.  I stated it seems you are controlling the pH of the bottom with shells just as a farmer does with agricultural lime.  "Yes, we are and one more thing think about the soil."  It was the first time I had heard the bottom referred to as soil (1974-75).  Then he steamed out beyond Charles reef off Madison, set the dredge, engaged the pump and then stopped it mid-dredge.  By turning the water off, he took a chunk off the bottom in the dredge and hold hauled it up.  It contained a piece of orange brown  bottom – Clay Frank explained, no good for clams.  You could turn (meaning "cultivate") this over and over again with no clams – you cultivate the bottom we do, that is if the bottom is good – closer to the beach is mud/sand we can work that, out deep is clay/sticky bottom and that rarely works. We learned that we could take good bottom and cultivate it using the dredge then shell it slightly and get a set of hard clams.

Mr. Dolan recounted how it was by accident that this was discovered.  They had years of experience of catching hard clams under shell cover from oyster operations in New     Haven Harbor.  They initially thought the shells protected the clams from predation.  Only later did the concept of controlling pH and examining soil structure for          suitability develop for hard clam "aquaculture."   They were farmers and rotated cultivated prepared "fields."   It was just the same to him.

When the first hydraulic dredges can into existence, Connecticut clam production soared but consisted of almost entirely of market "chowders."  In the first 5 or 8 years, everyone caught clams and, at times, there was a market glut.

Eventually, all these chowders were caught and production declined.  (He stated it was in the mid-1960's.) From time to time, boats would rig up for clams, especially if the market price improved.  On one of these trips, they returned to a bed in the Thames River to relay clams to clean water and, much to their surprise, they found small clams, thousands of small "necks" and seed. This was the same bed several years that before had   only chowders.  They believed that the hydraulic clam "cultivation" aspect had done some good.  They then started to return to some of the other areas and found much the same thing.   The shell cover aspect seemed to work on grounds with no shell cover and, if, the bottom was sticky (high clay) or had shells pitted and soft (the white cloud in the pail of water), the  bottom was acid.  They once had a shipment of Thames River clams rejected because they tasted "bitter" and took them and planted them in Guilford for 3 months.   

The bottom had shells on it and other clams, and when resold, they were told they "tasted great."  He never had the time to pursue this except if on acid bottoms they would often taste bitter, on shelly bottoms clams tasted "sweeter."  It wasn't proved.  However, if the bottom started to "sour," they would dredge up some buried oyster shells and scatter them on the  clam bottoms.  In one interesting conversation, he recalled a situation when  they did this with oyster shell, and they didn't realize it had an oyster set on it.  When they checked on the bed several months later, they discovered a good crop of seed oysters and moved it to the Hammonasset River so it wouldn't be killed by starfish. It didn't take long for other clammers to realize that they could manipulate beds for setting.  It worked most of the time but in some instances, it didn't, so they would need to "check it" every  so often.  Key to the production is that beds were rotated, cultivated, lightly shelled and then wait.  Mr. Dolan said it was usually 5 to 7 years, again, depending upon the bottom conditions.  They didn't publicize this feature. (It took a while to get Mr. Dolan even to confide in me.  After all they had learned it the "hard way" and it was a   competitive business.)  Only recently have other researchers and industry people acknowledged this aquacultural practice.

Recently, articles have appeared about the same practices on the east and west coasts and in Canada.

Mr. Dolan stated that during harvesting oysters, if they ran off the line (area of planted oysters), they would hit the clams under a thin layer of shells. The problem was they weren't worth that much (pre-1945). Everyone (oyster growers) knew hard shell clams set under the shells. It was a common occurrence in New Haven Harbor Mr. Dolan's  beds were listed as Little Stone House in New Haven after a restaurant they owned.

He felt hard shell clams preferred a sandy soil closer to shore, and he rarely fished in waters over 30 feet deep.  He could tell by squeezing a clump of mud; if it held a ball, he would say too much clay and not worth  cultivating. They looked for old beds that still had clams believing if some were still alive the bed could support additional clams.  Some of the densest clam beds he ever worked were in the Thames River in old oyster beds.  If they contained clams, if they could be cultivated.  Mud and sand, 80% sand, 20% mud over 50% mud, clams would grow slow – acid would dissolve the new shell. Mr. Dolan felt good sets followed storms, washed mud from the soil and also  loosened the beds allowing dredges to catch better.  He did note that the clams responded to dredging by burrowing  deeper.  After several days the clams would go deeper – he thought a self defense perhaps from storms.

