摘要:

A wedge-shaped pattern of variation in stream fish standing stock estimates relative to a habitat variable, in which range of standing stocks increases as a function of the variable, is consistent with the concept that the habitat variable is a limiting factor for fish populations. This pattern of variation complicates interpretation of parameter estimates and significance of ordinary least-squares (OLS) regression models of conditional mean standing stock; slopes of these regression models may have little or no relation to slopes of models describing standing stock limits. We modeled standing stock limits by testing for homoscedastic error distributions, screening plots of coordinate pairs for evidence of a wedge-shaped pattern of data, and estimating 90th regression quantiles for simple linear models. Application of this technique to data sets supporting 35 previously published OLS regression models of stream fish standing stocks led to rejection of homoscedasticity (P< 0.10) in 13 of the 35 data sets. Eight of these heteroscedastic data sets had wedge-shaped patterns of variation in standing stock and slopes of 90th regression quantiles that differed from slopes of OLS regression models. For three of these eight data sets, tests rejecting homoscedasticity were more significant than tests rejecting zero slope parameters in OLS regression models. In a separate exercise, analysis of simulated standing stock data generated from known distributions indicated that our technique can detect heteroscedastic error distribution patterns and yield 90th regression quantile models of standing stock limits from data sets characterized by OLS regression as having no correlation between mean standing stock and a habitat variable. Identification of correlations between habitat variables and standing stock by OLS regression is a common method of determining whether a variable is to be used for habitat assessment. Application of our technique to data sets that display wedge-shaped patterns of variation should help identify variables that may be limiting standing stock from data sets that do not yield significant OLS regression models of mean standing stock.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0104:MSFHLF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Angler surveys can yield inaccurate results because of the failure of some anglers to participate or return their questionnaires. If nonrespondents are different from respondents with respect to the variables in the survey, some segments of the angler population will be under- or overrepresented, and the inferences made from the respondents about the population of interest will be subject to nonresponse bias. Errors introduced by nonresponse can be greater than sampling error, making it impossible to assign useful confidence limits to survey results. A 10-page mail questionnaire was sent to a stratified random sample of 9,981 Texas fishing license holders. Information was collected on fishing experience, fishing participation, species preferences, attitudes, and orientation to fisheries management efforts. A response rate of 62% was obtained (exclusive of questionnaires that could not be delivered). Adjustments for nonresponse were made by means of response propensity stratification. Individual response probabilities were estimated by means of logistic regression with a binary variable indicating response as the dependent variable and age, sex, race, and purchase date of fishing license as independent variables. Response probabilities were inverted to obtain the nonresponse adjustment weights. Unadjusted survey variables were considered significantly different from adjusted variables if their 95% confidence interval did not contain the adjusted mean. Several variables were subject to significant nonresponse bias, which indicates the need to make adjustments when nonresponse is present.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0118:ETEONB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Coexistence of northern pikeEsox luciusand muskellungeEsox masquinongyin the Niagara and St. Lawrence rivers has been hypothesized to depend on segregation during spawning. However, large overlap in the use of spawning areas by these two species occurs in the Thousand Islands section of the upper St. Lawrence River. In this study, egg collections in Point Marguerite Marsh in the upper river revealed a partial temporal and spatial overlap in egg deposition by northern pike and muskellunge. Northern pike began spawning earlier but overlapped with muskellunge spawning for 2 weeks, May 13–27. Northern pike eggs were collected over a larger area than muskellunge eggs and at all locations where muskellunge eggs were collected. Both species deposited eggs over three dominant genera of vegetation: pondweedsPotamogeton, duckweedsLemna, and stonewortChara. Northern pike spawned over a wider range of water depths (0.5–2.6 m) than muskellunge (0.8–1.5 m) and selected habitats with denser, taller vegetative cover. The temporal and spatial overlap of northern pike and muskellunge egg deposition suggests that mechanisms other than spawning segregation permit these two species to coexist in the St. Lawrence River.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0127:NEDASH>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Maximum daily consumption (Cmax) by adult white crappiesPomoxis annularis(164–532 g live weight) provided ad libitum rations of prey fish was determined at 18, 21, 24 and 27°C. Observed increases inCmaxbetween 18 and 24°C followed by a sharp (two-thirds) decline at 27°C indicated that a low to negative physiological “scope for growth” exists for white crappies at 27°C and above. Examination of temperature and dissolved oxygen (DO) profiles from numerous Missouri impoundments for May–August 1991 suggested that white crappies were forced to occupy water of 27–32°C (warm water) in 40% of these impoundments by early June and 85% by early August. White crappies were forced into warm water in only a slightly lower percentage of the deep (>5 m) impoundments we examined than in shallow (≤5 m) ones. Evaluation of year-to-year differences (1988–1991) in time periods when white crappies were forced to occupy warm water in Lake Pomme de Terre, Missouri, showed that range (15–64 d) and time of occurrence varied substantially. Our findings suggest that the warm and annually variable summer temperature and DO regimes of many U.S. impoundments may substantially underlie the slow growth rates and among-year variation in size structure and recruitment that are characteristic of crappie populations in these environments.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0132:TDOMDC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

–Lake herringCoregonus artediwere videotaped while feeding separately on seven different zooplankton taxa. If a fish reacted to a prey item, I observed whether the prey item entered the buccal cavity of the fish. Copepods were captured at a lower percentage of the time (mean = 48.9%) than were cladocerans (mean = 86.7%).Limnocalanus macrurus, a large copepod, was captured less frequently (30%) than smaller copepods such asDiaptomus sicilis(42.5%),Cyclops vernalis(57.5%), and diaptomid copepodids (65%).Daphnia galeata mendotaewere captured less frequently (80%) than smaller cladocerans such as juvenile daphnids (87.5%) orBosmina longirostris(92.5%). The differences between copepods and cladocerans and sizes of each likely result from differential swimming strengths and behaviors of these various taxa. These results confirm observations from other planktivores that the evasive ability of zooplankton greatly reduces the successful completion of the planktivory process (encounter, attack, capture, ingestion). Additionally, the planktivory process should be examined in its entirety because my results are counterintuitive to those expected from classical size-selective planktivory.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0139:CPOLSZ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Acute toxicities of oxytetracycline hydrochloride (OTC) and calcein to juvenile striped bassMorone saxatilis(48 ± 5 mm total length) were determined by immersion. Fish were held in test solutions for 6 h, then placed in clean water and observed for 96 h post-exposure. Both OTC and calcein bind to calcium and fluoresce under ultraviolet light, which makes them useful for marking bony structures of fish. Information on toxicity of these chemicals to juvenile striped bass will help establish maximum concentrations that can be used to mark hatchery fish stocked for population enhancement or establishment. The no-observed-effect concentration (NOEL), 96-h LC 10, and LC50 (concentrations lethal to 10 and 50% of test fish) values for the 6-h chemical exposure were 447, 322, and 597 mg/L for OTC and 125, 160, and 240 mg/L for calcein.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0143:TOOACT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We compared marking success for larval and juvenile fishes immersed in alizarin red S (ARS) to that of fish immersed in alizarin complexone (AC). Postlarval and juvenile central stonerollersCampostoma anomalumand southern redbelly dacePhoxinus erythrogasterand larval white suckersCatostomus commersoniwere immersed in ARS or AC at concentrations of 50–400 mg/L for 6–24 h. Both chemicals imparted a violet-red mark, visible in the whole otoliths under a bright-field light source. Immersion in ARS at 200–300 mg/L for 12 or 24 h resulted in optimal marking success (100%) and minimal mortalities (0–3%). Marking success and mortalities were similar for ARS and AC in comparable treatments. Alizarin red S marks were retained for at least 160 d.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0146:ASMFMF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-125.1.150

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-125.1.151

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-125.1.154

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor