摘要:

Optimal harvest rates for mixed stocks of fish are calculated using stochastic dynamic programming. This technique is shown to be superior to the best methods currently described in the literature. The Ricker stock recruitment curve is assumed for two stocks harvested by the same fishery. The optimal harvest rates are calculated as a function of the size of each stock, for a series of possible parameter values. The dynamic programming solution is similar to the fixed escapement policy only when the two stocks have similar Ricker parameters, or when the two stocks are of equal size. Normally, one should harvest harder than calculated from fixed escapement analysis.

ISSN:0706-652X    

DOI:10.1139/f76-001

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Production by brook trout (Salvelinus fontinalis) in four infertile streams on the Canadian Precambrian Shield was estimated to be between 14.5 and 66.4 kg/ha per yr during 3 successive yr of study (1971–73). These values represent the range of total fish flesh elaborated annually in these streams because trout was the only species present. Differences between streams in annual production and P: B ratios arose from variations in stream cover (and its effect on carrying capacity), recruitment, and total biomass. Variations in age-specific growth rates were not critical. Production in the two most productive streams was judged to be controlled by food, while in the other two streams lack of suitable cover for adult trout limited production.

ISSN:0706-652X    

DOI:10.1139/f76-002

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Predation of rainbow trout (Salmo gairdneri) on migrant sockeye salmon (Oncorhynchus nerka) fry in experimental streams was higher on fry at an earlier development stage, in moonlight by contrast to cloudy night light intensities, at lesser turbidities, and at lower stream velocities. At dusk light intensities, from.05 to.30 ft-c, mortality from predation was inversely related to light intensity. The longer the period of exposure of fry to naturally declining light intensities prior to downstream movement, the lower was the loss to predators. Exposure of predators to high light intensities prior to the downstream movement of fry resulted in decreased fry mortality. Fry that had survived exposure to predators in an experimental stream 1 and 2 days previous were less vulnerable to predation than "naive" fry. Successive exposures further decreased the loss to predation. Fry enumerated at a counting fence suffered less predation than fry not enumerated. Experienced fry moved downstream more rapidly than naive fry.In laboratory aquaria, experienced fry formed compact schools prior to and in response to stimuli, while naive fry formed loose schools or did not school. Experienced fry were less active in responding to stimuli. Enumerated fry resembled experienced fry; nonenumerated fry resembled naive fry.Various techniques of enhancing sockeye salmon fry survival during downstream migration are suggested by these results.

ISSN:0706-652X    

DOI:10.1139/f76-003

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Eleven axenic or unialgal cultures of blue-green algae, 10 producing geosmin (trans-1, 10-dimethyl-trans-9-decalol) and 1 producing 2-methylisoborneol (2-exo-hydroxy-2-methyl-bornane) were isolated from saline lakes in southwestern Manitoba. These compounds are responsible for the muddy flavor in fish and water in some lakes. Algae producing geosmin wereOscillatoriacf.prolifica(Greville) Gomont,O.tenuisAgardh,O. cf.cortianaMeneghini,O. cf.variabilisRao,O.agardhiiGomont,O. cf.splendidaGreville,O. sp.,Symplocacf.muscorum(Agardh) Gomont,Lyngbyacf.aestuarii(Mertens) Liebman, andL. sp.Lyngbyacf.cryptovaginataSchkorbatov is the first alga reported to produce 2-methylisoborneol.Actinomycetes, which are known to produce these muddy flavor compounds, were not detected in these lakes.

ISSN:0706-652X    

DOI:10.1139/f76-004

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Several aspects of the cellular composition and metabolism ofAphanizomenon flos-aquae(L.) Ralfs were measured during the course of four blooms in small prairie lakes. Much larger changes were observed in these than in the nutrient concentrations of the water, suggesting the former to be more sensitive indicators of the progress of the bloom. These changes were reminiscent of the changes in batch cultures growing into nutrient deficiency. All four blooms developed characteristics of P deficiency, and to a lesser extent of N deficiency. In spite of their similar characteristics, three blooms collapsed dramatically, while the fourth did not. While P deficiency seems to play an important part in setting conditions for a collapse, it is not the factor that triggers the collapse.

ISSN:0706-652X    

DOI:10.1139/f76-005

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The thermal discharge from the Nanticoke Generating Station caused both yellow perch (Perca flavescens) and white sucker (Catostomus commersoni) to increase sharpness of turns, decrease distance between turns, and to orient into the current generated by the discharge. Conversely, fish released in thermally unaffected habitats referenced movement to the shoreline, turned less sharply, and swam greater distances between turns. The tendency for localization of movement was increased for both species when in the influence of the discharge. Swimming speeds were less for fish encountering the discharge; however, these fish had to contend with currents generated by the effluent thus making comparisons anomalous. Exposure of fish to elevated temperatures was brief and ranged from a few excursions into thermally elevated areas to approximately 9 h. Fish transplanted from unaffected areas to the discharge area showed behavior similar to fish caught and released at the discharge site. Two fish tracked when cooling water was discharged at ambient temperature suggested that current had a role in causing the observed changes in behavior.

ISSN:0706-652X    

DOI:10.1139/f76-006

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The effects of incubation temperature, pH, sodium, potassium, and ATP concentration, and ouabain on the activity of Na+–K+-activated ATPase of the gills of seawater-adapted juvenile coho salmon (Oncorhynchus kisutch) were determined. The temperature and pH optima were 40 C and 7.4, respectively. The apparent Km for ATP at equimolar Mg++concentration was 0.2 mMat Na+and K+concentrations of 100 and 20 mM, respectively. Maximal enzyme activity for Na+concentration of 10.50 and 100 mMoccurred at K+concentrations of 12.5, 15.0, and 20.0 mM, respectively. The Kifor ouabain was 2 × 10−6 Mand 7 × 10−6for K+concentrations of 10 and 20 mM, respectively.A large portion (up to 60%) of the ouabain-sensitive ATPase activity in freshwater fish was activated by sodium ions in the absence of potassium ions (Na+-activation). Exposure to sea water resulted in a large increase in total ouabain-sensitive activity and a sharp decrease in the proportion of sodium activation. These changes occurred within 14 days after transfer to full strength sea water.On a seasonal basis, total ouabain-sensitive enzyme activity in juvenile freshwater coho was low (less than 5 μmol Pi/mg N per h) to the end of November, increased to a peak (over 125 μmol Pi/mg N per h) in mid-January, and subsequently declined by late February. A slow, steady rise in activity occurred during the smoking period of March and April and the relative contribution of sodium ions to the total activity declined in this period.

ISSN:0706-652X    

DOI:10.1139/f76-007

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Six ration levels were established among 120 large, adult winter flounder (Pseudopleuronectes americanus) by setting different feeding frequencies, but with unlimited feeding at each meal. All fish were maintained at 7 C. With decrease in feeding frequency, fish ate less food per month but more food per meal — i.e. ration compensation was attempted. At the lowest frequency, two meals per month, fish did not compensate. At any one feeding frequency, fish ate progressively more per meal from the first to the fourth (final) month of the experiment.Maintenance ration was 7.9 gcal/g per day. Weight loss on starvation was equivalent to 2.14–2.35 gcal/g per day. Gross conversion efficiency ranged from 1 to 16%, and was positively correlated with ration. Net conversion efficiency averages 24.3% and was not related to ration.Positive correlations were found between mean calories consumed per day and condition, liver weight, percent fat in the liver, percent of fish with yolk-bearing ovaries, ovary weight, and percent of ovarian follicles with yolk. The decrease in proportion of yolked oocytes with decrease in ration was not due to increased follicular atresia, but to a decrease in number of oocytes starting vitellogenesis.Comparisons with flounders sampled directly from Passamaquoddy Bay, N.B. showed that the negative correlation between condition index and percentage of oocytes not in vitellogenesis was the same for Bay and laboratory fish, the range of response being greater in the laboratory fish. The existence of this relationship was interpreted as evidence that some flounders within the Bay were not getting all the food they could use. In the face of food scarcity, the winter flounder’s adaptive reproductive strategy seems to be to sacrifice egg production and maintain body weight, and so when a good year comes its body will be large and able to carry a larger ovary.

ISSN:0706-652X    

DOI:10.1139/f76-008

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Electroshocking elicited an immediate increase in plasma corticoid and lactate concentrations and thrombocyte:leucocyte ratio in rainbow trout (Salmo gairdneri). Plasma glucose concentrations increased significantly after 3 h. Plasma protein, calcium, magnesium, and androgen levels were not measurably affected. Plasma lactate returned to preshock levels within 3 h, but corticoid and glucose concentrations remained elevated for at least 6 h. The fish coughed violently or did not resume normal breathing rates for 60 s post shocking. Although breathing frequency did not increase, buccal pressure increased substantially and required at least 1 h to return to preshock levels. Cardiac activity was irregular immediately after shocking, but no predictable alterations in rate were evident thereafter. The height of the T wave in ECGs increased markedly 1–3 min after shocking. The electrophoretic patterns of 13 isoenzymes from liver, white muscle, and plasma did not differ between fish captured by dipnet and those captured by electrofishing.Responses exhibited by fish to shocking are most likely attributable to combined effects of trauma, factors associated with paying off of an oxygen debt, and attributes associated with the general adaptation syndrome of stress. A substantial period of time of more than 6 h is required for fish to return to "normal" preshock conditions.

ISSN:0706-652X    

DOI:10.1139/f76-009

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Many streams in southern Ontario experience excessive seasonal growth of aquatic plants such asCladophoraandPotamogeton. A direct relation, with a regression coefficient of 0.87, was observed between ambient P concentration in the water and P content of plant tissue in six rivers. Critical or growth controlling total P concentration of 60 μg/liter in stream water and 1.6 mg/gram dry weight in plant tissue were determined. Unlike P, no significant correlation was observed between N content of plant tissue and N concentration in water. The correlation of total P with plant growth can be used to estimate the waste load which would result in maximum growth rate ofCladophora.

ISSN:0706-652X    

DOI:10.1139/f76-010

出版商:NRC Research Press    

年代:1976

数据来源: NRC