摘要:

not available

ISSN:0706-652X    

DOI:10.1139/f63-021

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

1. A population which, before exploitation, includes upwards of 12–15 age-groups in appreciable quantities, is very sensitive to fishing. For example, even as little as 5% catch per annum eventually causes a major reduction in the relative weight of older fish in the stock. With unchanging recruitment the absolute size of the total stock also declines markedly, or even catastrophically, under moderate exploitation—so much so that it seems likely that recruitment must usually increase when the stock is first thinned, partly compensating for the removals.2. A population that produces its greatest sustained yield at a high rate of exploitation—say 75% or more at average recruitment—is then close to a point where recruitment will fall off rapidly if utilization becomes only slightly more intensive. This fact, and the aggravating effect of environmentally-caused variations in recruitment, suggest that any really close approach to the point of optimum yield will usually be too dangerous to be practical.

ISSN:0706-652X    

DOI:10.1139/f63-022

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

Whitefish (Coregonus dupeaformis) ages were determined for small samples from Nueltin, MacDonald and MacEwen Lakes, N.W.T., Canada. Growth rate was comparatively fast in MacEwen Lake, intermediate in the others. Natural annual mortality rates of 57, 81 and 74% respectively were derived.

ISSN:0706-652X    

DOI:10.1139/f63-023

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

Two female specimens of the black scabbard fish, 103 and 109 cm long, were captured by otter trawl at 380–400 fathoms (695–732 m) on the Northeast Newfoundland Shelf, on September 30 and October 5, 1959. An additional specimen, a 110–cm female, was caught by longline at over 300 fathoms (> 550 m) off Sable Island Bank in mid August 1960. Meristic, body–proportion and other characteristics of these specimens were within the possible range of variation forAphanopus carboLowe from the eastern Atlantic.

ISSN:0706-652X    

DOI:10.1139/f63-024

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

During the summer months of 1956 to 1959 inclusive, the stomach contents of 2963 Heming Lake whitefish from 5–15 inches in length were examined. Data on stomach contents of 194 whitefish taken in 1945 were examined and included in this analysis. Most stomachs contained food, but lesser quantities of food per stomach and many empty stomachs were found in July and August of each year. Mayfly nymphs occurred in the stomachs most often. Other, insects eaten included dipterous larvae, especiallyChaoborusand chironomids. Incidental items, constituting a smaller though important part of the fish's diet, included aquatic coleopterans, hemipterans, trichopteran larvae, cladocerans,Hyalella, hydrachnids, gastropods and, seasonally, aerial insects from the surface of the lake, and small fish. Cyclopid and calanoid copepods were found in about 1% of the stomachs. This apparently low incidence of cyclopids in the diet is considered to be sufficient to establish the relatively high infection levels ofTriaenophorusfound in Heming Lake fish. Some differences in diet between fish of different sizes and between seasons were shown.

ISSN:0706-652X    

DOI:10.1139/f63-025

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

Past and current research by the Fisheries Research Board of Canada related to olfactory and visual responses in Pacific salmon is reviewed, including comments on some of the sensory and behavioural relations important in migration.An innate ability to perceive highly dilute odours supports the view that olfaction can be instrumental in detecting a distant source, but the problems of following a well directed course indicate likely support from other sensory paths including visual and acoustico–lateralis responses.A threshold visual sensitivity of about 1/300 that of bright moonlight and an ability to orient at night, with view of the sky only, provide evidence that retinal images may be useful as migratory cues as long as turbidity does not interfere.

ISSN:0706-652X    

DOI:10.1139/f63-026

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

The average straight line distance between release and recapture points of 253 tagged lobsters free 10 to 12 months was 7.3 nautical miles (13.5 km). Carapace-length growth increments per moult among 870 punch-marked lobsters recovered from the fishing grounds were independent of size and averaged 0.47 inches (11.9 mm) for males and 0.42 inches (10.7 mm) for females. Weight increments per moult varied from 4.0 to 7.5 ounces (113–213 g) for males and from 3.3 to 5.4 ounces (94–153 g) for females. Of the males, 17.8% moulted twice; of the females, 7.4%. Survival over a 10-month period was estimated to be 76.4%.

ISSN:0706-652X    

DOI:10.1139/f63-027

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

At Great Slave Lake, N.W.T., 3629 fish marked with Petersen tags were released during 5 years from 1946 to 1955. The time at large and movement of 505 recoveries, mostly lake whitefish,Coregonus clupeaformis, and lake trout,Cristivomer namaycush, are analyzed. Most of the tagged fish were caught in the summer commercial fishery; returns during the fall and winter were scarce. The median recapture time was 268 days; the maximum, for a lake trout, was 4027 days. Movement was generally limited; its median was 5 statute miles (8 km). A few fish travelled relatively long distances. There was no overall directional pattern to the movement, but some aggregation of the recaptured fish was noted. The fish populations are regarded as sedentary rather than mobile.

ISSN:0706-652X    

DOI:10.1139/f63-028

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

A 13-acre pond was formed at head of tide on Wilmot Stream, Prince Edward Island, to hold brook trout (Salvelinus fontinalis) moving between stream and saltwater estuary for greater availability to anglers. Trout continued to move between pond and estuary via an artificial outlet, predominantly during the spring and early summer. Improved angling conditions resulted in capture of 8,215 trout from pond and upper reaches of estuary at rate of 1.2 per rod-hour over three angling seasons. Shallowness of water limited trout-holding capacity of the pond and curtailed better angling success. Other hydrographic conditions and food supply in the pond were favourable for brook trout.

ISSN:0706-652X    

DOI:10.1139/f63-029

出版商:NRC Research Press    

年代:1963

数据来源: NRC

摘要:

The opercular fold inSalvelinus fontinalis(Mitchill) begins as a bulging, outward and backward, of the undifferentiated dorsally-packed mesenchymal tissue of the hyoid arch in embryos of 6.0–6.5 mm total length. From 6.5 to 9.0 mm, backward growth takes place although no gill arches are covered. The epithelium of the opercular anlage is 2- to 3-layered laterally and 1- to 2-layered with smaller nuclei medially. From 9.0 to 14.0 mm, i.e. hatching, the membranous lateral opercular and ventral branchiostegal portions extend posteriorly to cover the four gill arches. Ossification commences in the opercle, the jaws and the pectoral girdle. The epithelium which has scattered goblet cells is 3- to 4-layered antero-laterally, 1- to 2-layered postero-laterally and one cell in thickness medially. From 14.0 to 30.0 mm length ossification of the skeletal elements of the opercular apparatus takes place. The musculature of the operculum is complete at hatching.

ISSN:0706-652X    

DOI:10.1139/f63-030

出版商:NRC Research Press    

年代:1963

数据来源: NRC