摘要:

The one-dimensional channel equations are integrated numerically to determine the periods and structures of the lowest three longitudinal modes of free oscillations of the Bay of Fundy. It is found that the period of the lowest mode is 9.047 hr rather than somewhere in the vicinity of the M2tidal period of 12.42 hr, as has been supposed hitherto. This estimate of the free period is obtained without considering the effects of rotation and friction, but an approximate treatment of these effects shows that their effect on the period is very small — rotation tends todecreasethe period by less than 3% and friction tends toincreaseit by 1% at the most. The periods of the second and third modes are found to be 5.383 and 3.475 hr. The modal structures and their modification produced by rotational effects are presented.

ISSN:0706-652X    

DOI:10.1139/f68-097

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

When frightened, sockeye and kokanee salmon dive into deeper waters. This is termed the "sounding response."The sounding response in these fish is accompanied by the expulsion of gas from the swimbladder via the pneumatic duct. This gas loss is active and results from the contraction of the circular muscle fibers in the wall of the swimbladder.Gas loss on sounding is reduced or obviated after exposure to adrenergic blocking agents and enhanced in fish treated with sympathomimetics. Circular muscle fibers in intact and isolated strips of swimbladder contracted in response to sympathomimetics, but this response was prevented after adrenergic blockade. These results suggest the concentration of the swimbladder and associated gas expulsion is under adrenergic control.In untreated fish, an average pressure of 28.1 mm Hg was required to force gas out of the swimbladder through the pneumatic duct. In antropine-treated fish this duct-release pressure fell to an average of 0.2 mm Hg. This suggests constriction of the pneumatic duct is under cholinergic control.Histologically, the pneumatic duct was continuous with the oesophagus and extended as a convoluted duct to the anterior end of the swimbladder. Smooth muscle fibers surrounded the duct along its length and some striated fibers were present at the point where the duct joined the oesophagus. Occlusion of the pneumatic duct may be through the contraction of either of these types of fibers.The term "Gasspuckreflex" as originally used by Franz described the loss of gas from the swimbladder of physostomes in response to decompression. The authors suggest this term be reserved for this passive loss of gas, and not applied to fright-induced gas loss, resulting from active contraction of the bladder wall.

ISSN:0706-652X    

DOI:10.1139/f68-098

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The feeding periodicities of five common cohabiting fish species in Lake Opinicon, Ontario, were defined for the early summer period of accelerated feeding by determining the mean weights of stomach contents per gram of body weight at intervals of 2–3 hr throughout the 24-hr cycle. Two, and in sunfish three, feeding peaks per 24-hr period were indicated.Perca flavescenswas diurnal;Lepomis macrochirus,L.gibbosus, andFundulus diaphanuswere largely diurnal (with a nocturnal component); andAmbloplites rupestriswas equally nocturnal and diurnal. In the two sunfish there were clearcut differences in the organisms eaten by day and night. The technique developed here is a useful method for determining the mean minimum daily ration for a population of fish in the field. The results are comparable with those obtained by other workers in aquarium feeding experiments.

ISSN:0706-652X    

DOI:10.1139/f68-099

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

In 1961 a creel census was begun on Pigeon Lake in south-central Ontario to assess the contribution to the fishery of maskinonge transplanted from nearby Nogies Creek Fish Sanctuary. A correction being made for a tag loss of 58%, it was estimated that 30% of the transplanted fish had appeared in the anglers' catch. The mean catch of maskinonge from Pigeon Lake for the seasons of 1961–65 was estimated to be 1318 fish per year. About 4% of the annual catch from Pigeon Lake was attributed directly to fish transplanted from Nogies Creek.From a catch curve the rate of total mortality of Pigeon Lake maskinonge age V or older was estimated to be 43% per year. Partitioning this into mortality due to fishing and mortality from other causes yielded estimates of 24.5% for each of these components.

ISSN:0706-652X    

DOI:10.1139/f68-100

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

A conditioning procedure was used to determine auditory thresholds of cod at frequencies 35.3, 70.7, 141, 283, and 400 Hz at four levels of background noise. The noise was produced in octave bands centered at the test frequencies, and ranged in level from −14 db to +4 db (re 1 microbar). Up to 283 Hz thresholds varied directly with background noise, and signal-to-noise levels at thresholds remained approximately the same at all background noise levels for each frequency. Thresholds at 400 Hz were much higher and showed no relationship to noise. Mean signal-to-noise levels are calculated.

ISSN:0706-652X    

DOI:10.1139/f68-101

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Hemioniscus balaniSpence Bate, a parasitic isopod with a world-wide distribution in temperate waters, was not found among intertidal populations ofBalanus balanoidesexamined between 1959 and 1965 on the east coast of North America from Newfoundland to Cape Hatteras, except for a small area near Halifax, Nova Scotia.The North American variety ofBalanus balanoides, when transplanted from Woods Hole to North Wales, was found to be much more susceptible than the European variety to parasitisation byH.balani.

ISSN:0706-652X    

DOI:10.1139/f68-102

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Buoyed and anchored nets were evaluated as a method of sampling larval Atlantic herring,Clupea harengus harengusLinnaeus, in tidewaters. The method permitted exploratory sampling in areas difficult to reach with towed gear, and provided a large number of samples from predetermined depths without towing from vessels. The nightly variation of catch rates was small under similar tidal conditions, and seasonal changes in larval catches were similar to those determined by towing nets from a boat. The buoyed net also provided information relating the distribution of larvae to tidal currents that could not be readily obtained with towed gear.

ISSN:0706-652X    

DOI:10.1139/f68-103

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

An effort has been made to introduce a greater degree of standardization and reliability into descriptions of the benthic environment made by biologically oriented observers. Comparisons of field descriptions and mechanical analyses showed an encouraging ability to distinguish among four major sediment types in Lake Michigan. The bottom of the lake has been described in terms of these types, which usually occur in the following order with respect to depth: sand, silty sand–sandy silt, silt–clayey silt in a thin layer overlying stiff plastic clay, and silt–clayey silt only. Each sediment type tends to exhibit its own range of organic carbon values, with the amount of carbon increasing with depth. Hard or rocky bottom occurs in more restricted areas and is considered a fifth recognizable bottom category. Certain features of the distribution of the sediments may be related to gross water movements and to the locations of the mouths of large tributary rivers. Limited comparative studies in Lakes Huron and Superior showed similar distributions of sediment types and organic carbon content. It is suggested that the observed uniformity of maximum organic carbon values in the sediments of all three lakes may be related to processes of oxidation.

ISSN:0706-652X    

DOI:10.1139/f68-104

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Field studies on low temperature feeding in freshwater fishes were carried out as follows: (1) Fish Lake, near Picton, Ontario, January–March 1966 and 1967, 1200 fish netted from under the ice at a temperature of 4 C; (2) Little Cataraqui Creek near Collins Bay, April 1966, groups of fish (total, 544 individuals) netted at intervals of several days as the water temperature rose from 6.8 to 11 C; (3) Upper Jones Creek, near Mallorytown, two extensive collections (total, 1005 individuals) made between April 27 and 30, 1966 (at a water temperature of 8 C), and May 15 and 17 (15 C). The following findings resulted.Some members of all six species in Fish Lake contained food but the percentage varied from 50% inUmbra limidown to 10% inFundulus diaphanus. Hence feeding was erratic. Within species the smaller individuals invariably contained more food (0.005–0.02 g of alimentary contents per gram body weight) than larger fish (0.002–0.005). The same was true of smaller, as compared with larger, bodied species, with the exception ofF.diaphanus.After the thaw in Little Cataraqui Creek active feeding commenced at different temperatures in the various species: it was already under way at 6.5 C (when the study started) inIctalurus nebulosusandPomoxis nigromaculatus, but did not start inLepomis gibbosusandAmbloplites rupestrisuntil the water temperature reached 8.5 C. Prior to this the stomachs of species were shrunken, mucous-filled, and drawn far forward in the body cavity. FewPerca flavescens, active winter feeders, fed in April, immediately prior to spawning.In most of the Jones Creek fishes there was a marked increase in weight of alimentary contents (gram per gram body weight) between 8 and 15 C. Exceptions were the largerSemotilus atromaculatus, which were than spawning, andU.limiandEucalia inconstans, which were sampled before their peak daily feeding times. To the differences in weights of alimentary contents at 8 and 15 C must be added accelerated digestion rates at 15 C.In all the waterways studied the fish consumed a much smaller range of prey items at low temperatures than at higher ones. This applied in midwinter, compared with summer, in Fish Lake, and in April and October, compared with summer, in Jones Creek. A few foods, e.g. chironomid larvae and Cladocera, were especially prominent in the diet at low temperatures, and species food specializations were suppressed. There was probably not, however, any increase in interspecific competition at temperatures approaching zero, because of the relatively low metabolic requirements of the fish.

ISSN:0706-652X    

DOI:10.1139/f68-105

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The method of population estimation based on change in composition of a dichotomous population was applied to Bristol Bay sockeye salmon to estimate the mortality rate of 3-ocean (3 years at sea) fish during their final year in the ocean. A difference in freshwater age composition between 1-ocean immatures in 1964 and 2-ocean immatures in 1965 was evident in samples taken in the high seas. This difference was apparently due to a greater tendency of 2-freshwater fish than 1-freshwater fish to mature after 2 years at sea. The known quantities of these two freshwater categories in the mature 2-ocean run of 1965 enabled an estimate of the population of 2-ocean immatures at sea in 1965. From this estimate and the quantity of 3-ocean matures in the 1966 run, the annual mortality rate was estimated to be.42.

ISSN:0706-652X    

DOI:10.1139/f68-106

出版商:NRC Research Press    

年代:1968

数据来源: NRC