摘要:

The effect of diel or semidiurnal vertical migrations on the horizontal dispersal of fish larvae in a partially mixed estuary, and the external stimuli triggering these migrations, were investigated. The vertical distribution of ichthyoplankton and microzooplankton was estimated at 1-h intervals for 129 h, at a fixed station of the St. Lawrence upper estuary. With increasing length, capelin (Mallotus villosus) larvae congregated closer to the surface. This resulted in a length-dependent acceleration of the seaward drift of this species. Larger capelin developed a weak but significant pattern of diel vertical migrations limited to the surface (0–20 m) layer. The average vertical position of early postlarval Atlantic herring (Clupea harengus harengus) was close to the depth of null longitudinal velocity. Vertical migrations about this average level followed a semidiurnal cycle which brought the postlarvae toward the surface during flood. This synchronization minimized seaward tidal drift linked to incursions within the surface layer. The large-scale cyclonic circulation prevailing at depth appears responsible for the maintenance of early postlarval herring in the upper estuary. Both the average depth and the semidiurnal migrations of this species were closely related to the vertical distribution of prey.

ISSN:0706-652X    

DOI:10.1139/f83-179

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

A population of lake whitefish (Coregonus clupeaformis) in the waters off eastern Manitoulin Island in Lake Huron was sampled from 1950 to 1982 by an experimental pound net in the outer basin of South Bay. Year-class strength increased markedly from 1947 to 1977; the increase began with the decline of the 1943 year-class. The fork length attained by age 1–3 fish decreased during the study, but no trend was apparent for older fish. Natural mortality of year-classes varied considerably, and was probably related to the abundance of lamprey. The annual exploitation rate increased from 1 to 37% between 1960 and 1977. Year-class strength was not correlated with the thermal regime during spawning and hatching. Recruitment was a function of parental stock size, and there was evidence that survival from the egg to juvenile stage was inversely correlated with parental stock size. Instantaneous growth rates (G) during the 2nd year of growth were inversely related to year-class strength. Growth (G) in the 1st year was positively correlated with estimated surface water temperatures. The sizes attained by ages 2 and 3 were inversely related to total population abundance. Catchability coefficients in 144-mm-mesh gill nets were inversely related to estimated population sizes. An intrinsic mechanism of population regulation is proposed whereby recruitment is a function of parental stock size, juvenile survival is inversely related to stock size, and growth is inversely correlated with population abundance.

ISSN:0706-652X    

DOI:10.1139/f83-180

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Manipulative field experiments were conducted in Carnation Creek, British Columbia, to determine whether particle-size composition of the stony substrate influenced macroinvertebrate microdistribution if substrate detritus was standardized. A standardized quantity of alder (Alnus rubra) detritus was added to five substrate mixtures ranging from homogeneous gravel to a heterogeneous gravel, pebble, and cobble mixture, and the substrates imbedded in a riffle to allow macroinvertebrate colonization. Densities and biomasses of most macroinvertebrate taxa (16 of 19) were not significantly different among the wide range of substrate types containing the standardized alder detritus, even though surface area, intra-substrate current velocity, and interstitial space varied significantly between treatments. However, in the treatment that did not have the standardized detritus, the biomasses and densities of nine taxa, and the totals of all taxa combined, were significantly lower than in an identical substrate mixture that contained the detritus. We concluded that the differential colonization of substrates demonstrated for many macroinvertebrate taxa in previous studies was more likely related to differences in organic sedimentation. Although detritus is a major determinant of detritivore microdistribution, substrate composition may be an important factor to other trophic groups such as filter-feeders.

ISSN:0706-652X    

DOI:10.1139/f83-181

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Ten-day bioassays were conducted to assess the sensitivity of eyed embryos, newly hatched alevins, and buttoned-up alevins of coho (Oncorhynchus kisutch), chinook (O.tshawytscha), sockeye (O.nerka), pink (O.gorbuscha), and chum (O.keta) salmon to low pH. Acid sensitivity varied significantly both with stage of development and with species. The various stages and species were ranked in order of decreasing sensitivity to low pH on the basis of significant differences (P < 0.05) in 10-d LC50 values. Stage sensitivities (10-d LC50 pH range) were ranked buttoned-up alevins (4.4–5.2) > newly hatched alevins (4.4–4.9) > eyed embryos (3.6–4.0) for all species except coho. Coho were more sensitive as newly hatched alevins than near button-up. Species sensitivities were ranked (chum, pink) > sockeye > chinook > coho for eyed embryos, coho > (chinook, sockeye) > (pink, chum) for newly hatched alevins, and (chum, pink, sockeye) > chinook > coho for buttoned-up alevins. Ten-day LC10s for eyed embryos ranged from pH 3.82 for chinook to pH 4.18 for chum. LC10s for the most sensitive alevin stage of each species ranged from pH 5.01 for coho to pH 5.74 for chum. Incipient lethal levels could not be estimated for any stage or species because no toxicity curves approached a pH threshold during the test period. Aberrant behavior was noted in buttoned-up alevins of pink and chum exposed to pH 6.0–6.1 but not in other species at levels above those causing acute mortality.

ISSN:0706-652X    

DOI:10.1139/f83-182

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Juvenile guppies (Poecilia reticulata) were fed ad libitum and maintained for 11 d at oxygen concentrations ranging from 0.5 to 8 mg/L (25–26 °C). With access to the surface, guppies showed high growth rates and low mortality at all concentrations. Without surface access, they exhibited a progressive reduction in growth rate below 2–3 mg/L and did not survive below 1 mg/L. Activity was influenced by oxygen concentration and surface access. Feeding rates declined sharply with oxygen concentration for fish without surface access and to a lesser extent for fish with access. Percent time in contact with the surface increased as oxygen decreased. Aquatic surface respiration is used even when this behavior is not necessary for survival. We suggest that aquatic surface respiration increases the energy available for growth under hypoxic conditions by augmenting oxygen supply, which permits greater ingestion rate, and possibly by decreasing the cost of ventilation.

ISSN:0706-652X    

DOI:10.1139/f83-183

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Retention of phosphorus (P) and iron (Fe) was estimated from mass budget calculations of Bob Lake, Ontario. Ratios of Fe to P in sediment cores were used to test the reliability of the concurrent retention estimated. However, a 300% range in Fe to P ratios measured in vertical profiles in sediments was many times larger than the uncertainty associated with mass budget measurements. Sediment cores showed a near-surface maximum of iron but not phosphorus. There was reasonably good agreement between P retention as computed by mass budget and by sediment accumulation methods, though the latter were slightly higher.

ISSN:0706-652X    

DOI:10.1139/f83-184

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Groups of hatchery reared juvenile chum salmon (Oncorhynchus keta) from Conuma River, British Columbia, were tested for compass directional preferences in experimental tanks. Chum salmon generally moved in the direction appropriate for migration through Nootka Sound to the North Pacific Ocean. Fry orientation was not disrupted by covers over the tanks. Stainless steel coded wire tags inserted into the heads of the salmon had little effect, regardless of whether they were magnetized or not. A 90° change in the external magnetic field influenced fry directional movements, but the magnitude and direction of the change were not readily explainable.

ISSN:0706-652X    

DOI:10.1139/f83-185

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Periodic changes in the oviducts ofDiaptomuscharacterize a reproductive cycle in which females oscillate between gravid and nongravid conditions. The duration of the nongravid condition sets an upper limit for rates of clutch production. In laboratory studies ofDiaptomus leptopus,D.pygmaeus,D.pallidus, andD.dorsalis, the cycle was unaffected by photoperiod but showed a strong temperature dependency. At a given temperature, the four species had a common cycle period but spent different amounts of time in the two phases of the cycle. Interspecific differences in the duration of the nongravid phase produced substantial variation in reproductive potential.

ISSN:0706-652X    

DOI:10.1139/f83-186

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Gel chromatography has been used for the separation of32PO4and a high molecular weight "colloidal"32P-labeled fraction from32PO4-labeled lakewater. When the labeled filtrate is treated with reagents required for the molybdenum blue method for orthophosphate analysis, only a small fraction of the "colloidal" peak is hydrolyzed to orthophosphate. As the reduced molybdophosphoric acid is strongly adsorbed to the dextran gel, quantitative elution of32PO4can be achieved with 0.05 mol∙L−1NaOH and 0.3% NaCl. In hardwater lakes, care must be taken to eliminate the possibility of orthophosphate precipitation at higher pH. In these lakes, it is unlikely that the discrepancy between32PO4bioassays and chemical analyses can be solely attributed to acid hydrolysis of "colloidal" phosphorus. Microparticulate apatite also has the potential to release soluble reactive phosphate when the acidic molybdenum blue method is use

ISSN:0706-652X    

DOI:10.1139/f83-187

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Characteristics of the infective stage ofCeratomyxa shastawere studied in the Deschutes River of central Oregon from 1972 through 1981. The infective stage remained viable < 10 d in Deschutes River water maintained in aerated, river-temperature-controlled aquaria. Live-cage exposures of susceptible rainbow trout (Salmo gairdneri) indicated that infectiousC.shastaemanate from the bottoms of two reservoirs. Epilimnions of both reservoirs did not contain the infective stage during thermally stratified periods. InfectiousC.shastaoriginating in one reservoir passed down the Deschutes and Columbia rivers. During spring and summer, infectiousC.shastain the other reservoir did not reach the outlet, located 56 m above the bottom. In the Deschutes River, the infective period began before March 31 in 1978, between April 3 and 10 in 1979, and between April 16 and 23 in 1981 when river temperatures were between 6.9 and 8.6 °C. Consecutive exposures of trout to the same water in aquaria indicated that all infectiousC.shastawere removed or inactivated during initial exposures. Progressively doubling numbers of test fish exposed in different aquaria showed that oneC.shastais capable of causing the death of one susceptible fingerling rainbow trout. Peak abundance ofC.shastain Deschutes River water during 1979 was estimated at 148 infectious units/m3on June 4. Abundance decreased significantly between 1978 and 1981, presumably because of elimination of ceratomyxosis-caused deaths of hatchery rainbow trout and associated spore deposition in one reservoir. Both the formation of reservoirs and liberation of susceptible host fish can lead to an increased number ofC.shasta, and result in seriousC.shasta-induced losses in native salmonid populations.

ISSN:0706-652X    

DOI:10.1139/f83-188

出版商:NRC Research Press    

年代:1983

数据来源: NRC