摘要:

We examined the relationships of timber harvest, stream habitat complexity, and diversity of juvenile anadromous salmonid assemblages in 14 small- to intermediate-sized basins in coastal Oregon between 1985 and 1989. Diversity (the inverse of a species dominance index) of assemblages in streams in basins with low harvest levels (≤25% of the basin area harvested) was greater than in streams in basins with high harvest levels (>25% of the basin area harvested) (P= 0.02). Assemblages in basins with high levels of harvest were more dominated by a single species than were assemblages in basins with low harvest, Percent of basin harvested was more strongly associated with assemblage diversity (P= 0.07) than were basin area (P= 0.90) or gradient (P= 0.22) when the influence of the other two factors was controlled. Habitat features were compared between three pairs of streams. Streams in basins with low timber harvest had more complex habitat, as manifested by more large pieces of wood per 100 m (P< 0.01). We conclude that a community and basin-level perspective is necessary to fully assess the effects of timber harvest and other human activities on stream fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0309:DOJASA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Black drumsPogonias cromiswere sampled from commercial and recreational catches in the northern Gulf of Mexico from July 1987 to September 1990, Seasonal onset of spawning, evidenced by the presence of postovulatory follicles in ovarian tissue sections and by elevated gonadosomatic indices, occurred in January of each year (one female with hydrated oocytes was sampled in December 1988). Atretic oocytes observed in mid to late April indicated imminent cessation of spawning. Two of 115 females less than age 5 had achieved sexual maturity; all females age 5 and older were mature. Fifty percent maturity of females was attained at 640–649 mm fork length and all females larger than 690 mm were mature. Male black drums entered the breeding population at a younger age (>50% maturity at age 4) and a smaller size (50% maturity at 610–620 mm). Multiple oocyte stages observed throughout the annual spawning seasons verified groupsynchronous oocyte development and multiple batch spawning. Estimated batch fecundities of 41 females with hydrated oocytes ranged from 0.51 million to 2.42 million ova. Mean batch fecundities were 1.22 million ova for the 1988 spawning season, 1.65 million ova for 1989, and 1.21 million ova for 1990, Batch fecundity was positively correlated with total weight, fork length, eviscerated body weight, and age, Spawning frequencies estimated from the proportion of mature females with postovulatory follicles were one spawning event per 3.0 d in 1988, one per 4.2 d in 1989, and one per 3.9 d in 1990. A protracted spawning season, generous batch fecundities, and frequent spawning provide black drums with annual fecundities of 13 million to 67 million ova.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0318:RBAAVO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Deepwater snappers are a valuable component of fisheries on slopes and banks in Hawaii and in much of the world's tropics. Their ecology and trophic relationships in these deepwater habitats are poorly known. Line fishing in this study simultaneously collected six of the seven lutjanid species that commonly occur in the major deepwater snapper fishery at Penguin Bank, Hawaii. The catch rate of each species showed diel variability; the patterns of some species were distinctly different. The depth distribution of feeding, as indicated by depth of capture, differed considerably among species; all species were taken within several meters of the bottom. Size (fork length) of the predator species did not appear to be stratified by time of capture (daylight versus darkness) or median capture depth. Regurgitation of gut contents seemed to be reduced when fish were retrieved at a rate that was slower than used in commercial practice but rapid enough to prevent death or morbidity while hooked. The food remaining in line-caught specimens appeared to be representative of what was originally eaten. The six snapper species ate considerable amounts of a wide range of pelagic animals and demersal fishes and much smaller quantities of a few invertebrate benthic groups.Etelis coruscans,Etelis carbunculus, andAprion virescensformed a distinct, primarily piscivorous feeding guild.Pristipomoides filamentosusandPristipomoides sieboldiiformed a distinct guild dominated by zooplankton feeding. The few specimens ofPristipomoides zonatusappeared somewhat intermediate in diet. Important planktonic prey groups included crustaceans, pteropods, and large, pelagic, colonial urochordates (e.g., salps). Urochordates made a significant contribution to the diet even for some of the primarily piscivorous species. Major diel and seasonal shifts in diet were found only inP. filamentosus; they involved the relative proportions of fish, and especially of the major planktonic groups. Our information on diet composition and depth and time of feeding (catch) suggests that considerable resource partitioning occurs among these deepwater snappers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0328:FEODLS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We examined the diets of 374 age-0 bluefishPomatomus saltatrixcollected in the Hudson River estuary from July to October 1989. Fish were the primary prey, accounting for 96–99% of the diet by weight. Anadromous fishes, including striped bassMorone saxatilis, blueback herringAlosa aestivalis, American shadAlosa sapidissima, and Atlantic tomcodMicrogadus tomcod, constituted a large portion of the diet of bluefish of all sizes. There was a positive linear relationship between prey size and predator size, Small and medium-sized bluefish consumed mostly bay anchoviesAnchoa mitchilli, striped bass, and white perchMorone americana, whereas the largest bluefish primarily preyed on Atlantic tomcod. Bluefish fed opportunistically on the most abundant prey (bay anchovies, striped bass, and white perch) but larger bluefish exhibited a preference for Atlantic tomcod. We also detected an ontogenetic shift in prey type that may have been determined by changes in the size and relative abundance of prey that occurred as the season progressed. Predation by age-0 bluefish may represent a substantial source of mortality for age-0 anadromous fishes in the Hudson River estuary.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0348:PBABOA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We used time-lapse video with infrared illumination to record feeding activity of pumpkinseedsLepomis gibbosusin two patches of littoral habitat in a shallow, mesotrophic Ontario pond. Observations were made for 72 consecutive hours in each of eight ice-free months and include extensive, relatively nonintrusive field observations of pumpkinseed behavior at night. We tallied numbers of passes above the substrate and numbers of substrate strikes (at substrate or at vegetation). Variation among months accounted for 40–50% of the total variation in rates of daytime passing and substrate striking, which peaked in May and September. Among-day variation in daytime foraging activity within months was high, accounting for 50–57% of the total variance, and the variances we measured can be used to plan replication levels necessary to achieve adequate statistical power in future studies involving measurements of daily ration or comparisons of exploitation rates in different habitats. Simultaneous video monitoring at multiple sites allows one to factor out the day-to-day variance and provides a sensitive way to compare foraging variables in different sites or habitats. Although pumpkinseeds are usually considered diurnal feeders, some foraging occurred at night in each month. The median rate of fish passing at night was about half the median diurnal and crepuscular rates. Rates of substrate striking were much lower at night than during the day, but planktonic feeding at night was higher, so that nocturnal striking rates on plankton plus substrate were more than 75% of the diurnal values. Nocturnal feeding by other visually feeding fishes is more important than we currently acknowledge, and needs to be incorporated into our thinking about interspecific competition and predation among littoral fishes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0357:DASVIF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We explored the importance of experience with feeding on live prey, of cataracts, of strain, and of maternally transferred contaminants for the feeding rate and predator avoidance behavior of young lake troutSalvelinus namaycush. Hatchery-reared and feral juvenile lake trout were tested separately as predators on lake trout fry in tanks with artificial cobble reefs. Feral fish captured more prey per day and more prey per strike than did hatchery lake trout. The predatory performance of hatchery and feral fish did not improve significantly with experience. Feeding rates did not differ between lake trout with unilateral cataracts and normal-eyed fish, but significantly diminished for lake trout with bilateral cataracts. Neither strain nor contaminant background affected the ability of fry to feed or to avoid predators. Of the factors studied, previous experience with live food under natural conditions (i.e., the experience of feral fish) was the most important factor affecting feeding behavior of young lake trout.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0366:FAFBAS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Soft-bodied annelids, arthropods, and occasionally globular molluscs were primary foods of the threatened Gulf sturgeonAcipenser oxyrinchus desotoicollected from the mouth upriver to kilometer 221 of the Suwannee River, Florida, in 1988–1990. In spring, large subadults and adults that immigrated from the estuary had fed primarily on lancelets, brachiopods, amphipods and other crustaceans, polychaetes, and gastropods. Small Gulf sturgeons that remained near the mouth of the river during spring fed on epibenthic and hyperbenthic amphipods and grass shrimp and on isopods, oligochaetes, polychaetes, and chironomid and ceratopogonid larvae found in the intertidal zone, Subadults of more than 5 kg and adults in the freshwater middle river reaches between km 55 and 221 essentially fasted during the summer and fall. Gulf sturgeons in the Suwannee River were indifferent to abundant potential freshwater foods and apparently had stored sufficient nutrient reserves while in the estuary. A presumably young-of-year or year-old Gulf sturgeon captured in summer at the most upriver site (km 221) had fed on aquatic insects and oligochaetes. Most Gulf sturgeons of all sizes had ingested detritus or biofilm.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0378:FOTGSI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Energy densities and percent dry matter of zooplankton were estimated from both field collections and from stomach contents of rainbow troutOncorhynchus mykiss. Dry-mass energy densities were similar for zooplankton collected from the field and from fish stomachs, averaging 22.7 kJ/g. The percent dry matter of zooplankton from fish stomachs was approximately twice that of zooplankton from field collections, although species composition was similar. Energy density of wet zooplankton was consequently twice as high in fish stomachs as it was in field collections. These results indicate that the wet-mass energy density of zooplankton prey used in fish bioenergetics models should be increased over values that have been reported in the literature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0386:NETEDO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We report the rare, natural occurrence of triploidy in a brown bullheadAmeiurus(formerlyIctalurus)nebulosus. This is to our knowledge the first report of naturally occurring triploidy within the family Ictaluridae. The nuclei of blood cells were studied by flow cytometry, volume measurement, and computer-assisted image analysis. The triploid had a genome size of 3.29 pg DNA/cell compared to 2.23 pg DNA/cell (SD, 0.02 pg) for 28 diploid brown bullheads. Volume measurement and image analysis were able to detect the triploid condition; however, flow cytometry was the most precise technique and had the greatest resolution.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0390:NOOTIA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Age at sexual maturity has not been described previously for the pallid sturgeonScaphirhynchus albus, an endangered species. Age and reproductive development data were obtained for five male and nine female pallid sturgeons collected from 1983 to 1991. Spawning bands were observed in pectoral fin ray sections of age-25 and age-41 females. Males reached sexual maturity at ages 5–7. Females began egg development at ages 9–12 and first spawned at age 15. Eight of the specimens we examined were collected from the headwaters of the Atchafalaya River, where pallid sturgeons had not been previously reported.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0393:AASMOT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor