摘要:

Ungava Crater Lake, at 73° 41′ W.L. and 61° 17′ N.L., lies in a meteoritic crater of the northern Quebec tundra. The lake is nearly circular, 1.7 miles in diameter, with steep walls and a maximum known depth of 825 feet. Secchi disc transparency was 35 metres. Summer surface temperatures were 3–4 °C., of the deep water a little less. Surface oxygen was abundant, pH was 6.5–6.6. Total solids in the water were less than 20 parts per million, and hardness was only 1.7 p.p.m. Three kinds of mammals and 14 of birds were found in the crater region. Arctic char,Salvelinus alpinus, were the only fish taken in the crater lake. Specimens up to 21.8 inches fork length and 18 years old were taken; they fed on insects and other char. Char in other nearby waters grew somewhat faster but ate the same foods; mature females as small as 4.0 inches were seen. Lake trout,Salvelinus namaycush, in a lake near the crater reached 33.5 inches and 15.8 pounds. Growth was very slow, the greatest age determined being 21 years, at 13 pounds. Twenty-nine species of vascular plants were collected close to the crater.

ISSN:0706-652X    

DOI:10.1139/f55-027

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Incidental information on the ecology of the common (Eastern) whitefish,Coregonus clupeaformis, and the Rocky Mountain whitefish,Prosopium williamsoni, was collected in the course of the Skeena River Salmon Investigation of 1944–1948. The common whitefish has been found in only four Skeena lakes, which have characteristics that are mainly oligotrophic. Rocky Mountain whitefish were taken in all the lakes where netting was done, which included warm and shallow, as well as deep and cold, bodies of water. The bottom fauna of Lakelse, Babine and Morrison Lakes was described. During the summer common whitefish were most abundant in depths of 10–15 m., and Rocky Mountain whitefish at 5–10 m. The food of the two species was very similar, and consisted mostly of bottom organisms. An exception was that of common whitefish in Morrison Lake, which had fed almost wholly upon plankton crustaceans. This situation was associated with the paucity of bottom fauna in the lake. The important competitors for food of the whitefishes, identified on the basis of common food and habitat, were peamouth chub,Mylocheilus caurinum, and squawfish,Ptychocheilus oregonense. Chief predators of the whitefish were lake trout,Cristivomer namaycush, and ling,Lota lota. However, there was no evidence that predation upon either whitefish was particularly serious. The oldest common whitefish were X years of age (473 mm. fork length), and Rocky Mountain whitefish IX years (365 mm. fork length). No food organisms occur in the Skeena lakes in such abundance as do certain amphipods in other Canadian lakes where the common whitefish is fished commercially. This scarcity of suitable food is considered to be the main condition limiting the abundance of the Skeena populations of common whitefish.

ISSN:0706-652X    

DOI:10.1139/f55-028

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

To determine whether certain environmental factors may affect standing crop, an analysis was made, primarily by regression methods, of the published estimates of standing crops of fish in lakes and ponds. Standing crop estimates derived by draining and those by poisoning appear to be equally accurate, but marking and recovery estimates may not be directly comparable with the other two. Average standing crops in river backwaters and oxbows were almost 500 pounds per acre; in midwestern reservoirs, almost 400 pounds per acre; in other reservoirs and ponds, 200 to 300; in warm-water lakes, 125 to 150; and in trout lakes, less than 50 pounds per acre.No correlation could be shown between areas of lakes or ponds and their standing crops per acre. There was a tendency for standing crop per acre to decrease with increase in maximum depth of trout lakes, of warm-water lakes, and probably of reservoirs. Significant increase in standing crop per acre with increase in carbonate content of the water was found in trout lakes, warm-water lakes and midwestern reservoirs.Elton's pyramid of numbers was demonstrated in an analysis of standing crop per acre by species. Competition between species at the same food level may be mitigated by habitat segregation. Standing crop per acre increases as the number of species increases or as the niches are filled. However, standing crops of given species were usually highest when only one or two species were present. Regressions of the standing crops of one species upon those of other species may give clues as to the degree of competition or of protocooperation, but these clues must be critically evaluated since the regressions may be due to factors other than the presence of the other species.

ISSN:0706-652X    

DOI:10.1139/f55-029

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The presence of larvalAnisakisin British Columbia herring was examined during the winter fisheries of 1950–51 and 1951–52. In the commercial catches in the Strait of Georgia the incidence was found to be between 80 and 90%. In Hecate Strait, on the west coast of Vancouver Island and in the mainland coastal area of Queen Charlotte Sound it was between 90 and 100%. The intensity of infection varied greatly in different fishing areas (i.e. in different herring populations). Generally, the maximum level of infection occurred in the Queen Charlotte Sound coastal regions, and decreased both north and south of this area. Fish on the west coast of Vancouver Island were more heavily infected than those on the east coast (Strait of Georgia). The level of infection increased with age, I-year fish (i.e. fish in their first year of life) being uninfected. The intensity of infection remained constant throughout the winter for any particular age and area and was the same for both sexes. In most areas the level of infection was a little lower in 1951–52 than in 1950–51.

ISSN:0706-652X    

DOI:10.1139/f55-030

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Four species of chaetognaths were found in samples from 11 representative areas along the coastline of western Canada.Sagitta eleganswas the most abundant and widely distributed species, occurring, at least in small numbers, in all the areas sampled. It was characteristic of the mixed coastal waters over the continental shelf and of the inland waters.Eukrohnia hamata, an oceanic form, occurred in most regions in small numbers as an immigrant, and was abundant toward the edge of the continental shelf.Sagitta lyra, strictly a deep sea species, was found only in the open waters along the outer coasts, and a few specimens ofSagitta decipiens, another oceanic form, were also taken in deep hauls from areas exposed to open ocean influence. The outer limit ofSagitta eleganscorresponded with the inner limits of all three oceanic forms, thoughEukrohnia hamatainvaded the inland waters to some extent.

ISSN:0706-652X    

DOI:10.1139/f55-031

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

A stocking, partial-poisoning and creel census experiment was carried out on a stratified lake in an effort to increase the crop of speckled trout,Salvelinus fontinalis. Except for a single year in which adult trout were planted, a negligible proportion of the introduced trout was recaptured. Application annually for five years of about one-half part per million of derris dust to the three-meter zone of the lake during summer stratification produced a heavy kill of coarse fish without harming the trout. Shiner,Notemigonus crysoleucas, perch,Perca flavescensand chub,Semotilus atromaculatuswere eliminated from the lake. Sucker,Catostomus commersoni, was drastically reduced. Killifish,Fundulus diaphanus, and eel,Anguilla bostoniensis, were not appreciably reduced, despite large annual kills. Smelt,Osmerus mordax, stickleback,Gasterosteus aculeatus, and trout,Salvelinus fontinalis, were killed in very small numbers during one or more poisoning years.Three independent estimates of the effect of the experiment upon the trout production of the lake are put forward: (a) The decrease in mass of the fish competing with trout for food, when calculated from the annual kills, amounts to 40 kg. The pre-poisoning mass of trout was 85 kg., calculated from a capture-recapture census. Thus if trout replaced its competitors quantitatively, the standing crop of trout would be increased to 150%. (b) The volume-time of water (i.e. percentage of the lake volume multiplied by the fraction of a year) which would be made available to trout by removing competitors from the part of the lake where summer temperature conditions would limit trout to between 50 and 100% of their full activity is calculated. If trout occupied this volume-time at the same density as they did the more favourable water, the standing crop of trout would be increased to 240%. (c) The total yield of the lake to anglers showed a steady increase following poisoning, to about 230% of the control value, or from less than one pound per acre to nearly two pounds per acre. These three estimates agree very well, considering the errors inherent in the method.

ISSN:0706-652X    

DOI:10.1139/f55-032

出版商:NRC Research Press    

年代:1955

数据来源: NRC