摘要:

The movements of 67 Gulf sturgeonAcipenser oxyrinchus desotoiequipped with radio transmitters were monitored in the Suwannee River, Florida, from March 1989 through August 1992. The objectives of this study were (1) to determine the seasonal movement patterns and distribution of Gulf sturgeon while in freshwater, (2) to document relationships between water temperature and Gulf sturgeon movement, and (3) to determine whether springs were used as thermal refugia by these fish. Gulf sturgeon were detected entering the river from mid-February through April; they moved upstream at an average speed of 3.5 km/d to areas where they remained until October or November. Gulf sturgeon moved no more than 0.6 river km (on average) upstream or downstream from their established summer area. Gulf sturgeon began leaving the Suwannee River from mid-September through early November and moved downstream at an average speed of 6.2 km/d; all fish returned to the Gulf of Mexico by early December. Water temperatures associated with spring and fall migrations averaged 22.1°C (range, 16.0–28.0°C) and 21.3°C (range, 16.9–26.8°C), respectively. Gulf sturgeon were frequently close to springs throughout the warmest period, but none were located within a spring or the thermal plume emanating from a spring.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0302:SMOGSI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Feed utilization and growth of hatchery-reared, postsettlement stage Nassau grouperEpinephelus striatus(mean weight = 3.20 g) were compared for 63 d at temperatures of 22, 25, 28, and 31°C under controlled laboratory conditions. Final weights (Wf) and specific (SGR) and relative (RGR) growth rates were significantly (P< 0.05) higher at 28 and 31°C (Wf= 10.5–12.4 g, SGR = 1.95–2.07%/d, RGR = 246–273%) than at 22 or 25°C (Wf= 7.33–8.70 g, SGR = 1.32–1.52%/d, RGR = 131–164%). Temperature unit requirements per gram of growth (range = 342–234°C × d/g) also appeared to decrease with temperature within this range. Higher growth with increasing temperature was related to feed consumption (% body weight/d), which increased significantly (P< 0.05) from 1.60 at 22°C to 2.23 at 31°C. Feed conversion ratio (weight fed/weight gained: range = 1.23–1.04) and condition factor (103× weight/length3; range = 30.6–31.7) did not differ among treatments. Survival did not differ and remained high (range = 96.4–100%) under all treatments. The results demonstrate that sea temperature within an ecological range has pronounced and direct effects on feeding and growth of juvenile Nassau grouper. Based on in situ sea temperature data in a known juvenile habitat, we hypothesize that timing of spawning in relation to seasonally changing sea temperatures in these habitats may be important in determining juvenile growth rates, vulnerability to predation, and hence, year-class strength. A temperature range of 28–31°C is recommended for culture of early juveniles, although higher temperatures may be feasible.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0309:TEOFUA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We studied the use of compensatory growth (CG) to grow fish larger than control fish that were fed every day without restriction. Five treatment groups of 10 juvenile hybrid sunfish (F1hybrid of female green sunfishLepomis cyanellus× male bluegillL. niacrochirus) received repeating cycles of no feeding and refeeding; fixed no-feed periods of either 2, 4, 6, 10, or 14 d distinguished the treatment groups. No-feed periods elicited the CG state and were immediately followed by days of ad libitum refeeding. Refeeding periods within each treatment group (D2, D4, D6, D 10, or D14) were continued until mean daily food consumption by fish no longer exceeded that of controls fed ad libitum every day (i.e., ad libitum refeeding was continued for as long as hyperphagia persisted, then another no-feed period began). Fish in two groups, D2 and D 14, consumed more food and significantly outgrew controls by 2 and 1.4 times, respectively, in 105-d experiments. Gross growth efficiency (GGE, fish weight gained/weight of all fish consumed) did not differ among the control and treatment groups over full experimental periods; however, GGE was higher than controls during some refeeding periods in group D14 (i.e., when CG was active). Findings show that the CG response can be exploited in some fishes to cause them to substantially outgrow conspecifics that are fed every day without restriction, with no loss of growth efficiency. Our use of hyperphagia to gauge durations of refeeding periods was critical to achieving growth improvements through CG.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0316:NUOCGT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Spatial variation in stream fish populations and habitats can be partitioned into many hierarchical levels (e.g., among drainage basins, streams within basins, and sites within streams). Studies of site level habitat relationships in more than one stream are common in fisheries research. Analyses of such data typically involve multiple regression to relate site level habitat features and fish population characteristics (e.g., biomass). Because sites within streams may not be independent, multiple-regression models should also include qualitative stream effects. As we show here with hypothetical and real examples, ignoring stream effects can lead to erroneous conclusions about the significance of site level habitat variables. Site and stream level effects may function independently or interactively in relation to fish populations. Alternatively, site and stream level effects may be confounded. An example with data on trout populations revealed that highly significant site level effects were only marginally significant after adding qualitative stream effects to the regression model. Further examination of the data revealed that consideration of variation among streams added much insight and complexity to understanding how site level effects may be related to trout populations. Inclusion of stream (or other large-scale) effects in regression models of site level habitat relationships may be a valuable method to more fully understand the spatial scale of habitat variability fish are responding to.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0323:ISLVIA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We examined microhabitat selection by the Gulf sturgeonAcipenser oxyrinchus desotoia subspecies of Atlantic sturgeon that is listed as threatened by the U.S. government. Individuals and groups of sturgeons were placed in a Ferguson flume at low (4–6 cm/s) and high (5–17 cm/s) water flows, and their distributions relative to substrate and water velocity were recorded with a video camera. A Jacobs' selectivity index (D) was used to evaluate substrate and velocity preference by the fish. Distribution of individual fish, relative to water velocity, differed significantly in the low (X2= 11.8, df = 2,P< 0.05) and high (X2= 39.0, df = 12,P< 0.05) water flows. Groups also selected velocities within low (X2= 36.1, df = 2,P< 0.05) and high (X2= 63.8, df = 12,P< 0.05) flows. Individual fish did not select substrates in low flow but moderately preferred cobble (D= 0.32) in high flow. Groups moderately preferred sand (D= 0.40) and moderately avoided cobble (D= –0.47) in low flow. No selection was observed by groups in high flow. Differences in use of substrate types by individual fish were not significant in low flow (X2= 4.43, df = 2,P≥ 0.05); however, the differences were significant in the other treatment combinations (group, low flow:X2= 134.2, df = 2,P< 0.05; group, high flow:X2= 21.05, df = 2,P< 0.05; individual, high flow:X2= 11.03, df = 2,P< 0.05). Results from this laboratory experiment have implications for future microhabitat studies and represent the first quantified look at microhabitat selection by age-0 Gulf sturgeons.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0330:ALEOWV>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We used electrofishing and gill netting to sample paddlefishPolyodon spathulain the Alabama River drainage during the 1992–1993 spawning migrations. Electrofishing was effective for collecting adults in riverine habitats as well as juveniles in shallow lacustrine areas. Gill netting did not cause immediate mortality, whereas electrofishing was responsible for an overall immediate mortality of 10%. Across sites, paddlefish collected by electrofishing were smaller than those collected by gill netting. In standardized sampling, electrofishing collections yielded a catch per unit effort more than twice that of collections by gill netting. These results provide a benchmark for a sampling technique rarely used with paddlefish and not previously published. Our observations suggest that boat-mounted electrofishing can provide a viable alternative technique for sampling this species, particularly when factors such as excessive current speed and an abundance of submerged timber may preclude the use of other gear.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0334:BEAATF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

PaddlefishPolyodon spathulawere tagged with 2-mm-long coded wire tags (CWTs) inserted 2 mm into the distal end of the rostrum to determine if the relative position of CWTs changed as the rostrum grew. Thirty fish were randomly selected weekly for measurements of body length (anterior edge of eye to tail fork), rostrum length (anterior eye to distal end of the rostrum), and relative position of the tag (determined from X rays). Mean body length of tagged paddlefish increased from 79 mm on 30 June 1995 to 183 mm on 10 August 1995. Mean relative position of the tag (length from tag to tip of rostrum/rostrum length) varied from 9.7% of total rostrum length on 30 June 1995 to 18.6% on 3 August 1995. We believe that the change in relative position of CWTs is a function of rostrum growth rate, and the change would probably be highest in age-0 paddlefish and decline as age increases.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0338:RPOCWT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fishes in the Little Colorado River in the Grand Canyon, Arizona, were sampled monthly from July 1991 to June 1995 as part of a study of the ecology of endangered humpback chubGila cypha. Diets of five introduced predatory fish species were examined. Stomach contents varied among species and were low in diversity and dominated by algae (primarilyCladophora), aquatic insects, and fishes. Humpback chub plus other native species were a significant component of the diet (13.7% frequency of occurrence among 219 of 408 stomachs that contained food). Predation mortality from introduced fishes may significantly affect the native species by depleting numbers and reducing recruitment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0343:PBIFOE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-126.2.347

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor