Ecological History of Pontchartrain, an Estuarine Community

REZNEAT M. DARNELL

•

Reprinted from [HE AMERICAN MIDLAND NATURALIST Vol. 68, No. 2, pp. 434-444, October, 1962 University of Notre Dame Press Notre Dame, Indiana Ecological History of Lake Pontchartrain, an Estuarine Community'

REZNEAT M. DARNELL Marquette University, Milwaukee, Wisconsin

ABSTRACT: During the past 5,000 years since stabilization of the level of the , the Lake Pontchartrain basin has undergone drastic environmental changes. About 2,000 years ago when the Missis- sippi established its course in the area one of the early deltaic distributaries impounded an arm of the Gulf, creating the Lake Pontchartrain basin. Since this time the basin has undergone rapid filling from a variety of sources, as well as gradual freshening. Associated with these changes, as revealed by the fossil record, the sedentary benthic invertebrates have included a progression of species reflecting the respec- tive environments from the marine tidal flat community of 5,000 years ago (Dosinia and Mercenaria), through the brackish-water assemblage of 2,000 years ago ( Crassostrea and Thais), to the present-day near- fresh community ( Rangia, Mytilopsis, etc.). Along with filling and freshening the lake has apparently come under greater influence of weather conditions which now induce sudden and severe changes in the hydrographic environment. This physical instability is also reflected in the nature of the fauna. Although over 300 species are currently recog- nized from the lake, only about 4 maintain large endemic populations as year-around residents, a clam ( Rangia cuneata), crab (Rithropano- peus harrisii), copepod ( Acartia tonsa), and fish ( Anchoa mitchilli). Most of the remaining abundant species are migratory and spawn else- where, invading the lake as seasonal transients. Their population levels and the species composition of the fauna, in general, vary dramatically from one season to another and from year to year, apparently reflecting to a large degree the influence of the physical factors on larval migration and establishment. Impoundment has apparently been followed by a great increase in the availability of humus from decaying marsh grass, a retardation of flushing, an increase in siltation, and a general rise in tur- bidity. As a result the community appears to have progressed toward a heterotrophic condition in which the consumer species are greatly de- pendent upon organic detritus originating, in large measure, outside the lake. Detritus feeders are now among the most successful species com- prising the community of this lake. Community relations within Lake Pontchartrain, a , have recently been described in some detail (Darnell, 1958; 1961) . It is of further interest to review the history of the environment and the community, insofar as they are known, in order to place the present-day community in historical perspective. Considerable infor- mation is available in the literature on the geological and the Lower area, and much of this material relates directly to the Lake Pontchartrain basin. The present discussion draws heavily upon the works of Fisk (1944, 1947a, 1947b) and Steinmever (1939) . Other pertinent material is included in the papers of Fisk, et al. (1938), Frink (1941), Gunter (1952b, 1953),

1 Contribution No. 1 from the Laboratory of Hydrobiology, Department of Biology, Marquette University. 434 1962 DARNELL : ECOLOGICAL HISTORY OF LAKE PONTCHARTRAIN 435 and Russell (1936, 1940, 1948). Thanks are extended to the following persons for taxonomic aid in relation to present-day invertebrates from the lake: W. J. Clench and A. Solem, gastropods and pelecypods; G. L. Voss, cephalopods; M. S. Wilson, copepods; and F. A. Chace, decapods.

ORIGIN AND HISTORY OF THE LAKE PONTCHARTRAIN BASIN The succession of geological events occurring in the area is related primarily to (1) fluctuation in the level of the Gulf of Mexico with alternating periods of subaquaeous deposition and subaerial , (2) migration and alternate delta formation by the Mississippi River, and (3) continual subsidence of the coastal deposits. Associated phenomena include impoundment, river overflow, wave dissection of marsh shore, and salinity changes of the aquatic environment. Faulting with displacement of sediments appears to have been of little over-all consequence in the history of Lake Pontchartrain. The late Pleistocene and Recent history of the area is summarized in Table I. The point of departure for the present discussion is the late Pleistocene (Peorian) interglacial period, of about 50,000 years ago. During this time the Gulf level was high, and the widespread Prairie Formation was laid down in shallow water. The subsequent advance of the late Wisconsin ice sheets was accompanied by lowering of the Gulf level which reached a maximum depression of about 450 feet below present sea level until about 18,000 years ago (Russell, 1957) . The exposed Prairie Formation was then subjected to leaching of soluble carbonates with oxidation of iron remaining in the surface clays. Erosion of uplands and stream cutting resulted in deep entrench- ment of the Amite drainage which flowed through the area now occupied by Lake Pontchartrain and of the Mississippi River which then flowed to the Gulf considerably west of New Orleans (Fig. 1A) . With retreat of the last glacial sheets and rise in level of the Gulf, fluviatile and estuarine deposition filled the trenches. About 8,000 years ago the rising sea first covered the divide between the old Amite and Mississippi River trenches, and widespread marine and brackish water sediments were being laid down over the oxidized clays. The Lake Pontchartrain area at this time was an open bay or shallow arm of the Gulf. When sea level reached its present stand about 5,000 years ago (Russell, 1957), the area was still characterized by tidal-flat species. During the above periods, the Mississippi River occupied a course west of New Orleans. With stabilization of the Gulf level, the river successively formed and abandoned a series of deltas, which still centered to the west. Subsequent meanderings were followed by an upstream diversion of the river about 2,000 years ago. At this time the Mississippi River established its course in the New Orleans area and alternately formed a series of deltas, one of which TABLE 1.—Late Pleistocene and Recent geological history of the Lake Pontchartrain area (compiled from several sources) Approx. date Position of ( years from Glacial stage Sea level Mississippi Condition of Lake Pontchartrain present) River -50,000 interglacial; begin- high; falling west of New Orleans deposition of widespread Prairie Formation clays on fling of late Wis- gradually subsiding shelf consin glaciation -18,000 maximum exten- maximum depres- west of New Orleans exposure of Prairie Formation;

sion of late Wis- sion; ±450 ft. be- erosion, leaching, oxidation of exposed Pleistocene clays ; consin ice sheets low present level maximum stream entrenchment followed by fluviatile deposition within trenches. -8,000 glaciers retreating rising; Amite-Mis- west of New Orleans open bay or shallow arm of gulf; marine to brackish- sissippi R. divide water sediments deposited over oxidized clays first covered by sea -5,000 more or less stable sea level reached west of New Orleans; brackish-water sediments deposited; tidal flat species in- present stand migrating eastward habiting area; gradual freshening of water -2,000 stable more or less stable course established in lake area impounded; environment brackish to nearly at present stand New Orleans area ; fresh; marginal marsh and swamp encroachment; wave Metairie - Gentilly dissection, offshore distribution and deposition of ridge formed, creat- marsh humus (continuing to present) ; periodic silta- ing southern bound- tion from Mississippi River natural overflow ary of Pontchartrain depression Historical stable stable stabilized in area by sedimentation of lake bottom continued by: natural and artificial 1. persistent wave dissection of marsh shore, esp. in south and east, 2. infrequent Mississippi River overflow (crevasses) through broken levees or (since 1937) through Bonnet Carre Floodway, 3. steady inflow of sand and silt from north shore streams ; rounding of shore contours by wave action, esp. during hurricanes; continued subsidence of basins; artificial bottom changes due to operations. 1962 DARNELL : ECOLOGICAL HISTORY OF LAKE PONTCHARTRAIN 437

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Fig. 1.—Relation of late Pleistocene and post-Pleistocene drainage features to the present topography of the Lake Pontchartrain area. A. Late Pleistocene stream entrenchment. Note positions of the Amite trench system and the buried stream divide in relation to the city of New Orleans and Lake Pontchartrain ( modified from Fisk, 1947a). B. Successive formation during post-Pleistocene time. Only the major deltas of the eastern series are shown. This figure is modified from Fisk (1944), and his system of naming and numbering the deltas has been retained (D, Maringoin delta; H. Cocodrie delta; 1, Teche and LaFourche deltas; 12-15, Plaquemines and St. Bernard deltas). 438 THE AMERICAN MIDLAND NATURALIST 68(2) extended to the and divided the Pontchartrain-Borgne basin, thereby impounding the Pontchartrain Depression. The present Bayous Metairie and Sauvage occupy the main channel of this short-lived distributary, and the Metairie-Gentilly ridge which passes from Kenner through New Orleans and disappears in the marshes to the east marks the old natural levees of this stream (Fig. 1B) . Following impoundment the history of the Pontchartrain Depres- sion has been characterized by rapid filling, and the present Lake Pontchartrain occupies only a portion of the lake basin. waters and overflow from the Mississippi River have added enormous quan- tities of silt and clay to the western part of the lake, and as late as 1890 one-third of the flood volume of the Mississippi River (402,556 second-feet) was discharged through breaks (crevasses) into Lake Pontchartrain (Steinmeyer, 1939). During historical time the construction of artificial levees along the Mississippi River has deprived Lake Pontchartrain of its major source of siltation. The opening of the Bonnet Carre Floodway in 1937, 1945, and 1950 re-established this process on a minor scale by diverting Mississippi River flood waters into the lake through the site of an old crevasse (Fig. 2) .

