摘要:

Auditory masking was determined for cod by using five half-octave bands as masking stimuli and as signals. For each of 15 cod, masking noise was kept constant at 10 db re 1 microbar in one band while thresholds were determined for signals in all five bands. Results indicate masking to be most pronounced when noise and signal coincide in frequency, and to drop off as frequency separation between noise and signal increases. Masking is calculated in terms of threshold in relation to masking noise level, and varies from about 11 db when signal and noise are in the same band to about −19 db when they are in bands furthest removed from each other. Estimates of critical bands are made from the results.

ISSN:0706-652X    

DOI:10.1139/f69-102

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Distribution of drills (Urosalpinx cinereaSay) was worked out from critical examination of museum holdings, from assessment of published and several unpublished occurrence records, and from field collection in new areas. Drills occur in warm inlets on the Nova Scotia coast of the Bay of Fundy, possibly in one inlet of the outer Atlantic coast of Nova Scotia, and in several inlets of the southwestern Gulf of St. Lawrence. Only in the last were oysters found with the drills and there is only one record of serious damage to young oysters. Distribution patterns suggest that drills reached the Gulf of St. Lawrence by spreading eastward from Cape Cod, through the Bay of Fundy, then through a channel that is believed to have connected the Bay and the Gulf. There is no evidence of long-term restriction of distributional range since that pioneering period, but local distribution seems to have contracted so that now drills occupy only the warmest parts of their range. In the last 30 years, drill abundance in some important oyster-producing sections of the Gulf of St. Lawrence has decreased, perhaps because of low sea temperatures. Old colonies persist but do little damage in oyster areas. No new colonies seem to have sprung up. In our area the species seems to be bordering on extinction. Drills are not a threat to the Canadian east-coast oyster industry.

ISSN:0706-652X    

DOI:10.1139/f69-103

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Natural phytoplankton populations were enriched with various nutrients both singly and as mixtures. After 4 or 5 days of incubation in natural light, the effects of enrichment were assessed by measuring the rate of14C uptake or changes in chlorophyll. Off Baja California, in June 1964, September 1965, and November 1966, increases in chlorophyll or14C uptake occurred in treatments containing added nitrate or trace metals. In February 1967, three enrichment experiments done in nutrient-poor water well offshore and both north and south of the Equator showed that nitrogen was the most likely limiting nutrient. In two experiments in equatorial upwelling water, no nutrient appeared to limit phytoplankton growth since chlorophyll increases were nearly as great in controls containing no enrichment as in treatments containing a complete mixture.

ISSN:0706-652X    

DOI:10.1139/f69-104

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Effects of gonadectomy on the cytological structure of the pituitary gland of sockeye salmon were investigated. Castration of fully grown, but sexually immature, fish appeared to prevent differentiation of any periodic acid–Schiff (PAS) positive cells. On the other hand, castration of mature sockeye induced degranulation of this cell type. These cells later disintegrated. Although the acidophil cells of the proximal pars distalis in the immature castrates showed an apparent increase in number, those in the gonadectomized ripe fish exhibited marked hyperplasia and hypertrophy. In view of the "rejuvenation," including the considerable increase in body weight that occurs after castration of sexually ripe sockeye, it is thought that the changes in the acidophils noted in this experiment may reflect an increased production of growth hormone. Where the gonadectomy was incomplete it was noted that very small remnants of gonad were able to induce, or maintain, all the external secondary characteristics of full sexual maturity. The pituitary of these fish exhibited cytological features intermediate between those of the controls and the complete castrates.

ISSN:0706-652X    

DOI:10.1139/f69-105

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Weekly sampling of a small woodland stream in Quebec between March 1966 and March 1967 revealed at least 120 species of insects in sand, gravel, stones, leaves, and leaf detritus habitats. Fallen leaves were the primary food source. Characteristic communities of insects were found in each habitat. Widely distributed species were usually more abundant in one of the five habitats than in the others. Some species changed their habitats with age. Congeneric species either occupied different parts of the stream or developed at different times of the year. Linear distributions of insects were determined by the substrate type, by the extent of summer drought and the ability to avoid desiccation, and in some species by upstream flying of adult females. The species composition of each community may be characteristic of small, slow-flowing streams in deciduous forests in eastern Canada.

ISSN:0706-652X    

DOI:10.1139/f69-106

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The belly skin of 4-month-old coho salmon fry was extracted with 0.5 MNH4OH, and the extract was analyzed by paper chromatography for UV-absorbing and UV-fluorescing substances. Six fluorescing and three absorbing substances were isolated and characterized by Rfvalues, UV-absorption spectra, and chemical reactions, and were identified with known compounds where possible. The three UV-absorbing substances were identified as guanine, hypoxanthine, and inosine monophosphate. Three of the UV-fluorescing substances were identified as ichthyopterin, pterin 6-carboxylic acid, and 7,8-dihydroxanthopterin. A fourth fluorescing substance appeared to be an artefact produced by the action of NH4OH on ichthyopterin. The remaining two fluorescing substances appeared to be unknown glycosides, presumably isomers, both containing glucose, xylose, and mannose.

ISSN:0706-652X    

DOI:10.1139/f69-107

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Ages of adult sockeye and chum salmon were estimated from examination of the second anterior pectoral fin ray, and were compared with estimates from their scales or otoliths. For sockeye, only the ocean age could be estimated. Freshwater annual rings could not be distinguished on their fin rays even though they were present on their scales or otoliths. In general, the three methods provided the same estimates of ocean age. Agreement of estimates of ocean age by one to five readers ranged from 78.9 to 98.8%. For chum salmon, the scale and fin ray methods generally provided the same estimates of total age. Agreement of estimates of total age by one or two readers ranged from 73.8 to 99.3%.

ISSN:0706-652X    

DOI:10.1139/f69-108

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Records from research surveys and commercial landings for American plaice from the Magdalen Shallows, or the southwestern Gulf of St. Lawrence, showed decreases in percentage of old, large fish and in catch per unit of effort from 1955 to 1962. The changes in age composition were clearly relatable to the fishery, which was mainly by otter trawl. Ricker models indicated that wastage of deck-exposed subcommercial plaice is currently a greater mortality factor than predation by cod. Increased landings in particular years were associated with successful year-classes. Other factors affecting landings were annual differences in fleet dispersal, which were related to movements of cod, a cohabiting species. No clear decrease or increase in absolute recruitment of plaice was demonstratable because quantitative comparisons of research surveys by different vessels using different gears and with different skippers, would be misleading.Mortality estimates of adult plaice by three methods showed agreement, indicating that instantaneous rate of natural mortality was between 0.09 and 0.13. The instantaneous rate of fishing for 1957–62 was 0.46. Increasing mesh-size would reduce cod catches and have little effect in conserving plaice, but marketing small fish would increase plaice landings. Voluntary release of small plaice promptly on capture would help maintain the stock, as would reduction in numbers of large cod, the main predator of small plaice. Increased numbers of small cod since 1959, as reported by other workers, could result in greater food competition with small plaice, effectively reinforcing the ecological dominance of cod over plaice.

ISSN:0706-652X    

DOI:10.1139/f69-109

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Acantholiparis caecusis described for the first time and reported to occur off the northern Oregon coast. The range of its congener,A.opercularis, is extended south off Newport, Oregon.

ISSN:0706-652X    

DOI:10.1139/f69-110

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Cutthroat trout (Salmo clarki) showed in-season homing after displacement from their spawning tributaries to Yellowstone Lake during June–August 1966 and 1967. Of 300 nonanesthetized trout tagged and displaced from Clear and Cub creeks to three release points (0.5–22.0 km) in the lake and to the mouth of Clear Creek, 38.3% homed, 10.0% strayed, 2.7% were caught by anglers, and the remainder were unaccounted for. Anosmic (olfactory chambers plugged) and blind-anosmic fish homed in significantly lower percentages than nonanesthetized and control groups. Fish released just outside the mouth of the homestream had the shortest average homing time, but the average homing time for fish displaced 22.0 km from the homestream was shorter than for those displaced 5.0 km away. Homing percentages for trout tagged after being tracked individually in the open lake were similar to those for trout in the group tagging experiments, but the former had longer average homing times than the latter.The directions of orientation of fish tracked in open water were generally toward the homestream, the directions usually coinciding with those of the sun azimuth. However, fish taken from the east side of the lake went west-northwest when tracked late in the afternoon and fish taken from the west side of the lake went east-southeast when tracked in the morning, these directions being away from those of the homestreams. Orientation was affected by current. Mean directions for males and females were generally not significantly different. Average swimming speeds and vector lengths for males and females were about the same. Immature cutthroat trout were trained to use a light source as a reference point for orientation.

ISSN:0706-652X    

DOI:10.1139/f69-111

出版商:NRC Research Press    

年代:1969

数据来源: NRC