Genetic structure of bay anchovy (Anchoa mitchilli) populations in Chesapeake Bay

To determine the genetic structure of the bay anchovy (Anchoa mitchilli) within Chesapeake Bay, 16 isozyme systems encoding 21 loci for 20 population were examined using horizontal starch gel electrophoresis. Contingency Chisquare analysis revealed significant allelic frequency differences at nine loci (AAT-1, AAT-2, ALD-1, CPK-2, GAP-1, GLY-1, LDH-1, MDH-1, and MDH-2). Two loci, ALD-1 and MDH-1, were responsible for nine of 14 tests not conforming to Hardy-Weinberg expectations, with some of these deviations attributed to possible scoring and/or sampling error. Estimates for mean average heterozygosity were relatively high, ranging from 0.40 to 0.096, with 33–57% of the loci polymorphic. A low F_st value (0.041) along with high genetic identity estimates (I=0.997) indicated little substructuring of bay anchovy populations within Chesapeake Bay.     

Temporal variation in the utilization of an intertidal creek by the bay anchovy (Anchoa mitchilli)

A brackish-water, intertidal creek was sampled 19 times during the summer of 1976. Samples were analyzed to determine occurrence, abundance, and diversity of fish species present and to determine patterns of daily fish movement and utilization of intertidal creeks in an old rice field. Samples were collected from the primary station on the ebbing tide with a channel net. Three secondary stations were each sampled twice for comparative results and total biomass and average length per species calculated for each sample. We collected 125,579 individuals with a total biomass of 11.7 kg which represented 23 families and 37 species. Anchoa mitchilli was the dominant species and comprised 96.3% of the total numbers of individuals caught. The next two most abundant fish, Menidia menidia and Fundulus heteroclitus, represented 2.5% and 0.4% of the total numbers caught. The data from the nineteen sample collections were ordered by time of day and the resultant time series sequence of collections simulated a sample collection taken about once every 1.5 hours over 24 hours. A pattern of occurrence was noted for A. mitchilli as increased fish numbers occurred when the creek flooded during the daylight hours and there were significantly reduced numbers when the creek flooded during the early evening or at night. A relationship between light intensity, feeding, and predator avoidance is proposed to explain the creek loading pattern of A. mitchilli.     

Spatial and temporal growth rate variation of Bay Anchovy (Anchoa mitchilli) larvae in the Mid Hudson River estuary

Estuaries are critical habitats for larvae and juveniles of many marine fishes, possibly because they promote high growth rates and survival rates. We investigated spatial and temporal changes in growth rate of larval bay anchovy (Anchoa mitchilli), in the middle Hudson River estuary where abundance of larvae is high. In two consecutive summer seasons, we sampled larvae at 4 sites evenly spaced over 45 km, at weekly intervals for up to a month. We examined otoliths to determine age in days and then used age-length regressions to estimate growth rate. In 1995, larval anchovy growth rates varied from 0.39 to 0.88 mm d⁻¹ (median=0.48 mm d⁻¹). In 1996, growth rates varied from 0.41 to 0.77 mm d⁻¹ (median=0.55 mm d⁻¹). In both years, we found significant spatial and temporal variation in growth rate. Larvae collected in the upper portion of Haverstraw Bay tended to grow more slowly than larvae collected in other sites. The dates on which the most rapidly growing larvae were collected varied from site to site. Neither temperature nor salinity variations explained growth rate differences. Growth rate variation, probably governed by patches of zooplankton, occurred on temporal scales of a week and spatial scales of 15 km.     

Regional and temporal variability in distribution and abundance of bay anchovy (Anchoa mitchilli) eggs, larvae, and adult biomass in the Chesapeake Bay

Patterns and variability in reproductive output of pelagic fish are seldom determined at the ecosystem scale. We examined temporal and spatial variability in spawning by bay anchovy (Anchoa mitchilli), and in distribution and abundances of its pelagic early-life stages, throughout Chesapeake Bay. On two cruises in June and July 1993, ichthyoplankton and zooplankton were collected on 15 transects at 18.5-km (10 nautical mile) intervals over the 260-km length of the bay. Finer-scale sampling was carried out in a grid of stations between two transects on each cruise. Regional abundance patterns of bay anchovy eggs and larvae in the lower, mid, and upper Bay were compared with zooplankton abundances, environmental variables, and biovolumes of two gelatinous predators—the scyphomedusa Chrysaora quinquecirrha and the lobate ctenophore Mnemiopsis leidyi. Abundances of anchovy eggs, and, especially, larvae were higher in July than in June. Baywide daily egg production increased from 4.25×10¹² in June to 8.43×10¹² in July. Concentrations of zooplankton that are potential anchovy prey nearly doubled on a baywide basis between June and July, while biovolumes of the ctenophore declined. Except for scyphomedusan biovolumes, all analyzed organisms differed regionally in abundance and were patchily distributed at 1-km to 10-km sampling scales. Negative correlations between larval anchovy abundances and gelatinous predator biovolumes suggested that predation may have controlled abundances of bay anchovy early-life stages. Biomasses of adult anchovy, estimated from daily egg productions, were higher in the lower Bay and remarkably similar—23,433 tons in June and 23,194 tons in July. Most spawning by bay anchovy occurred during July in the seaward third of Chesapeake Bay, emphasizing the importance of this region for recruitment potential of the Bay's most abundant fish.     

Eggs and early larvae of the bay anchovy,Anchoa mitchilli,and the weakfish,Cynoscion regalis,in lower Chesapeake Bay with notes on associated ichthyoplankton

The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.     

Upper temperature tolerance of spot,Leiostomus xanthurus,from the cape Fear River estuary,North Carolina

The temperature tolerance and resistance times of postlarval (<25 mm SL) and small juvenile spot,Leiostomus xanthurus, from the Cape Fear Estuary, North Carolina were tested in the laboratory. Critical thermal maximum techniques were used to determine first equilibrium loss (FEL) and critical thermal maximum (CTM) end points and thermal shock methods were used to determine 96-h upper incipient lethal temperatures (LT₅₀). Acclimation temperatures ranged from 10 to 35°C and acclimation salinities were 10, 20 and 30‰. A quadratics model was fit to the CTM and FEL data; r² values were 0.924 and 0.928 respectively. Acclimation salinity, estimated weight, acclimation salinity by acclimation temperature interaction and acclimation temperature by estimated weight interaction were the significant components of the CTM model. Predicted CTM values ranged from 30°C at 10 °C and 30‰ acclimation to just over 40°C at 30 °C and 30‰ acclimation. Acclimation temperature, acclimation temperature squared, estimated weight and acclimation temperatures by estimated weight interaction were the significant components of the FEL model. Predicted FEL values ranged from around 28°C at 10°C and 10‰ acclimation to about 39°C at 30°C and 30‰ acclimation. The 96-h LT₅₀ values of spot acclimated to 20‰ increased linearly with acclimation temperature to 25°C. From about 25 to 35°C, LT₅₀ values increased very little with acclimation temperature. The ultimate upper incipient lethal temperature of postlarval and small juvenile spot was estimated at 35.2°C. Increased salinity increased resistance time but decreased LT₅₀ estimates. Thermal shock tests were better for predicting the effects of thermal addition than were CTM tests.     

Network analysis of nitrogen inputs and cycling in the Neuse River estuary,North Carolina,USA

The Neuse River estuary, North Carolina, United States, has demonstrated various symptoms of eutrophication during the past 20 yr. We contributed to an environmental assessment program, through ecological network analysis, a group of algorithms to evaluate networks of material flows within a structured system. Networks of nitrogen (N) cycling for 16 consecutive seasons were constructed based on previous field and laboratory studies. Network analysis provided understanding of the relationship between N loading and recycling, the fates of N and the expected interseasonal variation of both model inputs and outputs. Various indices indicated that recycling of imported N was very high, supporting measured observations. There was little correlation between estimates of loading and N uptake by phytoplankton, although loading of total and particulate N did correlate positively with export. Because of the high degree of recycling of N, the rate of loading of new N is a small fraction of the total processing of N or of the needs for primary production alone. We predict that on a short-term basis the controls on primary production tend to be associated with conditions in the estuary rather than import. This condition is likely to postpone easily observable responses to loading reduction over the entire estuary and in the short term, although improvements in water quality should occur over time.     

Denitrification rates measured along a salinity gradient in the eutrophic Neuse River estuary, North Carolina, USA

Denitrification rates along a salinity gradient in the eutrophic Neuse River Estuary, North Carolina, were quantified using membrane inlet mass spectrometry (MIMS) within short-term batch incubations. Denitrification rates within the system were highly variable, ranging from 0 to 275 μmol N m⁻² h⁻¹. Intrasite variability increased with salinity, but no significant differences were observed across the salinity gradient. Denitrification rates were positively correlated with sediment oxygen demand at the upstream sampling site where sediment organic carbon levels were lowest. This relationship was not observed in the more saline sampling sites. Denitrification rates were highest during winter. On an annual basis, denitrification accounted for 26% of the dissolved inorganic nitrogen and 12% of the total nitrogen supplied to the system.     

The relationship between beam transmission and concentration of suspended particulate material in the Neuse River estuary,North Carolina

Monthly measurements made at 15 stations along the axis of the upper Neuse River estuary show a highly variable degree of correlation between concentration of suspended particulate material (SPM) and attenuation of light (c) as measured by transmissometer. Coefficients of determination along transect lines ranged from 0.12 to 0.93 and calibration slopes ranged from 0.50 to 5.63. When examined on a station-by-station basis, coefficients of determination ranged from 0.21 to 0.96 and calibration slopes ranged from 1.04 to 4.94. Surface calibrations made at individual stations over the full 13-month period were the most consistent of all observations and were considerably better than calibrations made using all of the stations on a given day. Organic content, which can dominate the suspended sediment load during some months, does not appear to explain the variations in reliability of the calibrations. However, an abundance of large aggregates with time-varying size and shape distributions may be partly responsible for variations in optical properties of the sediments, and thus may confound the relationship between SPM and c in the Neuse River estuary. Time-varying calibrations to account for non-negligible changes in optical properties may not suffice in complex estuarine environments where the in situ particle dynamics are poorly understood.     

Abundance and size of larval fishes outside the entrance to Beaufort Inlet, North Carolina

Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics.     

Recruitment and growth of the Eastern oyster,Crassostrea virginica,in North Carolina

The effects of location, salinity, and depth on recruitment and growth of the eastern oyster Crassostrea virginica in Pamlico and Core sounds, North Carolina, were investigated from 1988 to 1990. We measured length and density of spat settling on oyster cultch deployed at deep (～3 m) and shallow (～1 m) depths at six sites in areas with low salinity and six sites in areas with high salinity. These data were compared with similar data taken at some of these sites by the North Carolina Division of Marine Fisheries since 1981 as part of their cultch planting program. Recruitment was generally greater in the high salinity sites, compared to the low salinity sites. Recruitment was less at shallow depths compared to deeper depths. In all three years the highest recruitment occurred in August and September, corresponding to the months of maximum water temperature. Recruitment was highly variable in space and time, but appeared to diminish from 1988 to 1990. Recruitment was reduced by sedimentation and a variety of sessile organisms. All sites appeared to have a similar potential for growth.     

Estimation of Groundwater and Nutrient Fluxes to the Neuse River Estuary, North Carolina

A study was conducted between April 2004 and September 2005 to estimate groundwater and nutrient discharge to the Neuse River estuary in North Carolina. The largest groundwater fluxes were observed to occur generally within 20 m of the shoreline. Groundwater flux estimates based on seepage meter measurements ranged from 2.86?×?10⁸ to 4.33?×?10⁸ m³ annually and are comparable to estimates made using radon, a simple water-budget method, and estimates derived by using Darcy’s Law and previously published general aquifer characteristics of the area. The lower groundwater flux estimate (equal to about 9 m³ s^?1), which assumed the narrowest groundwater discharge zone (20 m) of three zone widths selected for an area west of New Bern, North Carolina, most closely agrees with groundwater flux estimates made using radon (3–9 m³ s^?1) and Darcy’s Law (about 9 m³ s^?1). A groundwater flux of 9 m³ s^?1 is about 40% of the surface-water flow to the Neuse River estuary between Streets Ferry and the mouth of the estuary and about 7% of the surface-water inflow from areas upstream. Estimates of annual nitrogen (333 tonnes) and phosphorus (66 tonnes) fluxes from groundwater to the estuary, based on this analysis, are less than 6% of the nitrogen and phosphorus inputs derived from all sources (excluding oceanic inputs), and approximately 8% of the nitrogen and 17% of the phosphorus annual inputs from surface-water inflow to the Neuse River estuary assuming a mean annual precipitation of 1.27 m. We provide quantitative evidence, derived from three methods, that the contribution of water and nutrients from groundwater discharge to the Neuse River estuary is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment sources of nutrients. Locally high groundwater discharges do occur, however, and could help explain the occurrence of localized phytoplankton blooms, submerged aquatic vegetation, or fish kills.     

Parasites and cyclopoid predators of age-0 fish in the Roanoke River,North Carolina

Altered river flow has been suggested as a cause for the low recruitment of striped bass,Morone saxatilis, in the Roanoke River (North Carolina) because of its effect on the proximity of zooplankton and larval striped bass. This results in unsuccessful feeding and subsequent starvation, which was considered to be a major mortality factor. Other mortality factors, such as parasitism and copepod predation on age-0 fish, may also be regulated to some extent by changes in river flow. The relationship of cestode plerocercoids, trematode metacercaria, mussel glochidia, and cyclopoid copepod predators with age-0 fish was evaluated in the lower Roanoke River and western Albemarle Sound from plankton net collections made in 1984 to 1986 and 1988. Plerocercoid prevalence was higher under low river flow conditions than under high flow conditions in darters (Percidae; 16.7% vs. 9.2%), minnows (Cyprinidae; 28.8% vs. 4.7%), andMorone (1.9% vs. 0%). Gut analysis of the age-0 fish revealed that copepods (source of the plerocercoids) were a major diet component ofMorone and darters but not of minnows or herring (Clupeidae). Decreases in river flow were associated with increases in copepod density (Pearson r=?0.62; p=0.0001) and plerocercoid prevalence inMorone (Pearson r=?0.29; p=0.03). The low correlation value forMorone may be quite strong considering the complexity of the variables associated with prevalence. Metacercaria were found only inMorone and minnows, and prevalence and mean intensity were less than that found for plerocercoids. Mussel glochidia prevalence was less than 0.5% for all affected taxa, an order of magnitude less that that found in other studies. The low value may indicate that the mussel population in the Roanoke River is declining. Prevalence of attacks by the predatory copepodMesocyclops edax on age-0 fish was similar to that in Chesapeake Bay, and striped bass was the primary prey. Spatial and temporal proximity of copepods and fish prey may be the key factors in regulating copepod attacks. The low prevalence of parasites and copepod predators seen in this tudy would suggest that mortality from these sources may not be a major factor in age-0 recruitment in this system. Confirmation of these conclusions would require a more controlled experimental approach.     

Sources and transformations of organic matter in surface soils and sediments from a tidal estuary (North Inlet, South Carolina, USA)

Surface soil and sediment samples collected along a forest-brackish marsh-salt marsh transect in a southeastern U.S. estuary were separated into three different fractions (sand, macro-organic matter, and humus) based on size and density. Elemental, stable carbon isotope, and lignin analyses of these samples reveal important contrasts in the quantity, composition, and sources of organic matter, between forest and marsh sites. Elevated nitrogen contents in humus samples suggest nitrogen incorporation during humification is most extensive in forest soils relative to the marsh sites. The lignin compositions of the macro-organic and humus samples reflect the predominant type of vegetation at each site. Lignin phenol ratios indicate that woody and nonwoody litter from, gymnosperm and angiosperms trees (pines and oaks) is the major source of vascular plant-derived organic matter in the forest site and that angiosperm, grasses (Juncus andSpartina) are the major sources of lignin at the marsh sites. The phenol distributions also reveal that oxidative degradation of lignin is most extensive in the forest and brackish marsh zones whereas little lignin decay occurs in the salt marsh samples. In forest soils, most organic matter originates from highly altered forest vegetation while at the brackish marsh site organic matter is a mixture of degradedJuncus materials and microbial/algal remains. Organic matter in the salt marsh appears to be composed of a more complex mixture of sources, including degradedSpartina detritus as well as algal and microbial inputs. Microbial methane oxidation appears to be an important process and a source of¹³C depleted organic carbon in subsurface sediments at this site.     

Dissolved and particulate organic carbon in the North Inlet estuary,South Carolina: What controls their concentrations?

Water samples have been taken daily at 1030 EST from three locations within North Inlet (South Carolina) since June of 1980 in order to evaluate the tidal, seasonal, and eventually annual variability in carbon concentrations within this system and generate hypotheses explaining the observed trends. Dissolved organic carbon (DOC) concentrations within North Inlet (South Carolina) vary inversely with salinity (r²=0.65), suggesting the main source of DOC in North Inlet is freshwater entering from the adjacent forested watershed. This assertion is supported by an observed decrease of tidal water salinity with the onset of streamflow. DOC variability is also associated with (1) groundwater advection and/or runoff and seepage from the marsh surface; (2) removal from tidal water via either physical sorption or biological uptake; (3) sampling location; and (4) origin of water mass. Particulate organic carbon (POC) concentrations vary seasonally, higher values found during the summer. POC variability is controlled by a series of physical and biological factors. Evidence suggests that in the smaller tidal creeks, POC concentrations are associated with (1) rain events scouring the marsh surface, (2) phytoplankton concentrations varying as a function of tidal stage, and (3) removal of particulate material from the marsh surface on the ebb tide. In the larger tidal creeks tidal water velocity appears to be the main factor influencing POC values.     

Reversal of eutrophication following sewage treatment upgrades in the New River Estuary, North Carolina

The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km², located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During 1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately 57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate, chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO of 0.9 to 1.4 mg l⁻¹, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for fish and shellfish.     

Recruitment failure of the bay scallop,Argopecten irradians concentricus,during the first red tide,Ptychodiscus brevis,outbreak recorded in North Carolina

In the presence of the first recorded red tide (Ptychodiscus brevis) outbreak in North Carolina, autumn 1987 recruitment of bay scallops (Argopecten irradians concentricus) in the state’s most productive scallop beds was a virtual failure. Recruitment averaged across all of Bogue and Back sounds was only 2% of the mean of three previous red tide-free (control) years. Only from central Core Sound northward, where the red tide occurred later and not as intensively, was bay scallop recruitment normal (93% of control years). Mortality of adult scallops from early December 1987 to late January 1988, while red tide was at bloom concentrations but fishing was prohibited, was 21%. No comparable natural mortality data exist for control years because intense fishing mortality in this period is confounded with natural mortality. Data on abundance of articulated pairs of empty shells strongly suggest that the red tide caused mortality of both adult and newly recruited bay scallops. Bay scallop recruitment in autumn 1988 again failed to restock the traditionally productive scallop beds in western Bogue Sound and in Back Sound, perhaps because the only concentrations of spawners surviving the red tide in central Core Sound and further north were too far distant for successful transport of bay scallop larvae in sufficient abundance to these traditional beds. This potential explanation implies continuing impact of the red tide on North Carolina’s bay scallop fishery until spawning populations increase in Back Sound and western Bogue Sound.     

Finfish utilization of man-initiated and adjacent natural creeks of South Creek estuary,North Carolina using multiple gear types

Three gear types were used to collect finfish species from several tributaries of the South Creek estuary near Aurora, North Carolina, to ascertain whether a man-initiated marsh and creek system resembled adjacent natural areas in finfish species composition and abundance. Project Area II was the man-initiated area constructed in 1983 as up-front mitigation by North Carolina Phosphate Corporation prior to its anticipated mining in the headwaters of nearby natural wetlands. Two creeks served as controls throughout the study: Drinkwater Creek and Jacks Creek. Otter trawls were used monthly from July 1984 through December 1988. Wegener rings were used in April, July, and October from 1984 through 1987. An experimental gill net was used monthly from June 1984 through 1985. A total of 48 finfish species was captured during the study; only 14 species (29.2%) were common among gear types. The species collected were mud sunfish, blueback herring, alewife American shad, striped anchovy, bay anchovy, inland silverside, American eel, silver perch, Atlantic menhaden, crevalle jack, common carp, spotted seatrout, weakfish, sheepshead minnow, gizzard shad, ladyfish, chain pickerel, banded killifish, mummichog, striped killifish, rainwater killifish, mosquitofish, naked goby, green goby, white catfish, brown bull-head, pinfish, longnose gar, green sunfish, pumpkinseed, bluegill, redear sunfish, spot, Atlantic croaker, largemouth bass, white perch, striped bass, striped mullet, white mullet, golden shiner, summer flounder, southern flounder, yellow perch, bluefish, Atlantic needlefish, hogchoker, andTilapia species. Abundance of finfish species was a function of gear type. Bay anchovy and spot represented about 85% of all fish in trawl samples. The remainder was comprised of 27 other species. In Wegener rings, five species—bay anchovy, menhaden, rainwater killifish, spot, and inland silverside—each represented over 10% of all fish collected. Croaker and striped mullet each comprised more than 5% of all fish collected in Wegener rings, but were present in substantial numbers only in 1985. Based on trawl samples, the total number of finfish collected from Project Area II during the period 1984–1988 was statistically similar to those collected from the control creeks; Wegener ring data analysis indicated significantly greater catches in Project Area II compared to the control creeks. Bay anchovy catches were not significantly different among the three creeks by either trawl or Wegener ring. The same result was true for Atlantic menhaden and southern flounder. The abundance of spot in trawl samples from Project Area II was significantly greater than for the control creeks; abundance in ring samples from Project Area II was statistically similar to Jacks Creek, but significantly higher than Drinkwater Creek. The number of Atlantic croaker in Project Area II trawl samples was significantly lower than for the cotnrol creeks. Wegener rings did not sample croaker effectively.     

