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Geology topics

J. H. Johnson

Publications and source records attributed to J. H. Johnson.

35 records · Page 2Linked to original sources
USGS1997

Food habits of Atlantic sturgeon off the central New Jersey coast

Limited information exists on the marine diet of the Atlantic sturgeon Acipenser oxyrinchus oxyrinchus . We examined the food habits of 275 Atlantic sturgeon (total length, 106–203 cm) caught in the commercial fishery off the coast of New Jersey. Stomachs were provided by fishermen. Significantly more stomachs were empty in the spring than in the fall. Sand and organic debris were a major component in the stomachs (26.3–75.4% by weight). Polycheates were the primary prey group consumed, although the isopod Politolana concharum was the most important individual prey eaten. Mollusks and fish contributed little to the diet. Some prey taxa (i.e., polychaetes, isopods, amphipods) exhibited seasonal variation in importance in the diet of Atlantic sturgeon. Identification of the offshore diet of Atlantic sturgeon is an important step in developing a better understanding of the life history requirements and marine ecology of this species.

New Jersey↗
USGS1997

Evidence of secondary consumption of invertebrate prey by Double-crested Cormorants

The piscivorous nature of the Double-crested Cormorant (Phalacrocorax auritus) is well documented. However, many researchers who have used regurgitated pellets to describe the diet of cormorants report that invertebrates compose a small but consistent portion of the diet. We examined the hypothesis that invertebrates found in pellets are primarily the result of secondary consumption. We used odds ratio analysis to examine associations in 2,846 individual pellets between the presence of specific invertebrate prey and the presence of fish species known to consume those invertebrate taxa. Significant (P < 0.05) relationships occurred between gastropods and pumpkinseed (Lepomis gibbosus) and ictalurids, and between decapods and rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu). Significant (P < 0.05) relationships were also found between pelecypods and pumpkinseed and ictalurids. We suggest that the invertebrate prey we observed in pellets were present in the digestive tracts of fish that were consumed by Double-crested Cormorants and hence represent secondary consumption by cormorants. We conclude that consumption of invertebrates by Double-crested Cormorants may be overestimated in the literature in instances where the diet was described using pellets.

Waterbirds↗
USGS1996

Pellets versus feces: their relative importance describing the food habits of double-crested cormorants

We compared the amount of taxonomically identifiable (diagnostic) fish remains in double-crested cormorant ( Phalacrocorax auritus ) feces to that exiting the birds via regurgitated pellets. Feces and pellets were collected concurrently during June 1994 from cormorant colonies on Little Galloo Island, eastern Lake Ontario. About 90% of the diagnostic fish remains were found in pellets and 10% in feces. However, only 4% of the diagnostic remains in the feces represented fish that could not be accounted for in the pellets. Pellets provided better information than feces for determining diet composition. Because of the increased effort to collect and analyze fecal material, and the limited amount of additional information provided, examination of feces in addition to pellets is probably not necessary in most studies of double-crested cormorant feeding ecology.

Journal of Great Lakes Research↗
USGS1995

Estimating losses to predation of recently released American shad larvae in the Juniata River, Pennsylvania

Predation on recently released larval American shad Alosa sapidissima was quantified in the Juniata River, Pennsylvania, on 10 occasions during 1991 and 1992. Of the four sites examined (the stocking site and 100, 200, and 350 m downstream) predation on shad larvae was highest at the stocking site; 44% of the total estimated losses occurred within this 30-m zone. Percentage predation mortality was weakly and inversely related to the number of shad larvae released, and it ranged from 0 to 2.2% among sites. Overall percent mortality of larvae within the first 2 h of release was about 5% (range, 2–10%). Major predators included juvenile smallmouth bass Micropterus dolomieu , the spotfin shiner Cyprinella spiloptera , and the mimic shiner Notropis volucellus . Predation by these species varied among sites. Percent mortality of American shad larvae after nocturnal releases (0.17%) was significantly lower than after diurnal releases (1.18%). For most predators, the length of shad eaten increased with predator length. However, among predators of similar size, there were significant differences in the length of shad consumed. Estimated losses to predation were about equally divided among small (<50 mm, 30%) medium (50–99 mm, 37%), and large (>99 mm, 33%) predators. Because 30% of the estimated number of shad larvae lost to predation were eaten by predators less than 50 mm long, releasing slightly larger shad might reduce predation.

Pennsylvania↗
USGS1993

Dieldrin variation in diet composition of a riverine fish community

Although diel food habit studies have been undertaken on a number of individual species, few studies have examined diel variation in the diets of fish communities. We examined the diel diet variation and feeding periodicity of a fish community in the Juniata River, Pennsylvania. Nine species, totalling 1,098 fish, were collected at 4-h intervals over a 24-h period in October 1989, in numbers sufficient to describe their diel variation in diet composition. Diel variation in diet composition was evident in all species, as no single prey taxon was dominant in the diet of any species during any 4-h interval. Ephemeropterans were the most important prey taxa for four species of centrarchids, whereas chironomids were the main prey of banded killifish, mimic shiners, and spotfin shiners. Algae was the major component in the diet of spottail shiners, whereas bluntnose minnows contained mostly detritus. Feeding activities of rock bass, redbreast sunfish, and pumpkinseed occurred at low levels throughout the day; peak feeding occurred from 2000 to 0400 hours. Food consumption of smallmouth bass increased throughout the day with peak consumption occurring at 2000 hours. Non-centrarchids fed little during daylight hours and showed peak activity at 2000–2400 h. Construction of a 24-hour diet from six 4-h interval estimates and feeding periodicity data provided a comprehensive representation of the diel feeding ecology of all species collected.

Hydrobiologia↗
USGS1992

Evaluating enhancement of striped bass in the context of potential predation on anadromous salmonids in Coos Bay, Oregon

We describe an approach for evaluating the predation on anadromous salmonids that could result from enhancement of striped bass Morone saxatilis in Coos Bay, Oregon. Predation by striped bass on juvenile salmonids has been documented there since 1930. To provide a basis for the decision about enhancement of striped bass in Coos Bay, we estimated the losses of anadromous salmonids in 1950 and 1960–1964. In this evaluation, we used information on striped bass in Coos Bay and collateral information about striped bass in other waters. Estimated numbers of juvenile salmonids consumed by striped bass in Coos Bay (April–June) ranged from more than 41,000 in 1950 to about 383,000 in 1963. Estimated losses of adult salmonids ranged from about 1,000 in 1950 to about 46,000 in 1963. This approach was useful in conveying the potential consequences of large‐scale striped bass enhancement to decision makers and to the public. The evaluation also helped identify information needs that are now considered in managing the fishery and in evaluating impacts on salmonids.

Oregon↗
USGS1957

Geology of Saipan, Mariana Islands; Part 2, Petrology and soils

The rocks that comprise the volcanic formations of Saipan are of two principal types: dacites, which are characteristically glassy, and andesites, which are comparatively crystalline. The dacites consist primarily of silicic glass, oligoclase, and silica minerals (quartz, tridymite, cristobalite, chalcedony, and opal). Minor constituents in these rocks are green hornblende, biotite, magnetite, and hematite. The andesites are composed principally of labradorite, hypersthene, augite, and subcalcrc augite. Minor but also characteristic constituents of the andesites are quartz, tridymite, cristobalite, anorthoclase, and accessory magnetite, ilmenite, rutile, and apatite. Nine varieties of dacite and andesite are recognized on the basis of chemical composition, mineralogy, and texture. These are dacite, dacite vitrophyre, dacite perlite, hornblende-bearing dacite porphyry, augite-hypersthene andesite, quartz-bearing augite-hypersthene andesite, quartz-bearing augite-hypersthene andesite porphyry, augite andesite, and hypersthene andesite.

Professional Paper↗