IMEP #146 - Part 1: The Bay Scallop Small Boat Fisheries 1870-2015

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IMEP #146 - Part 1: The Bay Scallop Small Boat Fisheries 1870-2015

"Understanding Science Through History"
Bay Scallop Inshore Fisheries Need Colder Temperatures

Eelgrass as a Habitat Engineer and the Collection of Composts in Shallow Water
The Chemistry of Bay Scallop Habitats Change Over Time in Response to Climate

Viewpoint of Tim Visel, no other agency or organization
Thank you, The Blue Crab ForumTM for supporting these Habitat History and Environment reports – over 350,000 views to date

February 2020 – This is a delayed report
Revised to August, 2023
Tim Visel retired from The Sound School June 30, 2022
This is Part 1 of a two-part series, readers should review Part 2 if possible


A Note From Tim Visel


To early shellfish managers, the scallop fishery was unlike no other.  It was free of the overfishing charge that so often impacted the clam and oyster fisheries.  Scallops provided a year-old growth line, a division in the shell growth that creates a line or "raised ridge."  This line is usually visible so it is easy to distinguish a year-plus scallop.  As scallops spawn in the summer of the second year during summer, a late fall harvest ensures the reproductive success of the species – or does it?  If any species shows boom and bust, it is the southern New England "Bay Scallop" Aequipecten irradians.  That has caused questions about bay scallop populations for decades.


Fishery managers a century ago did not review the terms of habitat refugia or the concept of larval traps – areas of the coast which act, at times, as a refuge from natural predators and hold the last survivors of a great set.  Small boat fishers went to look for certain species as knowledge of habitat/species abundance was recorded by observations.  Certain habitats were found to be associated with the American eel, Anguilla rostrata, found most often in winter hibernating below "eel grass."  It was Nelson Marshall who recorded observations of scallopers with scallop association to Agardhiella sublata, a corraline red algae, or for some of us "Agard's weed" – it is here on pg. 100 of his renowned work published in 1960 titled "Studies of The Niantic River, Connecticut With Special Reference to The Bay Scallop" is found this section:


"It is noteworthy that fishermen of the Niantic River refer to such algae as "scallop grass."  


This was a red algae, not eelgrass.  The scallop life history has plagued fishery managers for over a century – why does the scallop after spawning once continue to grow (and compete with its young for food) and perish just before a second spawning?  The answer to that question is it might be just cool enough to allow bay scallops to exist for one spawning but not cold enough to provide for two.  Its genetic clock (lifespan) is not aligned to climate.  Only in the coldest of times did bay scallops present two growth lines.  I was given a small collection of these 1950's scallop shells after a meeting in East Lyme in the mid-1980's.  These very large scallop shells all had a pronounced second growth line.  We may find that drowned rivers and those bays with barrier spits form a larval trap for the bay scallop.  Following strong storms and cooler seawater temperatures might be the best conditions to catch "bay scallops" in shallow water – my view, Tim Visel.


The Climate Impacts Upon Habitats


In IMEP #80 Part 2, I talked about the energy and temperature impacts of climate to bay scallops.  Their ability to move or be driven by storms has left bay scallop remains throughout Long Island Sound.  Almost every dredging project collections of dredged material has contained remnants of bay scallop shells.  This movement separates bay scallop from intense sets of oysters and clams, which largely cannot move but live in the soil for the most part in which they land as spat.  This is not true for the bay scallop as its ability to move or be moved is found in the historical shellfisheries literature and within different habitats.  The US Fish Commission bulletin series contains this segment (1887), pg. 568, Ingersoll, The Scallop Fishery, referring to this point, (being driven by storms, T. Visel):


"Captain S. Pidgeon of Sag Harbor (a village on the southeastern fork of Long Island, New York, T. Visel) says that, if possible, when driven before a storm, they will work to windward, and he has seen them swimming in schools 10-feet deep."  


And also, the movement of seed on floating eelgrass into Oyster Bay Long Island, NY:


"In the spring of 1880, the grass came into the Bay, bringing young scallops, thus the abundance that year accounted for."


This provides evidence of a scallop set in deeper water, not in the bay itself. In addition, observations include late night movements (various bays) and schooling behaviors just before a storm.  John Hammond, a retired oyster grower, had his oyster business start in the Oyster Pond River just before the 1938 Hurricane.  Just before the 1938 Hurricane hit patches of adults and small scallops started leaving the Oyster Pond and Stage Harbor inlet for Nantucket Sound.  An important seasonal fishery around December, he termed it the "Christmas crop" as its peak catches were around the same time.  Oyster growers watched as their "Christmas crop" swam out to sea - a few hours later, the winds started to pick up, larger storm waves were soon to follow.  It was September 20, 1938.  


When I worked on Cape Cod, some of the scallop fishermen said that accounts on the movement were related to food supply as well, that particularly dense beds of bay scallops would suddenly disappear only to be found a short time later in another area in which there was only a few days before.  Some attributed this behavior to "locusts" arriving in great numbers, consuming all available food and then moving along.  I guess it is easy to assume this belief as unsupported until you look at similar reports in oyster culture, the ability to consume so much plankton that waters can become clear.  Sudden scallop arrivals are also noted in the small dredge fishery – areas which were barren would suddenly have thick populations of scallops (See IMEP #60: Anthiers Pond Martha's Vineyard, Massachusetts Beach Restoration Project – A Dredging Project Created a Deep Channel Which Soon Filled With Bay Scallops, posted February 7, 2017, The Blue Crab ForumTM).
 
If this is true that bay scallops can consume so much algal food in shallows, they would need to move.  It also fits that cold would provide more bacterial nitrate to feed nitrate-sustaining algal strains that bay scallops need.  It might be easier to think that cold allows more nitrate to form and become available to these plankton species, especially diatoms.  Davis and Marshall (1961) in The Feeding of the Bay Scallop found large numbers of diatoms in bay scallop stomachs (they identified 26 species of diatoms).


Chlorella species became dominant in Long Island Sound in the colder 1950's.  Its nutritional value to the bay scallop is low, however; its tough cell wall structure is hard to digest.  Victor Loosanoff, shellfish researcher at the Milford Shellfish Laboratory, mentions chlorella in a September 1957 National Geographic magazine article about Long Island waters.  "It's almost pure chlorella, could produce far more protein that you can get from an acre of land even when planted with soybeans."  It (chlorella) is a cool water species that is able to utilize nitrate as a nitrogen source.  In the 1990's, brown algal strains, Aureococcus anophagefferens, were dominant in Long Island Sound, not chlorella.  This strain utilized ammonium as a primary nitrogen, not nitrate.  This was a time of increasing mild winters and hot summers.  These became known as the "brown tides."


