A report upon the scallop fishery of Massachusetts, including the habits, life history of Pecten irradians, its rate of growth, and other facts of economic value

Front matter

Glass.

Book.

®l)e C0mtitonroealtl) of itta05acl)U0ettB»

Chapter I. — Introduction

Dr. George W. "Field, Chairman, Massachusetts C ommission on Fisheries and Game, State House, Boston, Mass.

Sir : — ■ I herewith submit the following repoi't upon the life history and habits of the scallop {Fecten irradians). All investigations herein were made in accordance with the provisions of chapter 74, Resolves of 1906. The work was conducted by D. L. Belding, assisted by W. G. Vinal in 1907, 1908 and 1909, and by W. H. Gates and C. L. Savery in 1906.

Respectfully submitted,

David L. Belding, Biologist.

The following report embodies the results of the experiments and investigations conducted on the Massachusetts coast during the years 1905 to 1909. The facts discussed in this paper are intended for the inspection of three classes of readers : the fisherman, the consumer, and the scientific student, each accustomed to the daily use of terms with which neither of the otliei's is familiar. This circumstance, added to the fact that the subject-matter of the report is largely technical in character, renders it doubly hard to present the material in clear and comprehensive form. As the investigations were primarily designed for the benefit of the fisherman, the terms as far as possible will be those used by the practical seacoast inhabitants, while the report is arranged so that sections which are purely scientific may be omitted without impairing the value of the whole paper. Whenever a scientific or colloquial name is used in the text the common name is either given with it or a more complete definition is appended in the glossary.

The circumstances which led to the legislative act authorizing the investigation were briefly as follows : In the years previous to 1905 the scallop industry, while still an important source of winter revenue for the southern coast towns of Massachusetts, manifested signs of serious decline, especially in the Buzzard's Bay region. A natural resource of sufficient importance to bring into the Commonwealth a yearly revenue of nearly $150,000 could not be neglected, and the result was that the Legislature directed the Bepartment of Fisheries and Game to study methods of improving the scallop fishery. The laws which were at that time in force were based on very defective knowledge of the life history and habits of the scallop, and it early became apparent that a knowledge of these important points was essential for jjroper legislation for the conservation of the industry. It is earnestly hoped that an immediate result' of this investigation will be the passage of suitable legislation for the i^reservation of the scallop fishery.

Object. — The aim of this report is to publish all known facts about the life and habits of the scallop, and to show their proper bearing upon the present fishery. At the beginning of the investigation certain important questions of a practical nature presented themselves.

(1) Is the scallop supply of Massachusetts in danger of extermination? If so, hoAV can this be avoided?

(2) Is the present protective legislation based on accurate knowledge of the life and habits of the scallop?

(3) Can the scallop be propagated artificially?

(4) How can the present industry be increased?

In order to obtain satisfactory answers to these questions it was found necessary to obtain information upon: —

(1) The distribution and range of the scallop.

(2) The anatomy and its relation to the habits of the animal.

(3) The spawning, reproduction, early life history and propagation.

(4) The habits of the young and of the adult.

(5) The rate of growth and length of life.

(6) The scallop fishery, — its present extent and possibilities. Presentation. — Information on the above points, as comi^letely as

possible, is presented in the following pages, each topic in the form of a chapter; and the practical bearing on the four questions is considered whencA^er feasible under each subject, and is summarized in the general conclusion at the end of chapter VI. It is realized that there are various facts AA'hieh still require further study, and that it will take years of investigation to complete the historj- of the animal. The anatomical description in chapter II. is by no means complete. The object is merely to give the reader a general idea of the structure of the animal, and to make clear the more intricate development of the various organs as they appear in chapter III. No claim is made for marked originality or for detailed work in the chapter on anatomy; the general scheme given by Drew (1) is closely followed, and only a simplified description is given. Likewise, the embryology of all the lamellibranch moUusks have such a close similarity, not alone in the general course of development, but even extending in some cases to very minute details, that the description of any species might be applied equally well during its early stages to any other closely related species. Thus, although our work uiDon Pecten irradians was begun fo^^r years ago, and carried on entirely independently, and is, we believe, the only work upon this species which even professes to approximate completeness, its general features closely parallel the admirable work of Drew (1) upon Pecten tenuicostatus (the deep-sea scallop). Many of our results, therefore, are entirely new for Pecten irradians, and, since they confirm the earlier published observations on this and other species by Drew (1), Jackson (4) and others, to whom due credit is given, are of use not alone as confirmatory evidence; but since they contribute new observations and original applications of these facts to the practical solution of how best to develop and maintain our scallop fishery we trust that they are not without value. The life history is given in narrative form and is not explained in detail, as could be done by sectioning the developing eggs and embryos. As it is the purpose of this paper to present not only neAv material but also a rather complete account of the life and habits of the scallop, it has been frequently necessary to reprint or refer to previous works on the subject. In most cases these observations have been verified by our experiments, and are printed with the consent of the authors.

Courtesies. — At the start of the investigation in 1906 there was found a general lack of knowledge among the fishermen upon such important points as the spawning season, rate of growth and length of life of the scallops {Pecten irradians). Indeed, little literature on the subject was available, Kellogg (5), Jackson (4), Ingersoll (8) and Risser (2) compi-ising all publications on Pecten irradians. Of these, Risser alone dealt with the spawning, gTowth and length of life in his report upon the life history and habits of the scallops in Narragansett Bay, Jackson with the young scallojD, and Kellogg and Ingersoll with the industries. While the paper by Risser was of great as'sistanee at the start of the work, the diverse natural conditions in Massachusetts Avaters often rendered our results at variance, and unfortunately made this excellent report only valuable for comparative purposes. In addition to these publications the following papers proved of special value in the work: Drew (1) was of great assistance in studying the embryology and in preparing the chapter on anatomy; Jackson (4) furnished considerable help and useful methods in tracing the post-embryonic development; and Kellogg (6) was found a most comprehensive and valuable paper for general reference work.

The writer is. deeply indebted to Dr. George W. Field for his general supervision and helpful advice in the investigations and in the preparation of the report; to Prof. James L. Kellogg of Williams College, and Prof. Oilman A. Drew of Maine University for their kindly criticism; and to the scallop fishermen of Massachusetts for their friendly assistance. More especially is acknowledgment due to the assistants in the investigation. In the summer of 190G W. H. Gates and C. L. Savery ably assisted in the post-enibryological investigations and general gTowth experiments. During the summers of 1907, 1908 and 1909 W. G. Vinal, together with D. L. Belding, brought the embrj'ological and post-embryological work to a completion. The work of all three assistants, particularly the continued investigations by W. G. Vinal, is worthy of special commendation.

Methods of Investigation. — The greater part of the work on the scallop was conducted at Monomoy Point in the town of Chatham. Near the end of this point an enclosed body of water, some 6 acres in area, connected with the ocean by a shifting channel through which the tide joassed every twelve hours, Avas acquired by the State for experimental purposes. This body of water, called the Powder Hole, is a natural breeding ground for shellfish, and proved an excellent place to study their life history and habits. A few scallops were found in the Powder Hole at the beginning of the investigations; more adults were brought there for breeding purposes and the basin was transformed into a natural aquarium. In this way it was possible to keep close observation on several successive generations of scallops in regard to their growth and length of life under completely natural conditions. A small laboratory was erected on the shore, and a raft 20 feet long by 10 feet wide was securely moored in the deepest part of the cove. The raft proved an invaluable aid in catching and rearing the young, some of the most important experiments being conducted on it.

While Monomoy was the central station for the scallop work, observations were made in other parts of the State under as diverse conditions as possible. Records of the spaAvning, growth, migration and habits were kept at Edgartown, Nantucket, Chatham, North Falmouth, Marion and Monument Beach. In this manner the entire scalloping territory of the Commonwealth was under surveillance. Under chapter VII. the specific methods of work will be given in greater detail.

The Scallop Family. — The scallop belongs to the class of mollusks called the Lamellibranchia, or. to use an older nomenclature, the PelecypodM. The family of the Pectenidce includes a great many species, totalling' about forty, of which the most imjDortant commercially is the shallow-water variety, Pecten irradians. Of the four species found on the Atlantic coast only two are of commercial importance in New England, Pecten irradians and Pecten teniiicostatus, the giant or deep-sea scallop of Maine. These are rivals in the Boston market, but the smaller scallop is usually preferred by reason of its more delicate flavor. Several different species of the Pectenidce are used as food in other countries. Fossil Pectens have been found as far back as the Carboniferous age.

Names. — Pecten irradians is more commonly given as the scientific name for the shallow-water scallop of the Massachusetts coast, but the later and more exact title of Pecten gibbus, var. borealis Say., is now used. In New England the animal is ordinarily called by the name " scallop," sometimes Avritten " escallop." This word, according to Ingersoll (8), is derived from either the French " escallope " or the Dutch " schelp," meaning a shell. In Italy the scallop is called " cape saute," in Holland " mantels," in England " fan shells," " frills," " queens," and '' squims."

Distribution. — Pecten irradians has a wide geographical range, extending from Massachusetts Bay to the Gulf of Mexico, where it has been reported in the vicinity of the Chandeleur Islands in Louisiana by Professor Kellogg (7). It is occasionally found along the Atlantic seacoast Avherever the coast is sufficiently broken to afford sheltered bays and inlets. In 1880 Ingersoll (8) reports its presence in North Carolina, where it was used for local trade at Moorehead City. The scallop inhabits quiet waters, where it is protected from heavy winds and storms, which would wash it high on the sandy beaches. Long Island Sound is very productive of scallops, and many thousands of gallons are shipped from its waters in a successful season.

In Massachusetts this species occurs commercially only in the waters south of Boston (Fig. 78). It is usually found in abundance along the southern shore of Cape Cod, in Buzzard's Bay and about the islands of Nantucket and Martha's Vineyard. According to a map in the Boston Museum of Natural History a small bed formerly existed in the waters off Nahant. Shells are often picked up on the North Shore beaches, but at present no live scallops are found in this State north of Boston. It is reported that a few are to be found in some of the warm bays of the Maine coast. Thus the scallop fishery in Massachusetts is only a partial industry, as it concerns only the Vineyard Sound and Buzzard's Bay shore.

The bathymetrical range of the scallop is extensive, as many thousand acres of eel-grass flats, extending even to a depth of 60 feet of water, are covered at times with this bivalve. Usually the scallop is found in water from 5 to 30 feet deep. Scallops are often abundant on the high fiats where there remains but a foot or two of water at low tide, as on the Common Flats at Chatham. These exposed places with the thick eel grass seem to I'eceive the heaviest sets, but the young often jDerish in the cold winters. Scallops can arbitrarily be separated into two classes : (1) the channel or deep-water scallops, found in water 15 to 60 feet deep, and (2) the shallow-water or eel-grass variety, from low-water mark to 15 feet.

While the extent of the scalloping area is large, owing to the wide range of the animal, only portions are ever productive at any one time. A set may be in one place this year and the next year's spawn may " catch " in a diiferent locality. Thus, while all the ground is suitable for scallops, only a small part is in jDroductive operation each year. The natural barrier to the distribution of the scallop is the exposed nature of the coast, as this mollusk cannot live in rough waters.

Chapter II. — Anatomy

The loss of the anterior adductor muscle in Pecten, as shown by Drew (1) and Jackson (4), has been accompanied by a shifting of the soft parts, so that the antero-posterior axis, instead of running parallel to the hinge line, forms with it an angle of at least 60°. While this fact is recognized, for simplicity the relation of the hard and soft parts in the following description is considered as in a typical lamellibranch. The animal is oriented: (1) dorso-ventral axis or height, from the hinge to the opposite edge of the shell; (2) antero-posterior axis or width, the distance across the shell; (3) lateral axis or thickness, the distance between the two valves (Fig. 65).

