摘要:

not available

ISSN:0706-652X    

DOI:10.1139/f79-207

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Synchrony of cohorts is one of the life history features having most important effects upon the estimation of benthic secondary production, because most methods depend heavily upon recognition of discrete cohorts. The Hynes method, intended to circumvent the necessity of cohort distinction, still depends upon determination of trophic level, voltinism, minimum and maximum sizes, and length of aquatic life. Knowledge of preferred habitat, distribution, and behavior are essential for accurate production estimates. Use of the production:mean standing stock (P/B) ratio (fairly constant at about 5 for cohort P/B of benthic invertebrates) to approximate production from standing stock data, also must account for trophic level, voltinism, and length of aquatic life. Various life history features are compared as to their probable effect on production estimation; in addition, they are compared to the effect of sampling errors.Key words: benthos, life history, production, secondary production, productivity

ISSN:0706-652X    

DOI:10.1139/f79-208

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Zooplankton population dynamics were monitored in meromictic saline Waldsea Lake, Saskatchewan, during 1974–75. The dominant zooplankton species wereDiaptomus connexus,Brachionus plicatilis,Hexarthra fennica, andDaphnia similis.Diaptomushad a 1-yr life cycle. Overwintered late-stage copepodites molted into adults in May and June and were followed by sequential peaks in numbers of eggs, nauplii, and copepodites. The estimated annual production of this species was 0.6 g dry weight∙m−2or 0.3 g C∙m−2. About 4% of the annual planktonic primary production would be required to supportDiaptomusif it is 10% efficient. The standing crop ofBrachionusandHexarthrawas highest in the spring and declined thereafter;Hexarthrawas more abundant thanBrachionus. The standing crop ofDaphniawas much lower than that of either rotifer and showed a spring and fall peak in abundance. Differences in vertical distribution were present among the zooplankton species but no real vertical migrations were observed.Key words:Diaptomus connexus, zooplankton, population dynamics, production, saline meromictic

ISSN:0706-652X    

DOI:10.1139/f79-209

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The mineral composition in alkaline earth elements of whitefish scales from fresh- and saltwater of the La Grande River area were studied. While calcium and magnesium concentrations remained unchanged, regardless of site or age, the strontium concentrations changed markedly according to basin and water salinity. The variations in strontium are used to differentiate anadromous and freshwater populations, and to caracterize certain portions of La Grande River.

ISSN:0706-652X    

DOI:10.1139/f79-210

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Intensive profiling of the shelf/slope water boundary south of Nova Scotia has been made with a Batfish vehicle measuring physical and biological parameters consisting of chlorophylla, zooplankton, conductivity, temperature, and depth. Continuous profiling (~30 h) through the boundary zone revealed intrusions at the subsurface front consisting of plumes of ascending slope water overlying descending surface coastal water both moving vertically and horizontally. Movements of the intrusions were coherent with M2tidal cycles and exhibited localized turbulent mixing ascribed to shear instabilities. This mixing gives rise to a potentially efficient mechanism for vertical transport of heat and salt particularly as input to the Scotian Shelf. These intrusions also form inversion layers consistent with earlier observations which showed that these layers can decay over longer time scales by double diffusion processes. The vertical mixing at the subsurface front may also account for the anomalously high productivity along the front by means of continual replenishment of nutrients from below.Key words: physical oceanography, biological oceanography, Scotian Shelf, profiling

ISSN:0706-652X    

DOI:10.1139/f79-211

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Solutions are offered to the problems of data transformation and the design of efficient programs for sampling the benthos of lakes and large rivers. All types of benthic animals from many types of substrate, sampled with diverse sampling gear, are aggregated in a similar fashion. Aggregation can be indexed by the unbiased exponent of the power relationship between density and variance. A single variance stabilizing transformation can be used for all macrobenthos population data since the relationship of sample variance to mean density is similar in all taxa of benthic animals. Stabilized variance in population data satisfies one of the main assumptions of the analysis of variance and allows use of normal statistics provided that the other assumptions are met. The fourth-root transformation stabilized the variance in all macrobenthos samples while either the commonly used square root or logarithmic transformations did not. Sampling programs can be optimized empirically. Standard deviation (s) is predictable from mean density (M; m−2) and sampler size (A; cm2) from the equation: log10s = 0.581 + 0.696 log10M − 2.82 × 10−4 A. The data show that it is easier to obtain a precise estimate of macrobenthos density at high densities. Small diameter samplers are most efficient in obtaining high levels of precision. Data were taken from the literature.Key words: aggregation, benthos, freshwater, regression, sampling, transformation

