摘要:

The following expression is derived expressing the instantaneous growth rate (G) in terms of length (l) the power of the weight–length relationship (b), and the Bertalanffy growth parameters (KandL∞):G = bK(L∞/l − 1). Since this is valid for a length (or age) range in which growth conforms to the Bertalanffy model, a plot of G vs. 1/lshould be linear with the intercept on theGaxis being −bKand on the 1/laxis being 1/L∞. Since the variables can be measured independently, deviations of points from the regression can be tested and the limits of validity of the model ascertained. In addition, confidence limits ofKandL∞can be estimated. Two examples compare results with those using previous methods.Key words: method, Bertalanffy, growth, statistical, estimates, parameters

ISSN:0706-652X    

DOI:10.1139/f77-164

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Spawning runs of lentic-dwelling brown trout (Salmo trutta) and rainbow trout (S.gairdneri) in Swamp Creek, an inlet of Lake Eucumbene, were studied for 4 consecutive yr, and 3517 browns and 415 rainbows were tagged during 1968–70. A further 240 browns and 229 rainbows were marked in other inlets. Recaptures of marked browns in 1969 and 1970 showed a high incidence of repeat homing, up to 25.7 and 10.6% returning after 12 and 24 mo, respectively. Few rainbow trout homed. Tag loss and the mortality and maturation of marked browns were estimated and percentage homing and straying in 1969, 1970 and 1971 was calculated. High percentage homingin 1969–70 and the variance in external form in the lentic population suggested some genetic isolation within the brown trout population. Homing ability was not influenced by fish age. Percentage homing fell markedly in 1971 after the removal of nearly all resident brown trout from Swamp Creek and suggested racially distinct stream trout populations to be an important navigational cue to homing brown trout.Key words: repeat homing,Salmo trutta, homing frequency, navigation, racial cue, Australia

ISSN:0706-652X    

DOI:10.1139/f77-165

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Certain physical measurements intended to shed light on the circulation in large plastic enclosures (60–2000 m3) induced by the changing environment in which they are moored are described. Layers of dye were generally seen to diffuse vertically although some important advection effects were also observed. Estimates of an average coefficient of turbulent diffusivity yielded values in the range.05–.26 cm2∙s−1.Measurements taken with recording thermistor chains both inside and outside the enclosures show strong damping of external fluctuations with periods significantly less than 1 day. Various possible sources of mixing energy are considered and it is concluded that thermal forcing through the wall may be significant and could account for the observed range of coefficients.The significance of the observed mixing and circulation to the ecology of the enclosures is discussed. Of particular importance is the vertical mixing of nutrients that influences phytoplankton sinking rates and thus plays a crucial role in determining variations in algal concentration at different depths.Key words: mixing, enclosures, controlled ecosystem pollution experiment, circulation, temperature profil

ISSN:0706-652X    

DOI:10.1139/f77-166

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The abundance and distribution of six littoral zone fish species (Notropis volucellus,Hybognathus nuchalls,Notemigonus crysoleucas,Pimephales notatus,Fundulus diaphanus, andEtheostoma nigrum) in Lake Memphremagog were influenced directly by a nutrient-driven production gradient existing along the long axis of the lake. The biomass of the six littoral zone fish species was approximately 3 times greater in the more productive southern areas than in the less productive northern areas. Interspecific competition for food was more intense in the less productive northern areas than in the more productive southern areas, and strongly influenced the patterns of food utilization. However, interspecific competition did not appear to play the major role in determining the distribution of the species on the gradient. Distribution of individual species was principally governed by the relative abundance of preferred food resources. The distribution of only one species,Fundulus diaphanus, appeared to be determined primarily by direct competition.Key words: littoral zone, Lake Memphremagog, nutrients, production, resource utilization, fish, food availability

ISSN:0706-652X    

DOI:10.1139/f77-167

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A substance characterized as a glycoprotein, isolated from the supernatant fluids of broth cultures ofAeromonas salmonicidaby a combination of ammonium sulfate and ethanol precipitations followed by chromatography on DEAE-cellulose, was cytolytic for rainbow trout (Salmo gairdneri) leukocytes, and antigenic when injected into rabbits. The ratio of protein to hexose determined by analysis of the purified fraction was between 0.35 and 0.45, and small amounts of amino sugars were detected. A virulent strain ofA.salmonicidaproduced much more of this factor than an avirulent strain. This factor was cytolytic for leukocytes in vitro and also produced a pronounced leukopenia when injected intravenously in adult rainbow trout. When injected in small coho salmon (Oncorhyncus kisutch) 8–13 cm long together with about one LD50 of liveA.salmonicida36 of 40 fish succumbed to the combination, whereas only 14 of 40 died from an injection of the bacterium alone. Thus, the pathogenicity of the organism was enhanced, presumably by increasing the susceptibility of the host. Hence, this glycoprotein apparently is one of the virulence factors of this bacterium.Key words: leukocytolytic factor,Aeromonas salmonicida, glycoprotein, virulence factor

ISSN:0706-652X    

DOI:10.1139/f77-168

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Data were collected from 227 ringed seals (Phoca hispida) and bearded seals (Erignathus barbatus) killed by polar bears (Ursus maritimus) in the western arctic and the eastern high arctic. During periods of high ringed seal productivity, pups constituted at least half of the seals killed in both areas during the spring. Bearded seals were taken less often than ringed seals in both areas but were more important as prey to polar bears in the western arctic. Carcass utilization was significantly higher in the eastern high arctic than in the western arctic although the reason was not apparent. Scavenging of unutilized seal remains is probably of great importance to the survival of large numbers of arctic foxes (Alopex lagopus) through the winter.Key words:Ursus maritimus,Phoca hispida,Erignathus barbatus, predation, interspecific relationships, Arctic Ocean mammals

ISSN:0706-652X    

DOI:10.1139/f77-169

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Depensatory predation mortality on salmon when added to a Ricker production model can create a system with at least two stable equilibria and two domains of attraction. The behavior of such a fish system is different from a single equilibrium situation and a simple mechanism is described through which commercial exploitation changes the ability of such multiple-equilibrium fish populations to respond to perturbations in survival rates. Furthermore, it is shown that this change in size of stability regions is proportional to the exploitation rate and that classically defined maximum sustainable yield (MSY) exploitation rates are inevitably close to the rates that would cause a drastic decrease in the population. The uncertainties inherent in environmental effects on survival and in achievement of desired exploitation rates precipitate the need to back away from the usual MSY exploitation rates and set up (through enhancement) a system of stocks whereby feedback information is provided to the manager. This approach of adaptive management seeks reasonable yields while gaining information about the state (or changes in state) of the system. Some applications of catastrophe theory are discussed, especially with reference to harvesting multiple-stock salmon systems.Key words: stability, resilience, exploitation, salmon, depensation, multiple equilibria, adaptive management, enhancement, catastrophe theory

ISSN:0706-652X    

DOI:10.1139/f77-170

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Ringed seals,Phoca hispida, showed rapid absorption of hydrocarbons from Norman Wells crude oil into body tissues and fluids when exposed by both immersion and ingestion. Relatively low but significant levels were found in tissue, blood, and plasma. Levels in bile and urine were high, indicating these to be routes of excretion.Key words: petroleum, hydrocarbons, benzene, ringed seal, immersion, ingestion, uptake, clearance

ISSN:0706-652X    

DOI:10.1139/f77-171

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Partial and complete life-cycle toxicity tests with fish, involving all developmental stages, have been used extensively in the establishment of water-quality criteria for aquatic life. During extended chronic exposures of fish to selected toxicants, certain developmental stages have frequently shown a greater sensitivity than others. In 56 life-cycle toxicity tests completed during the last decade with 34 organic and inorganic chemicals and four species of fish, the embryo–larval and early juvenile life stages were the most, or among the most, sensitive. Tests with these stages can be used to estimate the maximum acceptable toxicant concentration (MATC) within a factor of two in most cases. Therefore, toxicity tests with these early life stages of fish should be useful in establishing water-quality criteria and in screening large numbers of chemicals.Key words: fish, embryos, larvae, chronic toxicity, early life stages

ISSN:0706-652X    

DOI:10.1139/f77-172

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Advice from the scientific advisers under the auspices of ICNAF to the international commissioners for 1977 was that the total allowable catch (TAC) for harp seals (Pagophilus groenlandicus) should not exceed 170,000. This advice, in part, was based on the scientific arguments presented in this paper. A stochastic model is developed that takes into account the variations in natural mortality and the landsmen's high arctic and Greenland catches. The Canadian–Norwegian large vessel hunt is controlled under quota regulations. The model is nonlinear, a result of changes in fertility and fecundity rates in response to shifts in population size. The maximum sustainable yield (MSY) 1 + population size is determined to be 1.6 million seals, or a breeding stock size of 375,000 seals. The MSY is approximately 240,000 seals assuming the hunt continues its present pattern. The 240,000 can further be split into 200,000 pups and 40,000 1 + seals. Present stock size is approximately 1.2 million and a TAC of 170,000 seals will allow the population size to reach to MSY level in 10–15 yr. A number of other management strategies are considered, in addition to prospects for future research.

ISSN:0706-652X    

DOI:10.1139/f77-173

出版商:NRC Research Press    

年代:1977

数据来源: NRC