摘要:

Atlantic croakersMicropogonias undulatusundergo a transition from a coastal, pelagic, planktonic stage to an estuarine, demersal stage. Atlantic croaker larvae were collected at five descrete depths (0 m, 1 m, 6 m, and bottom) at stations along three transects north, south, and inside the mouth of the Chesapeake Bay in September 1980. Vertical distribution of the larvae was compared with salinity and temperature at the collection sites. Distribution patterns on the larvae were not uniform with depth but were related to hydrography. In vertically homogeneous water, larvae were found throughout the water column. In stratified water, they were found in the inward-flowing, lower layer, though not necessarily on the bottom. The distribution of Atlantic croaker larvae at the mouth of the Chesapeake can be accounted for by both passive and active transport mechanisms.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0673:ERMOLA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We concurrently sampled larvae (2.15-9.45 mm) of the weakfishCynoscion regalisand their potential prey in Delaware Bay during the 1986 and 1987 spawning seasons. Gut content analysis revealed that larval weakfish fed primarily on copepods (41% of diet by dry weight), larvae of the polychaetePolydora ligni(34%), and pelagic invertebrate eggs (14%). As larval weakfish grew, their diet changed from several small prey types to a few larger ones. Mean abundance of prey occurring with larvae smaller than 5.55 mm notochord length was 172.3 μg/L compared with 166.1 μg/L for prey occurring with larvae 5.55 mm and larger. Prey abundance around these means varied up to 1,000 times for small larvae and 100 times for large larvae. Comparison of these results with laboratory work suggests that prey abundance encountered by weakfish larvae less than 5.55 mm in Delaware Bay ranges over scales that can cause large variations in larval growth and survival.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0684:DOLWAP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We reared larvae of weakfishCynoscion regalisat different prey abundances in the laboratory (20.5°C). Larvae began to feed 52 h after hatching. When prey was withheld up to 72 h after larvae had the ability to feed, there was no increase in starvation-induced mortality. However, when prey was withheld more than 24 h, growth was significantly reduced. Times to yolk exhaustion (70 h posthatching) and irreversible starvation (168 h posthatching) were similar to those measured for other marine fishes reared at similar temperatures. We measured growth and mortality of 3–9-d-old larvae at prey abundances approximating those found in Delaware Bay and concluded that natural variations in prey abundance in systems such as Delaware Bay are sufficient to cause large variations in the growth rate of young weakfish larvae.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0693:DSAGOL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Eggs in plankton samples from lower Chesapeake Bay indicated that the spawning season of the bay anchovyAnchoa mitchilliin 1988 extended from early May to mid-September. Oocyte stages in adults were used to determine daily spawning time and frequency as well as batch fecundity. Spawning was temporally synchronized and lasted for about 1.5 h each night. Spawning time became later each month (2000 hours on 6 June to 2330 hours on 31 August). Spawning frequency per individual was every 4 d in early June and every 1.3–1.9 d in other months. Batch fecundity was a linear function of fork length and of body weight; regression slopes on 6 July and 4 August were significantly higher than those on 6 June and 31 August. Estimated mean total spawnings per female in 1988 was 54. Total egg production for a fish of average size was 45,110, which is equivalent to 346% of body biomass energy. Age determinations based on lagenar otoliths showed that some fish spawned when as young as 2.5–3 months. The bay anchovy has a greater reproductive potential than is known for other anchovy species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0701:RBOTBA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Total densities of wild brown troutSalmo truttaages 1 to 7 varied widely (range, 130–1,304/hectare) among 12 sample sections in Spring Creek, a 35-km-long stream in a limestone area of central Pennsylvania. During a 2-year study we determined the relative importance of spawning habitat and other habitat features on spatial variation in density. Densities of age-0 and of all age-1 and older brown trout were positively correlated with redd densities. Embryo survival was lowest in sections with low brown trout densities, but embryo survival was not as important as redd density in determining population size. Redd density appeared to be a function of availability of suitable spawning substrate. Habitat variables such as depth, pool area, cover, and substrate were not correlated with brown trout density. Spawning habitat and other habitat features were quantified with the habitat suitability index model. Scores derived from the model were poorly correlated with densities of age-0 and of age- l and older brown trout. We concluded that juvenile brown trout do not disperse widely from natal areas, and that local population densities are largely a function of the availability of spawning habitat.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0711:IOSAOS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

I compared feeding, aggressive behavior, and spatial distribution of differently ranked individuals of hatchery and wild coastal cutthroat troutOncorhynchus clarki clarkiin an artificial stream. Both hatchery and wild groups established stable dominance hierarchies that seemed to be based on size differences. Hatchery and wild fish within a hierarchical rank fed at similar rates. Hatchery fish were more aggressive than their wild conspecifics, irrespective of rank. Dominant hatchery fish were evenly distributed in pools and riffles, whereas dominant wild fish were three times more often in pools than in riffles. In both groups, socially intermediate fish were almost evenly distributed between pools and riffles, and subordinate fish spent most of their time in pools. On average, hatchery fish spent 57% of their time in pools and 43% in riffles, whereas wild fish spent 71% of their time in pools and 29% in riffles. These results support the hypothesis that excessive expenditure of energy for unnecessary aggression, use of fast-flowing water, or other purposes contributes to poor survival of hatchery fish after they are stocked in streams. Poor survival would reduce the efficacy of using hatchery stocks to supplement wild production.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0723:VIFAAP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Juvenile rainbow troutOncorhynchus mykissstocked in midelevation reservoirs in Utah inhabit shallow nearshore areas and are vulnerable to predation from piscivorous fish and birds. We determined the use and importance of nearshore habitats by (1) measuring habitat selection by, prey availability to, and feeding of juvenile rainbow trout in two reservoirs with populations of predators, and (2) measuring survival and growth rates in the presence and absence of cover in a pond experiment where adult brown troutSalmo truttawere predators. In the reservoirs juvenile rainbow trout (60–120 mm standard length) were abundant in complex inshore habitats but avoided simple habitats such as sand and gravel during the day. At night, however, juvenile rainbow trout in both reservoirs were observed in more exposed areas, and they rested on the bottom. Measurements of gut fullness indicated that juvenile rainbow trout fed actively on largeDaphniaspp. during the day but little at night. Because large daphnia were usually more abundant offshore than inshore in both reservoirs, selection of inshore cover is believed to be primarily a response to greater predation risk offshore. In the pond experiment, the presence of brown trout significantly increased mortality of juvenile rainbow trout, decreased their growth rates, and caused them to avoid open-water areas. The presence of cover significantly decreased predation rates but did not affect growth of the juvenile rainbow trout. Fisheries managers should consider augmenting cover in reservoirs and lakes where juvenile trout are stocked to minimize losses of trout to predators.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0728:PRATIO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Total mortality, mortality due to predation, and the contribution of parasite-induced mortality were estimated for yellow perchPerca flavescensinfected with the nematodeRaphidascaris acus. Total annual natural mortality of yellow perch in Dauphin Lake, Manitoba, was approximately 61%; predation by northern pikeEsox luciusaccounted for 19% and 45% of natural mortality for female and male yellow perch, respectively. Yellow perch harbored 18 species of parasites, of whichR. acuswas the most abundant; 95% of allR. acuslarvae inhabited the liver. The number of free and encapsulated larvae and nodules in the liver of yellow perch varied seasonally and with fish gender, but it was not correlated with water temperature or fish habitat. Mean intensity but not recruitment increased with age of yellow perch. Density ofR. acus(larvae per gram of liver) was highest in young, immature yellow perch and decreased with age in mature yellow perch. Yellow perch with high-density infections had lower condition factors, and their weight-at-age curves showed reduced slope (males and females) or a shift toward the ordinate (males). Reduced weight was most pronounced when densities of larvae were high (>50 larvae/g liver). Parasite-induced mortality accounted for much of the unexplained natural mortality of yellow perch. Many small yellow perch males with high-density infections apparently failed to mature; those that did mature had reduced weight. Females with high-density infections either died soon after the onset of vitellogenesis or matured later. Sex-related, parasite-induced mortality might explain the preponderance of females and the bimodal weight distribution that develop with age in natural populations of yellow perch. Furthermore, parasites (especially tissue-invasive types) may play a significant role in the regulation of yellow perch populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0739:ROPAPI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We applied the index of biotic integrity (IBI) to the portion of the Arkansas River basin within the Southwestern Tablelands ecoregion, located on the Great Plains of southeastern Colorado. Only nine IBI metrics were appropriate for this region, largely because of the depauperate and tolerant ichthyofauna. The modified index was then used to assess effects of U.S. Army mechanized infantry training on biotic integrity of the Purgatoire River at 12 sites adjacent to the Pifion Canyon Maneuvers Site, a remote and relatively undisturbed canyon reach on a seventh-order Arkansas River tributary. Decrease in abundance of adult red shinersCyprinella lutrensis, a tolerant omnivorous species, over a 6-year period (1983–1989) caused marked increases in the IBI at 9 of 12 sites despite lack of obvious changes in environmental quality after training began in 1985. Neither sampling variation nor the magnitude and timing of floods were sufficient to explain the large decrease in red shiner abundance. Other attributes of the biota, such as presence of long-lived fishes and lack of introduced species, provided no evidence for detrimental change. The majority of potential IBI metrics were hampered by the low fish species richness, the preponderance of trophic and habitat generalists, or other attributes of the depauperate ichthyofauna. Moreover, human perturbations that cause change in fish communities of midwestern U.S. streams are suspected in many cases to mimic natural disturbances in this system, so they may have relatively little effect. Conversely, some perturbations considered benign in more mesic environments are likely to cause dramatic changes. We therefore propose that our understanding of the structure, function, and natural variation of fish communities in western Great Plains streams must increase substantially before we can define fully appropriate measures of biotic integrity for these lotic systems.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0752:VFCATI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A statewide angler survey was conducted in New York in 1988 in part to estimate the net economic value of the state's recreational fishery. Willingness-to-pay questions from the National Survey of Fishing, Hunting, and Wildlife-Associated Recreation were adapted to a mail survey format and respondents were asked how much they would be willing to pay above current expenditures for a specific fishing trip. The net economic value estimated from the responses exceeded $284 million for the freshwater fisheries of New York in 1988. Although inland fisheries accounted for 76% of the statewide net economic value, $69 million was associated with the portion of the Great Lakes assigned to New York. Comparisons with a 1976–1977 analysis of the net economic value of New York's Great Lakes fishery, which used a variation of the indirect travel cost methodology, showed a major shift in net economic value from trips for warmwater species to trips for coldwater or for both warm and coldwater species. Baseline data are now established for a variety of waterways in New York. Future research is needed to measure changes in value after environmental changes occur.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0770:NEVOTF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor