摘要:

Ninety-eight percent of recently surveyed papers in fisheries and aquatic sciences that did not reject some null hypothesis (H0) failed to report β, the probability of making a type II error (not rejectingH0when it should have been), or statistical power (1 – β). However, 52% of those papers drew conclusions as ifH0were true. A falseH0could have been missed because of a low-power experiment, caused by small sample size or large sampling variability. Costs of type II errors can be large (for example, for cases that fail to detect harmful effects of some industrial effluent or a significant effect of fishing on stock depletion). Past statistical power analyses show that abundance estimation techniques usually have high β and that only large effects are detectable. I review relationships among β, power, detectable effect size, sample size, and sampling variability. I show how statistical power analysis can help interpret past results and improve designs of future experiments, impact assessments, and management regulations. I make recommendations for researchers and decision makers, including routine application of power analysis, more cautious management, and reversal of the burden of proof to put it on industry, not management agencies.

ISSN:0706-652X    

DOI:10.1139/f90-001

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

We examined the retention characteristics of commonly used 0.2-μm nucleation-track (Nuclepore®, Poretics®), polymer (Millipore®, Sartorius®) and inorganic membrane (Anopore®) filters. Scanning electron micrographs of the filter surface showed many to contain large holes or pores, some 5 × larger than the manufacturer's stated nominal pore diameter. Electron micrographs of filtrates from both fresh and seawater samples contained a variety of organisms, including viruses, ultramicrobacteria, bacteria, phototrophic picoplankton, and larger nano- and microphytoplankton (e.g. diatoms), which we believe passed through the large openings. Total particles in the size range 1.0–12.8 μm passing through the various 0.2-μm filters tested ranged from 2.2 to 14.3%, with 'best' retention (>97%) by the Anopore®. Average particle retention for all 0.2-μm filters tested was 92.5%. Higher passage rates (lower retention) are predicted for even smaller (<1.0 μm) particles (prochlorophytes, bacteria, viruses) and investigators are urged to use care when using polycarbonate or matrix type filters for partitioning size fractions for chemical, physiological, and ecological work, and caution when interpreting results, especially if separations have not been verified by microscopy, incubation, or culture.

ISSN:0706-652X    

DOI:10.1139/f90-002

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

This paper presents an approach to the analysis of growth, maturity, and survivorship data that unifies an extensive biometrics literature, particularly in fisheries and forestry. The model involves a probabilistic responseyto a positive factorx. Because the relationship is asymptotic, the model can also be interpreted as a descriptor of biological growth, in which the asymptotic size is scaled to 1. The model generalizes earlier work by Gompertz, von Bertalanffy, Weibull, Richards, Chapman, and Schnute; it also extends the logit method introduced by Berkson. We identify reasonable curve families for the model, in which a transform parameter associated withxorydetermines the curve shape, and we provide a complete analysis of curve types. We describe likelihood functions associated with two classes of data, typified by (1) size-at-maturity data and (2) time–mortality data. We illustrate the model's application to both data classes and show that it provides a useful extension to past methods of analysis.

ISSN:0706-652X    

DOI:10.1139/f90-003

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The ash-free dry mass (AFDM) of detritus, invertebrates, and algae in the diet of juvenile white sucker (Catostomus commersoni) was determined by quantitative microscopy. Fish were collected from a northern Michigan pond from January through October 1986 and their seasonal diet was compared with benthc invertebrate abundance. The quantity of detritus in sucker foreguts was inversely related to benthic microcrustacean densities. In July, microcrustacean densities were high and they comprised 95% of the AFDM in foregut contents. By October, microcrustacean densities had declined to 13% of their maximum density and detritus comprised over 90% of the sucker's diet AFDM. In laboratory aquaria, sucker that were fed detritus mixed with four different densities ofArtemiaingested significantly more detritus from diets that provided lowerArtemiadensities. In the presence of highArtemiadensities, sucker completely rejected detritus and ingested onlyArtemia, The fact that juvenile sucker can separate detritus from invertebrates that they swallow demonstrates that detritus is not ingested incidentally. Both laboratory and field data support the hypothesis that detritus is ingested intentionally when preferred invertebrate prey are scarce.

ISSN:0706-652X    

DOI:10.1139/f90-004

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The nutritional significance of detritus in the diet of the juvenile white sucker (Catostomus commersoni) was evaluated by experiments designed to assess assimilation efficiency and growth of sucker fed detritus and other foods. Sucker in laboratory aquaria assimilated detritus with the following efficiencies: dry mass = 19.6%, ash-free dry mass (AFDM) = 59.7%, total amino acids = 68.9%, energy = 69.4%. Assimilation efficiencies calculated for invertebrates and natural field diets were slightly higher. Diatom assimilation was low (5.5%). In growth experiments, sucker fed detritus ad libitum lost weight, while those fedArtemiaad libitum grew rapidly. However, detritus increased the growth rate of sucker fed a limited invertebrate ration and reduced the rate of weight loss relative to unfed fish. The ratio of digestible protein to digestible energy calculated for natural detritus diets (3.2 mg amino acid/kj) indicates that the protein content of detritus is too low to support growth. Detritus provides energy which complements limited invertebrate protein to enhance growth or reduce the rate of weight loss when invertebrate prey are not available.

ISSN:0706-652X    

DOI:10.1139/f90-005

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Large scale aquatic effects of acidic deposition have become a prominent environmental issue in North America and Europe. Models are required to assess the potential future impacts of current levels of acidic deposition, and the potential benefits of emission controls. This paper presents a model that uses measurements of current lake chemistry and assumptions about the processes governing acidification, to first estimate original (i.e. preacidification) lake chemistry and then predict the eventual chemistry expected given a specified level of acidic sulphate deposition. The model is deliberately kept simple, so that its input requirements are modest and thus can be met on a regional scale. When applied on a regional scale the model predicts the expected eventual distributions of alkalinity and pH. Application of the model is illustrated for a watershed in north-central Ontario, which includes the area immediately to the south and west of Sudbury. Model-based estimates of current alkalinity are very similar to observed alkalinities. The predicted eventual alkalinity distributions, given current levels of deposition, indicate a trend towards recovery, consistent with other observations in the Sudbury region. A sensitivity analysis of the model indicates that its outputs are highly sensitive to estimates of preacidification lake sulphate levels, and less so to assumptions about the catchment's ability to neutralize incoming acidity. Simple, regional models such as the one presented in this paper should play a more central role than they presently do both in assessment and in the definition of future research and monitoring needs.

ISSN:0706-652X    

DOI:10.1139/f90-006

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

In this, the second of two papers on the development and application of a regional model of surface water acidification, we present the results of initial applications of the model to sensitive regions of eastern Canada. Data used for regional application of the model were obtained from a variety of sources, including acidic sulphate deposition monitoring data and regional lake water chemistry surveys. While these data do not provide a random sample of eastern Canadian lakes, we argue that there are no a priori reasons for expecting highly misleading biases in the data. Results of model applications are presented for observed 1980 sulphate deposition levels and for three alternative emission scenarios. The emission scenarios were simulated using a transfer matrix derived from the AES-LRTAP model. The results suggest that substantial additional damage (declines in surface water alkalinity and pH) is expected in some regions (e.g. northeastern Ontario), even at current deposition levels. The consequences of simple emission reduction strategies differ significantly among regions, suggesting that more complex strategies may be required to produce equitable benefits. To assist interpretation of a complex array of results, we propose an integrated representation of regional impacts that uses quantile-quantile plots of regional distributions of lake chemistry. Finally, we argue that while the results presented are highly uncertain, there are reasons to believe that, if anything, our damage estimates are conservative.

ISSN:0706-652X    

DOI:10.1139/f90-007

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The distribution of sub-ice macrofauna was investigated in the Barrow Strait area near Resolute, N.W.T. from April–June, 1985, 1986, and 1987, and in January 1986. Invertebrates were sampled using remotely deployed net and video camera systems. Ten species of amphipods and two species of mysids were found, but over 90% of the biomass was made up of only four species of amphipods:Weyprechtia pinguis,Onisimus litoralis,Gammarus setosus, andOnisimusspp. juveniles. Species composition varied annually, withW.pinguisdominating in spring 1985,O.litoralisin 1986, andG.setosusin 1987. There were also areal differences in species composition over distances of 50–200 km. Underlying water depth was the major environmental correlate of both total biomass and species composition; total biomass decreased with increasing underlying water depth, being near zero over >100 m depth. We hypothesize that spring sub-ice distribution is a reflection of summertime benthic distribution. Total biomass decreased with increasing snow depth early in the spring, probably because the attenuation of incident light by snow reduces the concentration of sub-ice algae. Total biomass was lower within 1 km of the ice edge than in areas further from the ice edge.

ISSN:0706-652X    

DOI:10.1139/f90-008

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

We quantified woody debris in the river swamps of the sixth order Ogeechee River and several smaller tributaries in the Coastal Plain of the southeastern USA, compared swamp wood with woody debris in the channel, and studied wood movement in the swamp and main channel over 20 mo. Woody debris in the Ogeechee River swamps was relatively low (0.362–0.880 kg ash-free dry mass (AFDM)/m2) in comparison to several mixed temperate deciduous forests. Similarly, wood in the tributary swamps was low (mean = 0.82 kg AFDM/m2), and there were no trends along the river continuum. Wood in the channels of both the Ogeechee (6.46 kg AFDM/m2) and a fourth order tributary (2.24 kg AFDM/m2) were significantly higher than found in their adjacent floodplains. Woody debris appeared to increase in stream channels from smaller tributaries to the sixth order river, opposite of that observed in other river systems. Tagging of logs showed that only 17% of wood in the Ogeechee channel had moved after 3 major floods, much less than in the swamps (21–84%). The abundance and stability of woody debris in the main channel allows it to be a major habitat type and source of food for both riverine invertebrates and fishes. The fate of most swamp wood appears to be decomposition and fragmentation, rather than import to the river channel.

ISSN:0706-652X    

DOI:10.1139/f90-009

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Physical, chemical and biological variables were measured in the Great Salt Lake during 1985–87, when salinity in the mixolimnion was near 50 g/L, much lower than the 250 g/L maxima recorded in 1963. Decreased salinity has been accompanied by a change in macrozooplankton from one species (Artemia franciscana), to an assemblage with one rotifer, two copepods,Artemia, and the corixidTrichocorixa verticalis. Predation by the corixid may now limitArtemiato low densities (<100∙m−3). The low biomass ofArtemiaand other zooplankton has reduced grazing pressure on the algal community so that high chlorophyll levels (5-44 mg∙m−3) and low Secchi depths (0.8–2.7 m) are now present throughout the year. The algae presently reduce soluble reactive phosphorus and inorganic nitrogen in the mixolimnion to below 5 and 50 μg∙L−1, respectively. Shading in the 7-m thick mixolimnion by algae, and by purple-sulfur bacteria in the chemocline, decreases light penetration so that the monimolimnion now maintains a nearly constant temperature (9–11 °C) throughout the year. The data support the hypothesis that the effects of corixid predation have cascaded through the Great Salt Lake, affecting herbivores, nutrients and thermal stratific

ISSN:0706-652X    

DOI:10.1139/f90-010

出版商:NRC Research Press    

年代:1990

数据来源: NRC