摘要:

In Lake Memphremagog a north–south gradient in algal production and biomass exists during the ice-free period, with highest production in the southern areas. In response, the mean annual benthic standing stock (dry weight) in the south basin was 2.8 times greater than in the north basin at comparable depth. Mean annual standing stock ofProcladius denticulatusandChironomus anthracinuswere significantly (5.8 and 3.1 times, respectively) higher in the south, while that ofChaoborus punctipennusdid not differ significantly between areas. Annual production ofP.denticulatuswas greater in the south (0.861 g/m2) than in the north (0.143 g/m2). Similarly forChironomus anthracinusannual production was greater in the south (3.393 g/m2) than in the north (1.264 g/m2). Production ofChaoborus punctipenniswas greater in the north (0.066 g/m2) than in the south (0.348 g/m2). P:B ratios were less variable.Key words: Lake Memphremagog, benthos, production, nutrient gradient, mortality

ISSN:0706-652X    

DOI:10.1139/f77-268

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Capelin (Mallotus villosus) larvae in the St. Lawrence estuary and northwestern Gulf of St. Lawrence were most abundant in 1974 and 1975 in the upper estuary in early June; this coincided with the spring peak in primary production. A spectacular decline (>99%) in larval abundance between June and September resulted principally from their downstream transport by currents. In October and November larval capelin were concentrated in a large counterclockwise gyre located in the northwestern Gulf between Anticosti Island and Pointe des Monts. This region is within the area of maximum primary production in the estuary and Gulf and may serve as an important feeding area for larval capelin. Length of capelin larvae at the end of the first growing season in the estuary and northwestern Gulf was greater than that of capelin from Newfoundland, Labrador, and Greenland. However, this difference may have resulted from sampling biases. Daily growth rates of capelin larvae from these areas were similar.Key words: capelin,Mallotus villosus, St. Lawrence, seasonal distributions, larval transport, growth, vertical distribution

ISSN:0706-652X    

DOI:10.1139/f77-270

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The distribution of juvenile and adult capelin (Mallotus villosus) in the estuary and western Gulf of St. Lawrence was similar in 1974 and 1975. Juvenile (age 1 and 2) capelin were largely restricted to the western Gulf, which appears to serve as a nursery area for larval and juvenile capelin, throughout the summer and fall. During the summer and early fall capelin occurred in small schools which were widely distributed over most of the western Gulf. Concentration of juvenile and adult capelin into dense schools and their movement into the lower estuary in November were interpreted as the initiation of a contranatant migration to the spawning areas in the estuary. Spawning occurred first in the upper estuary (April–May) and was progressively later in the lower estuary and western Gulf. Postspawning mortality was high and resulted in a rapid decline in the abundance of adult capelin in the estuary and western Gulf following spawning. A concentration of juvenile capelin in and near the mouth of the Saguenay River throughout the year was apparently supported during the late summer by zooplankton production in the river. These fish, in turn, contribute heavily to the food resource of a large population of beluga whales that summer in the area. Capelin from the study area reach a greater mean size at the end of the 1st yr than do those from Newfoundland, Labrador, and Greenland. Subsequent growth was similar to that of stocks from southern Newfoundland but was faster than in stocks from northern Newfoundland and Labrador. Capelin populations in the estuary and western Gulf matured earlier and had younger mean ages than those from other areas in the Canadian Atlantic.Key words: capelin,Mallotus villosus, Gulf of St. Lawrence, seasonal distribution, vertical distribution, growth, spawning

ISSN:0706-652X    

DOI:10.1139/f77-271

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Fluctuations in mortality rather than in growth rates produced most of the year-to-year differences in biomass accumulation of three different populations of the crayfishOrconectes virilis. Yearly biomass changes resulted from density-dependent control of mortality and fecundity during certain portions of the life cycle. Density-dependent changes in mortality rates controlled population size for adults in all lakes and for young-of-the-year in two of the three study lakes. Growth rates were much less responsive to fluctuating densities. Disparity between the number of ovarian and attached eggs increased as density of age I+ crayfish increased. This provided a strong density regulator on fecundity. Differences occurred in the number of recruits produced by a brood stock that survive to the end of the first growing season in the various lakes. Yet the number of females surviving to reproductive age 2 yr later was strongly regulated. Strong population regulation produced two female recruits of breeding age for every two–six parental breeding females. The high biomass and production levels of crayfish discovered in West Lost Lake in 1962–63 also occurred in the other area lakes. Higher but variable levels of recruitment resulted in larger standing crops and production in West Lost lake. This resulted from less effective density controls on the mortality rates of younger age-groups in that lake. Despite great variation in biomass of from 46 to 213 kg/ha and annual production from 60 to 142 kg/ha, the annual turnover ratio of the biomass was found to vary only between 0.94 and 1.53.Key words: crayfish,Orconectes virilis, population dynamics, annual production, Michigan lakes

ISSN:0706-652X    

DOI:10.1139/f77-272

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Populations of the crayfishOrconectes viriliswere exploited using the Paulik–Bayliff modification of the Ricker model in two small lakes. After harvesting with traps at maximum sustained yield (MSY) for 3 yr, fishing effort was increased fourfold in one lake, West Lost, for two successive seasons, while in North Twin Lake it was not changed. In West Lost yields were stable during MSY; yields increased with overexploitation, but growth and recruitment declined. Distortions occurred in the age composition of the catch. In North Twin this pattern was repeated except that in 1975 the catch dropped drastically even though fishing effort had not been increased. Because of declining recruitment, North Twin was actually overfished by about 20% in 1974 and greatly overfished in 1975. Decreased recruitment in both lakes can be attributed to two factors: (1) a decreased survival of hatchlings in both lakes due to a decline in nursery habitat; as a consequence the stock-recruitment relationship was altered; and (2) an increase in the density of age I (subadult) females due to the selective fishery for males; as a result density-dependent mechanisms lowered the survival of females from age I to II, producing fewer spawning adults. However, the high density of these age II females at age I decreased the egg production per adult female. The changes in the productivity of the lakes for crayfish during the period of exploitation were related to loss of microhabitat for hatchlings. This change in productivity offset the benefits of MSY management and resulted in a drastic drop in stocks when deliberate overfishing took place. West Lost gave good yields prior to its certain collapse. Yields in weight were an unreliable indicator of the impact of the fishery.Key words: crayfish,Orconectes virilis, potential yield, production, recruitment, stock assessment, experimental fishery

ISSN:0706-652X    

DOI:10.1139/f77-273

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Stomach content data on 14,796 spiny dogfish (Squalus acanthias) from British Columbia waters are presented. The major dietary components based on occurrence were 55% teleosts, 35% crustaceans, and 5% molluscs. The principal food items were herring (22%) and euphausiids (14%). Prey was largely pelagic (80%), with fishes predominating in winter and invertebrates in summer. Fishes became more important in the diet with increasing dogfish size. Dogfish consumed twice as much food in summer as in winter. Annual consumption varied from 5 times biomass for small dogfish to 2.5 times for larger animals. Preliminary analyses suggest that dogfish consume over 5 times the current annual commercial catch of herring, but insignificant quantities of salmon.Key words: dogfish,Squalus, feeding, food, biomass, predation, metabolism, seasonality, survivorship, digestion

ISSN:0706-652X    

DOI:10.1139/f77-274

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Atmospheric contamination by sulfur dioxide in the Sudbury region and the associated acidification has reduced population densities of fishes in the La Cloche Mountain lakes, 33–90 km away. Surviving rock bass (Ambloplites rupestris) responded to decreased abundance with increased growth rate. Variation in abundance among surviving populations could be monitored by means of individual growth rates and mean lake depth. Our findings suggest that growth rate of fishes, in conjunction with the morphoedaphic index, may serve as an indicator of environmental stress.Key words: environmental indicator, environmental stress, lake acidification, fish growth rate, morphoedaphic index, population density, rock bass

ISSN:0706-652X    

DOI:10.1139/f77-275

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Fathead minnows (Pimephales promelas) were exposed during a partial chronic toxicity test to two DDT concentrations in the water, one in the diet, and combinations of water and diet for 266 days through a reproductive period of their life cycle. Tissue residue analyses were performed at preset intervals throughout the exposure and also on embryos, larvae at hatch, and 30- and 60-day progeny. The contribution of DDT from each source was monitored with gas chromatography and liquid-scintillation techniques. The fish were fed a diet of clams that had accumulated14C-DDT when exposed at a DDT water concentration similar to that in the high fish exposure. Higher total DDT tissue residues were accumulated from the water than diet. Residues contributed by dietary DDT were additive to those from the water. Mean concentration factors were 1.2 for the diet and 100,000 for the water. Fish exposed to DDT in both water and diet had higher mortality rates than those exposed to only one or the other of these sources. DDT in the diet significantly reduced the probability of survival of the test fish (P = 0.025). Estimated maximum acceptable toxicant concentrations for DDT are 0.9 μg/ℓ for fish exposed to DDT in the water only and 0.4 μg/ℓ for fish exposed to DDT in both water and diet. Embryo residue levels and larval mortality rates were about twice as great for those from parent fish that had been exposed to DDT in both the water and diet as for those from parent fish exposed to only DDT in the water.Key words: toxicity, DDT, pesticides, food chain,14carbon, bioassay, minnows, clams, aquatic ani

ISSN:0706-652X    

DOI:10.1139/f77-276

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Gametogenesis in the giant scallop,Placopecten magellanicus(Gmelin), occurs in early summer and spawning takes place during August and September. The gonad differentiates between March and May, when the water temperature is low (0 to −1 °C) and food supply high. Gonad growth also begins at this time. Energy reserves from the previous year do not seem to play a significant part in subsequent growth and maturation of the gonad. There is no accumulation of metabolic reserves in the scallop gonad after spawning; in winter, the gonad is very small and inactive. Levels of lipid (mostly phospholipids and free sterols), protein, low molecular weight carbohydrate, and glycogen increase in the plasma during the period of gonad growth and maturation. The amount of glycogen in the circulating hemocytes is greater in summer than in winter.Key words:Placopecten magellanicus, bivalve, scallop, reproductive cycle, blood, hemolymph, hemocyte, blood chemistry, glycogen, phospholipid, sterol

ISSN:0706-652X    

DOI:10.1139/f77-277

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The horizontal distribution of nutrients in the St. Lawrence estuary during early July of 1975 is presented. The major sources of nutrients to the estuarine system appeared to be from the St. Lawrence River and the intermediate layer of the Laurentian Channel. By the assumption of simple mixing and conservation, the surface distribution of nutrients has been calculated. Differences between the calculated and observed values may be attributable to consumption, variability of the freshwater source and of the internal tide amplitude.Key words: nutrient distribution, estuarine circulation, mixing

ISSN:0706-652X    

DOI:10.1139/f77-278

出版商:NRC Research Press    

年代:1977

数据来源: NRC