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2.—Cross-sectiona1 geology of the Lake Pontchartrain depression. Note the extensive marsh and swamp deposits underlain in most areas by marine and brackish-water sediments. A, north-south section at western edge of Lake Pontchartrain through Frenier and Bonnet Carre Floodway; B, north- south section through center of lake at level of Mandeville and New Orleans; C, northeast-southwest section through eastern edge of lake from Slidell through New Orleans (modified from Fisk, 1947b). Inset shows location of transects. 1962 DARNELL : ECOLOGICAL HISTORY OF LAKE PONTCHARTRAIN 439

Considerable quantities of sandy sediments have been deposited in the Pontchartrain Depression by north shore streams, principally the Tangipahoa, Tchefuncte, Amite, and Pearl and Bayous Chinchuba, Bonfouca, and Lacombe. Subaquaeous tidal deltas have been deposited near the mouths of passes. Also active in filling the depression has been the persistent encroachment by marginal marsh and swamp. Wave dissection of such vegetation has resulted in round- ing of shore contours and offshore deposition of great quantities of humus. This process is currently active and has been most pronounced during hurricanes which are known to have raised the water level as much as 10 feet above normal. Subsidence in the lake bottom has continued to the present time. Fisk (1947b) reported information from Indian artifacts indicating a minimum subsidence rate of 14 feet in 2,000 years for Lake Pontchartrain and within the city of New Orleans, six feet in 60 years!

MOLLUSCAN FAUNA IN RELATION TO THE HYDROGRAPHIC HISTORY With formation of the Pontchartrain Depression there has been a gradual freshening of the environment. About 5,000 years ago, as revealed by the fossil record, the community was characterized by such mollusks as Dosinia discus and Mercenaria (=Venus) mercenaria (see list of Steinmeyer, 1939) . As pointed out by Parker (1956, 1960) these bivalves are shallow-water marine species which are normally found on the inner Gulf shelf at depths of 2 to 12 fathoms or in association with barrier islands. These species are now encountered in the open Gulf outside of the Chandeleur Islands and to some extent in Chandeleur Sound where salinities vary from about 30 to 35°/00. The marine community was subsequently replaced by Crassostrea (=Ostrea) virginica, Thais haemostoma, and other oyster reef species. These are typically found in waters of intermediate salinity of roughly 10 to 30°,/. Banks of ancient oyster shells may still be seen on the northwestern shore of Lake Pontchartrain just west of the mouth of the . This oyster reef community is now found in and in the shallow lagoons among the marsh islands to the south. Today the salinity of Lake Pontchartrain normally varies from 0 0 3 to 8 /00 with an average of around 5 100. Extremes of 1.2 and 18.6`)/00 have been noted following exceptionally heavy rainfall and tropical Gulf disturbances, respectively. The bottom community throughout the lake is now dominated by enormous populations of the clam Ran gia cuneata. The mussel Mytilop.sis leucopheata and the small gastropods Littoridina sphinctostoma and Probithinella protera are also widespread and abundant. Smaller populations of the bent mussel Mytilus recurvus inhabit the eastern sector of the lake, and single small specimens of the oyster Crassostrea virginica and the clam Polymesoda carolinensis and two specimens of the clam 440 THE AMERICAN MIDLAND NATURALIST 68(2)

Angulus sybariticus have also been taken. Fresh-water clams of the genus Unio have been reported from fresher areas of the western shore.

MOTILE SPECIES IN RELATION TO THE HYDROGRAPHIC HISTORY Following stabilization of the Gulf level, changes in the physical environment (noted previously) have been accompanied by faunal change from what was probably a more-or-less stable marine assem- blage to an unstable estuarine community containing a great many migratory species. It is a notable fact that the vertebrate and in- vertebrate fauna of and brackish waters in general is almost exclusively of marine origin, and only when the environment is nearly fresh do significant populations of the fresh-water species appear (Gunter, 1942, 1945, 1950, 1956a, 1956b, 1957; Gunter and Shell, 1958) . Associated with freshening of the Pontchartrain environment the number of marine species visiting the lake undoubtedly has progressively diminished, but this must have taken place without significant invasion by fresh-water species until quite recently when the environment has begun to approach truly fresh conditions. In the present community there are, strictly speaking, only about four prominent species which maintain large endemic populations as year-around residents. These include a clam (Rangia cuneata), crab (Rithropanopeus harrisii), copepod (Acartia tonsa), and fish (Anchoa mitchilli). Over 300 species have been identified from the lake, how- ever, and among the transient species many achieve quite large seasonal populations. Of especial note are two penaeid shrimp (Penaeus aztecus and P. setiferus), blue crab (Callinectes sapidus), menhaden (Brevo- ortia patronus), hardhead catfish ( Galeichthys felis), Atlantic croaker (Micropogon undulatus). and spot (Leiostomus xanthurus) (Darnell, 1958, 1959, 1961 and Suttkus, 1954, 1956) . The writings of numerous observers suggest that shallow, im- pounded near-shore estuaries and lagoons are subject to considerably greater fluctuation in factors of the physical environment than are the more open sounds and deeper bays of the Gulf (see, for example, Engle, 1948 and Parker. 1956) . There now seems to be a certain stability in the environment of the more marine areas as around the Chandeleur Islands (Humm and Darnell, 1959) in comparison with Mississippi Sound (Springer and Bullis, 1952, 1954), Lake Borgne (Butler, 1952; Butler and Engle, 1950), or Lake Pontchartrain itself (Gowanloch, 1950; Gunter, 1952b, 1953; Owen and Walters, 1950; and Viosca, 1928, 1938). With impoundment, the Lake Pontchartrain area has become shallower and fresher and subject to greater influence of flooding from local rainfall and river overflow. In turn, the shallow- ness has rendered the lake more susceptible to wind disturbance and temperature fluctuation. Even moderate winds now are capable of roiling the bottom in the deepest basins (18 feet). So far no mass population mortality has been noted for Lake Pontchartrain such as 1962 DARNELL : ECOLOGICAL HISTORY OF LAKE PONTCHARTRAIN 441

Gunter (1941, 1947a, 1947b, 1952a) described for shallow lagoons of the Texas coast following cold waves, but pronounced population migration correlated with drastic temperature change has been re- ported by Suttkus (1954) . In the experience of the present writer these movements may indeed be extensive involving long-distance migration by many species of fishes and invertebrates. The species composition and population levels of the migratory portion of the present community vary greatly from one season to the next and apparently from year to year. Most of these transients enter the lake during the larval or juvenile stages. Their success in gaining entrance and their survival and growth inside apparently depend upon favorable water currents for transport and favorable conditions of salinity, turbidity, temperature, etc., within the lake. These conditions, in turn, reflect such weather-related phenomena as average rainfall, high winds, storms, hurricanes, , and cold waves. Thus, although biological factors such as competition and predation may greatly influence the population levels of many species, the success of a particular year-class of most of the transient species must depend first of all upon the prevailing physical rather than biological factors (cf. Darnell, 1958, 1961; Darnell and Williams, 1956; Gunter and Hildebrand, 1954) . During times of high salinity a large element of typically marine species may enter the lake including large medusas (Dactylometra quinquecirrha), squids (Loligo pealii and Lolliguncula brevis), and scombrid fish (Scornberomorus macula- tus), whereas during periods of very low salinity such typically fresh- water forms as river shrimp (Macrobrachium ohione), largemouth bass (Micropterus salmoides), and channel catfish (Ictalurus puncta- tus) may appear in some numbers. Between these extremes a graded series of faunal types is found which are clearly (in some cases) or probably (in other cases) related to prevailing salinity conditions. Gunter and Shell (1958) have discussed the importance of small salinity differences in determining the distribution of aquatic animals in Louisiana estuaries. Analysis of the present community has revealed several sets of biological factors which may be considered as potential buffers against population fluctuation and which therefore should act as stabilizing forces for the community. These include the presence of great taxo- nomic diversity, omnivory by a large share of the consumers, and detritivory by many of the consumer species (Darnell, 1961) . Such stabilizing factors, however, appear to be overwhelmed by severe and often sudden variations in the immediate physical environment. Although some fluctuation in population levels is probably character- istic of northern Gulf-coastal communities in water of all degrees of salinity, within such shallow brackish areas as Lake Pontchartrain population instability must approach a maximum. In such environ- ments the community probably never really becomes stabilized before a new set of equilibrium conditions is established and the process begins over again (cf. Odum, 1959:80) . 442 THE AMERICAN MIDLAND NATURALIST 68(2)

TROPHIC HISTORY Although quantitative estimates of productivity are lacking, it appears likely that during the last five thousand years, as the estuary has developed from a high saline to a low saline environment, the community has become progressively more heterotrophic. Prior to impoundment fresh marsh humus was probably less available than in more recent time, flushing was undoubtedly greater, and the rate of accumulation of humic material must have been correspondingly slower. In addition, the water itself was probably much clearer, as is now the case around the Chandeleur Islands, permitting a higher level of photosynthetic activity. With impoundment, the rate of siltation and humus accumulation must have increased considerably. Today the waters of Lake Pontchartrain are exceedingly turbid, and, as pointed out elsewhere (Darnell, 1961) , the present community appears to be trophically unbalanced. Much of the primary organic matter by which consumers of the community are nourished apparently originates outside the lake. Enormous quantities of such material enter in the form of humus from wave-dissected marshes and as plankton from adjacent fresh- and salt-water passes. Steinmeyer (1939) pointed out that one marshy shore in the south-east sector of the lake has been receding under the influence of wave erosion at an average rate of 14 feet per year for at least 50 years. Within the lake this material undergoes bacterial decomposition, and as detritus it is apparently ingested in quantity by most of the important species of invertebrates and fishes which inhabit the lake. In fact, those fishes and invertebrates in which organic detritus makes up a large percentage of the diet are among the most successful species inhabiting the lake.

REFERENCES BUTLER, P. A. 1952. Effect of floodwaters gn oysters in Mississippi Sound in 1950. U.S. Fish and Wildl. Serv., Res. Rept., 31:1-20. AND J. B. ENGLE. 1950. The 1950 opening of the Bonnet Carre Spill- way — Its effects on oysters. U.S. Fish and Wildl. Serv., Spec. Sci. Repts., Fisheries, 14: 1-10. DARNELL, R. M. 1958. Food habits of fishes and larger invertebrates of Lake Pontchartrain, Louisiana, an estuarine community. Publ. Inst. Mar. Sci., Univ. Texas, 5:353-416. . 1959. Studies on the life history of the blue crab ( Callinectes sapidus Rathbun) in Louisiana waters. Trans. Am. Fish. Soc., 88:294-304. 1961. Trophic spectrum of an estuarine community based on studies of Lake Pontchartrain, Louisiana. Ecology, 42(3): 555-568. AND A. B. WILLIAMS. 1956. A note on the occurrence of the pink shrimp Penaeus duorarum in Louisiana waters. Ecology, 37(4) :844- 846. ENGLE, J. B. 1948. Investigations of the oyster reefs of Mississippi, Louisiana, and Alabama following the hurricane of September 19, 1947. U.S. Fish and Wildl. Serv., Spec. Sci. Rept., 59:1-70. 1962 DARNELL : ECOLOGICAL HISTORY OF LAKE PONTCHARTRAIN 443