That all habitats, regardless of climate and energy, are essentially the same – has created a huge bias in habitat understanding as it assumes that observations link the bay scallop only to shallow areas.  Shallow areas, which do support bay scallop fisheries, are subject to greater predation, natural loss from high heat or cold and finally habitat succession of soil chemistry.  When you look at the first scallop industry reports, they happened in deep water – at the very limits of the fishing technology of the time, dredging by sail.  This is mentioned in the Narragansett Bay deep water scallop fishery of the 1870's.  When you examine the bay scallop fisheries, you see the impact of climate change.  Even though most reports start for this fishery after 1871, the movement east and north are quite clear.  In the 1870's, which was cold, Greenwich, CT coves were filled with bay scallops.  This was a time of extreme cold and powerful storms.  Bay scallop shells often appear in dredge spoil examinations in Greenwich today.  Even an occasional adult scallop is caught in oyster operations (Hillard Bloom, personal communication to Tim Visel, 1980's).


The US Fish Commission report (1887), pg. 571 has this section:


"At Greenwich, CT, I was told that ten or fifteen years ago (1872) one could fill a dredge in a few rods, and a boat would take 50 to 100 bushels a day.  Now, only about 10 bushels as day was the average catch."  


And further on pg. 577:


"A few years ago, it is said, scallops were common enough off Bridgeport, Connecticut, but have now wholly disappeared."


It is important to recognize that 1872-1874 was some of the coldest winters in a half-century.  New Haven recorded a temperature of negative 30oF during the winter of 1872-73.  It may seem odd to think of Greenwich, CT as having a substantial bay scallop population, but it once did when it was cold.  Periods of high energy (storm frequency) and cold would keep both oxygen and nitrate levels high.  As the climate moderated, you can see this bay scallop cooler retreat to the east over time.  Greenwich, Norwalk in the 1870's, Milford 1880's, Clinton 1930's, Niantic 1940's-1950's, Stonington 1950's-1960's.  If you extend this review during the very warm 1990's, the Cape and Islands are frequently the last communities to have a bay scallop fishery.  Eastern Long Island, New York shares a similar experience, and in recent years, intense heat produced sulfides that nearly wiped out the Peconic Bay scallops in 2021.  High sulfides have the ability to discolor shellfish meats – a gray disease (See Appendix #3).


In time, even research conducted by the EPA has backed away from the eelgrass-bay scallop relationship.  Studies conducted in the EPA Atlantic Ecology Division Laboratory Narragansett, Rhode Island suspended research in scallop spat collection in 2005.  Eelgrass may provide an important indicator for the presence of sulfide rather than the bay scallop.  It may give us an indicator for the transition of compost nitrate to low-oxygen compost ammonia.  A hot summer organic composting tends to produce ammonia.  Oxygen levels tend to be low in hot seawater and sulfate-reducing bacteria thrive.  To complicate this change from nitrate to ammonium is the aspect that bacteria produce substances toxic to other bacteria.  Those are termed antibiotics today.


The winter cold water nitrogen pathway ends with nitrate – the bacteria that convert nitrate to ammonia have receded as they do well in warmer water.  They are still present in this bacterial organic compost but could be called in a semi-hibernation state.  They would need late spring warmer waters before a huge base of nitrate became an easier energy source.  Therefore, during the winter months, nitrate builds up (not during the bay scallop growing season) to supply the spring blooms of algae diatoms that need nitrate.  This was quite evident in the colder springs and longer winters of the 1950's when New England scallop populations were much larger.  These springtime surges in algae were termed "blooms" but without the colors of their terrestrial counterparts.


In many times, population observations were unique to a certain viewpoint or training.  With the great fluctuations in bay scallop abundance, biologists looked at biological reasons, such as spawning potential, fishery managers looked at seasons or catch limits (overfishing does not occur here after the raised growth ring year they do not generally spawn again).  While a growing conservation movement moved to protecting resources, concepts of habitat failure from climate were still a generation away.  Observations became a powerful foundation for policy and because the concept of habitat succession did not exist for marine habitats, observations made one year was expected to carry over to the next.  These observations became fixed and associations linked certain habitat characteristics.  One of these associations was that bay scallops needed colder habitats regardless of eelgrass.  This association, one of the strongest over the last century, is one made in shallow water, habitats in which the (bay) scallop was the most vulnerable to change.  The 1887 US Commission of Fish and Fisheries, Section V, Vol. 2 written by Ernest Ingersoll of New Haven, CT, describes this cold habitat bay scallop relationship on page 568:


"I have not heard what effect the subsequent severe winter (1880-1881) had upon these (Oyster Bay) scallops.  They come to anchor and stay there (Oyster Bay) unless driven away by heavy storms, as often happens.  Under such an accident, thousands of bushels are often driven up on the shores of the bay and die there by freezing."


Shallow waters less than 10-feet deep at low tide are some of the most unstable habitats for shellfish.  Areas that are poorly flushed act as a larval trap during cold but extinguish the scallop in high heat – a bacterial sulfide response to low dissolved oxygen.


A comment made to me on Cape Cod always left a question – habitat stability and the scallop's short lifespan, 26 to 32 months.  As compared to oysters and clams, which need habitat stability and take years to mature, the bay scallop has no similar habitat commitment.  It can move, consume food and then move on.  Another advantage is that they are hermaphrodites, able to switch sex.  They were described as a type of "marine locust" at times reaching tremendous densities, making shallow water clear and then at some point moving onto better feeding opportunities.  We know that diatoms make up a large part of the bay scallop's diet (Marshall & Cooper, 1963) and that diatoms consume large amounts of nitrate.  Diatom blooms (called diatom flowering) can consume large amounts of nitrate released by bacteria over the winter.  This is where the concept of habitat clocks comes in – something that John Hammond detailed that several factors needed to be aligned.  Cold temperatures would support the nitrate bacterial pathway, which in turn could support diatom flowering, its primary source of food, supporting a potentially large scallop crop. 


Perhaps in cold, bay scallops reflect a certain habitat succession, one that matches its life cycle – short and opportunistic.  This is a factor that helps explain why the sudden surge in fisheries immediately after energy events.  Not only are seed scallops driven into the shallows, but soils reflect lower sulfides after soil cultivation by the storm.  Bay scallops could appear immediately after a storm (with areas of no eelgrass) and exist if waters were cool.  Many reports mention eelgrass taking over scallop grounds but this is a part of natural habitat succession.  This would also be noticed by scallopers, who claim that eelgrass first started out as isolated batches and grew over time to cover entire regions.  Reports from Massachusetts biological bulletins (1950s-1960s) reported many times that eelgrass did precisely that.


