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Geology topics

J. H. Johnson

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

At least 55 records · Page 3Linked to original sources
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↗
USGS1996

Feeding ecology of larval and juvenile American shad (Alosa sapidissima) in a small pond

Release ponds are used as part of a multifacet effort to restore American shad ( Alosa sapidissima ) in the upper Susquehanna River basin. Little information exists, however, on the feeding ecology of young shad in small ponds. Consequently, we examined feeding ecology and prey selection of 299 larval and 299 juvenile American shad in a small pond during spring and summer. Larval shad mainly consumed copepods (37.7%) and cladocerans (37.4%) whereas juvenile shad ate chironomids (43.1%) and ostracods (28.4%). Larval and juvenile shad exhibited diel variation in diet composition and feeding periodicity. Food consumption by shad was minimal at night; feeding activity was highest during the day, peaking at 2000 h for both larvae and juveniles. Electivity values of shad larvae for prey taxa were highest for cladocerans (+0.27) and lowest for ostracods (−0.07). Electivity values of juvenile shad were highest for chironomids (+ 0.21) and ostracods (+ 0.09), and lowest for copepods (− 0.08) and baetids (− 0.14). Our data indicate differences in diet composition, prey preference and, to a lesser extent, feeding patterns between larval and juvenile American shad in small pond environments.

Journal of Applied Ichthyology↗
USGS1996

Comparative diets of hatchery and wild Atlantic salmon smolts in the Merrimack River

We examined diets of smolts of 224 “wild” and 150 hatchery Atlantic salmon Salmo salar ; wild smolts had been released as fry from the hatchery 2 years before collection, whereas hatchery fish were released as smolts from the hatchery 3–15 d before. Smolts were collected from 1991 to 1993 at trapping facilities at dams in the Merrimack River during spring outmigration. About 50% of the hatchery smolts and 50% of the wild smolts examined had empty stomachs. For smolts containing food, terrestrial invertebrates were the major prey of both hatchery and wild salmon. Adult aquatic dipterans (i.e., chironomids, culicids, and simuliids) also composed a large portion of the diet of both groups of salmon. Hydropsychid and chironomid larvae were the main benthic taxa consumed. Surface‐oriented prey dominated the diet of hatchery (73.7%) and wild (62.4%) smolts. The coefficient of dietary overlap ( C λ) between hatchery and wild smolts was high during all years and ranged from 0.83 to 0.93. Stomach fullness of hatchery smolts was significantly less than that of wild smolts. Further research is needed to determine if the low food consumption of hatchery smolts affects survival.

Massachusetts, New Hampshire↗
USGS1995

Diel feeding ecology of three species of aquatic insects

Aspects of the diel feeding ecology of the odonate nymphs Anax Junius and Ischnura verticalis and the ephemeropteran Callibaetis fluctuans were examined over a 24-h period in a small pond. Detrital material was the primary food of both A. Junius and I. verticalis. Aquatic insects (mainly C. fluctuans ) were the second ranking prey in the diel diet of A. Junius , whereas ostracods were the second most important prey consumed by I. verticalis. Diet overlap between A. Junius and I. verticalis was high ([xbar] = 0.76) when detritus was considered but fell to 0.25 when detrital material was omitted. Food consumption by the odonate nymphs was highest at 0800 h and was generally lowest from 2400 h to 0400 h. Conversely, feeding activity by C. fluctuans peaked between 2400 h and 0400 h with the least feeding occurring at 0800 h. Differences in diel feeding patterns between the ephemeropteran and odonate species may reflect predator avoidance behavior by C. fluctuans.

Journal of Freshwater Ecology↗
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↗