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Pulsation rate ofChrysaora quinquecirrha medusae was inversely and linearly related to bell diameter over the natural temperature range (15–32 C) of this life history stage of the sea nettle in the upper Chesapeake Bay. At unnatural, elevated temperatures this relationship was disrupted. Pulsation rates generally increased with temperature increase from 15 C to 30 C and then decreased at higher temperatures. The rate-temperature curve for acclimated medusae was similar in shape (increase and decrease in pulsation rate with temperature change) to rate-temperature curves reported for warm water medusae; its shape was different from those reported for cold water medusae. Acclimation of pulsation rate to changed temperature was faster than acclimation of upper lethal temperature, although both were measured in hours. Upper lethal temperatures measured over 20–30 C were directly related to acclimation temperature and were similar to those reported for sea nettle polyps (34–35 C). Medusae were more sensitive than polyps to cold, with death occurring at 10 C. Thermal discharges into the upper Chesapeake Bay which raise water temperature above 30 C are probably stressful to sea nettle medusae. Temperatures above 38 C could be lethal in a few minutes.

The seasonal dynamics of Mn, Fe, Zn, Cu and Cd were investigated in a genetically similar population of hatchery-reared American oysters, Crassostrea virginica, maintained in plastic trays in the Rhode River, a tributary of the Chesapeake Bay. Samples were collected monthly from September, 1971 through May, 1973. Annual cycles resulting in the turnover of large portions of the body burden were observed for all metals studied. Subtly different patterns of metal dynamics were observed as a result of the reduction in biological variations realized by employing genetically similar oysters. Metals are grouped into two classes according to their dynamics: (1) Mn and Fe concentrations in soft tissues are significantly correlated with shell deposition. A high rate of Mn turnover in soft tissues (approximately 2 times the body burden per day) occurs during the shell growth season. (2) Zn and Cu concentrations are not correlated with shell growth. Zn and Cu body burdens exhibit a gradual increase during the spring and early summer followed by a rapid loss during August–September in which 33% of the Zn and 50% of the Cu is lost in less than 4 weeks. Cd behavior is similar to zn and Cu with a 50% reduction in body burden during an 11 week period between July and October.

The clay-silt fraction of two cores from the entrance to the Chesapeake Bay was analyzed for boron concentration. Paleoecologic data are used to corroborate, qualitatively, the relationship between boron concentration and salinity. The results demonstrate that the boron concentration reflects a salinity trend that could accompany the Holocene emergence and subsequent submergence postulated for the baymouth. This is interpreted as evidence supporting both the Holocene evolution of the baymouth and a relationship between the boron content of argillaceous sediments and the salinity of the depositional environment.

An investigation into the dynamic balance of Chesapeake Bay waters is carried out by means of a two-dimensional, plan view numerical model. The results of this investigation show that neither the Coriolis force nor the advective terms in the governing vertically integrated equations can be neglected without changing the tidal dynamics and circulation patterns of this Bay. Also, a bottom friction coefficient of 0.0025 produces the most realistic simulations of observed tidal data.

The Chesapeake and Delaware Canal connects upper Chesapeake Bay with the Delaware River. The results of two years of intensive sampling effort in the C&D Canal suggest that this area may be one of the more important spawning grounds of striped bass, Morone saxatilis (Walbaum), in the Chesapeake Bay region. Concentrations of striped bass eggs found during the period of peak spawning may be the highest that have been reported. Limited evidence suggests that the C&D Canal has provided a favorable alternative to now destroyed historical spawning grounds of striped bass in the lower Susquehanna River.

Gonadal development and total gonadal DNA of M. manhattensis were studied. Evidence of atrophication and of phagocytosis of residual gametes was found during histological examination. Colorimetric estimations of gonadal DNA indicated that at least two spawning peaks occurred during the summer and suggested that egg release was suppressed by water temperatures above 20 C.

Fully developed polyps of Chesapeake BayAurelia aurita reared in the laboratory from known medusae were found to have circular mouths instead of the typical cruciform shape. This characteristic distinguishes them from those ofChrysaora quinquecirrha andCyanea capillata in the same region and could be useful for identification purposes in field collections. Laboratory-reared polyps ofAurelia aurita from Delaware Bay and the Gulf of Mexico also retained a circular mouth throughout their development. This mouth shape distinguishes the polyps from these three regions from those of the same species from higher latitudes and appears to be a deviation from the normal development of the organism.

Descriptions and illustrations of larvae and juveniles of the ballyhoo,Hemiramphus brasiliensis (Linnaeus) andHyporhamphus sp. are provided, based on specimens from Chesapeake Bay and its tributaries. The first captures of youngHe. brasiliensis in estuarine conditions are recorded and the first documented record of this species from Maryland waters of Chesapeake Bay is offered.

Bacteriological studies were carried out to determine a causative agent of soft-shell clam mortalities occurring in Chesapeake Bay, i.e., Eastern Bay to the Wicomico River, in midwinter, 1970 and through 1971. Several screening tests were performed in preliminary experiments designed to detect the presence of potential pathogens. Growth of 57 cultures isolated from count plates was tested at cold temperatures over long periods of time. Sixteen strains grew under the conditions employed in this screening and of these, eight strains were found to cause death of all animals within 48 hours and to show good growth at 4 C within one week. Numerical taxonomy was employed to identify and classify the isolates. Two of the eight strains, one identified as a member of the Enterobacteriaceae and the other as a Vibrio sp., were considered to be potential pathogens for the soft-shell clam. Direct evidence of the pathogenicity of these strains is not yet conclusive, although pathogenicity is strongly indicated from the results of experiments carried out in this study.

LarvalAlosa pseudoharengus may be distinguished from larvalA. aestivalis by differences in the relative termination of the vent. The number of myomeres between the insertion of the dorsal fin and the vent is diagnostic. The mean number is 8.0 inA. pseudoharengus and 11.8 inA. aestivalis. Also of use in distinguishing between larvae of the two species are the number of preanal myomeres, the regression of the distance from snout to vent on standard length, the regression of the distance from vent to tail on standard length. Methods of distinguishing larvalA. pseudoharengus andA. aestivalis from commonly associated species in the Chesapeake Bay region are discussed.

1. Apparently significant trends within moderately long (50-year) series of meteorological or hydrological data should be regarded with suspicion until justified on the basis of much longer term information. 2. Extra efforts should be directed toward securing the continuance of routine observations at stations where long data histories are already available and where the termination of such records might be regretted at some future time. 3. Mean annual air and water temperatures at different sites may be quite highly correlated even when the points of measurement are very widely separated. 4. The annual average water temperature at one station close to the Chesapeake Bay appears to be normally distributed with a standard deviation of 0.7°C about a stationary overall mean value of 14.6°C. Its 1000-year departure is ±2.2°C.

Blueback herring (Alosa aestivalis), American shad (Alosa sapidissima), and striped bass (Morone saxatilis) larvae from the Chesapeake Bay region were subjected in the laboratory to time-excess temperature histories typical of those experienced by organisms entrained by power plants with a variety of design and operating criteria. The maximum excess temperature ranged from 7° to 20°C above the base temperature (the average surface water temperature on the spawning grounds); the time of exposure to a maximum excess temperature from 4 to 60 minutes; and the period of cooling to the final temperature from 60 to 300 minutes. An excess temperature of 20°C resulted in virtually total mortality of larvae of all three species. Striped bass larvae were the most tolerant of the, three species and could withstand excess temperatures of up to 10°C with no significant increase in mortality. The response patterns of the other two species were more complicated.

Nest success was determined for 330 osprey nesting attempts along Eastern Bay, Maryland, from 1966 through 1974. Young were fledged in 45 percent of the nesting attempts on offshore structures and in only 24 percent of the attempts in trees. The average number of young fledged per active nest was 0.71. This average is among the poorest in the country, it is appreciably lower than that of adjacent areas studied in the Chesapeake Bay and it is well below the ratio estimated to be necessary for population stability. Known causes for loss of nests, eggs and young are documented.

Bacteria belonging to the order Hyphomicrobiales comprised less than 0.01% of the planktonic bacterial community of water samples collected from the Chesapeake Bay and surrounding tributaries. These budding bacteria, however, were present in all of the 15 samples assayed. Two strains of Hyphomicrobia were isolated, one from the mouth of the Patuxent River and another from a Rock Creek tributary (Hyphomicrobium RC).

An aerial survey in association with several intensive ground surveys yielded the first estimate of the size of the osprey (Pandion haliaetus carolinensis) nesting population in Chesapeake Bay. The 1973 population was estimated at 1,450±30 pairs, of which 713 were on the western shore and 737 on the eastern shore. A small percentage of nonbreeders (possibly 2–5 percent) may be included in this estimate. Only 31.7 percent of the population was nesting in trees; the remaining birds utilized duck blinds (28.7 percent), channel markers (21.8 percent), and miscellaneous man-made structures (17.8 percent). The geographical distribution of nesting ospreys has quite likely changed during the last several decades as suitable artificial nesting sites have become more available. Furthermore, limited evidence suggests that birds nesting on the man-made sites were more successful than those nesting in trees. This study provides a basis for monitoring future changes in numbers and distribution.

Food habits and seasonal abundance of the American eel, Anguilla rostrata (Lesueur), were studied from the brackish water regions of three Virginia rivers. Abundance in trawl surveys was related to water temperatures with fewer eels being caught during the colder months. Polychaetes, crustaceans and bivalves were the most important dietary items of A. rostrata in brackish water. There was much predation on the commercially important species Mya arenaria and Callinectes sapidus.

Destruction of Zostera beds in the York River, Virginia, is attributed to the digging activities of the cownose ray, Rhinoptera bonasus. The physically stable Zostera habitat with high faunal diversity and density was replaced by an unstable sand habitat with low faunal diversity and density.

Seasonal fluctuations in zooplankton abundance between July 1973 and July 1974 showed a clear peak in total copepods and rotifers in February–March, and a less pronounced peak in July–August. Standing crop and production estimates for the two dominant copepods,Acartia tonsa andEurytemora affinis, revealed that the February–March peak was primarilyE. affinis and sustained far higher biomass (218·6 mg/m3) and production (20·5 mg/m3·day) than did the August peak ofA. tonsa (biomass 16·3 mg/m3, production 7·5 mg/m3·day). The Rhode River has low standing crop and production of copepods relative to the much larger Patuxent estuary. These results are consistent with the theory of Williams et al. (1968) that shallow embayments have lower standing crops; however, the statistical basis for their statement is shown to be spurious.

Male rock crabs,Cancer irroratus, were collected from the lower Chesapeake Bay during the winter dredge seasons of 1970–1973. Crabs migrate into Chesapeake Bay in late fall, molt extensively in January, remain in papershell condition until late March and April and leave the bay in May. Most crabs held in the laboratory molted in January, only 18% in February, thus confirming the pattern observed in the field. The molting season of male rock crabs appears to be related to decreasing seawater temperature.

Sand shrimpCrangon septemspinosa were collected during monthly trawl surveys of the Chesapeake Bay and York River estuary from January 1971 to April 1972. Over 9000 shrimp were captured within wide ranges of temperature (0.5–24.1 C), salinity (10.3–31.1‰) and dissolved oxygen concentration (2.1–12.7 mg/liter). Relative abundance of shrimp in the channels varied seasonally. Maximum concentrations occurred in winter when bottom water temperatures were between 5 C and 11°C. The concentration of shrimp was reduced in spring when the temperature exceeded 15 C. Salinity limited the upstream penetration of the species. Occasionally shrimp were found in salinities as low as 10–12‰, but they were usually collected when salinities exceeded 16‰. Low levels of dissolved oxygen concentration (2–5 mg/liter) in summer coincided with reduced catches and absence of shrimp.

This paper contains the first published radiometrically determined contemporary sedimentation rate, a rate characteristic of the past few decades, for any part of the Chesapeake Bay estuarine system. Cores collected from a station in the main body of the Chesapeake Bay off Tilghman Island (38°41′30″N, 76°24′00″W) were analyzed for Pb210, organic carbon, nitrogen, and selected metals. A mean sedimentation rate of between 0.09–0.12 cm/y was inferred from the Pb210 data. The distributions of C and N are typical of many areas of the Bay. The distributions of extractable Ni, Cr, Cu, and Pb increased in the upper 10–15 cm of the core. The increases in metal concentrations over the past century or so may be a result of man’s activities.

The use of relatively small hydraulic tow dredge for sampling hard clams (Mercenaria mercenaria) is discussed in conjunction with a sequential sampling plan. The sequential sampling plan, in which the number of replications was not predetermined, was employed to categorize hard clam densities into high, medium and low classes. Its application resulted in a 70% saving in sampling effort compared with a comparable fixed sampling plant when the objective was the classification of density rather than the estimation of a density parameter.

Fecundity data for 24 northern puffer from the lower Chesapeake Bay indicate production of up to 0.5 million eggs by 300 mm TL fish. The left ovary averaged 1.6X larger than the right. Despite the physical difference in ovary size, eggs from Gilson’s solution treated ovaries were of equivalent size in both left and right ovaries. Fecundity versus total body length and body weight are presented.

Early summer concentrations discovered by sportfishermen in Chesapeake Bay allowed tagging and release of twenty fish. Six returns were received from sport catches up to five years after release (1,855 days). Sport fishing mortality was 0.30 ±0.21 with P=95%.