The Shell. — The scallop shell consists of two lateral valves joined together on the dorsal edge, the hinge line (HIi), by means of a thin ligament. The two valves, which open on the ventral or lower edge, are nearly round and of equal curvature. The right or lower valve, on which the animal rests, is of a lighter and cleaner color and differs from the upper in having a byssal notch (B) or foot groove. In the scallop less than a year old this notch is lined with several projecting teeth, which are absent in the old animal. If the shell of an adult is broken along the notch a row of thirty-five or more of these teeth can be seen extending back to the umbo. The adult scallop is somewhat wider than high, the average dimensions being: height, 2% inches; width, 2% inches; thickness, l%o inches.

On the outer surface of the shell are prominent ridges and furroAvs (R, F) which radiate from the beak to the free margin, giving the animal a beautiful fan-like appearance. The number of ridges does not vary in the individual scallop, the adult having the same number as the very young animal. In different scallops the number of ridges varies from 14 to 19, the average being 16. Crossing the radiating ribs are concentric growth lines, which almost show the daily accretion of the shell. Age and wear cause these to be less conspicuous toward the beak and on the lower valve. During the winter months growth ceases and when again resumed in the spring, a heavy line has formed by the thickening of the edge of the shell, comparable to the annual ring of a tree. This is the so-called growth line, which defines a '' seed " or immature scallop. Such marks may not always represent the end of the season's growth, but may indicate that unfavorable conditions for a certain length of time checked the building processes of the animal. When scallops were transplanted from Inward Point to Monomoy Point, being confined several days, the change caused a mark similar to the annual growth line.

In old age these growth lines may pile up and form a very slight re-entrant in the shell, due to retrogressive development. The re-entrant is not so conspicuous in Pecten as in other lamellibranchs which have a thicker shell. If the edge of one valve is broken, the opposite valve grows down abnormally to protect the soft parts. Both valves are needed in place to get a normal growth in the same manner as rodents require both sets of incisors to wear on each other.

Besides these markings the outer surface of the shell may be engraved by various enemies. The oyster drill often punctures a small hole in the shell and through it sucks out the soft parts. The boring sponge does not attack the scallop as frequently as it does the oyster and other mollusks which lead a sedentary life, but occasionally parts of the shell are dissolved by the secretions of the sponge. In the older scallop of fifteen months the upjDer valve is usually covered with various forms of life, such as Serpula (worm tubes), barnacles, young oysters, Anomia (silver shells), Crepidula (quarter deckers), Acmeea and such sea weeds as Enteromorpha, Ulva and Champi parvia. Many old scallops are doubtless killed by the accumulation of foreign growth, which at times fastens the valves together.

The inner surface of the shell is very smooth and somewhat vitreous, due to the nacreous or pearly material secreted by the mantle. The ridges and furrows exist but are not conspicuous. The scar, which marks the attachment of the adductor muscle, can be seen indistinctly outlined slightly to one side of the center of the shell.

The hinge line (HH) is curved in most lamellibranchs, but in Peeten it is straight, and extends to the end of the well-developed " ears." A V-shaped spring in the central part of the hinge tends to keep the valves apart after the same manner of doubling a large piece of rubber in the hinge of a door. When the animal is at rest the large adductor muscle is relaxed and the valves remain open.

The calcareous shell is formed by the secretions of the mantle. Although it is added to slightly by the surface of the mantle, the main inci'pase is in height and width at llie edge of tlie mantle. These two secretions differ in structure; the inner pearly or nacreous portion being' formed of thin layers, the outer of prisms. The valves increase in size as the direct consequence of the increase in size of the soft parts.

The shell is well adapted to the life of the scallop. Being light in ■weight it is suitable for moA^ement through the water, while the rounded outline is the form which offers the least resistance for swimming. The opposite ridges and furrows fit tightly together when the valves close. Thus, when the animal moves, streams of water are forced by the aid of the mantle through the small openings below the " ears," or from the ventral edge of the shell.

The Mantle. — The shell of the scallop is lined with a thin ciliated organ called the mantle (Fig. 73, m). The thickened margins of the two mantle lobes are free ventrally but are united dorsally and to a slight extent on the anterior and posterior ends in the region of the " ears." In a scallop of 52 millimeters the mantle lobes are united posteriorly for 13 millimeters and anteriorly for 6 millimeters. This corresponds roughly to the width of the " eai's " of the shell, 12 millimeters and 6 millimeters respectively. The shorter union anteriorly pei'mits the extrusion of the foot. The free edge of the mantle, often brightly pigmented, jjossesses tentacles (t) or tactile organs, and beadlike eyes of a bright blue color. These sensory organs are not so numerous or so large near the byssal notch and the corresponding posterior edge. Each lobe of the mantle is attached to the inner surface of the valve about one-half inch from the free edge. The broad face of each lobe rests on the inner surface of the shell except when the animal is disturbed and the mantle withdrawn by the retractor muscles. While resting, the mantle lobes are held slightly apart, the guard tentacles forming a lattice work between the perpendicular flaps of the mantle through which the water passes. As previously stated, the mantle also functions in the formation of the shell.

Tentacles. — The sense organs of the mantle are of two kinds, tentacles and eyes. There are numerous tentacles near the free edge of the mantle, which vary greatly in size and formation. These tentacles can be divided into two classes, (1) the mantle tentacles, which are situated on the external edge of the lobe in several rows, and (2) the guard tentacles, situated on the edge of the perpendicular flap of the mantle, 5 to 6 millimeters from the edge. Each class differs in form and function; the mantle tentacles are larger, capable of greater extension and contraction, and armed with papillary projections, while the guard tentacles are smaller, less extensible and of a bright color. The tentacles have a sensory or tactile function, and when the scallop lies undisturbed, the mantle tentacles, lengthening out, wave slowly in the currents of water. They can be withdrawn immediately at the passing of a shadow or at any slight distxirbance in the water. When contracted each forms a slight conical projection.

Eyes. — Situated between the band of tentacles and the outer edge of the mantle are many well-developed eyes, brilliantly lined with bine and brown pigment, which help to make the scallop attractive to snmmer colonists. When sectioned, these eyes are fonnd to be specialized organs eomjj arable to the eyes in the higher animals. They vary in size and nnmber, the larger ones usually occupying the grooves of the shell, although in the adult definite arrangement appears to be lacking. To what degree the eyes react to light and to external stimuli is problematic, and offers a field for research. They ajapear to be keenly sensitive to any change in light and shade, possibly observing the approach of an enemy by its shadow or movement in the water.

Muscles. — Unlike the soft clam (Mya) and the quahaug (Venus), which have two adductor muscles for closing the shell, the scallop has only a single adductor muscle (the so-called eye in the fisherman's vernacular), which is situated posterior to the center of the shell, forming a conspicuous part of the internal anatomy. The muscle is made up of two parts, a large anterior section and a small posterior division. As is shown in the development of the young scallop, this muscle is the posterior, the anterior adductor disappearing during the early shell stage. The' muscle is the edible part of the scallop^ and its shape is maintained when served on the table as " fried scallops." When the muscle is cut the valves immediately gape open, being forced apart by the V-shaped cartilaginous elastic pad in the middle of the hinge. The other important muscles are the retractor muscles of the foot, the gills and the mantle.

Gills. — There are four gills (Fig. 74, g) in the scallop, a pair on each side of the generative mass and ventral to the adductor muscle. Each pair has a free end posteriorly and extends in a curved line nearly around the posterior adductor muscle. The gills are attached dorsally near the adductor, the inner and outer gills having a common membrane. Each gill is made up of two lamellas of radiating filaments. Pine markings cross the filaments at right angles, thus giving each lamella a delicate lace-like appearance.

When a few grains of carmine powder are sprinkled on the gills the small grains pass to the base of the gills and then move toward the anterior end in a definite channel. This movement is due to the cilia between the filaments, which cause the grains to pass toward the mouth. The work of the gills is not only to strain out the food but to aid in resijii'ation. The impure blood flows into the capillary spaces of the gills, where the delicate membranes are bathed by the inflowing water, and, having acquired a new supply of oxygen, passes back to the heart. The area is increased by the folding of the lamella. If stimulated, thegills contract immediately, shoAving that iliej joossess a nervous mechanism.

Palps. — Just dorsal to the gills on the borders of the mouth are two pairs of delicate filaments similar in structure to the gills. These organs are the labial palps (Ip), which correspond to the lips of higher animals and function in conducting the food to the mouth. The central portion of these lips, which extend laterally for a distance equal to the thickness of the animal near the umbo, has arbor-vitas-like processes, concealing the mouth. The flaps which extend on each side of the branching area are united to the body dorsally and posteriorly, leaving the other edges free. The exterior surface is smooth, while the internal surface is covered with ciliated ridges and furrows which aid in conducting the food from the gills to the mouth.

Digestive System. — The digestive system of the scallop is comparatively simple. The mouth opens into a short oesophagnis or gullet, which leads into a gourd-shaped stomach (s). On the posterior end of the stomach is a curious hard socket into which fits the tip of a translucent gelatinous rod, the crystalline style. This rod extends along the intestine in a sort of pocket or groove as far as the lower part of the visceral mass (Fig. 75, vm). The stomach is enveloped by a dark-brown mass, connected with it by two short canals, one on each side. This large conspicuous organ is the digestive gland or "liver" (1), and "is only bounded in the region of the stomach by the sexual gland on its ventral surface." Kellogg (6). The liver (1) sends secretions into the stomach to aid digestion. The food is caught up as soon as it leaves the stomach by the eiHa of the intestine (i), which forms a double loop in the visceral mass (Fig. 76, vm). It then passes in a dorsal direction through the liver, curving posteriorly to pass through the heart, and finally ends posterior to the ventral portion of the adductor muscle.

Circulatory System. — The scallop has a blood system passing over the whole body and through the gill filaments, where the blood is aerated. The heart (ht), a three-chambered organ, is situated in a pericardial cavity dorsal to the adductor muscle. The intestine passes through the pericardium and is surrounded by the ventricle of the heart. The auricles are two filmy bodies connected with the ventricle. From the heart arise the different arteries which conduct the blood to all parts of the body, whence it is returned through the venous system to the sinus venosus, from there to the gills, and finally back to the heart.

Nervous System. — The nervous system of the scallop is complicated, and the animal is highly sensitive in all parts, especially in the region of the mantle, through the circumference of which passes a large nerve connecting with the tentacles and eyes. Several ganglia lie in the region of the mouth, foot and visceral mass. From these, numerous nerves pass to the various parts of the body.

Excretory System. — The kidneys are a pair of yellow-colored organs in the form of sacs, encircling the anterior part of the adductor muscle. These glandular organs open into the mantle chamber above the gills, where thej are joined by the openings of the reproductive organs.

Foot. — The foot (f ) of the adult scallop is a small muscular organ extending from the upper part of the visceral mass dorsally for about a quarter of an inch. It is nearly cylindrical, with a deep groove on one side and a hollow, sucker-like disc on its distal end (Fig. 42). It has a slight twist which places the cleft portion in juxtaposition to the right valve, instead of on the ventral border. This is of use to the young in crawling, as the sucker can be put down evenly on the surface without a twist of the foot to hinder the retraction. Jackson (4). The function of crawling is only for the young, and the adult has either lost the power of locomotion through degeneration or at least does not make use of it. A byssal gland (bg) is on the proximal end of the foot, and secretes the bundle of threads by which the moUusk anchors itself to various objects, as described under " Attachment " in chapter IV.

The Reproductive Organs. — The generative organs comprise a large share of the soft parts of the scallop, and lie, surrounding the folds of the intestine, in the lower portion of the visceral mass. The surface of this mass, which terminates bluntly some distance below the large adductor muscle, is usually covered with a black glossy pigment, which is especially noticeable previous to and during the spawning season, when it completely hides the bright color of the egg sac. Both the male and the female organs are found in the same scallop, whereas in P. tenuicostatus, the giant scallop of the Maine coast, the sexes are separate. Drew (1).