摘要:

Examinations were made of nematodes from the stomachs of 150 common porpoises (Phocoena phocoena) collected from 1952 to 1956 from the lower Bay of Fundy, one common porpoise from St. Ann's Bay, Nova Scotia, and one white whale, (Delphinapterus leucas) from Mace's Bay, New Brunswick.One adultPorrocaecumwas found. LarvalPorrocaecumin numbers ranging from 1 to 21 were found in about 25% of 50 porpoise stomachs collected in 1955 and 1956. Eighty larvalPorrocaecumwere present in the stomach of the white whale. No trace of reproductive organs was observed in any of the larvalPorrocaecum.It is concluded that the common porpoise in the lower Bay of Fundy is not an important host of adultP.decipiens.

ISSN:0706-652X    

DOI:10.1139/f58-001

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The abundance and distribution of the northern sea lion,Eumetopias jubata, in British Columbia are described chiefly on the basis of a survey conducted during the summer of 1956. Results of surveys and censuses made in the years 1913, 1916, 1938 and 1955 are included for comparison. Most major rookeries and hauling-out sites were visited in 1956. Some which were missed were surveyed by aircraft in 1957.The numbers of sea lions in British Columbia are estimated to be 11,000–12,000 in 1956–57. They have apparently changed little since 1913 and 1916 when the population is estimated less reliably to have been 12,000–13,000. Some changes have occurred in their distribution, mainly as a result of organized destruction of concentrations centred near to fishing areas. Numbers in the Sea Otter Group have been reduced to about one-quarter of their former abundance. Numbers on the Cape St. James rookery, where the population has seldom been molested, have doubled.Present rookeries include: Triangle, Sartine, and Beresford Islands, in the Scott Island group; Kerouard Islands off Cape St. James; and North Danger Rocks. The Virgin and Pearl Rocks in the Sea Otter Group are no longer rookeries. Sartine Island and North Danger Rocks are recorded for the first time as rookeries. The Scott Islands and Kerouard Islands rookeries accommodate approximately 70% of the entire population, and 90% of the pups during the summer breeding season.Destruction of approximately 1,000 sea lions annually, when many of these are pups, is shown to be ineffective in substantially reducing the total population. Where efforts are concentrated in one area such as the Sea Otter Group, however, a local population can be greatly reduced and pupping curtailed or stopped.Pups are born from late May until late June. Soon after giving birth, the cows are serviced by the harem bulls. The harem structure, which averages about 10 cows per harem bull on the rookeries, begins to disintegrate near the end of July when pups take to the water and dominant bulls are replaced by reserve bulls. Some cows, probably not more than 25% at any one time, may forgo the normal annual pregnancy and continue to nurse a pup for more than a year.It is calculated that more than 70% of the sexually mature females in this population are pregnant in any one year. Natural mortality among the pups appears to be slight, but severe storms in some years may cause heavy pup mortality and constitute an important check on population growth.

ISSN:0706-652X    

DOI:10.1139/f58-002

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The Schumacher and Schnabel estimates of population size are compared and reasons are given for preferring the Schumacher formula. This formula is extended to permit mortality and recruitment in the population. Confidence limits are provided according to standard regression theory.

ISSN:0706-652X    

DOI:10.1139/f58-003

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The literature on the survival of hatchery-reared trout after release in streams is reviewed and the conclusion is reached that survival is poor in lakes and streams where a resident trout population already exists. In streams the deaths of planted trout occur very soon after their release and have been referred to as "delayed mortality". However, a comparison of survivals after planting in occupied and non-occupied streams shows that many of the deaths are not attributable to hatchery-background or transportation methods, but largely to some aspect of competition with resident trout. Some investigations which have sought to measure the relative survivability of wild and hatchery trout have not usedresidentwild trout and thus a crucial aspect of the competition has been omitted. Investigations at the Alberta Biological Station test stream, Gorge Creek, are described; in these a significant difference in blood lactic acid levels was found between hatchery trout with and without competition from resident trout. A tentative role is assigned competition as follows: introduced trout must compete for niches and for food. In the early stages of this competition they are continuously exercising; they exhaust stores of some metabolite and die either of acidosis or starvation.

ISSN:0706-652X    

DOI:10.1139/f58-004

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

Lampetra ayresii(Günther), a species of parasitic river lamprey endemic to western North America, is redescribed on the basis of material from off the Skeena River, British Columbia, to San Francisco Bay, California. A neotype is designated. Transformed specimens differ from those of the EuropeanLampetra fluviatilis(Linnaeus) in having a larger eye, a longer prebranchial and a shorter branchial region, and possibly a lower second dorsal fin, an acute rather than an obtuse caudal fin, a higher average number of trunk myomeres, and an area of dark pigment on the caudal fin. Ammocoetes differ from those ofLampetra fluviatilisprincipally in having a higher number of myomeres, a dark caudal spot (which distinguishes them also from ammocoetes ofLampetra planeri(Bloch), the nonparasitic brook lamprey), and an absence of dark pigment on most parts of the head and on the precursor of the tongue. Specimens from Oregon are recorded for the first time. Specimens from Mill Creek, Tehama County, California, show that this species ascends the Sacramento River farther than previous records indicated. An annotated synonymy is included.Lampetra ayresiiis indicated as distinct fromAmmocoetes cibariusGirard, which is regarded as identical withEntosphenus tridentatus(Richardson).Lampetra ayresiiandLampetra fluviatilisare illustrated by a number of original drawings and photographs.

ISSN:0706-652X    

DOI:10.1139/f58-005

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The surface circulation on the Scotian Shelf has been investigated by means of 827 drift bottles released by the Naval Research Establishment in August, 1954. The study suggests a cyclonic circulation centred in the vicinity of Sable Island Bank but with the eastern part incompletely determined by the results. Calculated speed of drift varies from 0.11 to 0.15 knot.

ISSN:0706-652X    

DOI:10.1139/f58-006

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The presence of shipworms (Bankia setacea) in Steveston Cannery Basin in the Fraser River estuary is attributed to sea water intrusion. River discharge, tides, geometry of the river channel and basin, and density of the intruding sea water are factors affecting intrusion, which in turn influence larval settlement. Settlement may occur at depths where salinity is less than 15‰ but the larvae fail to survive. However, they will continue to develop where salinity exceeds 20‰. Dredging the channel to a continuous grade would eliminate permanent salt-water "pools" along the bottom and prevent infestation.

ISSN:0706-652X    

DOI:10.1139/f58-007

出版商:NRC Research Press    

年代:1958

数据来源: NRC