Fisx, H. N. 1944. Geological investigation of the Alluvial Valley of the Lower Mississippi River. Vicksburg: Corps of Engineers, Mississippi River Commission. vi, 1-78; 78 figs., 11 tables, 33 plates. 1947a. Geological investigation Veterans Hospital Site, New Orleans, La. (mineographed report). 1-40; 7 figs., 3 plates. . 1947b. Fine-grained alluvial deposits and their effects on Mississippi River activity. Vicksburg: Corps of Engineers, Mississippi River Com- mission. Vol. 2; 74 plates. , G. RICHARDS, C. A. BROWN AND W. STEERE. 1938. Contributions to the Pleistocene history of the of Louisiana. La. Dept. Conserv., Geol. Bull., 12, September. FRINK, J. W. 1941. Subsurface Pleistocene of Louisiana. La. Dept. Conserv., Geol. Bull., 19:367-419. GOWANLOCH, J. N. 1950. Fisheries effects on Bonnet Carre Spillway opening. La. Conserv. Rev., 2:12-13, 24-25. GUNTER, G. 1941. Death of fishes due to cold on the Texas coast. Ecology, 22(3) :203-208. 1942. A list of the fishes of the mainland of North and Middle America recorded from both and sea water. Am. Midl. Nat., 28(2) : 305-326. . 1945. Studies on marine fishes of Texas. Publ. Inst. Mar. Sci., Univ. Texas, 1(1):1-190. 1947a. Differential rate of death for large and small fishes caused by hard cold waves. Science, 106(2759) : 472. . 1947b. Catastrophism in the sea and its palaeontological significance, with special reference to the Gulf of Mexico. Am. J. Sci., 245(11) : 669-676. . 1950. Seasonal population changes and distributions as related to salinity, of certain invertebrates of the Texas coast, including the com- mercial shrimp. Publ. Inst. Mar. Sci., Univ. Texas, 1(2) :7-51. . 1952a. The import of catastrophic mortalities for marine fisheries along the Texas coast. J. Wildl. Mgt., 16(1) :63-69. . 1952b. Historical changes in the Mississippi River and the adjacent marine environment. Publ. Inst. Mar. Sci., Univ. Texas, 2(2) :119-139. . 1953. The relationship of the Bonnet Carre Spillway to oyster beds in Mississippi Sound and the "Louisiana Marsh," with a report on the 1950 opening. Publ. Inst. Mar. Sci., Univ. Texas, 3(1):17-71. . 1956a. Some relations of faunal distributions to salinity in estuarine waters. Ecology, 37(3):616-619. . 1956b. A revised list of euryhalin fishes of North and Middle America. Am. Midl. Nat., 56(2) :345-354. . 1957. Predominance of the young among marine fishes found in fresh water. Copeia, 1957(1):13-16. AND H. H. HILDEBRAND. 1954. The relation of total rainfall of the state and catch of the marine shrimp (Penaeus setiferus) in Texas waters. Bull. Mar. Sci. Gulf and Caribb., 4(2):95-103. AND W. E. SHELL, JR. 1958. A study of an estuarine area with water- level control in the Louisiana marsh. Proc. La. Acad. Sci., 21:5-34. 444 THE AMERICAN MIDLAND NATURALIST 68(2)

Humm, H. J. AND R. M. DARNELL. 1959. A collection of marine algae from the Chandeleur Islands. Publ. Inst. Mar. Sci., Univ. Texas, 6:265-276. ODUM, E. P. 1959. Fundamentals of Ecology. W. B. Saunders Co., 2nd ed. Philadelphia. OWEN, H. M. AND L. L. WALTERS. 1950. What Spillway really did. La. Con- serv. Rev., 2:16-19, 26-27. PARKER, R. H. 1956. Macro-invertebrate assemblages as indicators of sedi- mentary environments in east Mississippi Delta region. Bull. Am. Assoc. Petrol. Geol., 40(2) :295-376. . 1960. Ecology and distributional patterns of marine macro-inverte- brates, northern Gulf of Mexico, 1951-1958. In Recent Sediments, Northwest Gulf of Mexico, publ. by Amer. Assoc. Petrol. Geol.: 302- 381. RUSSELL, R. J. 1936. Physiography of lower Mississippi River delta. La Dept. Conserv., Geol. Bull., 8:3-199. . 1940. Quaternary . Bull. Geol. Soc. Am., 51: 1199- 1234. . 1948. Coast of Louisiana. Bull. Soc. Belge Geol., Paleo., Hydrol., 57(2):380-394. . 1957. Instability of sea level. Am. Scientist, 45(5) :414-430. SPRINGER, S. AND H. R. Buws. 1952. Exploratory shrimp fishing in the Gulf of Mexico, 1950-51. U.S. Fish and Wildl. Serv., Fish. Leaflet, 406. . 1954. Exploratory shrimp fishing in the Gulf of Mexico, summary re- port for 1952-54. Comm. Fish. Rev., 16(10) :1-16. STEINMEYER, R. A. 1939. Bottom sediments of Lake Pontchartrain, Louisiana. Bull. Am. Assoc. Petrol. Geol., 23:1-23. SUTTKUS, R. D. 1954. Seasonal movements and growth of the Atlantic croaker (Micropogon undulatus) along the east Louisiana coast. Proc. Gulf and Caribb. Fish. Inst., 7th Ann. Sess.: 1-7. . 1956. Early life history of the Gulf menhaden, Brevoortia patronus, in Louisiana. Trans. 21st N. A. Wildl. Conf.: 390-407. VIOSCA, P. 1928. Flood control in the Mississippi Valley in its relation to Louisiana fisheries. La. Dept. Conserv. Tech. Paper, 4:1-16. . 1938. Effect of Bonnet Carre Spillway on fisheries. La. Conserv. Rev., 6:51-53.