The association of eelgrass to bay scallops is a frequent one.  In reviewing the habitat history, over time you see a different picture of habitats.  The bay scallop fishery in shallow waters often occurs in habitats that have eelgrass.  That in itself raises the question "where is the parent spawning stock?" since after a severe storm or after many years of nearly complete absence, a huge crop of scallops suddenly occurs.   This has been a reoccurring question in the scallop fisheries history.  A boom means that somewhere there was a parent stock.  Often, it appears that parent stock was offshore in 20 to 35 feet of water that may or may not contain eelgrass.  We know from historic nautical charts the location of eelgrass flats.  In times of cold, bay scallops were, at times, abundant.  The fishery was often pursued in shallow waters, but again at one time Narragansett Bay supported a deep-water fishery (See IMEP #52 Narragansett Bay Deep Water Habitats, posted July 27, 2015, The Blue Crab ForumTM).  There could be a substantial difference in high energy cool water eelgrass and eelgrass in shallow water in high organic deposition areas.  Severe storms may set in motion habitat succession processes rarely understood even today.  This was explained to me by John "Clint" Hammond who felt that eelgrass in shallow water was not its primary habitat but one that happened by chance, not by its natural place.  He used the example of planting a tree in a desert does not mean it will rain.  But one may associate trees with sufficient rainfall over time to sustain it.  We call that droughts and in a doing so what happened to be a stable or good habitat is now bad or in today's terms, unsustainable.  Bay scallops and eelgrass suffer the same fate as waters warm – their hold on shallow water habitats fail over time with climate warming.  That is why in the historical eelgrass literature so many previous eelgrass transplants failed.


Eelgrass: A Soil Engineer


One of the things John Hammond mentioned to me was "new sand," storm-driven sand didn't immediately catch a set of clams.  It took two to three years before a set happened.  To him, the soil needed to stabilize and that could take time.  If one looks at burned forest soils, they also were sterilized by the heat of the fire and absent of important nitrogen-fixing bacteria.  Plants would need to have soil bacteria and that came about with bacterial food organic matter.  This wait explains observations of how eelgrass starts as isolated clumps or patches that, at first, derives important nitrogen through its leaves and water.  As roots build and blades slow currents, it traps organic matter and helps root symbiotic bacteria to grow.  These nitrogen-fixing bacteria's importance was identified at the University of Rhode Island in 1910 (See Bulletin #139 of The Rhode Island Agricultural Experiment Station, 1910).  Nitrogen-fixing bacteria (NFB) live inside the roots of seagrass and convert nitrogen gas N2 into ammonia – to this bacteria alive, the plant provides the bacteria with sugar.


This is similar to legumes, such as beans, peanuts, lentils and NFB – termed rhizobia on land.  The relationship between crop harvests and bacteria was well established by 1890 (P. E. Brown, Soil Inoculation 1918).  Eelgrass has similar root nodes, which like its terrestrial relatives, keeps a bacterial shield of nitrogen-fixing bacteria at times when other bacteria thrive.  A healthy plant is recognized by sufficient oxygen that allows the conversion of nitrogen into forms that can be absorbed by it.  When oxygen is short, eelgrass can compensate by moving oxygen from its leaves to its roots – but this compensation is limited and roots may lose its shielding bacteria to bacteria that use sulfate as a respiration oxygen source.  This is represented by sulfur toxicity, also a product of marine bacteria.


Aquaculturists know some of these bacteria by the function they exhibit in controlling ammonia in closed systems by the use of oxidizing-ammonia bacteria.


However, eelgrass may be responsible for changing the bacterial spectrum by collecting and producing a high organic soil.  High organic marine soils are known to harbor pathogenic Stramenopiles, one of which is a pathogenic clade of labyrinthula spp.


As legumes need bacterial interaction by way of symbiotic infection, which forms nodules that allow nitrogen ions to enter root tissue, so does eelgrass.


As plants grow together to form a meadow, eelgrass now obtains nitrogen from root bacterial growths it helped start.  The same type of habitat bacterial succession happened on burnt forest soils, grasses and wildflowers appear first gradually giving way to shrubs and low canopy under growths and then trees.  In the marine environment in northern regions, the frequency of energy (storms) prevents the growth of trees, such as the mangrove of southern regions but holds habitat succession at the grass level.  In time, eelgrass engineers its own high organic compost.  In "Recent Marine Sediments" (1955), Jensen estimates that eelgrass builds organic matter rapidly and amounts to 100 grams of organic matter per square meter or above what is yielded by the plankton community in the open sea near the coast of Denmark.  Parker T. Trask's paper – Organic Content – Recent Marine Sediments – National Research Council, 1955, details how quickly eelgrass can change the organic matter content of washed or new sand after storms.  This is from its own growth root and leaf tissue composting but also its ability to gather organic matter (plant tissue) from other sources.  In the shellfish literature, this engineering (perhaps a better word is composting, T. Visel) aspect is mentioned several times largely as a negative factor.  This is after the 1940's as eelgrass was a habitat succession factor that suffocated oysters and clams and reported in the historical fisheries literature during this time (See IMEP #121: Why Eelgrass Transplants Fail, posted April 23, 2023, The Blue Crab ForumTM, Eeling, Oystering and Fishing thread).


What was not reported then (and from a lack of knowledge) was how eelgrass could change over time soil chemistry.  The ability of eelgrass to change bacterial populations had in fact over time altered soil chemistry as it built peat and in heat helped the formation of a sapropel a marine compost that is temperature sensitive - in times of cold, favoring the bacterial release of nitrate, but in heat increasing the presence of ammonia.  This occurs in heat as low oxygen eliminates the bacterial strains that oxidize ammonia to nitrate.  Without that bacterial component, bacterial release eventually is dominated by the presence of ammonia (See IMEP #111-Part 2: The Eelgrass Question and Marine Habitat Succession, posted June 2, 2022, The Blue Crab ForumTM).  In times of oxygen drawdowns, it opens the bacterial pathway to sulfate-reducing bacteria – those bacteria strains that in times of oxygen shortage can use the compound sulfate dissolved in seawater.  This change can release sulfide that can complex heavy metal ions.


Energy and Temperature and the Bay Scallops


A consistent observation is that years with hurricanes (including the following year if cool or cold), the bay scallop fishery is good, even excellent in Connecticut.  Consider the year 1955 when Hurricane Connie hit Connecticut on August 13th.  Hurricane Diane hit August 19th but the fall of 1955 yielded 10,000 bushels from the Niantic River alone.  After the cold wave of 1957-1958, catches were near 30,000 bushels.  Estuaries tend to hold seed because the inflow has much more force – it is flowing into a lower resistance situation.  The exit flows are governed by the water that is already present, or a much modified tidal bore, a larval trap.  If it is cold, bay scallops can survive in shallow areas, but this is not a preferred habitat.  Predators are numerous and high heat causes sulfides to enter the water.  


