Ecology of Sheepscot River Estuary

SPECIAL SCIENTIFIC REPORT-FISHERIES No. 309

UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE

United States Department of the Interior, Fred A. Seaton, Secretary Fish and Wildlife Service, Arnie J. Suomela, Commissioner

ECOLOGY OF THE SHEEPSCOT RIVER ESTUARY

Alden P. Stickney Fishery Research BiolOgist Bureau of Sport Fisheries and Wildlife

Special Scientific Report- - Fisheries No. 309

Washington, D. C.

May 1959 Librarr cf Conpress cat log curd fo~ his! ublica ion:

Stickney, Alden P Ecology of the. heepscot Hi\' r (' tlWI'.\ ,Ya hina1011. T. . D pt. of th Int rio!', Fi h nnd Wildlifl' , Pl'vicf', JI ;,0.

iv, 21 p. llJu" map, flill!:r.. :!7 I'lIl II '1111 "'( 'nldi filII rI II her! ,no. 3(YJ) Bibliography: p. 20--21.

2 Ecolo::(v - ~[nlnp -:11 ' nlv r. I Title. (:-:; rles: C, f 1"11 IIrlli Wllellle, n In', In) I n Illc report-Il . herle , no 3tY.))

lnt ,j!)-~ 4

U. . Dept. of th 1 nterlM. Llhr ry for Library of ongre.·

Library of Congress catalog card for the Fish and 1; 'ildlife Service serial, 3pecial Scientific Report--Fisheries'

U. S. Fi8h and Wildlife Service. Special scientific report: fisheries. no. 1- (Washington] 1949-

no. iIlus., maps, dlagrs. 27 CIll. Supersedes in part the Service's Special sclentific report.

1. Fisheries-Research.

SH11.A335 639.2072 59-60217

Library of Congress

i1 CONTENTS

Page Introduction ...... 1 Methods and materials 1 Geography .... 1 Hydrography . . . . 3 Bottom sediments . . 6 Tides and currents 6 Plankton ..... 9 Other populations . . 9 Summary ..... 13 Literature cited . 20 Acknowledgments 21

ABSTRACT

Three Fish and Wildlife Service and three State of Maine organiza tions collaborated on a comprehensive study of the ecology of the Sheep scot River estuary. This paper gives background material to introduce papers to follow by describing the physical, and biological characteristics of the estuary: Its geography, hydrography, bottom sediments, plankton com position and distribution, and higher animals and plants in the several habitat zones. Lists of the common aquatic animals and plants are included.

iii Tidal falls at Sheepscot Village. Top: From an old photograph (circa 1900) showing one-time dam and tide gates. Tide is flooding. Bottom: Appearance of the falls at the present time. The view is ~rom a lower elevation. Tide is ebbing.

iv ECOLOGY OF THE SHEEPSCOT RIVER ESTUARY

In 1954 the Atlantic salmon research of (Oxner, 1920) and, where less accuracy was the U . S. Fish and Wildlife Service was oriented permissible, by means of specially calibrated to include a study of the ecological complex in a hydrometers. Temperatures were taken with a salmon river and its estuary. The project has mercury thermometer directly in the sampling been coordinated with the regular activities of bottle. ,As the time required to raise the bot State and Federal agencies concerned with the tle from the deepest water sampled was only a study of certain estuarine species and has been few seconds, change in temperature within the concentrated in a single river, the Sheepscot, bottle was disregarded. near Boothbay Harbor, Maine. Plankton was collected by two methods: Cooperating on this project are the Clam vertical hauls from bottom to surface with a Investigations, the Atlantic Herring Investigations, 1/2 -meter #2 silk plankton net and four -minute and the Atlantic Salmon Investigations of the U.S. surface tows with a Clarke-Bumpus plankton Fish and Wildlife Service; and the Department of sampler equipped with a # 10 silk net. Currents Sea and Shore Fisheries, the Department of In were measured according to a method described land Fish and Game, and the Atlantic Salmon by Pritchard and Burt (1951), in which a weighted Commission of the State of Maine. current cross is suspended at various depths and the wire angles resulting from the drag of The Sheepscot River was selected as a the current are measured to compute the direc suitable study area as it was convenient to a well tion and velocity of current. equipped fishery laboratory in Boothbay Harbor where personnel of four of the cooperating agen Fish were collected by means of gill nets cies were stationed; in addition, studies were and seines of several sizes, traps, fyke nets, already in progress on several economically and a small otter trawl. Intertidal invertebrate important species in that area, such as herring, populations were sampled by removing a 0.1 M2 alewife, smelt and clams. quadrat from the sediment to a depth of 10 centi meters. The material was then sieved through The Sheep scot River itself is not an im a 14 x 16 mesh-per-inch plastic screen. Sub portant salmon stream, but it does support tidal populations were sampled with a 0.1 M2 small natural runs of these fish and is regularly Petersen -type grab and similarly sieved. These stocked with hatchery-reared young. procedures were supplemented by numerous field observations and hand collections. A The purpose of the present report is to counting weir was constructed near the head -of give a comprehensive description of the study tide in the river to obtain information on the area to provide a background for other more movements of salmon and other anadromous fish. detailed reports covering specific problems. Stomach analyses were made on numerous fish It will also serve to complement the report of and some birds to aid in the study of certain Bryant (1956) which described the fresh -water food relationships. part of the river. Geography Methods and materials The Sheep scot River is a stream of mod A series of stations was first established est size !!which originates in the low uplands where regular observations were to be made, between the Penobscot and Kennebec valleys and (fig. 1). Water samples were collected at these flows generally southward to the Gulf of Maine. stations with a Kemmerer sampling bottle. Salinities were determined by titration with ij A description of the river proper may be silver nitrate according to Knudsen's method found in Bryant, 1956. See list of literature cited.

1 SCALE

o 2 3 4 NAUTICAL MILES

GULF OF MAINE !

Figure 1. - -Outline chart of the Sheepscot area showing the locations of principal geographic features, water masses, and sampling stations (numbers in circles).

2 Where it intersects the coastline it forms a deep, being greatest at the time of the spring thaw in narrow embayment superficially resembling a April or after heavy rains, and lowest during fjord. The valley, however, is river cut rather August and September. The salinity of the than glacier cut (Johnson, 1925) and has no sill estuary varies accordingly. at its seaward end. It is a typical submerged or "drowned" river valley. The size of this Tidal variation in salinity depends on portion of the estuary relative to the size of the the stage of the river and the particular locality, river itself is so large that it is not, strictly but fluctuations between high and low tides often speaking, an estuarine environment. For the exceed 15 0/00 in much of the upper estuary. purposes of this discussion, therefore, it will Seasonally, at a given location and tidal stage, be referred to as the lower estuary and distin salinity varies by about 15 to 20 0/00, as can guished from the upper or true estuary, which be seen from Station 13 in fig. 3. occupies a shallow valley about five miles long from the river mouth to the upper end of the In comparison, the lower estuary is lower estuary. The town of Wiscasset, Maine characterized by: deeper water, smaller tidal and the U.S. Route 1 highway bridge form a exchange ratiO, higher and less variable salinity, convenient dividing line between the two. and a narrower range of temperatures. Dilution by the Sheepscot River is rapidly attenuated be The lower estuary ranges from about 60 low Wiscasset and is hardly distinguishable five meters in depth at its seaward end to about 20 miles south of that town where, due to the nar meters at its upper end. For the most part its rownes s of the basin, swift currents mix the shores are steep and rocky. The upper estuary diluted surface water with the highly saline deeper is much shallower, with a channel from 1 to 10 layers. The mixed water extends southward to meters in depth at mean low water and bordered the region opposite the entrance of the Sasanoa by extensive mud flats and salt marshes. About River near Station 3 where the surface water is midway along this upper estuary at Sheepscot again diluted by an influx of low salinity water Village is a constriction between two headlands from the Kennebec. The area thus influenced where a transverse ledge of rock tends to hold extends southward along the western shore of back the water above it, creating a waterfall on the lower estuary to the Gulf of Maine. the ebbing tide. At one time a mill dam was erected at this site. There are other constric Below a depth of ten meters water of tions at several places in the estuary where rather uniformly high salinity extends the entire currents are rapid but without falls. There are length of the lower estuary. Fig. 2 shows the two major tributary branches to the upper estu vertical distributions of salinity on a longitudinal ary: Marsh River and Dyer River. Both are section of the estuary from the Gulf of Maine to largely tidal but are fed by streams. Wiscasset as it appeared on a typical spring day (showing the effect of the spring runoff) and on As can be seen in fig. 1, the lower estuary a typical summer day. Seasonal salinity trends is a complex affair of interconnecting channels are shown in fig. 3. including one, the Sasanoa River, which connects it directly with the nearby Kennebec River. There ace pronounced horizontal and vertical temperature gradients in the estuary, Hydrography particularly in summer. There are also seasonal and tidal variations, which are strongest in the In contrast to the lower estuary of the inner estuary or in other places where the water Sheepscot, the upper estuary has these char is shallow and protected. The greatest thermal acteristic features: shallower water, greater stratification occurs from mid-April to Septem tidal exchange ratio, lower and more variable ber' although during this period intermittent salinity, and a wider range of temperature. The mixing by waves, wind and current may partially upper estuary shows the effects of the river very dissipate it. After September the mixing over noticeably at all times of the year. The river comes any surface warming and temperatures discharge varies from about 20 to over 1000 cub are nearly uniform at all depths, although during ic feet per second during the course of a year, the coldest part of the winter the surface water may be somewhat cooler than that at the bottom. 3 :I: 0 ~ 0~ a: ~ 0 N Z

0 \(') ~ 0 If) If) \(') N If) 0\ 0)

U> 0 0

~ ~ c:{ :::> ~ -,

S~313~ o o o o o o o N ,..., 10 o o ~ N ~ 10

Figure 2. --Longitudinal section of the lower Sheepscot estuary from the Gulf of Maine to Wiscasset showing the distribution of salinity on a typical spring day (maximum river influence) and a typical summer day (minimum river influence).

4 S~L1 NITY

% 0 25

20 l / "\,:\ , \ , \ I 15 ~ I \ I STATION 13 \ , \ , \ I 10 ~ \ , \ I \ I 5 . 'J

30 \ \ I STATION 7 \ I \ I \ I CJl \ , "

25 STATION 3

ASONDJ FMA A S 0 S 0 1954

Figure 3. - -Seasonal salinity trends at four stations in the Sheepscot estuary. The lower curve in each pair represents surface salinity; the upper curve, bottom salinity. At Station 13 surface salinity only is shown. Dlshed portions indicate diversions from the normal trend occasioned by a January thaw and a heavy rain. Vertical temperature distributions on a longi to the low. The reverse is true under certain tudinal section of the lower estuary on a typical conditions, as in the case of the marginal flats summer and a typical winter day are shown in between grass marshes and tidal creeks with fig. 4. fast currents.

The interior water at Station 7 and above Silt is the predominant sediment in most is cooler from November to March and warmer intertidal areas, however, and large quantities from March through October than the water of of it are stirred into suspension with the flood the lower estuary. During the warm summer of ing tide to be redeposited on all exposed surfaces. 1955, the water temperature at Station 13 re Intertidal sediment'S also contain much organic mained above 20° C for about a month and a half debris, mostly sawdust or fragments of marsh and above 15° C for more than three months, grass (Spartina). while at Station 1 the temperature exceeded 15° C for only a month and a half. The seasonal temp Tides and currents erature trends at four stations for a two-year period are shown in fig. 5. Below the falls at Sheepscot Village the mean tidal range is 9.5 feet, decreasing to 8 .9 In winter, ice forms in protected places feet at the extreme seaward end of the estuary and where the water is brackish. The upper (U.S. Coast and Geodetic Survey data). Above estuary above the junction of Marsh River is the falls the mean tidal range is about 6 feet, sometimes nearly completely frozen over. there being about a 3 -foot drop in water level over the falls at low tide. The tide continues to Bottom Sediments ebb in the estuary above the falls for a little over two hours after it has begun to flood below. Thus Detailed studies of the bottom sediments the duration of the flooding tide above the falls is of the estuary have not been made, but some in only about four hours, while the ebb lasts about formation is available from U. S. C. G. S. charts, eight. Petersen -type grab samples, electronic fathome ter records, hand sounding lines, intertidal The inner estuary has a very high ex samples and trawl and dredge samples. change ratio, that is, the relationship of the volume of water entering or leaving during the Most of the bottom is covered by a muddy tidal cycle to the total high tide volume of the sediment composed largely of silt with some basin. This exchange ratio averages about 0.7, fine sand and clay, as well as organic detritus. and results in swift currents and extreme tidal Of the latter component, sawdust from numerous fluctuations in salinity. now defunct sawmills is often a prominent fea ture. Much of the organic material may also be Currents in the estuary have not been derived from leaves, twigs, seeds, and other studied in detail, but have been measured over a terrestrial plant remains which lie in profusion complete tidal cycle in a few localities. By mak on the bottom. In the narrower parts of the ing a few reasonable assumptions it is possible lower estuary and in much of the upper estuary, to deduce a general picture of circulation patterns. where currents are strong, the bottom sediments contain a large fraction of sand. Numerous and Between the Sheepscot and Kennebec sometimes extensive outcrops of bedrock inter estuaries is a system of shallow bays of irregu rupt an otherwise relatively smooth bottom. lar contour with three principal outlets: one (Sasanoa River) into the Kennebec; one into the Most of the intertidal area is either rock Sheepscot near Station 3; and one into the Sheep or mud-flat. Sandy or gravelly flats are rare scot near Station 7A. On the rising tide, water except for a few exposed beaches near the sea enters the system from the Sheepscot through ward end of the lower estuary and some small the two latter channels and leaves on the ebb. sandbars in the upper estuary. Intertidal flats Water from the Kennebec enters through the usually show a zonation of sediments ranging Sasanoa on the ebbing tide and, mixed with the from coarse to fine from the high water level other water present, passes into the Sheepscot.

6 ::I: I-a:: 0 0 z CD II') II') en - 0,.... &I') II')

0 en II) :r: 0 0 <..> .. a::: ct ~ 0 ~ It) :::>..,

CD en t&.I ..J 0 It) If) It) 2

I ~ :::> S~313~ 0 S~]13" If)

0 0 0 0 0 0 0 0 0 0 .., It) C\I ,.., It) C\I • • Figure 4. -- Longitudinal section of the lower estuary showing the distribution of temperature on a typical winter day and a typical summer day. 0

(/)

, J \ \ ID J ~ 10 171 ~

14-

a z

(/) \ \ ct \ , ., 10 \ 10 \ , .., (7) ~ ct

14-

a z

(/)

•10 ct(7) .., .,

<> • Figure 5. - -Seasonal temperature trends at four stations in the Sheepscot estuary. Solid lines indicate surface temp eratures; dashed lines, bottom temperatures. Current observations at Station 3 indicate Phytoplankton blooms occur from time to that water drains out of the Sasanoa system for time, some extend in from the Gulf of Maine and about an hour after the tide has begun to flood in others are local populations inside the estuary. the Sheep scot, producing a swift surface current Diatoms of several species, chiefly of the genera with an easterly set. The peak current from Thalassiosira, Thalassiothrix, and Chaetoceras this source occurs about three hours after high appear in the spring, mostly in the most seaward tide with the same direction at all depths. Dur parts of the estuary and outside it. Skeletonema, ing the last three hours of the flooding cycle, Asterionella and Rhizosolenia appear during the the dominant component of the current flows summer, often in local concentrations within the northerly up the Sheepscot while a lesser estuary. Coscinodiscus (several species) is westerly moving current flows into the nearly always present. Sasanoa system. The latter component is strongest in the deeper layers. Ceratium tripos, C. longipes, C. fusus, and one unidentified species are the most abun Plankton dant of the dinoflagellates but several species of Peridinium are common. Bigelow (1924) has Plankton sampling was done with the ob described the phytoplankton populations of the jective of providing general information about Gulf of Maine and the times of seasonal maxima, the abundance, composition and distribution of and the observations made in the Sheepscot agree plankton stocks in the estuary at different times in general with his account. of the year. Although plankton was sampled regularly over a two-year period at approxi The abundance of all plankton decreases mately monthly intervals only, some generaliza during the winter and early spring from November tions for the purpose of this report can be made to May. With the exception of a substantial in without much risk. crease in the local population of Acartia late in the summer and occasional local diatom blooms Volumetrically the plankton consists pre the plankton abundance diminishes as __one pro dominantly of copepods. Cladocerans, diatoms ceeds up the estuary. The plankton of the upper and dinoflagellates also make up suhstantial por estuary contains scattered elements from the tions of the total volume at certain times. Four more seaward regions and several species that characteristic species of copepod predominate: are indigenous to the area, e. g. Acartia longi Pseudocalanus minutus, Acartia longiremis, remis, Eurytemora herdmani, the nauplii of the Oithona similis, and .Microsetella norvegica. brackish water barnacle Balanus improvisus, The last occurs chiefly during the winter months and numerous mollusc and worm larvae. Marine and is most abundant near Station 3. Other and estuarine plankton can be found as far into common species of copepod are Eurytemora the estuary as any salt is detectable. Harpacti herdmani, Centropages hamatus, and Temora coid copepods (except for .Microsetella) are longicornis . more common in the plankton of the upper estuary than that of the lower. PelagiC larval stages of non -planktonic species are abundant seasonally: pluteus larvae Plankton abundance may vary from year of brittle stars (Ophiuroidea), barnacle nauplii, to year as can be seen in fig. 6. There also crab zoeae, and worm trochophores in spring may be variations in its taxonomic composition. and early summer; bivalve veligers and various worm larvae in middle and late summer. Larg Other populations er planktonic species were often taken in the hauls made with the 1/2 meter net, but these Important environmental variables exert (mostly medusae and ctenophores) were not ing an influence on the biota in the Sheepscot specifically identified. The jellyfish Aurelia estuary are temperature, salinity, tides, depth aurita and Cyanea arctica are abundant in the of water and the nature of the substrate. Com early part of the summer, the former often binations of these variables create a variety of appearing in dense concentrations. environments or habitats, differing enough in

9 1955 1.0

- 0.8

0.6

0.4

0.2 III I 00 • •• 1 ••- 1.4

1954 - 1.2

1.0

- 0.8

0.6

0.4

0.2 I I I ... STATION I 3 5 ' 7 I 3 5 7 I 3 5 7 I 357 I 3 5 7 I 357 JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER 0= No sample

Figure 6. --Comparison of plankton volumes (displacement) in milliliters per cubic meter taken at four stations in the lower estuary during the summer and fall of 1954 and 1955. Volumes are computed on the basis of vertical hauls from bottom to surface made with a 1/2- meter #2 silk net.

10 some cases to be distinguished from one another impounded the tidal water above it, and excellent as separate faunistic regions. For example, sets of oysters are said to have occurred there between the deep, cool, saline water of the lower each year. The maintenance of the oyster popu- estuary and shallow, warmer (in summer), 1ation is dependent, among other things, on fresher water of the upper, the physical differ favorable temperatures for spawning and larval ences are very noticeably reflected in the faunas. survival. With the high tidal exchange ratio in The number of species is far greater in the the upper estuary, more than half of the oyster lower estuary, even when an area of a size com larvae in the water of the upper estuary during parable to that of the upper estuary is considered. the period of a tidal cycle would be flushed out, The lower estuary contains populations of such their surrounding water mixed with the colder stenohaline creatures as lobsters, rock crabs, water of the lower estuary, and a consequent sea scallops, sponges and starfish which are loss of large numbers of them would take place absent in the upper. Besides a few euryhaline with each tide, either by simple dilution or species (e.g. soft-shell clams or mud shrimp) through mortality due to unfavorable temperature. the upper estuary contains numerous organisms This procedure, taking place day after day would which are limited to it by their requirements of tax the reproductive potential of the oyster popu higher temperatures or less saline water. The lation even though conditions around the beds temperature differential, which may be 5° C or were suitable for gametogenesis and spawning. more in the summer, particularly through limit When the dam was in place, the tidal exchange ations on larval survival, spawning activity or was conSiderably reduced and more larvae were gametogenesis, is an effective barrier to the able to remain in favorable water long enough to spread of certain species. These species may reach setting size. be called "relict", that is, they appear to be remnants of a more universal distribution at At present, small populations of mostly some past time when the coastal waters were older oysters are all that remain. The largest warmer than at present. Such relict populations beds are located in the inner extremity of Marsh are common on the strongly dissected coast of River . Setting of young occurs but seldom (Tax Maine. Those of Casco Bay, for instance, have iarchis, Dow, and Baird, 1954) although in unusu been discussed by Verrill (1873). aUy warm years a small number of larvae appar ently survive in numbers sufficient to produce a Marine populations along the coast of small set. Such an event took place in 1955, for Maine belong to a zoogeographical sub-unit to example. which the term "Acadian" is sometimes applied. Those farther south are sometimes called The foregoing discussion refers primar "Virginian". Three s-pecies in the Sheepscot ily to temperature barriers. A few species are estuary which are more typically Virginian than quite definitely limited to the upper estuary by a Acadian are the American oyster (Crassostrea salinity barrier. One of the most interesting of virginica) and the two mud crabs Neopanope these is the hydroid Cordylophora lacustris, the texana and Rhithropanopeus harrisi. These are salinity tolerance of which is a very narrow limited to the upper estuary. Another species range near the fresh water end of the scale. which is typically more southern in its distribu This hydroid is known from coastal estuaries tion is the horseshoe crab (Limulus polyphemus), and also from inland rivers. The amphipod and this species is most common in the upper Gammarus tigrinus occupies only the portion of estuary. Its ecological requirements, however, the Sheepscot estuary from the lower limit of seem to be less restrictive than those of the continuous fresh water to the level of Station 13. other three species mentioned, and its distribu tion along the coast of Maine in general is more Other species are more characteristic of widespread. the upper estuary than the lower, although by no means confined to it. The blood worm, Glycera Oysters are less abundant now than form dibranchiata, is an example. erly in the Sheepscot. Dlring the early part of this century, a dam was maintained across the The distribution of organisms is divided narrows at Sheepscot Falls. This partially on another plane by the depth of water and the 11 range of tides, producing the characteristic Fish populatIons in the e tu ry nclude zonation that parallels the shore line. The most both migratory and indig~nous pecles. Of the obvious environmental factors which may det r former, there arc such Sea nOll migr mts as mine this zonation are the exposure to air which the Atlantic hening and Atl, ntlc mac 'erc!; the organism must tolerat , exposure to wave anadromous sp<.;cies, uch as the American action and winter ice, and salinity and thermal smell, the alL!wlfe, and the Atlull lC almon; and stratification. the catadroll1ouf:i Am(:riCClll 1. Macker 1 ancl small IWI'ring appeal' in the wa cr )[ th lower Intertidally, the predomwant specIes L!stuary dUl"lng tIll! summer months. There living in sediments are the soft-shell clam, Mya uppea rs [0 IX! ()1l1e rt.!iatlOnshlp I tween their arenaria; a smaller clam, Macoma balthica; the lOLa I abundance: and the qu ntlly of pl. n'ton In sand worm, Nereis virens; and an amphipod, the wnter, hut tillS has nnt been conclu Ively Corophium volutator. Another worm, Nephtys demon tr.1tcd. Inshore hernng ~ncl mac 'erel caeca, is also abundant along the lowest edge of ut",h' ~,wcre smull r 1n 1 S5 than n 1 ~4, and the intertidal zone. In the corre::;ponding zone the ~umrnt.:r pi n "ton volumes wer al 0 mailer on hard substrate are the barnacle, Sa lanu during IlJ5~ thUll till! yenr I fore hown m balanoides; the snails Littorina littorea and fig. 6. me nppearance of alar ... hoolof obtusata; and the purple whelk, Thais lapillus. mackerel U1 a c vc ne r the laboratory 10 August In the upper estuary, Nerei diver::;icolor re 1 54 cUlnclded wah n ex remcly cI nse oncen places ~. virens and saxatilis replaces .!:-. tration of z plan "ton III Lhat cove on whIch the obtusata. mackerel were f CdlOg.

No attempt has been made to analyze The alewlfe (P molobu p eudohare~) further the tidal zonation, a subject which ha a 'cend mto frc.: h ,'ater in ay, follOWed b: the been treated thoroughly by the Stephensons (1949, glut herring (a tivuli) In June. Sea lampreys 1954), and the principles of which ar generally (Pctromyzon l1hHlnU ) a end the rIver m great applicable throughout this area, although there numbers In • lay, but ob::.ervation made at the are variations in particular species. Many counting wt.:ir indicate they rea h th h ad-of-tid species that ecologically are not intertidal are earlier than thi , probably orne time in Apnl . found in the intertidal zone since they occupy DJring ~1ay and Jun elver:. of the Amed ~an eel only its lowest margin, scarcely above the ascend the river, while adult · move down tream spring low tide level, and then are usually hid in both pring and fall. AtlantI almon are not den in sheltered spots or in tide pools. These abundant but a few ascend each year, mostly in species are usually members of subtidal or in the fall. Smelt (Osmerus mordax) enter the fralittoral communities, and include lobsters, estuary in the fall, remain in tile tidal creeks rock crabs, starfish, sea urchins, anemones, and the upper estuary during the winter, and and a host of other interesting creatures. ascend the nver and tnbutary brooks to spawn in April. Striped bass (Roccus sa."atili ) appear On the most seaward shores of the estu in the upper estuary during the summer and are ary are a few sandy coves, fringed by ledges said to have been abundant there all year round and boulders, but protected from severe wave when the dam was present at Sheepscot Falls. action. In such places the number and variety of intertidal and infralittoral organisms are No definitive check list of fish indigenous relatively great. In the more sheltered places to the estuary has been compiled, but certainly the abundance of silt appears to discourage all many of the species listed by Bigelow and but the hardiest species or those which normally Schroeder (1953) are regular inhabitants, at live in silty sediments. least in the more seaward parts of the estuary"

Subtidal fauna has not been studied in 2/ The information regarding the size of these detail, but studies currently being made by the catches has been obtained from the herring catch biologists of the Clam Investigation of the U. S . statistics on file at the Boothbay Harbor Labora Fish and Wildlife Service will provide much in tory and from interyiews with local fishermen formation relative to the distribution of these and distributors. subtidal populations. 12 Some of the more common species collected in marine and fresh water organisms are common the lower estuary have been cod, pollack, sil in the innermost part of the estuary. ver hake, mud hake, cunner, winter flounder and spiny dogfish. The mummichog, or killi Great blue herons and kingfisher s are fish, is ubiquitous but favors tidal creeks and numerous among the salt marshes and along the the shallow water of the upper estuary. Winter banks of the estuary and the river. Red breasted and smooth flounders, fourspined sticklebacks, mergansers, American mergansers, ospreys eels and tomcod are also common in the upper and other fish -eating birds have been observed estuary. from time to time, also. The American mer ganser appears to be a serious predator on Table 1 provides a partial list of both young salmon (White, 1939; Huntsman, 1941). fish and invertebrates that have been found in the Sheepscot estuary. Some mention should be made here of the characteristic aquatic vegetation in the estuary. The bottom organisms which constitute No attempt has been made to list all of even the a dietary staple of many kinds of fish are abund common species, but there are a few which can ant everywhere. Some of the chief food organ not escape notice. The common rockweeds isms of this sort - shrimps (Crago septemspin Ascophyllum nodosum and Fucus vesiculosus osus particularly), cumaceans, amphipods, are abundant on rocks and other solid substrata small bivalves and polychaete worms - are ex from the open coast to slightly above the falls at tremely numerous and widely distributed. Sheepscot Village, between the tide marks. Small forage fish are also abundant: herring Below the low tide level, sometimes exposed at brit, young alewives, silversides and mummi spring low water are Irish moss (Chondrus chogs, especially during the warmer months. crispus) and kelp (Laminaria spp.) but they do not penetrate as far into the estuary as the other There are a few predators which are im species mentioned. Enteromorpha intestinalis, portant because they attack species of commer a green alga, is common in the upper estuary, cial value. The spiny dogfish and the harbor extending almost to fresh water in the summer seal are very common and range far into the time. This plant was found, along with the estuary. Their depredations are at least trou diatom Melosira spp., to constitute an important blesome to the fishermen if perhaps less serious item in the diet of the mummichog (Fundulus). to the populations preyed upon. The double cre.sted cormorant is a fish eater and probably Eel grass (Zostera marina) is present like the two predators cited above, may be more in shallow protected places from the seaward a pest than a menace. On the other hand, the end of the estuary to somewhat above the falls green crab (Carcinides maenas) has been demon at Sheepscot Village, and it appears to be in strated to be a serious predator on the soft-shell creasing in abundance. Marsh grasses (Spartina clam and one of the chief factors involved in the alterniflora and ~. patens) border the upper recent decline in the populations of this shellfish estuary and many tidal inlets elsewhere, often (Glude, 1'955; Dow and Wallace, 1952). The forming broad expanses of salt marsh. ~. alter relative scarcity of this crab in the upper estu niflora was found to extend up the estuary some ary where the water reaches very low salinity what beyond the average penetration of saline levels may partly account for the successful water, where it was associated with various sets of clams that frequently occur in that area. species of sedge (Scirpus). These ubiquitous and hardy creatures do, how ever, manage to stray in small numbers so far SUMMARY into the estuary as to mingle with Similarly vagrant fresh water species, such as dragon fly Dlring the years 1954 - 1956, a general larvae. It should not be assumed from this that ecological and hydrographic survey was made of they normally penetrate fresh water. Dle to the estuary of the Sheepscot River, Maine. This the seasonal and tidal fluctuations in the loca was done to provide background information for tion of the transition zone between fresh and further more detailed studies of Atlantic salmon, brackish water, mixed populations of euryhaline clams, alewives, smelt, oysters and other

13 economically important species by cooperating Temperature and salinity characteristics Federal and State agencies. vary throughout the year and with locality and tidal stage so that a simple summary statement The estuary is large relative to the size cannot be made with respect to these variables. of the river, but its greatest area was found to However graphs are presented that summarize be not estuarine ecologically or hydrographically. this information reasonably well. It can be conveniently divided into two parts: an upper, or interior part, and a lower. The upper Animal and plant life in the lower estuary section, within about six nautical miles of the are characteristically neritic or coastal marine. river mouth, is characteristically estuarine, There is a much greater number of phyla and with marked dilution by the river and subject to species represented there than in the upper strong seasonal and tidal variations in salinity. estuary. The populations of the upper estuary The lower section, extending about 14 nautical are either isolated oligohaline species or mes miles further to the Gulf of Maine, is actually a ohaline species with some extension of euryhaline ria or long, narrow bay with typical neritic populations from the lower estuary. A few marine conditions. It is a complex system with species appear to be isolated in the upper estuary many islands and interconnecting channels, one by a temperature barrier as well. of which connects it with the estuary of the Kennebec River. This has the effect of produc ing a local lowering of salinity in the surface water toward the seaward end.

Table 1. * List of the more common aquatic animals collected or recorded from the Sheepscot estuary arranged according to habitat.

1. High salinity (28-30 0/00) intertidal sediments Polychaete worms: Nereis virens Sars sand worm Nephtys caeca Fabricius Polydora ligni Webster Streblospio benedicti Webster Heteromastus filiformis Claparede Arenicola marina Linnaeus lug worm Clymenella torquata Leidy bamboo worm Pectinaria hyperborea Malmgren trumpet worm Amphitrite sp. Molluscs: Mya arenaria Linnaeus soft-shell clam Macoma balthica Linnaeus Ensis directus Conrad razor clam Gemma gemma Totten

*/ This list contains but a sma11 fraction of the aquatic organisms in the estuary. The most interesting, conspicuous, or abundant species of fish and invertebrates are listed according to the habitat in which they are most likely to be found. It does not follow, however, that every situation where these various conditions prevail will be inhabited by every species listed for that habitat, nor that many species so listed will not be found elsewhere.

Most of these animals have no common names, but where such a name is in general usage it is included in the righthand column of the table as an aid to those not familiar with the Latin names. As a further aid, the species are arranged in groups of more or less related members.

14 Nassarius obsoletus Say mud snail Paludestrina minuta Totten Crustaceans: Corophium volutator Pallas Phoxocephalus holbolli Kroyer Protochordates: Dolichoglossus kowalewskii Spengel acorn wor m

II. High salinity. infauna of subtidal sediments Coelenterates: Cereantheopsis americana Verrill sea anemone Edwardsia elegans Verrill sea anemone Acaulis primarius Stimpson Polychaete worms: Pholoe minuta Fabricius Phyllodoce groenlandica Oersted Nereis virens Sars Nephtys incisa Malmgren Nephtys caeca Fabricius Lumbrinereis tenuis Verrill Ninoe nigripes Verrill Aricidea spp. Diplocirrus hirsutus Hansen Flabelligera affinis Sars Pherusa plumosa Muller Scalibregma. inflatum Rathke Ammotrypane aulogaster Rathke Maldane sarsi Malmgren Praxillela spp. Rhodine loveni Malmgren Ampharete acutifrons Grube Sternaspis scutata Ranzani Hartmania moorei Pettibone Molluscs: Yoldia limatula Say Yoldia sapotilla Gould Nucula spp. Thyasira gouldi~ Phillipi Cerastoderma pinnatulum Conrad cockle Clinocardium ciliatum Fabricius cockle Crenella decussata Montagu Thracia myopsis Muller Tellina agilis Stimpson Astarte undata Gould Crustaceans: Phoxocephalus holbolli Krbyer Orchomenella pinguis Boeck Leptocheirus pinguis Stimpson Corophium spp. Casco bigelowi Blake AmPelisca spinipes Boeck DJlichia sp. Diastylis quadrispinosa Sars Eudorella sp. 15 Echinoderms: Caudina arenata Gould sea cucumlX!r Ophiura robusta Ayres brittk stu r

III. High salinity, subtidal epifauna, solid substrate Sponges: Halichondria sp. Chalina oculata Pallas deud man' fmgt.:rs Coelenterates: Metridium dianthus Ellis ea anemone Urticina crassicornis Muller eu anem(JDe Obelia spp. Sertularia spp. Polychaete worms: Harmathoe imbricata Linnaeus caled worm Lepidonotus squamatus Linnaeus cal d \form Spirorbis borealis Dwdin Molluscs: Hiatella arctica Linnaeu s Anomia simplex Orbigny Jlngle hell Anomia aculeata Gmelin Ischnochiton ruber Linnaeu s Aeolidia papillosa Linnaeus Odostomia bisuturalis Say Crustaceans: Balanus crenatus Bruguiere barnacle Idothea baltica Pallas Idothea phosphorea Harger Aeginella longicorms Kroyer Gammarus marinus Leach bach flea Gammarus annulatus Smith Echinoderms: Asterias vulgaris Verrill common starfish Asterias forbesi Desor purple starfish Henricia sanguinolenta O. F. Muller blood starfi:;h Ophiopholis aculeata Linnaeus brittle star Gorganocephalus arcticus Leach basket tar Cucumaria frondosa Gunnerus sea cucumber Strongylocentrotus droehbachiensis O. F. Muller sea urchin Protochordates: Boltenia echinata Linnaeus sea squirt Amaroucium sp. Didemnum albidum Verrill Dendrodoa camea Agassiz

IV. High salinity, intertidal, solid substrate Molluscs: Littorina littorea Linnaeus periwinkle Littorina obtusata Linnaeus periwinkle Thais lapillus Linnaeus dog whelk Acmaea testudinalis Muller limpet Mytilus edulis Linnaeus cornman mussel

16 Crustaceans: Balanus balanoides Linnaeus barnacle Gammarus locusta Linnaeus beach flea

V. High salinity, subtidal, soft bottom epifauna Molluscs: Placopecten magellanicus Gmelin sea scallop Retusa obtusa Montagu Lacuna vincta Turton Nassarius trivittatus Say mud snail Cingula aculeus Gould Cylichna alba Brown Colus sp. distaff shell Crustaceans: Pandalus borealis Kroyer shrimp grago septemspinosus Say mud shrimp Echinoderm s: Echinarachnius parma Lamarck sand dollar

VI. High salinity, miscellaneous bottom types, wanderers Crustaceans: Homarus americanus Milne -Edwards lobster Cancer borealis Stimpson Jonah crab Cancer irroratus Say rock crab Carcinides moenas Linnaeus green crab Hyas araneus Linnaeus toad crab Pagurus bernhardus Linnaeus hermit crab

VII. Low salinity (0-27 0/00), intertidal sediments Polychaete worms: Nereis diversicolor O. F. Muller Glycera dibranchiata Ehlers blood worm Polydora ligni Webster Scolilepides viridis Verrill Heteromastus filiformis Claparede Hypaniola grayi Pettibone Molluscs: Mya arenaria Linnaeus soft-shell clam Macoma balthica Linnaeus Ensis directus Conrad razor clam Nassarius obsoletus Say mud snail Paludestrina minuta Totten Hydrobia salsa Pilsbry Crustaceans: Cyathura carinata Kroyer Corophium volutator Pallas

VIII. Low salinity, intertidal solid substrate Molluscs: Littorina littorea Linnaeus periwinkle Mytilus edulis Linnaeus mussel Volsella demissa Dillwyn ribbed mussel

17 Crustaceans: Balanus balanoides Linnaeus barnacle Gammarus locusta Linnaeus beach flea

IX. Low salinity, subtidal solid substra te Coelenterates: Obelia longissima Pallas Cordylophora l:lcustris Allman Molluscs: Crassostrea virginica Gmelin oyster Mytilus edulis Linnaeus llIussd Odostomia bisuturalis Say Crustaceans: Balanus improvIsus llirwin barnacle Rhithropanopeus harrisi Gould mud crab Neopanope texana Smith mud rab Jaera marina FabricIus Leptochelia rapax Harger Aeginella longkornis Kroycr Gammarus annulatus Smith hea h flea Gammarus tignnus Sexton beach flea Carinogammarus mucronatus Say bea h flea Corophium lacustre Vanhoffen Melita nitida Smith

X. Low salinity, subtidal sediments Polychaete worms: Nereis diverskolor O. F. 1uller Scolilepides viridis Verrill Hypaniola grayi Pettibone Molluscs: Mya arenaria Linnaeus ~oft- hell clam Paludestrina minuta Totten Crustaceans: Crago septemspinosus Say mud hrimp Cyathura carinata Kroyer Arachnids: Limulus polyphemus Linnaeus horseshoe crab

XI. Nekton (fish) of deep, salty, or cold coastal waters Squalus acanthias Linnaeus Atlantic spiny dogfish Raja erinacea Mitchill little skate Clupea harengus Linnaeus Atlantic herring Brevoortia tyrannus Latrobe menhaden Pollachius virens Linnaeus pollack Gadus callarias Linnaeus Atlantic cod Melanogrammus aeglefinus Linnaeus haddock Urophycis tenuis Mitchill mud hake Merluccius bilinearis Mitchill silver hake Pseudopleuronectes americanus americanus Walbaum winter flounder Scomber scombrus Linnaeus Atlantic mackerel Poronotus triacanthus Peck butterfish Myoxocephalus aeneus Mitchill sculpin 18 Hemitripterus americanus Gmelin sea raven Cyclopterus lumpus Linnaeus lumpfish Liparis liparis Linnaeus striped sea snail Pholis gunnellus Linnaeus gunnel Ammodytes americanus DeKay sand lance Tautogolabrus adspersus Walbaum cunner Lophius americanus Cuvier & Valenciennes goosefish

XII. Nekton of shallow, brackish, or protected waters Fundulus heteroclitus Linnaeus mummichog Microgadus tomcod Walbaum tomcod Liopsetta putnami Gill smooth flounder Pungitius pungitius Linnaeus ninespined stickleback Apeltes quadracus Mitchill fourspined stickleback Syngnathus fuscus Storer pipefish Menidia sp. Atlantic silversides Morone americana Gmelin white perch

XIII. Nekton, anadromous and catadromous, migratory Pomolobus pseudoharengus Wilson alewife Pomolobus aestivalis Mitchill glut herring Alosa sapidissima Wilson American shad Salmo salar salar Linnaeus Atlantic salmon ------Osmerus mordax Mitchill American smelt Roccus saxatilis Walbaum striped bass

XIV. Plankton, high salinity coastal waters Coelenterates: Cyanea arctica Peron & Leseuer red jellyfish Aurelia aurita Linnaeus white jellyfish Ctenophore s: Pleurobrachia pileus Fabricius sea walnut Chaeto gnaths: Sagitta spp. arrow worms Copepods: Calanus finmarchicus Gunner Pseudocalanus minutus Kroyer Centropages typicus Kroyer Centropages hamatus Lilljeborg Temora longicornis Muller Eurytemora herdmani Thompson & Scott Acartia longiremis Lilljeborg Tortanus discaudatus Thompson and Scott Microsetella norvegica Boeck Oithona similis Claus Cladocerans: Evadne nordmanni Loven Podon leukarti Sars Tintinnids: Tintinnopsis sp.

XV . Plankton, shallow, brackish, and protected waters Copepods: Acartia longiremis Lilljeborg Eurytemora herdmani Thompson and Scott 19 Table 2. List of the more common aquatic plant collected or recorded from the Sheepscot estuary.

I. High salinity coastal waters Algae: Laminaria longicruoris De la Pylaie 'clp Laminaria digitata Linnaeus kelp Fucus vesiculosus Linnaeus rockwecd Fucus spiralis Linnaeus ro",kw(!cd Fucus evanescens C. Agardh ro ... 'weed Ascophyllum nodosum Linnaeus rockweed Chorda filum Linnaeus Desmarestia aculeata Linnaeus Chordaria flagelliformis Muller Chondrus crispus Linnaeus In h mas Polysiphonia lanosa Linnaeus Polysiphonia flexicaulis Harvey Corallina officinahs Linnaeus Uiva latuca Linnaeus Enteromorpha compressa Linnaeu Seed Plants: Spartina aiterlllflora var. glabra Fernald mar h gr s Spartina patens Ait. mar h gra Zostera marina Linnaeus eel gra

II. Low salinity, protected waters Algae: Enteromorpha intestinalis Linnaeus Enteromorpha clathrata Roth Lyngbya sp. Melosira sp. Polysiphonia subtilissima Montagne Dasya pedicellata C. Agardh Ectocarpus sp. Ceramium sp. Seed Plants: Spar tina alterniflora var . glabra Fernald marsh grass Spar tina patens Ait. marsh grass Zostera marina Linnaeus eel grass Ruppia maritima Linnaeus

LITERATURE CITED Bigelow, H. B. 1924. The plankton of the Gulf of Maine. Atkins, C. G. Bulletin, U. S. Bureau of Fisheries, 1874. On the salmon of eastern North 40: 1-509. America and its artificial culture. U. S. Fish Commission, Report Bigelow, H. B., and W. C. Schroeder of the Commissioner Pt. I I, 1953 . Fishes of the Gulf of Maine. U. S . pp. 226-337. Fish and Wildlife Service, Fishery Bulletin 74, pp. 1-577.

20 Bryant, F. G. Stephenson, T. A., and A. Stephenson 1956. Stream surveys of the Sheepscot 1949. The universal features of zonation and D.!cktrap river systems in between tide marks on rocky coasts. Maine. U. S. Fish and Wildlife Journal of Ecology 37(2): 289-305. Service Special Scientific Report Fisheries, No. 195, pp. 1-19. 1954. Life between the tide marks in North America. III A. Nova Scotia Dow, R. L.,and D. Wallace and Prince Edward Island: Descrip 1952. Observations on green crabs tion of the region. Journal of (Carcinides maenas) in Maine. Ecology 42( 1): 14 -45. Maine Department of Sea and Shore Fisheries, Fisheries Circular Taxiarchis, L. N., R. L. Dow, and F. T. Baird, Jr. No.8, pp. 11-15. 1954. Survey of the oyster beds (Crassostrea virginica) in the Glude, J . B. Sheepscot River and its tributaries. 1955. The effects of temperature and Bulletin, Department of Sea and predators on the abundance of the Shore Fisheries, Maine, Sheepscot soft-shell clam (Mya arenaria) in Area Report No.1, pp. 1-14. New England. Transactions, American Fisheries Society 84: Verrill, A. E. 13 -26. 1873. Explorations of Casco Bay by the U. S. Fish Commission. B. Natural Huntsman, A. G. History. Proceedings of the Ameri 1941. Cyclical abundance and birds ver can Association for the Advancement sus salmon. Journal, Fisheries of Science, Portland meeting, pp. Research Board of Canada 5(3): 340-395. 227-235. White, H. C . Johnson, D. W. 1939 . The food of Mergus serrator on the 1925. The New England Acadian Shore Margaree River, N. S. Journal, line. John Wiley & Sons, Inc., 608pp. Fisheries Research Board of Canada 4(5): 309 -311. Oxner, M. * 1920. Chloruration par la methode de ACKNOWLEDGMENTS Knudsen. Bulletin de la Commis sion International pour l' explora The author is indebted to the following tion scientifique de la Mer Medi for their assistance and cooperation in the prepar terranee, No.3, pp. 1-36. ation of this manuscript: Mr. Robert W. Hanks of the U . S. Fish and Wildlife Service for per Pritchard, D. W./ and W. V. Burt mission to use some of his unpublished mater ial, 1951. An inexpensive and rapid technique particularly records of species collected; Mr. for obtaining current profiles in Ernest Marsh of Sheepscot Village for perm is - estuarine waters. Journal of sion to publish the photograph of the mill and Marine Research, 10(2): 180 -189. dam at Sheep scot and for prOviding interesting and valuable information about the area; and, * / A translation of this paper together with a the staff of the U. S. Fish and Wildlife Service photolithographic reprint of Knudsen's laboratory at Boothbay Harbor, to members of tables were prepared by the Woods Hole the Maine Department of Sea and Shore Fisheries, Oceanographic Institution in 1946. Department of Inland Fisheries and Game, and Atlantic Salmon Commission.

21 INT . DUP . , D. C . 59- 57912