摘要:

Concentrations of oil accommodated in sea water under laboratory conditions are directly related to the amount added and the degree of turbulence, but inversely related to temperature. The major fraction (87–98%) of this oil is in particulate form ranging in size from about 1 to 30 μ, presumably small droplets. The exact ratio of the particulate to subparticulate fractions is directly related to the apparent viscosity of each individual oil. Of the total amount of oil initially added, 9–15% appeared in sea water at the end of the 7-days experiments. Except in the proximity of recent oil slicks, the oil concentrations observed in these experiments are one to two orders of magnitude greater than the concentrations generally observed in the marine environment off eastern Canada.

ISSN:0706-652X    

DOI:10.1139/f73-259

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Water samples from the Fraser River and Georgia Strait, British Columbia were treated with different chlorinated hydrocarbons and incubated for up to 12 weeks at 13 C. 1) In the presence of bottom sediments from the same locations as the waters, no residues were found to escape into the atmosphere. 2) With the exception of lindane in ocean water, all detectable residues had moved into the sediments after 6 weeks. 3) Most of the lindane was metabolized. 4). Sterilization of the waters and sediments prevented the metabolism of lindane but had little effect on DDT and DDD. 5) Agitation of water samples containing γ-chlordane, incubated without sediment, had no effect on its disappearance, but the presence of 0.01% of a nonionic surfactant retarded this almost completely.

ISSN:0706-652X    

DOI:10.1139/f73-260

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Infectious hematopoietic necrosis virus (IHNV) was isolated from diseased fingerling rainbow trout (Salmo gairdneri) from a hatchery in West Virginia. Clinical signs, histopathologic findings, and origin of eggs provided a basis for diagnosis, and virus was isolated and presumptively identified by plaque characteristics. Serum neutralization tests provided positive identification of the agent as IHNV, and electronmicroscopy showed its rhabdovirus morphology. Experimental infections resulted in signs of IHNV and death; test fish had characteristic histopathologic alterations and appropriate virus titers. This is the first completely documented occurrence of IHNV beyond the Pacific Northwest.

ISSN:0706-652X    

DOI:10.1139/f73-261

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The problem of optimal regulation of a fishery is discussed. Of special interest is the problem of regulating an overexploited fishery by reducing effort to allow the fish population to build up to a suitable level.We first argue that the problem requires an economic analysis based on the concept of maximization of present value. From this concept we then deduce a simple, general rule, the "Fisher Rule," which we subsequently use to determine optimal exploitation. Among the principal results are the following: (a) an optimal mesh-size is determined, which, because of the discounting of future revenues, is smaller than the size corresponding to maximum sustainable yield; (b) the optimal recovery policy for an overexploited fishery is deduced; it consists of a fishing closure permitting the fish population to reach an optimal age; (c) the optimal development of an unexploited fishery is deduced; an initial development stage characterized by large landings and profits is rapidly transformed into a situation of optimal sustained yield, in which both landings and profits may be significantly reduced; (d) the optimal policy is deduced for a fishery in which gear limitations are impractical; the result may be a strongly unstable fishing industry; (e) the effect of high discount rates, which might be employed by private fishing interests, is discussed; such rates may result in overfishing similar to the case of a common-property fishery.

ISSN:0706-652X    

DOI:10.1139/f73-262

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

A microculture system was applied to the culture of brown bullhead (Ictalurus nebulosus) cells and used for the titration of channel catfish (Ictalurus punctatus) virus and corresponding antibody. As few as 1.7 × 104cells/well could be used for routine titrations. Simultaneous inoculation of virus with cells at the time of planting resulted in clearer endpoints as opposed to inoculation of preformed monolayers. When channel catfish virus antibodies were measured using plaque reduction and microculture titration assays as indicator systems, no significant differences in antibody titers were noted.

ISSN:0706-652X    

DOI:10.1139/f73-263

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

American lobsters,Homarus americanus, were fed diets containing 0, 5, and 20% starch for periods up to 37 days. Digestive enzymes in the stomach juices of these and fasted lobsters were assayed. The base-line, or true fasting enzyme level was considered to be those values found after feeding for 2 days on a 5% starch diet. Compared to this basal level both specific activities and absolute amounts of proteinase, lipase and, to a lesser extent, amylase were found to rise on prolonged feeding. Further feeding (all diets) allowed products of a greater proportion of proteinase than amylase or lipase; alteration of the starch content of the diet had no consistent effect.