Bay scallops are acutely sensitive to sulfides because over time, they did not develop a natural resistance to it.  Bay scallops prefer deeper waters with more circulation and a buffer to hot water.  It is the poorly flushed bays and coves that act as a larval trap during storms but need to remain cool to keep scallops alive.  But the same larval trap for seed or set causes waters to heat up faster and extend heat events in areas of deep organic deposits.  It is these organic deposits that foster sulfate-reducing bacteria (SRB) to release sulfide deadly to the scallop.  Sulfides can build up in the water during heat waves in late summer.  Shallow areas with a sulfide deadline kill scallops easily.  Research experiments have shown that at only .3 ppm (parts per million) exposure to sulfide bay scallops reduce feeding 30%, at only .7 ppm bay scallops perish (FAO Manual on Breeding and Culture of Bay Scallops, 1991).  A large sulfide release could quickly kill the bay scallop and suspect in a Peconic Bay dieoff (See Scallops Dying Off in Long Island, January 23, 2023 by J. D. Allen, WSHU interview with Christopher Gobler "We found that when placed in areas that were experiencing heat waves, all the scallops died.  Whereas the ones that were in cooler temperatures, they survived."


It is important to note that some areas that act as larval traps can hurt or enhance shellfish species with temperature.  


Some larval traps in heat can support oysters over high organic soils but the same areas in cold support scallops.  In the 1950's and 1960's, the Poquonnock River in Groton, CT was a huge producer of scallops while eighty years before becoming famous for its off-bottom oyster culture – oysters set on birch branches pushed into a soft high organic ooze.  The oyster spat was concentrated in the basins of the upper Poquonnock River and high sets of oysters, at times, completely covered any brush pushed into this waterway.  Oyster culture was stopped when suspected sulfide gases were thought to have caused a "miasma," an outbreak of foul putrid airs then thought to cause human disease.  In this case, the suspected sulfide gas release was linked to an outbreak of Scarlet fever (Streptococcus pyogene bacteria) in the spring of 1880.  It was very hot at this time and temperatures would continue to rise for the next two decades – and as the scallop fisheries declined, the oyster industry (aquaculture) recorded record-breaking harvests.


In southern New England for the next four decades, immense fish kills in salt ponds and coves would nearly always be preceded by what is termed the "smell of rotting eggs."  In 1895, a huge fish kill in Point Judith Pond caused "fishermen and oyster farmers of the pond approached scientists at the Rhode Island Agricultural Experiment Station to inquire if they could explore the reasons for the fish kill and somehow solve the problem" (The University of Rhode Island – Detailed History).  In 1896, the Rhode Island Agricultural Experiment Station opened its marine laboratory under the direction of G. A. Field at the end of Succotash Road in the village of Jerusalem.  It was Dr. Field who noted the importance of bacteria to nitrogen fixation in the form of nitrate and, in high heat, the increase of sulfur smells (See C. L. Devlin and P. J. Capelotti, 1996 – Proximity to Sea Coast: G. W. Field and the Marine Laboratory at Point Judith Pond, Rhode Island 1896-1900, Journal of the History of Biology).


In 1898, the upper portions of Narragansett Bay suffered an immense fish kill.  Dr. A. D. Mead of Brown University wrote in 1898 that "Myriads of shrimps and blue crabs came to the surface and to the edge of the shore as though struggling to get out of the noxious water."  If you lived in or near Mobile Bay, you would recognize this description as a "jubilee," a time to catch fish and crabs in shallow water.  A century later, Narragansett Bay would again see the signs of a jubilee – levels rose much from sulfate-reducing bacteria that, in high heat, utilize sulfate as a source of respiratory oxygen and waste sulfide as a byproduct.  High heat fish kills often carry an intense sulfide smell just prior to dead clams and fish.  In 1999, Christopher Deacutis, water resource specialist for the State of Rhode Island, wrote about his forming a group that would measure oxygen levels at night during the oxygen minimum of 1:00 a.m. to 4 a.m. in 2003.  This project was "spurred by much smaller fish kills and occasional reports of gray-colored water and hydrogen-sulfide odors" (Decade After Massive Fish Kill Narragansett Bay Healthier, But Work Remains, Richard Salt, The Providence Journal, August 20, 2013). 


In June 2012, the smell of the sulfide would return to eastern Connecticut Stonington but by this time sea cabbage is now called sea lettuce, Ulva species (See Appendix #1).  As waters warm the bacterial (composting) release of ammonia increases Ulva species, which thrive in ammonia rich waters.  The years 2010 to 2012 had some of the warmest waters and sea lettuce (as well as other plant species which utilized ammonia as a nutrient source) thrived.  On June 7, 2012 The Day newspaper published an article by Alex Nunes titled "Stonington Big Stink" residents of Stonington Borough" are up in arms" over the smell of hydrogen sulfide released by rotting algae.  Television reports included Stonington residents getting sick from rotting algae in an area with little tidal flushing.


The occurrence of heavy mats of sea lettuce and sulfide smells in high ammonia waters is mentioned many times in the coastal and fisheries historical literature.  High temperatures, heavy organic loading would favor the bacterial (compost) release of ammonia – the nitrogen compound upon which macroalgae thrives.  It would also become sulfide-rich when bacteria utilize sulfate as an oxygen source.  This would impact clam and oyster meats, making them watery or lead tasting.  The 1889 Bureau of Labor Statistics report on the oyster industry, pg. 141, contains this comment about the Thames River.  Nathaniel Chapman states "We cannot sell the river oysters owing to their bad taste, except for transplanting into clean, pure water.  The oysters then become fit for use."  For the scallop, high sulfide levels often proceeded massive dieoffs.


In a 1968 report titled Biological Aspects of Water Quality, Charles River and Boston Harold, Massachusetts July-August 1967 and printed in 1968 R. Keith Stewart, who was an Aquatic Biologist with the United States Dept of Interior – Federal Water Pollution Control Administration notes this condition on page 16: 


"Black oozy muds that emitted foul odors and contained much oily residue were found here, and the surface of the river was pock marked with bursting bubbles of hydrogen sulfide."


In 1975, Richard S. Caldwell produces a report titled Hydrogen Sulfide Effects on Selected Larval and Adult Marine Invertebrates" US Department of Interior Public Law 88-379.  Caldwell reports some species such as the oyster Crassostrea gigas killed at .32 mg/liter for only 2 hours.  Another clam, known to live in low oxygen, high organic soils Macoma balthica could tolerate 6.0 mg/liter of sulfide. (Macoma balthica is often used in dredge material as a successional transitional species.)


Studies in China on the bay scallop (the China Bay Scallop is actually from Groton and Stonington, CT) showed that the bay scallop is acutely sensitive to sulfide with only .7ppm causes bay scallops to cease feeding and are more susceptible to disease (See Appendix #2: FAO Training Manual on Breeding and Culture of Scallop and Sea Cucumber in China).


Many areas of the Charles River in Massachusetts (Stewart, 1967 observations) had signs of organic enrichment, and in some places, sulfide-tolerant polychaete worms reached densities of 964 worms per square foot, pg. 25 has this segment:


"If not grossly polluted, the Chelsea River bottom – animal populations would include organisms such as clams, crabs, nematode worms, and mussels, and polychaete worms would be few in numbers.'
 
