摘要:

Detailed records of the fishery for a small discrete population of winter flounders permit calculations of growth rate, natural and fishing mortality rates and recruitment which are used to construct yield- and value-isopleths. The analysis illustrates the value of such data in predicting equilibrium yields under different conditions. Results in the present instance indicate that near-maximum economic yields are now being realized by the fishery.

ISSN:0706-652X    

DOI:10.1139/f55-014

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

A significantly faster growth rate by native and planted eastern brook trout followed the addition of commercial fertilizers in sufficient quantities to provide potential additional concentrations of 0.39 mg. P, 0.21 mg. N and 0.27 mg. K per litre in Crecy Lake (20.4 ha.; mean depth, 2.4), New Brunswick. Largely because trout planted as fingerlings attained suitable angling size when yearlings, the rate of capture and the yield by weight to anglers approximately doubled. The improved growth rate, but not yields, persisted into the second and third years after fertilization. Coincident was an increase in predation by fish-eating birds and mammals. With predator control and the same stocking rates, the yield of trout flesh produced in the lake increased from 0.9 to 5.9 kgm. per hectare over the next two-year period. With predator control extended to trapping eels in the lake, a second comparable fertilization with respect to concentrations of P, N and K, and a doubling of the stocking rate, a yield of 9.7 kgm. per hectare was realized. The growth rate was somewhat depressed with the heavier stocking, notwithstanding a second fertilization. Facilities for natural reproduction were poor and planted trout (fingerlings and yearlings) sustained the fishery. Maximum survivals of planted trout (all marked) to anglers' catches were 20 per cent for fingerlings and 88 per cent for yearlings. Cropping of trout of age II was thorough. For the most part, movements of planted trout (trapped in outlet) from the lake would have occasioned minor losses.Neighbouring Gibson Lake (24.0 ha.; mean depth, 4.0 m.) was fertilized with one-half of the concentrations of P, N and K applied to Crecy. Stocking with trout was at comparable rates but no predator control was exercised. Little improvement was noted in the growth of the trout. Only when yearlings were planted late in the fall and angled early in the spring was there any improvement in the anglers' catches.

ISSN:0706-652X    

DOI:10.1139/f55-015

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Estimated standing crops of eels in eight Maritime lakes treated with fish poisons varied from 0 to 70.8 pounds per acre. Smaller standing crops were associated with greater distances of lakes from the sea, and with obstructions to ascending elvers. Few eels were found in small spring-fed streams. The eel is prominent in Maritime lakes, but frequently is not more successful than other fish considered inimical to game species. Seaward migrations of eels may represent major losses of organic matter to lakes.Scales appear on young eels at lengths from 16 to 20 centimetres, probably in their third or fourth year of age. Nine year-classes were found among eels with scales in each of three limnetic populations. Eels with three and four annual rings on the scales were dominant in the runs from lakes.Runs of eels from lakes occurred in April and May, and again, in larger numbers, from late August through November. These movements were at night, and usually coincident with rising water during and immediately following heavy rains. Silvering, an index of maturity, was manifest among only a portion of the largest of these eels. Fall runs of large eels from salt water into streams have been noted. Upstream movements of elvers are most prominent in May and June, although they attempted to bypass a barrier in the outlet of one lake throughout the summer.

ISSN:0706-652X    

DOI:10.1139/f55-016

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Collectors were exposed at various depths in water 2.3 m. deep in tideless Gillis Cove (Bras d'Or Lake, N.S.) and renewed morning and evening. Rates of settlement of oyster spat (Ostrea virginica) as high as 0.4 spat per sq. cm. per hour were observed. The catch varied directly with depth, was heavier by day than by night, and the level of most intense spatfall was closer to the surface by day than by night. The catch on lower surfaces was heavier than on upper but the difference was less by day than by night. These and other observations suggest that ready-to-settle oyster larvae have three behaviour characteristics: they are benthic; light stimulates them to settle; and they settle most readily on lower surfaces.

ISSN:0706-652X    

DOI:10.1139/f55-017

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The process of egg collar formation by naticid whelks is described in detail, with an account of the structure of the egg masses of nine species of Naticidae. The collars of five American and two European species are described together with three unidentified egg masses recovered from Canadian Atlantic waters. These are compared with the egg masses of other species, previously described in the literature, and a scheme of classification for the egg collars of the Naticidae is presented on the basis of these descriptions and comparisons.

ISSN:0706-652X    

DOI:10.1139/f55-018

出版商:NRC Research Press    

年代:1955

数据来源: NRC