Food habits and growth of juvenile striped bassMorone saxatilis, in Albemarle Sound, North Carolina

Juvenile striped bass,Morone saxatilis, collected in Albemarle Sound, North Carolina, during 1988–1992 were examined for food habits and growth. Ages estimated from otoliths collected in 1990–1992 were used to determine individual spawning dates and growth in total length and weight. The majority of striped bass examined had been spawned in mid-May 1990, mid-May to early June 1991, and June to early July 1992. Mysid shrimp was the dominant prey taxon and was consumed in all size classes examined. Mysid shrimp were consumed at twice the rate of copepods and 10 times more frequently than cladocerans. Fishes were a minor prey taxon. The number of mysid shrimp consumed increased with increasing length of striped bass. A higher percentage of mysid shrimp were consumed in the more saline waters of the central sound than in the less saline western sound. The opposite trend was found for consumed fishes. Increases in total length were linear from July to October, but increases in weight were not. Weight increased less rapidly in younger striped bass and more rapidly in older striped bass than either length or age. Quadratic and logarithmic equations accurately predicted weight from measures of total length but weight could not be predicted from age nor could age be predicted from total length. Estimating growth from total length at time of capture may be comparing fish of different ages. Age estimation from otoliths allowed us to determine that growth rates were similar among years and that differences in observed total length over time were due to different spawning times and not growth rates.     

Prograde and retrograde history of eclogites from the Eastern Blue Ridge, North Carolina, USA

Abstract The prograde metamorphism of eclogites is typically obscured by chemical equilibration at peak conditions and by partial requilibration during retrograde metamorphism. Eclogites from the Eastern Blue Ridge of North Carolina retain evidence of their prograde path in the form of inclusions preserved in garnet. These eclogites, from the vicinity of Bakersville, North Carolina, USA are primarily comprised of garnet–clinopyroxene–rutile–hornblende–plagioclase–quartz. Quartz, clinopyroxene, hornblende, rutile, epidote, titanite and biotite are found as inclusions in garnet cores. Included hornblende and clinopyroxene are chemically distinct from their matrix counterparts. Thermobarometry of inclusion sets from different garnets record different conditions. Inclusions of clinozoisite, titanite, rutile and quartz (clinozoisite + titanite = grossular + rutile + quartz + H₂O) yield pressures (6–10 kbar, 400–600 °C and 8–12 kbar 450–680 °C) at or below the minimum peak conditions from matrix phases (10–13 kbar at 600–800 °C). Inclusions of hornblende, biotite and quartz give higher pressures (13–16 kbar and 630–660 °C). Early matrix pyroxene is partially or fully broken down to a diopside–plagioclase symplectite, and both garnet and pyroxene are rimmed with plagioclase and hornblende. Hypersthene is found as a minor phase in some diopside + plagioclase symplectites, which suggests retrogression through the granulite facies. Two‐pyroxene thermometry of this assemblage gives a temperature of c. 750 °C. Pairing the most Mg‐rich garnet composition with the assemblage plagioclase–diopside–hypersthene–quartz gives pressures of 14–16 kbar at this temperature. The hornblende–plagioclase–garnet rim–quartz assemblage yields 9–12 kbar and 500–550 °C. The combined P–T data show a clockwise loop from the amphibolite to eclogite to granulite facies, all of which are overprinted by a texturally late amphibolite facies assemblage. This loop provides an unusually complete P–T history of an eclogite, recording events during and following subduction and continental collision in the early Palaeozoic.