And further (from the buildup of sludge – most likely sapropel, T. Visel):

"Sludge deposits in the Earl Point Channel were more than 3 feet deep, contained oily residues, and emitted four odors.  Hydrogen sulfide bubbles effervesced from the sludge in this reach, rose to the surface and burst, creating readily apparent odors like those of raw sewage and "rotten eggs."


Although bacterial composting of organic matter has long been assigned to human activity, nature has a role as well. In high heat, organic matter can be a huge source of sulfide, especially those areas often described as "tidally restricted." 
 
The Poquonnock River, for example, has an active barrier spit that responds to storm events.  As with many coves in New England, it undergoes closure in warm weather (saltwater is less dense) and can reopen from winter storms along the westerly end of Bushy Point Beach, and a headland of the Groton New London Airport.  Like most barrier spit openings, they are "dynamic" and can close up or become wider over time (storm surge).  In hot climate periods, the reduced flushing now becomes noticeable – an increase in ammonia and sea lettuce with the formation of hydrogen sulfide the smell of rotten eggs "the exit spit at low tide is only a few feet deep."  Sand bars could be easily moved by storms.  The physical history of the Connecticut Shoreline (1929) Henry Staats Sharp, pg. 68 and 70, describes the influence of sand and vegetation.  The freshwater flows keep the river open but are subject to cuts and wave over wash during heavy storms.  From Sharp pg. 68-69 (Hathi Trust):


"From Bluff Point, the headland immediately west of Groton Long Point, a mile long tombolo stretches in a beautiful crescent beach to a former island now Bushy Point.  On chart No 358 Bluff Point is called Mumford Point, but the usage of the United States Geological Survey and the local inhabitants sanctions the name Bluff Point.  This tombolo is free from vegetation and the debris lines indicate that waves wash over it during heavy storms.  It is composed of sand and pebbles, probably receiving its supply from the easting of Bluff Point, and Bushy Point, the latter being composed of moraine.  A good sized marsh is growing within the protection afforded by it, but as yet marsh material has not gained enough foot hold on the rear of the bar to obscure its origin as an open water farm.  The curve of Bushy Point Tombolo is very similar to that of the two Groton Long Point tombolos as its position in reference to its headland, these may be coincidences of no significance but it is more probable that they indicate the greater influence of waves coming from the South West, the quarter not protected by Fishers Island."


An examination of Mumford Cove just east of the Poquonnock River happened in 1981.  EPA organized the study to look at habitats that supported shellfish (See Appendix #3: Mumford Cove Shellfish Survey).


Also, in 1981, a Study of Coastal Embayments was undertaken by the staff of Anderson Nichols and Company Inc. titled "Connecticut's Embayments Study Phase I Inventory and Problems Analysis" funded by EPA and NOAA Federal agencies. 


Anderson Nichols' report deleted many of the coves and embayments - from the study on pg. 3.2 describes why and mentions railroad crossings among other conditions, including tidal flushing (my comments, T. Visel):


Groton -


"The estuaries of the Long Island Sound are fed by four drainage systems; Birch Plain Creek, Poquonnock River, Fort Hill Brook and Eccleston Brook.  The largest of the four drainage systems is Poquonnock River which includes the Groton Reservoir in its upper reaches.  The natural flows of these four systems have been disrupted significantly by railroad crossings and highways.


This is particularly true of Palmer Cove which is divided into three bodies of water by the solid – fill conrail causeways (this refers to the Poquonnock River as well, T. Visel) Tidal waters constricted by these linear structures are particularly subject to pollution problems.  Such problems are discussed in greater detail in this chapter."


Although coves and rivers were identified as seriously impacted by railroad causeways, many of these sites were deleted from the study. 


Not only did this prevent information from records and local resident inputs, it also ended any chance of federal funds to mitigate hydraulic displacement of shoreline flooding by railroad crossings – failed to identify many salt water habitats (marshes) that had lost all connection to the Sound, helped the spread of a coastal reed Phragmites, transitioned salt water habitats into those of lower salinity and prevented the movement of marshes (where possible) from sea level rise.  This was opposite previous causeway damage information developed by William Niering and R. Scott Warren in 1974.  On page 55, Tidal Wetlands of Connecticut (forward by E. Zell Steever) has this segment:  


"Historically, causeways represent one of the first major impacts of man, realizing that moving and firing of the marshes were probably practiced long before the construction of railroads and highways.  Of the 127 systems studied, 119 (or 94 percent) had their drainage patterns interrupted by one or more causeways.  A major rail line, Amtrak, crosses many of the marshes.  However, town and state roads represent the major impacts.  Although bridges or culverts are present, many are inadequate to accommodate natural tidal flushing.  In fact, many of these causeways have either reduced the productivity of the marshes behind them (Milford Harbor) or have resulted in replacement of salt marsh species by Phragmites.  In contrast, at Oyster River, Milford, a lobe of marsh cut off from the main system by a causeway except for a narrow bridge has been almost converted from patens high marsh to alterniflora.  This has apparently resulted from impoundment of salt water combined with minimal fresh water input.  This change in species composition has been documented from cores of the underlying peat.  It is of interest to note that the pile driven wooden bridge on Canfield Island Creek (Shorehaven Norwalk, west part) which permits full tidal exchange is reflected in a highly valuable marsh system."
Rationale for excluding certain coves from study is detailed on page 3.2 – Anderson Nichols' Report (1981):


"This study initially considered seven embayments for detailed analysis in this report.  Beebe Cove, Bennets Cove, Pine Island Bay, Poquonnock Cove (River?) and Bakers Cove, were dropped from the study for various reasons for example, the Beebe Cove circulation problem was relatively well defined and mitigation would have required modifying the railroad crossing.  Bennet (Beebe) Cove also was impacted by long term historical problems.


The problems of Pine Island Bay Poquonnock Cove (river) and Bakers Cove were already being investigated by the state or the town.  West Cove and Palmer's Cove were selected for further study in this report because they were subject to severe environmental problems, particularly sedimentation and tidal flushing."


Although Phase II 11-13 - Palmers Cove response identified severe tidal constructions (3 bridge/causeway systems) no apparent cost effective solutions for conditions that reduced tidal exchange were pursued.  On page 11 -2 is found this explanation:


"In other situations, only one option was evidently practical under existing environmental and/or economic constraints.  For example, many of the embayments experience constriction of flow and tidal exchange due to the railroad or highway causeways.  In this circumstance there is no feasible and cost effective way to alter the causeway form.  Reconstruction of a trestle, placement of culverts under the rail bed etc., would cost millions of dollars for each embayment, therefore a no action option was recommended as the only viable approach." 