He would move off the area and fish another when he returned all the clams were "at the surface again."  The hydraulic action was a mini storm and that larger storms like hurricanes prepared bottoms for big wide spread sets even out to the deeper water.  He felt it key to production that beds be "rotated" Mr. Dolan compared it to Christmas tree growing.  Problems happened when the beds were harvested early.  Newer people had this happen.  It's hard to wait but not waiting wasted a lot of small clams; they were dislodged to be eaten by predators.  Sometimes he would cultivate, and it could take 3 years to get a  set (New Haven Beds).

They knew it worked (cultivation) because if they got off the area, the bottom would be hard and contain dead clams just like   the previous conditions.

Problems with Hydraulic Dredges

One concern Mr. Dolan mentioned was regulations/control of the beds.  He had seen clam beds ruined by continuous hydraulic harvesting and not letting the crop mature.  He stated that continual harvesting jets out seed clams for predators (mostly tautog – blackfish).  In a very short time the person is in the business of raising "clam predators instead of clams."  Once the area is cultivated, it needs to mature.  Early harvesting can give the illusion of a good return, but he estimated that for every clam harvested, 100 small clams would be killed by predators.  He gave an interesting example of a school yard and quarters.  If you took 12 quarters and threw them onto a grass-covered school yard, chances are they would all be lost and none recovered.  Imagine if you took 10 thousand quarters and did the same thing – he guaranteed that people would become highly interested and attracted  to this activity.  He recounted that was the same thing that happens in the marine environment; early harvesting brings in predators, in some cases thousands of them.  (He thought the worst were blackfish and spider crabs) It can build up the predator population to a point that all the vulnerable clams, especially the small ones, can  be killed.  In one case, he remembered the spider crabs got so thick over the bed they couldn't dredge.  When he returned weeks later, nearly all the small clams had been eaten.  If the beds were cherrystones or larger, this "chum effect" is  reduced. One of the suggestions was the area be divided into "lots" and testing made to determine when  to open.  It would maximum economic harvests and increase the percentage of clams to the Town of Madison.  (Madison had asked that a percentage of the clam catch be relayed to shallow waters for recreational harvesters).

1)   Blackfish were confirmed off Charles Island in Milford 1986 - the sound of the pumps brought them under the boat before water was actually delivered to the dredge.
2)   First attracted to the beds were large adult flounder who he felt were getting sand worms and not clams as a result of the dredging.  Sometimes people would fish by the oyster boats for winter flounder and he could  see them catching them.

Environmental Conditions for Clams - Notes and Observations

Mr. Dolan was willing to share his observations about hard clams from almost 50 years in the  fishing business.  He felt that hard clam offshore beds set well only two or three times in his lifetime, in the 1930's, 1950's and 1970's.  He believed that they occurred after a hurricane or very bad winter (Northeasters).  He also felt that the conditions were better in the rivers for sets, second best was under oyster shells and lastly, in the open offshore  waters.

When he cultivated (although he had caught both razor       clams and surf clams in Connecticut), the only other commercial quantities of other clams he saw were soft shells off Ledyard and in New Haven.  That was associated with hard clams; the soft shells were so thick they jammed the clam dredge making hard shell clamming impossible.  If he hit the soft shells he had to stop.  He would occasionally hit razor and surf clams off Guilford but not in any large quantities.  He felt the dredge for hard clams was just  too small to catch the others.

River and Bank Edges

Mr. Dolan fished the Thames River from Montville to Green Harbor, New London. He felt sets occurred often but the bottoms turned mucky in the 1950's.   He believed that over 50% muck could slow growth or kill clams.  He also saw sea lettuce in Montville get so thick as to suffocate clams off the edge (away from the channel).  He also observed clams with soft sticky bottoms, their shells were often pitted and were soft, very much unlike the clam shells from cleaner sandy mud.  He felt that the clams off Montville and Ledyard were the most concentrated.  The soft shell clam bed off Ledyard was over a 100 acres in size.   The Connecticut River had too much fresh water for hard clams he felt.

He also found that heavy rains would wash leaves and sticks over the beds in rivers.  One day little "trash" after a heavy rain a lot of debris etc.  Rivers were good he thought because salt water predators also were fewer.  He felt the currents would clean off new edges preparing them for    sets. That would occur after heavy rains.  Some of the densest areas for hard shell clams was off Montville.

Near Oyster Leases

He (and the oyster growers) had seen multiple sets of hard shell clam occur under seed oysters for decades.  Oyster set had been planted, and when harvesting the oysters with oyster dredges, they would always get some clams below the oysters.  In fact, they knew the oysters were getting "thin" when greater amounts of hard shell clams would come up.  This is when the practice of cultivating and laying down shell started. If it was done on the edge of oyster ground, clams sets were nearly assured.  Sometimes they just planted a thin layer of shell over an area with no cultivation.  They often would get a set that way when moving oysters.
Open Areas - Offshore

These are the areas that obtained widespread sets but only very rarely.  This was the type of clam bed off Madison.  For them, he would just cultivate and leave them alone for a few years.  Later he would cultivate and add shell if there were few shells.  Usually they were enough dead shell on the bed so that this didn't happen.  However, if the shells were so old that they crumbled in his hand, he    would add new shell (if he could get it).  This was the riskiest of the three habitats; sometimes he would get a set, yet sometimes it was a complete "blank," and he never    knew why.

Impacts of the Sea Bottom

Mr. Dolan felt that hydraulic dredging was much less harmful than dry dredges.   Almost no clams were broken and the bottoms were cleaner after clamming.  He likened it to raking the leaves off your lawn so the grass could grow. In Connecticut, he had noticed the tendency of the     bottoms to go "sour" with muck.  Green Harbor in New London where he said he found the densest and concentration of clams ever went progressively to a muck sticky bottom.  Once the clams were harvested, no small ones appeared and they tasted bad (see previous reference).  What started off as sandy mud became sticky muck, in a few years sometimes so bad that the dredge get stuck in it.  After a while, they started setting the dredge with full pump pressure to avoid this from happening.  If the bottom was very sticky, they   didn't even bother.  The last time he sampled in Eastern Connecticut for the town of Groton, he stopped in at Green Harbor.  The place he used to fish was full of leaves and sticks; he called it a "dead bottom."  He tried for an hour to catch any clams but didn't even get one dead shell.

He thought the bottom had changed so much, he could not get down to the bottom he clammed 30 years ago.  It was now extremely "soft."  He said the bottom was like jelly.  One time he hit a patch in Green Harbor and harvested over 500 bushels of necks and cherries from an area about a third   of an acre.  He felt of properly cultivated the Thames River could become a huge shellfish producer.

Summary

One of the things that bothered Mr. Dolan is that he could never see "his farm," a problem I encountered with similar size operations.  He often wondered what the area looked like before and after he dredged.  He wondered about the fish, (he used to catch flounders and blackfish in the dredges once in a while) and if they watched the dredge or came in right after it.  He wondered if the bottom had sand worms in it – he thought it did.  I was able to provide Mr. Dolan with a copy of a video oystering in the East River, but I don't think he ever got to look at the "soil" he worked on his entire life while clamming.

Introduction for Appendix 1-3 The Cultivation of Marine Soils
The Hydraulic Harvesting of the Hard Shell Clam Mercenaria mercenaria

Timothy C. Visel

In 1990, a concern was raised that hydraulic clam harvesting off the coast of Madison was environmentally dangerous to the water and sediments.  The group which called itself Save our Shores claimed detrimental  impacts ranging from increased heavy metals to the source of bacteria on bathing beaches.  The research community weighed in and dismissed these claims.  Pet waste it appeared was more of a threat to Madison beaches in the form of storm street water runoff than hydraulic clamming.

The conflict in the end was more about noise than anything else and it was handled the way most noise issues were – regulations on exhaust and municipal ordinances.  It was also suggested that shellfish resource issues were a long standing problem in Madison.  According to local shellfishermen, policies that had existed for more than  half a century were also to blame," if I can't harvest them nobody else should" and references to his belief were  found in the Town of Madison Shellfish records (See Appendix  #3). The town once founded by farmers and fishermen had become an affluent shoreline community and had a history of  marine resource conflicts in recent years (Charlette Evarts, Town Historian).  In 1972 and 1973, oysters began to set  strongly in town waters.  Natural growth harvestors (seed  oystermen) asked to harvest seed oysters in major rivers and creeks – but were continuously opposed.  Only after oysters grew to depths of 6 to 8 feet deep impacting navigation in Neck River did the town allow commercial harvests, but by then approximately 80 to 90 thousand bushels of seed oysters had died from overgrowth (1978).   In 1971 most of Madison waters were closed to shellfish from bacterial contamination (runoff).  This accelerated the waste of oyster resources as no relaying or transplanting programs were then underway.  The waste of oysters in the East and Hammonasset rivers was enormous.  After 1980 Madison reached cooperative agreements with oysters and clams.  Shellfishers provided relays of shellfish to support recreational shellfisheries and the waste of shellfish ended.

In March 1990 when the first concerns were raised, I was employed by the University of Connecticut Sea Grant Marine Advisory Service and a life-long resident in Madison.  In ten years of shellfishing, the clam sets improved, including a large bed offshore of the Surf Club.

According to newspaper reports the conflict was very divisive one pitting wealthy shore front owners against people who liked to eat and harvest shellfish.  The Madison Shellfish Commission had for 15 years under cooperative management efforts had a part of the commercial catches  set aside for shallow recreational relays) which greatly had increased recreational permit sales – and the satisfaction of shellfishing a traditional fall activity for many Madison residents.  It is in this context that the information is contained and with a slide show presented  to the combined groups to demonstrate the techniques and impacts of hydraulic clam cultivation.  The aquacultural aspects are included in Appendix #1.  In general terms, the hydraulic cultivation had transitioned former large clams to littlenecks of much greater value.  Residents could see plumes of organics in the wake of clam vessels.

As it relates to the resuspension of bottom sediments clam fishermen claimed that storms and hurricanes resuspended more sediments that could possibly be accomplished by hydraulic dredging.  The group opposing hydraulic clamming claimed serious long lastly negative environmental  impacts. Several federal agencies provided testimony in support of  hydraulic clam fishing.  The long "dead beds" of clams had with cultivation became thick with living clams.

Yet to this day, the association of increased resource enhancement and cultivation of marine soils refuses to    go away.  Rather than avoiding the issue we need to objectively look at it and involve industry resource managers and regulatory agencies in these discussions.  In that way, aquacultural cultivation practices can be discussed in a non-emotional way with industry and     resource managers.  The practice of marine soil cultivation is continuously mentioned in research and industry  accounts.

I have listed some references as a way to demonstrate that Connecticut's example is not unique but forms part of an international research effort.  They were included after my slide lecture presentation at the Town Hall on the equipment and different types of   hydraulic dredges in the United States and Canada.  I have summarized sections of these handouts below.

On a final note – One prediction

One prediction that Mr. Frank Dolan a local shellfishermen made did come true but he did not live long enough to witness it.  The State waters did pick up strong sets of Mercenaria in 1987, following Hurricane Gloria and another following Hurricane Bob in 1992.  The harvest of hard clams soared in 1994 and continued to the year 2000 following these widespread sets, and as he predicted this event          would be followed by a decline just as the previous three cycles he had described.  He told the group that storms changed the bottom and moved more sediment than the hydraulic clam dredge could ever accomplish. "On rough night from a southwest wind moves more silt in an hour than we could in a  year."

Reference for the Cultivation of Marine Soils – Prepared for the Madison Shellfish Commission

Appendix #1 Aquaculture Aspects Associated with Hydraulic Clamming.

Note:  Most of the shell fishermen that I have had the benefit of meeting and engaging in conversation all told        me the benefits of "working the bottom" and negative associations of plants (marine grasses) and decaying plant matter. They seemed to be both indicators, clean, relatively mud free habitat was good and thick grass or heavy accumulations of seaweed, sticks or leaves were poor or low productive habitats.  There was consensus that clean good bottom can be ruined by excess plants, both terrestrial and marine.  This was more prevalent in the regions that suffer from nutrient enhancement.  The working the bottom aspect can be found in many clam fisheries, raking, tonging and dredging, only with hydraulic clamming did I find reference to the activity as a farming or soil cultivating activity aside from harvesting.  In this way,
the area was prepared for a set or harvest." Much as terrestrial farmers cultivated and prepared "soil". I have listed some references for the process - We absolutely, need more research in this area. Most of the research  today has been done by shellfish constables, shellfish commissions and the shellfishermen themselves. Although it is continuously mentioned by shellfish managers and the shellfish industry, it remains an area that is still      poorly understood by the general public.  As the concept of marine soil manipulation is often contrary to accepted policy norms and may infringe upon long standing environmental and regulatory provisions, it needs to have a historical context of shellfish utilization by early settlers and of course native Americans.  Much of the practice of hydraulic cultivation was utilized as a way to minimize the negative impacts of eutrophication and siltation.  The breaking and allowing to air penetrated terrestrial soils had long benefited agriculture.

