摘要:

Invertebrates, principally benthic forms, occurred most frequently in plaice stomachs from the Grand Bank. Fish, almost entirely capelin and sand lance, however, contributed the greatest proportion of total weight: 85% on the southeast part of the bank (ICNAF Division 3N) and 55% in the northeast section (ICNAF Division 3L).A seasonal feeding cycle was difficult to document because of the lack of winter samples, however, a greater proportion of empty stomachs occurred in February and March. The greater average weight of contents in spring samples (April–June) in Division 3L and in fall samples (October–November) for Division 3N was probably related to the availability of capelin and lance. The greater annual consumption of capelin and lance in Division 3N apparently accounted for the estimated higher caloric values of the average contents in this division than in Division 3L.

ISSN:0706-652X    

DOI:10.1139/f73-206

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

"Mechanism 1" has two aspects: catches taken at a given rate of exploitation are greater when rate of exploitation has been increasing than when it has been steady or decreasing; also, the yield taken from the progeny of a spawning of a given size is greater when rate of exploitation has been increasing than when it has been steady or decreasing. "Mechanism 2" is the fact that mixtures of stocks of unequal productivity, when harvested together, produce smaller recruitments than single stocks of the same original size and having the same optimum rate of exploitation. In addition, any fishery for a valuable species is likely to develop beyond the optimum rate of exploitation because there is no easily detectable symptom that the optimum is being passed. When this has happened, maximum sustainable yield (MSY) will not be achieved immediately if the optimum rate is imposed subsequent to a period of overexploitation; rather there will be a gradual approach to MSY that extends over several generations after the optimum rate is established. Both of the two mechanisms above, plus the likelihood of unrecognized overfishing, make for a catch maximum while fishing is still on the increase. For salmon this maximum is likely to be 30–60% greater than the sustainable yield. In addition, unavoidable difficulties of management make for even greater differences between the historical maximum and the mean equilibrium yield that can be achieved in practice. Good annual prediction of recruitment can improve this picture because rate of exploitation can then be adjusted to the quantity of fish available; however this procedure too is much less effective when mixtures of stocks are fished in common, because in general the recruitments to different stocks do not vary in exactly the same way. The phenomena described may also contribute to an historical early maximum of catch in fisheries for species such as cod, being independent of and additional to the maximum caused by "removal of accumulated stock."

ISSN:0706-652X    

DOI:10.1139/f73-207

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Concentrations of mercury (Hg) increased significantly with size (P < 0.001) in white muscle of bluefish (Pomatomus saltatrix) and a bathyl-demersal fishAntimora rostratabut concentrations of manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn) either remained constant or decreased. These results indicate that fish residing in two different ecosystems in the Atlantic Ocean may be in a steady state with their environment with respect to Mn, Fe, Cu, and Zn but not Hg. The observed variations in accumulation patterns of trace metals in muscle of these two species as a function of size are discussed.

ISSN:0706-652X    

DOI:10.1139/f73-208

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Twenty-four hour uptake rate of either203HgCl2or CH3203HgCl by rainbow trout (Salmo gairdneri) was not affected by esophageal ligation. Uptake of these two mercurials in non-feeding trout appears to be by way of the gills. Methyl mercury enters the fish at a faster rate than the inorganic form and anomalous tissue distribution of these two mercurials suggests that inorganic mercury does not require methylation prior to entry into the fish.In vitro experiments using radioactive mercurials demonstrated high affinity of methyl mercury for red cells (up to 90% was bound to red cells in 40 min). Only 9% of inorganic mercury was taken up by red cells, but, this percentage was increased up to 65% if the cells were washed and suspended in Ringer solution prior to incubation with mercury.

ISSN:0706-652X    

DOI:10.1139/f73-209

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The plasma half-life of sulfobromophthalein (BSP) for rainbow trout (Salmo gairdneri) was 13 min for doses of 5 and 10 mg/kg and 29 min for a dose of 15 mg/kg. The biliary BSP transport maximum (Tm) averaged 9.6 μg/min per kg for five fish while the blood clearance averaged 1.7 ml/min per kg for two fish. Normal bile flows of 0.87 μliter/min per kg in trout were increased upon anesthetization but were unaffected in fish allowed to recover from spinal transection. Spinal transection did not affect the plasma half-life of BSP.The data presented support the conclusion that the transport of BSP from liver cells to bile is the rate-limiting step in the excretion of this dye. When the BSP Tm of trout was compared to literature values for mammals and dogfish (Squalus acanthias), large differences were found which were probably caused by effects of different temperatures and blood flows. When the Tm values of the various species were based on blood clearance of BSP (reflecting liver blood flow) the differences were greatly reduced, suggesting similar abilities of the liver of the various species to excrete this dye.

ISSN:0706-652X    

DOI:10.1139/f73-210

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Eleven mature pink salmon (Oncorhynchus gorbuscha) were tracked in September 1967 for periods of 3–50 hr over distances from 2 to 127 km to determine migration patterns.The fish were classified as "active" or "passive." Active fish moved faster and their paths were straighter. Active tracks ended distant from and to the north (toward the Fraser River) of the release point; passive tracks ended near or south of the release point. Active fish did not follow shorelines, but travelled primarily along the axes of tidal currents. They moved both with the northward flood and against the southward ebb currents, during day and at night. Average ground speed of active fish was 62 cm/sec (2.2 km/hr).

ISSN:0706-652X    

DOI:10.1139/f73-211

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Sediment core oxygen uptake is correlated positively with primary production and inversely with mixed-layer depth in various aquatic ecosystems for which the input of organic matter is predominantly autochthonous. In these areas organic carbon sedimentation is proportional to the ratio of carbon input: mixed-layer depth, which reflects increased mineralization with increased depth of mixing. The ratio of primary production: mixed-layer depth is compared with the carbon equivalent of oxygen uptake by sediments to derive an expression which is used to calculate the amount of photosynthetically fixed carbon respired at the sediment surface.

ISSN:0706-652X    

DOI:10.1139/f73-212

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Gastric digestion of walleye,Stizostedion vitreum vitreum, and sauger,Stizostedion canadense, was measured by pumping stomachs at various intervals after experimental meals had been force-fed or voluntarily consumed. No significant differences in digestion rates were found between species or among walleye taken from three lakes. Repeated use of fish in digestion experiments failed to influence results. Gastric digestion rate increased with fish size, but was depressed by increased meal size, food particle size, and by force-feeding experimental meals.Food consumption rate and feeding chronology of the strong 1966 year-class of Lake of the Woods walleye were determined by applying results of laboratory digestion studies to stomach samples. An estimating technique that takes into account the effects of factors shown to influence digestion in the laboratory was developed and used to make calculations for the field population. Consumption averaged 1% of body weight during June, 2% during July, and 3% during August and September. Average temperatures were similar during June and September. Greater consumption during September resulted from higher food availability. Feeding was greatest during night and early morning hours in all months except June when it was continuous. Conversion efficiency of the 1966 year-class was described from estimates of growth and consumption rates for June through September and approximated 20% during each month.

ISSN:0706-652X    

DOI:10.1139/f73-213

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Setal development and proecdysial cuticular changes can be observed in the pleopods of the American lobster (Homarus americanus) from earliest D0through stage D3, and with pleopod staging criteria it is possible to follow proecdysis from beginning to end. A technique is described for recognition of all stages and substages of proecdysis, for evaluating effects of various treatments on proecdysis, and for predicting time of ecdysis where holding temperature is known. Histological comparisons between the pleopods and the general integument suggest a universal criterion for stage D2, and a need for adjustment in some accepted molt stage criteria. Development plateaus occur in stage D0instead of C4in this species, and this suggests that the concept of stage C anecdysis may be incorrect.

ISSN:0706-652X    

DOI:10.1139/f73-214

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

In an arctic intertidal environment on Hudson Bay,Macoma balthicahave a higher growth rate at a tidal level of 1.1 m above mean low water than at the mean low water level, in terms of both length and dry weight. Temperature, rather than food, appears to be the primary proximate factor involved, and summer air temperatures play a major role. The estimated growth rates are comparable to reported growth rates for intertidalMacomapopulations in Scotland and the Netherlands. A partial life table calculated from the death assemblage indicates thatMacomaat 1.1 m above mean low water have an annual mortality which increases from about 20% at age 2 to about 50% at age 7 years.

ISSN:0706-652X    

DOI:10.1139/f73-215

出版商:NRC Research Press    

年代:1973

数据来源: NRC