In December 2020, the EPA released a report titled "Tidal Restrictions Synthesis Review" (EPA – 842 -12- R- 2001).  An analysis of US Tidal Restrictions and Opportunities for their Avoidance and Removal.  It is an excellent report and long overdue - my view, Tim Visel.


Tidal coves and salt ponds have unique habitat histories as they are subject to temperature and energy shifts.  These changes are noted extensively in the alewife and shellfish fisheries under broad terms of stagnation especially the chemistry of climate change in the composting of deep accumulations of organic carbon rich residues.  It is the waxing and waning of sapropels that happens in salt ponds and drowned river mouths.  In times of heat and reduced energy it is a time in which barrier spits close or sand bars are driven into embayments reducing tidal flushing.  The reduced exchange allows waters to warm and with organics (both natural and manmade) enter a chemical composting process.  This process is accelerated by low oxygen in warm water and the availability of sulfate compounds dissolved in seawater.  This composting process is facilitated by sulfate-reducing bacteria.  As part of this living process, these bacteria free hydrogen sulfide. This is the strong sulfide smells that occur in heat and low flushing. It is, at this time, when coastal residents complain of sulfides, or the "smell of rotten eggs." 


Mumford Cove has an interesting habitat history - in the 1950's, reduced circulation and entrance to the cove became restricted.  Dredging projects filled an area of salt marsh at the head of the cove.  This dredged material was regraded and or removed in the 1980's.  In this area, Widgeon grass reestablished (Dreyer, 1995, Connecticut College Bulletin #34).


The cove, since 1947, obtained effluent from a waste water treatment plant and was discharging 3 million gallons of effluent and suspended solids a day which ended in 1987.  In 1981, an EPA survey showed dense thick mats of Ulva sea lettuce blocked sunlight to bottom soils.  When thick mats were encountered and raked it produced strong sulfide smells (T. Visel personal observations – June, 1981).  Massive blooms of microalgae follow hot periods in which ammonia levels increased.  Residents of the cove mentioned heavy growths of sea lettuce and sulfur smells during the summer months.


One of the most famous write ups of this also comes from Boston, MA – "The Sea Lettuce Problems of Boston Harbor," C. N. Sawyer, 1965.  (The pollution of Boston Harbor would explode nationally during the 1988 presidential campaign).  The sulfide was so strong from the Winthrop section -north of Boston Harbor that it discolored lead-based paints (The use of lead in paint was banned in 1978).  In 1965, Claire N. Sawyer was the Director of Research, Metcalf and Eddy Engineers Boston Mass.  This paper was presented at the spring meeting of the New England Water Pollution Association in Groton, CT June 5-6, 1963.  The Association was first organized in April, 1929 at the Griswold Hotel in Groton, CT.  Claire N. Sawyer was later recognized as an individual, who helped water pollution with innovative concepts in 1976.  A segment of her 1965 paper is shown below - from Sawyer, 1965:


The Sea Lettuce Problems in Boston Harbor 


"Within recent years persons living near certain areas of Boston Harbor have been subjected to a new and highly undesirable odor problem.  This has been related to extensive growths of an aquatic plant commonly referred to as "sea lettuce" one of the area most seriously afflicted has been the town of Winthrop which located on a peninsula that hems in the northerly part of Boston Harbor.  The records show that Winthrop suffered from odor problems due to aquatic growths around the turn of the century.  Subsequently, however, Shirley Gut, a channel between the southern extremity of Winthrop became choked with sand during a severe storm and never reopened.  By the summer of 1961, conditions became so intolerable on occasion that home owners in some areas had to keep windows closed and some were forced to leave their homes to seek relief from the nauseous odors."


Many coves and river lagoons in New England have this habitat history – the blockage or restricted opening of tidal exchange.  It is in these habitats that eelgrass and scallops can exist at times together.  It is this relationship which gave observers the impression of mutual dependence – when in fact that is not always possible.  While it is true that bay scallops are very susceptible to sulfate metabolism – the purging of sulfide, eelgrass growths help that composting in shallow areas in hot seawater.  In fact, we are gaining information that similar to land (terrestrial) composting – marine composts often held by eelgrass contains a huge bacterial spectrum of pathogenic bacteria including vibrio species – gram negative bacteria and other species that reduce organic matter without oxygen.


This composting process, even under water, can generate heat.  In surveys of the Poquonnock River in the middle 1980's with a 10-foot aluminum pole easily penetrated 3 to 4 feet of eelgrass peat at the river channel mouth (T. Visel observations).  These surveys located areas in the lower Poquonnock basin that had been previously been hard bottoms.  The bacterial process in eelgrass peat are often describes as "biogeochemical recycling processes" (Pg. 85 North Carolina Fishery Management Plan Amendment 2, 2015).  Although the eelgrass was thick in areas, it was easy to observe that over time eelgrass had acted to gather organic material and hold it in areas near or adjacent to a current swimming area (T. Visel - Elmer Edwards Russel Nelson Shellfish Surveys, mid-1980's).  This area of the Poquonnock River was now a low energy "composting" eelgrass habitat.  Some hydraulic surveys in the area of the swimming beach (Poquonnock River town swim area) yielded dead hard and softshell clams buried under 3 feet of eelgrass peat and sapropel.  No bay scallops were observed and that had become the primary interest of the Groton Shellfish Commission.  A Sunday, October 18, 1987 Hartford Courant newspaper article by Tommy Hine outdoors reporter mentioned a decline of bay scallops (following a modest 1986 scallop season) titled "Scallops Season In State Is A Shell Of Its Former Self" and comments from the Groton Shellfish Commission "Don't buy a permit" said Ronald Chappell, Chairman of the Groton Shellfish Commission "There are no scallops here."  The scallop season opened in Groton, and it will remain open for just a month only because local regulations require that the season be opened once a year.  The season opened there Wednesday (October 14, 1987) but daily permits were not available to scallopers until late Friday.  The scallop season didn't close in Groton that year until Dec 1st:


"A sudden reduction in eelgrass vital in the early stage of development in the scallop life cycle has been blamed by many officials for the drastic decline in the scallop population in the Niantic River, home of the nationally famous Niantic Bay Scallop even though its home is a river, not a bay.  The same eelgrass theory, though, doesn't hold true for the absence of scallops in Groton.  "We have a tremendous amount of eelgrass" said Chappell, we don't have scallops, no one knows why "If someone knew, he would be a millionaire."  (The Hartford Courant, October 18, 1987)


The Poquonnock River has produced large scallop crops in the middle 1950's.  This period is known for its strong storms (hurricanes) and much colder winters (Norfolk, CT low temperature was reported at -37oF on February 16, 1943).  In conversations with Ron Chappell and Elmer Edwards, the catches from the Poquonnock River in the 1950's would exceed 30,000 bushels.  (T. Visel, personal communication).  In reviewing bay scallop catch reports (mostly from newspapers) after very severe storms or series of storms, bay scallop fisheries existed.  This is likely from storm movement of bay scallops (mostly seed) into shallow estuaries.  As long as it remained cold and nitrate remained high (primary nutrient for bay scallop forage algae), bay scallop harvests were good.  We have an unusual case history from Florida that seems to agree with the storm – larval trap with scallops.