ISSN:0706-652X    

DOI:10.1139/f73-264

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The gymnoblastic colonial hydroidIchthyocodium sarcotretiswas found on the copepodSphyrion lumpion redfish from three areas of the northwest Atlantic: on copepods (three of ten) on deepwater redfish (Sebastes mentella) from about 200–500 m over great depths at the mouth of the Labrador Sea and, in bottom otter trawling, on copepods onS.mentellaor possiblyS.fasciatusfrom the Labrador Shelf (6 of 686) and the northeast Newfoundland Shelf (1 of 364). None were found on 492S.lumpifrom redfish taken on the continental shelf south and west of the northeast Newfoundland Shelf.The characteristics of the hydroid colonies and of their feeding polyps and reproductive hydranths and medusae are compared with published information on this hydroid found on the same hosts in the Irminger Sea and on the copepod,Sarcotretes scopeli, on the lantern fish,Benthosema glaciale, in the North Atlantic. The incidence of the hydroid onS.lumpion redfish may possibly help in distinguishingSebastesspecies in the northwest Atlantic.

ISSN:0706-652X    

DOI:10.1139/f73-265

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Stepwise multiple regression procedures have been used to develop equations expressing the fatty acid content of fingerling coho salmon,Oncorhynchus kisutch, as a function of fish length and the time the salmon had been maintained in the laboratory on a specific diet. High correlation coefficients from the multiple regressions were obtained for most of the fatty acids studied and from the derived equations the fatty acid content of individual fish could be predicted with a fair degree of precision.Under the specified experimental conditions changes in wet weight, the total mass of fatty acids per salmon, and the mass of most individual fatty acids per salmon were dependent on the time in the laboratory and on the product (interaction) of time in laboratory with length of the salmon. At 8-cm length body weight was increasing 30 mg daily and the fatty acid content 7.3 mg daily.A detailed analysis is presented for several fatty acids whose predicting equations are representative of the different relationships observed. A case is presented for the unique role of fatty acid 22:6 in fish.

ISSN:0706-652X    

DOI:10.1139/f73-266

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Whitefish catches have fluctuated since 1952, and except in 1964 each successive peak has decreased in magnitude. Recently the overall trend has been a diminishing fishery with increasing effort.There has been a drastic change in age composition with time. Age-groups 5, 6, and 7 accounted for 81% of the catch from 1944 to 1948, age-groups 4, 5, and 6 for 89% from 1949 to 1955, age-groups 4 and 5 for 86% from 1959 to 1968, and age-groups 3 and 4 for 88% in 1969. The fishery is now dependent upon two age-groups instead of three. Natural failure of one or more important year-classes would result in a serious decline in catch, and partial or complete collapse of this fishery.Annual survival rate decreased from 34%, 1944–48 to 12%, 1959–69. Instantaneous natural mortality rate was estimated to be 0.72, and may be overestimated. The 1938–39, 1945–47, 1949, and 1957 year-classes were strong, while the 1940–44, and 1956, 1958, and 1961 year-classes were weak. The 1959 and 1960 year-classes appeared to be somewhat above average. Examination of data on total dissolved solids and temperature indicated that ecological changes were not responsible for the decline of whitefish in Lake Winnipeg.We judge that the optimum rate of fishing has been exceeded, and that the fishery itself is largely responsible for the depleted condition of the whitefish stocks in Lake Winnipeg. Fishing effort must be reduced to the point where the fishery is again dependent upon three year-classes. This should result in higher catches, and provide less fluctuation in annual catches.

ISSN:0706-652X    

DOI:10.1139/f73-267

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Divergence in the growth pattern of Pigeon Lake and Buck Lake whiteflsh (Coregonus clupeaformis) began during the winter months in young-of-the-year fish. The growth rate of individuals in the Pigeon Lake whitefish population has declined over the past 12 years whereas individuals in the Buck Lake population have maintained a relatively stable growth pattern. These differences did not appear to be genetically controlled. Increased interspecific and intraspecific competition for the available food supply likely suppressed the growth rate of the Pigeon Lake whitefish population. Reduction of predator numbers in Pigeon Lake by the removal of habitat and increased angling pressure accelerated recruitment to both the white-fish population and other competitive feeding forage fish. A predator–prey relationship conducive to the maintenance of a faster growing lake whitefish population has been maintained in Buck Lake over the same period of time.

ISSN:0706-652X    

DOI:10.1139/f73-268

出版商:NRC Research Press    

年代:1973

数据来源: NRC