1.   Biological Effects on Hard Clams of Hand Raking and Power Dredging
   October 1953 - By John B. Glude and Warren S. Landers Fisheries #110 United States Dept. of the    Interior Fish and Wildlife Service

"Narragansett Bay, Rhode Island, has supported an intensive commercial fishery for the hard-shell clam, Venus Mercenaria, known locally as the quahaug or quahog, for many years.  Hand diggers, using tongs or bullrakes, are allowed to fish in any unpolluted waters in the State.

Power dredgers have been restricted to the southern half of the Sakonnet River except for a short time during World War II when additional areas were opened to increase food production.  Locations of fishing areas are shown in  Figure 1.

Controversies continually arise between fishermen using power methods and those who harvest the clams by hand. Rakers and tongers claim that they are using the only method which do not harm the bottom or destroy young clams. They claim the dredges tear up the bottom, breaking many     of the clams which are caught as well as those which go through the bag of the dredge and are left to die.  They also believe the dredges bury the small clams so deeply that they are smothered, and that the bottom is sometimes plowed to such an extent that current action causes scouring which prevents a new "set" from surviving.

Dredgers claim that they are merely cultivating the bottom and preventing it from becoming too compact for the clams to live.  Dredging, they state, really improves the   bottom, inducing new sets and increasing the growth rate of those clams which are left.

Bottom samples confirmed the indications of the underwater photographs that surface appearance of the three areas was similar.  Mixing of the sandy-mud layer and the underlying clay was more pronounced in both fished areas than in the control.  Fished areas were also softer and had less odor of decomposition than the control (most likely sulfide T. Visel).  No differences in the above physical characteristics was observed between               dredged and bullraked sections.

This experiment shows no biological basis for restricting either method of fishing."

2.   Fisheries Research Board of Canada 1962 -

"The Martha's Vineyard hydraulic clam rake (Mya) is the proto type from which the present machine was developed. We believe the hydraulic rake, which operates on flats while they are submerged is a better harvesting tool.  It causes so little damage to clam stocks that it must be ranked high as a saving gear.  We wish to thank Dr. Matthiessen who in 1959 acquainted us with Martha's Vineyard fishermen who were using hydraulic rakes."

3.   Yankee Magazine October 1974 -

"Rev. Richard Burton, founder of Project Dominion, demonstrates his homemade cultivator, seawater pumped through the device agitates the surface of an ecologically stagnant clam flat and adds oxygen and nutrients – resulting in a healthy set of clams." {Mya}

4.   Hydraulic Harvesting of Soft Shell Clams – Results of Soil Cultivation Experiments – MacPhail Model of the Hydraulic Rake – Page 9

Bourne – Sandwich Shellfish Assn. September 8, 1980, March 20, 1981 – hydraulic soft clam rake

"When the manifold was rolled across the bottom, gases formed from the decaying matter were observed bubbling to the surface.  The substrate was devoid of the usual  animal life, such as sea worms and the winkles.  After pumping these areas, and removing the harvestable clams, the conditions improved remarkably.  The surviving seed was able to return to the newly turned over bottom, while the dead shells and decaying matter remained on the surface.

The mortality rate of the remaining seed dropped drastically, and an increased growth rate was noted.

We have also encountered certain spots where this dying process is complete, and only the many clam shells remain beneath the substrate.  Though the area has since repopulated with sea worms, and other marine life, as yet, no clams have re-set there.  One explanation could possibly be taken from the 1930 Belding Report, which states:
"Clams are usually absent from soils containing an abundance of organic material.  Organic acids corrode their shells, and interfere with the shell- forming function of the mantle.  Such a soil indicates a lack of water circulation within the soil itself, as indicated by the foul odor of the lower layers, the presence of hydrogen sulfide, decaying matter, dead eelgrass, shells and worms. If such a soil could be opened up by deep plowing, or resurfaced with fresh soil to a sufficient depth, it would probably favor the growth of clams."1
1   Belding, David L. MD; The Soft-shell Clam Industry of Massachusetts, November, 1930.

5.   University of Maine Orono, August 1984 – Development of   a Harvester for soft shell seed clams

"There had initially been some concern regarding damage to the fragile young clams, and disturbance of the flats themselves by the action of this hydraulic harvester. Both these aspects were studied. Samples of clams harvested by the machine were taken to Orono and placed in the    shellfish laboratory running sea water system. After three days a count of dead clams was made and the percentage mortality calculated. For no sa