In 2003, a cooperative project between The Mote Marine Laboratory, The Fish and Wildlife Research Institute and the Charlotte Harbor National Estuary Program (EPA) looked the larval trap concept of "Boom or Bust" Restoring Bay Populations In Florida."  In 2003, researchers developed a man-made larval trap in Pine Island Sound, Florida.  The project released scallop larvae but booms did not allow excessive larval dispersal.  By 2005, Pine Island Sound experienced a 100-fold increase in scallop production compared to 2004.  This happened during a storm-filled period, and the 2004 hurricane season had Hurricane Frances, Hurricane Charley followed by Ivan and then Hurricane Jeanne's.  


Energy is found associated in the South Carolina scallop fishery, following an immense winter kill of shrimp in 1977.  By the winter of 1978, an immense scallop bed was located 50 miles south of Charleston, SC.  North Carolina bay scallop history also has experienced this boom and bust landings – from a 1928 high of 1.4 million pounds of meats to a low in 1987 thought to be from a red tide bloom.  In 2004, the North Carolina harvest dropped to only 150 lbs.  Virginia's bay scallop fishery collapsed in 1930.  A 1933 (August 23rd) hurricane was reported to remove scallop habitat (eelgrass) in shallow waters.  We may find that colder temperatures and storms have a role in more fully understanding the boom and bust bay scallop reports in southern areas as well.      


Catches After Severe Storms Were The Highest 


Climate of Storms and Cold – may signal improved bay scallop populations. Below are noted some well-known storms.


The Blizzard of 1978


The Rhode Island and Connecticut scallop fisheries improve –
1979 Rhode Island good season 1980 – 10,000 bushels in Niantic River (The Day, April 6, 1981)
Bay scallops plentiful in Poquonnock River 
(Auster and Stewart Journal Northwest Atlantic Fish Science Vol. 5, pp. 103-104, 1984)


Hurricane Gloria 1985
The Rhode Island and Connecticut scallop fisheries improve 
1986 Bay scallop season 16,000 bushels Niantic River 
1987 Poor season in Niantic and Poquonnock Rivers 


Hurricane Bob – August 18-19, 1991
Bay Scallop season generally good 


Hurricane Irene and Sandy 
Bay Scallop season generally good in 2011 and 2012 after hurricanes
Season closed after 2012 – The Day, October 19, 2013 "Scallop Population Down: Season Scrapped"


The 2014 Season – Cold and Storms record snows 
Bay Scallop season was good – Niantic River sees plentiful scallop season after two-year drought, The Day, December 30, 2015


Between these storm events, bay scallops were few and seasons poor.  It is thought that from Northeasters and strong easterly winds transport seed scallops from Rhode Island to Connecticut.  It is colder temperatures and strong storms that pushed bay scallop seed into the shallows.  If it was cold enough to offset the shallow warming thermal effect bay scallops both adults and seed could survive and mature into a fishery.  But this was not the preferred habitat – it prefers deeper waters offshore of the coves to live between or hear high energy eelgrass/bars.  Deep water eelgrass could live in clear waters between sand bars in areas of slow currents.  They utilized eelgrass both as a breakwater and a signal for higher alkaline soils.  Eelgrass in high energy areas could not build a peat, organic matter residues could not collect, because coastal storms even in warmer climates did not allow it.  It is here that dredge fisheries could operate and the use of view boxes or spotters could be only used in very shallow waters of subtidal sand flats or the edges of salt ponds.  This gear type needed cold clear waters in which to catch scallops.


There is evidence that the development of view boxes and small ring nests happened because scallops in colder temperatures were in areas to shallow to dredge.  That history was detailed by Clyde MacKenzie Jr. in a segment of The Dukes County Intelligencer – Vol. 34, No. 1 – August 1992 about the shellfisheries of Martha's Vineyard.  In 1874 the scallop dredge came into use – this was following the bitter cold winter of 1872-1873.  From reports, bay scallops thrived and once considered a shunned or poisonous food, a fishery developed.  Here Dr. Clyde MacKenzie, Jr. describes the first hand-hauled dredge used in Edgartown on pg. 5:
    
"The drag had two straight arms made of iron connected by an iron blade 2.5 feet wide, fastened to the arms in hook and eye fashion, its net which held about a bushel and filled the space between the arms, had a wooden bar at the back to aid in dumping."


In the early 1980's, I would be given one of these very old blacksmith dredges by John Healy of Rhode Island.  At first, I thought it was a seed oyster dredge because it had a blade or bar and not chain.  I could also tell it was old by the chain ring bottom bay.  I used to use it for displays while at UCONN Sea Grant and currently can be found in the storage facility of the Connecticut River Museum but miss labeled as a seed oyster dredge I thought I had lost it but rediscovered it in 2014 in storage, see 109-B The Northeast Atlantic Oscillation and the Bay Scallop posted May 3, 2022.  This dredge was a light one as it was hauled by hand on hard grass free bottoms – and had a bar not a chain sweep.  I thought I had lost it but while working on the shad ring net project for the museum in 2014 found the scallop dredge.  I thought I had lost it in 1990 when leaving UCONN (See IMEP #123: The Historical Fisheries of the Connecticut River).  I had helped with a CT River Museum display and exhibit for Connecticut oystering and George McNeil in 1986 and never picked it up.  I was so glad to see it and have it in a museum – it was so much of the early bay scallop history and described in IMEP #52: Narraganset Bay Deep Water Bay Scallop Habitats of the 1870's, posted July 27, 2015, The Blue Crab ForumTM, Fishing, Eeling and Oystering thread.  (Although labeled as belonging to George McNeil, it was actually a blacksmith scallop dredge from Rhode Island, 1890.)


According to John Healy, these were hard bottom dredges and sometimes described as a "scrape."


As the cold intensified in the 1920's, this is when storms were casting up huge amounts of bay scallop seed into the shallows and in winter they would freeze and perish.  Efforts were allowed that moved small seed from shallows to deeper water to prevent this loss with hand hauled dredges.  What was not mentioned is that bay scallops needed the cold (and the storms as well) to sustain their habitats scallopers had the best catches when millions of bay scallops froze in winter ice.  In a newspaper article in the Barnstable Patriot Dec 6th 1973 by Peter Owens titled "Ranta's World" Peter Owens (from John Hammond, Chatham Cape Cod) part 3 – Scallops has this segment which includes habitat, climate and loss of seed (my comments, T. Visel):


"Their growth is rapid, but they remain vulnerable to destruction during its early days.  For the first several weeks of life, it is highly – vulnerable to storms, unusual tides, vast fluctuations in water temperature, and most end up being washed off shore to die.  Last year (1972, T. Visel) millions of seed scallops were destroyed in Barnstable Harbor by storms and adverse weather, a crop which could have led to a banner harvest this fall but which was lost in entirely."