ISSN:0706-652X    

DOI:10.1139/f79-212

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The indirect fluorescent antibody technique demonstrated the enzootic nature of bacterial kidney disease in 224 of the 605 wild salmonids sampled from the Margaree River system and some adjacent waters. Asymptomatic infections were observed in 33.4% of 456 Atlantic salmon (Salmo salar) parr and 35.1% of 37 returning adults in samples taken from the source of the Margaree River to and including saltwater areas off the coast.Key words: kidney disease, Atlantic salmon, wild, distribution, fluorescent antibody

ISSN:0706-652X    

DOI:10.1139/f79-213

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Fresh and processed commercial seafoods were analyzed for the polycyclic aromatic hydrocarbon carcinogen benzo(a)pyrene using a thin-layer chromatographic separation technique and quantitation by fluorescence. Commercial samples of vertebrate fish did not contain detectable levels, except where fish were packed with vegetable oil, an exogenous source of carcinogens. Levels in most shellfish samples were generally less than 10 ng/g wet weight, but occasional samples contained up to 36 ng/g. Crab and shrimp samples contained little or no benzo(a)pyrene (NDto 0.5 ng/g). Commercial lobsters contained 0.8 to 7.9 ng/g. The source of contamination of lobsters was further investigated, utilizing high pressure liquid chromatography to measure 13 polycyclic aromatic hydrocarbon isomers. Freshly caught lobsters had less than 1 ng/g benzo(a)pyrene. Lobsters which had been kept in a commercial tidal pound constructed of creosoted timber contained highly elevated levels of benzo(a)pyrene and other carcinogenic hydrocarbons, including chrysene, benzo(a)anthracene, benzo(b)fluoranthene, dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene The maximum level of benzo(a)pyrene was 2300 ng/g wet weight in digestive gland, and 281 ng/g in edible tail meat. These levels are substantially higher than previously reported for any foodstuff, and are most probably attributable to creosote contamination during impoundment.Key words: benzo(a)pyrene, polycyclic (polynuclear) aromatic hydrocarbon, carcinogen, seafood, lobster, shellfish, creosote

ISSN:0706-652X    

DOI:10.1139/f79-214

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The relative merits of various methods for estimating the parameters of the Schaefer model from catch and effort data and of controlling the fishery are compared by simulation techniques. Estimation procedures compared are the linear and nonlinear methods for the discretized Schaefer model and Schnute's method for the continuous form of the Schaefer model. The control systems compared are feedback effort limitation, quota control for fixed escapement policies, and application of equilibrium effort. It is found that all estimation systems frequently fail to provide reasonable estimates of the Schaefer model and will produce poor catches, especially when managing long-lived, low productivity species. These estimation problems are most severe when the catch and effort data series begins after the stock has been heavily exploited. The failure of the estimation systems is primarily due to insufficient contrasts in the two independent variables of the multiple regression used for estimation, effort and catch per effort. The need for alternative policies that will explore the effort, catch per effort space is discussed. Application of the equilibrium effort may frequently be preferred to a fixed escapement policy; average catch may not be reduced, and variability in catch is much lower. Quota regulation is dangerous when the stock is heavily exploited and the biological parameters of the stock uncertain; at other times the quota method produces results comparable with effort limitation.Key words: Schaefer model, feedback control, catch and effort, fisheries regulation, adaptive control

ISSN:0706-652X    

DOI:10.1139/f79-215

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The problem of representing the length dependence of acoustic target strengths of fish is addressed by studying the legitimacy of merging target strengths that are inhomogeneous in species or frequency. The target strengths are of two kinds: maximum and averaged dorsal aspect target strengths, which are derived from measurements of gadoid target strength functions of three species at two ultrasonic frequencies. The target strengths are expressed variously according to unnormalized, wavelength-normalized and length-normalized schemes. Overall coincidences and coincidences of slopes among simple linear regressions of target strength on fish length, when segregated by target strength type and manner of representation, are investigated through analysis of covariance. Examination of computed significance levels demonstrates that merging of target strengths in species or frequency is generally unjustified and that no one representation method is superior to another in facilitating the merging of such data. The unnormalized representation is to be preferred when merging is justified because of its simplicity and avoidance of the frequency bias inherent in the normalized representations. The hypothesis of scaling of target strengths is refuted.Key words: target strength, regression, covariance analysis, fish abundance estimation

ISSN:0706-652X    

DOI:10.1139/f79-216

出版商:NRC Research Press    

年代:1979

数据来源: NRC