One hundred ninety-four larvae ofSymphurus plagiusa were taken in the lower Chesapeake Bay during a three-year zooplankton survey 1971–1974. Early larval stages (1.3–6.2 mm NL) are illustrated and described. Recently hatched larvae (1.3–2.8 mm NL) are distinguished by pigment patterns, gut configuration, and a fleshy occipital hump. Later larvae (2.8–6.2 mm NL) are identified by pigmentation, gut configuration and produced dorsal rays.

The only publications attempting to list the species of fishes known to inhabit Maryland and Delaware (Uhler and Lugger 1876, 1877; Fowler 1911; Truitt, Bean, and Fowler 1929) are now outdated. Musick (1972) listed the fishes known from the Chesapeake Bay and adjacent Coastal Plain tributaries, and Mansueti (1957) and Davis (1973) provided keys to the freshwater fishes expected in Maryland. Although there are numerous references to various freshwater fishes in this area, there has been no recent effort to provide a documented list of the species known from these states. We are presently compiling information on the freshwater fishes of Maryland and Delaware (descriptions, distributions, ecology, and zoogeography). The following lists are based on this work. Table I includes all

An epizootic caused by a sporozoan,Minchinia nelsoni, commonly known as “MSX”, began in large plantings of oysters at the mouth of the York River, Virginia, in 1959. In 1960 all public and private beds in lower Chesapeake Bay experienced heavy losses. Commercial plantings in this area ceased in May 1960. Three slightly wet years were followed by three very dry years, which permitted the parasite, MSX, to spread farther up Chesapeake estuaries. After seven years, no important changes in patterns of timing or intensity of activity have been observed in epizootic areas. Distribution of MSX in Virginia for typical years is depicted with an attempt to categorize areas as to amount and frequency of damage to be expected. The history of the epizootic and some effects on the oyster industry are described. Prevalences of MSX and death rates over a seven-year period are compared.

Length-frequency distribution and scale samples of spot,Leiostomus xanthurus, were examined from 1955–58 pound-net catches in lower Chesapeake Bay. The scale method of age determination was validated for this sciaenid species. Few spot older than three years were found in the fishery to which they are generally available from April to October. Larger members of the young-of-the-year group may enter the fishery in July. A rapid rate of growth for the first two years is indicated with considerable overlap in sizes by age groups of older fish. Exploratory trawl data for 1956–58 indicated seasonal distribution within the York River system and lower Bay, and annual variations in abundance, particularly that of young-of-the-year fish. A close apparent relation existed between annual recruitment to pound nets and trawl catch-per-unit-effort of young fish. Change of age composition in the pound-net catch and higher than average trawl catches of the 1956 year-class suggest this year-class was produced in dominant numbers.

Lengths of 14,508 weakfish from pound-net catches in Chesapeake Bay during the 1954–58 period showed little variation from year to year; modal lengths ranged from 220 to 235 mm. Spring catches included larger fish than were taken in summer and fall. Age composition, based on scale samples from 4,516 fish, changed little from year to year and was estimated as: 62 per cent, 1-year olds; 28 per cent, 2-year olds; 8 per cent, 3-year olds; and 1 per cent, 4-year olds. Two- and 3-year old fish dominated spring catches, 1-year old the summer and fall catches. Annual catch per net ranged from 50,000 to 70,000 pounds. In some months almost half of the catch was utilized as scrap. A single year class (1955) contributed about 200,000 fish per net. Before conclusions may be drawn concerning fishing mortality or the effect of the Virginia fishery on weakfish stocks further north, the complex migratory patterns of weakfish must be more clearly known.

An analysis was made of the functioning of 45 groins constructed to control beach erosion at Scientists Cliffs, Calvert County, Maryland. The results show that the height of groins, non-spillover length of groins, and availability of coarse sand are critical factors affecting height of sand accumulation and width of beach between groins. Very fine sand particles, smaller than 0.125 mm in diameter, are transported by wave action seaward and form very little of the sand accumulation between groins.

The host-parasite relationship between the spot,L. xanthurus, andT. tenuicornis was studied in Chesapeake Bay during the summers of 1959 and 1960. Of 272L. xanthurus examined during 1959, 207 (76.1 per cent) were found to be infected. The worm burden ranged from 1 to 87 with a mean of 6.5 worms per fish. Supplemental collections during 1960 yielded similar results. The incidence and intensity of infection in spot over 13 cm in standard length were greater than in smaller fish; noT. tenuicornis were found in 23 spot that ranged from 4.4 to 9.0 cm S. L. The condition factors for parasitized and non-parasitized fish were similar.