Rhode Island reports huge increases in Narragansett oyster sets (1900's) while the bay scallop fishery of the 1870's was gone.  As the heat continued into the 1890's with some huge fish kills (including lobster in 1898) in its salt ponds and Narragansett Bay by 1910 bay scallops dropped from Rhode Island Shellfish annual reports until 1923.  This is an excerpt from The Annual Report Of The Rhode Island Commissioners of Shellfisheries – January session 1926 is found this section, Chapter 209 of The Scallop Fisheries, 


"We have probably had the largest crops of scallops during the fall season of 1923 ever known in the history of Rhode Island, at least not within the memory of the oldest inhabitant has such a fine crop, both in size and number been harvested as has been taken since the first day of September, and this in spite of the fact that the winter of 1922-1923 was one of the most severe that we have had in a number of years." 


And further,


"We attribute it somewhat to the fact that during the fall of 1922 permission was given the free fisherman to move under the supervision of our deputies seed scallops from the shallow waters inshore where they invariable area winter killed, to deeper water offshore, where the chances are good that they will survive the cold weather and become strong and healthy.  As we stated in 1922 report, about 3,000 bushels were thus moved."


In 1924, Rhode Island continues this program moving 67,000 bushels of seed scallops as reports of catches are listed as 300,000 bushels and most likely as high as 400,000 bushels. The climate was now much colder and strong storms more frequent.  The scallop fisheries increased as oyster setting declined, often as the same habitat or leased beds.  This was a massive climate-induced change, bay scallops that thrive in the coldest of winters died off in high summer "heats."  Oysters that do better in heat died back in the colder period after 1922.

Appendix #1

New London, The Day, November 11, 1889
Quiambaug Oysters
____________________
Fresh Water and a Hybrid Plant Has Destroyed Many Bivalves

Mystic Bridge, Nov. 11 – "The oyster crop in Quiambaug Cove this year is nearly a total failure. Of some 4000 to 5000 bushel of seed oysters planted last spring a good part are dead and the rest are very poor and watery, with the exception of a few that have been taken up and transplanted near the shore and which are in fair condition. The main trouble, as far as can be learned, is caused by a cabbage like plant* (as the growers term it), which grows over and entirely, covers the beds. It is also said the trouble is in part caused by the unusual amount of fresh water that has flowed into the cove the past spring and summer. A well-known Norwich oyster grower by the name of Church put in some 1200 to 1500 bushels of seed last spring. Despairing of their even fattening he came down about a week ago, dug up the whole lot and sorted them over. About half of them were dead. Church carried the remainder to Norwich and transplanted them, with the hope of their fattening up in time for market.


*Suspected to be sea lettuce (Ulva lactuca)"

Appendix #2

FAO TRAINING MANUAL ON BREEDING AND CULTURE OF SCALLOP AND SEA CUCUMBER IN CHINA

CHAPTER 1
STRUCTURE AND BIOLOGY OF SCALLOPS

• Argopecten irradians, the bay scallop, has a wide geographical distribution along the Atlantic and Gulf coasts of the United States. After being transplanted into China in 1982, the bay scallop gradually became one of the dominant species of scallops cultivated in China.
• Furthermore, heavier mortality occurs with higher culture density and bigger sized individuals.
• An unsuitably high culture density may be the main cause of mortality. The reasons are: (1) the scallops cannot obtain sufficient food; (2) a greater amount of metabolic waste is produced, the decomposition of which will consume great quantity of dissolved oxygen; (3) the products of decomposition, especially sulphide, are toxic to scallops; some experiments have shown that when the sulphide concentration reaches 0.3 ppm, the filtration rate of scallop is reduced by about 30 %, and at 0.7 ppm, feeding and respiration stop; and (4) the weak individuals in a crowded and adverse environment are susceptible to disease.
• Other important factors that cause mortality are high temperature and high density of fouling organisms.

Oceanology of China Seas – Volume 1, Edited by Zhau Di – Kluver Academic publishers
"The decomposition of fecal pellets of parent scallops, food debris and dead scallops by enculture bacteria as well as metabolic wastes may produce toxic ammonia. When waste materials are sedimented and oxygen in the tank is exhausted, toxic hydrogen sulfide is produced. Aeration serves to replenish oxygen in the water resulting in converting hydrogen sulfide into hydro-sulfate and at the same time restricts the growth of anaerobic bacteria, thereby reducing the production of toxic ammonia. Lowering the pH of the water can have a diluting effect on toxic ammonia."

Appendix #3 

"Gray Muscle Disease" of Scallops Identified

By Robert Ballou

Graduate Research Assistant

URI Marine Advisory Service

Maritimes, Pg. 14

May 1984

Commercial fishermen working off Nova Scotia and Nantucket first reported an incidence of sea scallops whose meats were flaccid and grayish.  Some of these moribund scallops were brought back to URI where they died when held in tanks under observation.  A follow up study found that 80 percent of samples collected from Narragansett Bay were similarly infected.
It thus appeared that the so-called "gray muscle disease" was fairly prevalent among the sea scallops in Narragansett Bay.  Had the disease pervaded the scallop population along the entire New England coast?  If so, a commercial fishery valued at over $100 million annually was at stake.  With major funding from Sea Grant, a cooperative research project was undertaken.  The study involved New Bedford scallop fishermen, the National Marine Fisheries Service, and a team of researchers from URI.
While Pei Wen Chang, professor of animal science, took on the task of identifying the organism responsible for the disease, Saul Saila, a URI oceanographer, handled the field sampling aspects of the study.  Tows were made with a scallop dredge in an area of Narragansett Bay where diseased sea scallops were originally found.  Surprisingly, only "clappers" – empty scallop shells still joined at the hinge – were found, indicating that the entire scallop population at the study site had been decimated.
Chang and his associates quickly determined that the culprit is a rickettsia-like organism, a type of bacteria usually transmitted by an arthropod and harbored in the gills and shell lining of the scallop.  It is believed that the parasite's interference with important metabolic functions of the gills leads to muscle degeneration and atrophy (gray muscle disease) and eventual death.
No evidence of either the rickettsial organism or gray muscle disease was found in offshore scallop populations in any of the samples, leading to the conclusion that the disease agent is a coastal phenomenon.
Some of these disease-free scallops have been tagged and transplanted to cages.  With the help of divers and a boat furnished by the Rhode Island Department of Environmental Management, the cages are being continuously monitored for possible disease recurrence.
The many-pronged approach adopted by the URI team successfully identified the disease-causing agent and effectively characterized the scallop mortality in Narragansett Bay as an isolated incident.  Most important, the study showed that – for the present, at least – the disease does not pose a threat to the offshore scallop fishery.