摘要:

Quantitative evidence that early postmetamorphic stages of zebra mussel (Dreissena polymorpha) can disperse in the water column and colonize substrates has been obtained using off-bottom scouring pad collectors and plankton sampling in a nearshore, shallow-water area (2–7 m) near Wheatley, Lake Erie, during August 1991. Collectors were deployed for 24–72 h, thus minimizing growth of recruits during deployments. Size criteria determined through an in situ growth experiment were used to discriminate between individuals arriving at a collector as (1) settling larvae or (2) postmetamorphic stages. During certain periods, 20–80% of individuals settling on collectors were postmetamorphic stages. Plankton samples taken near collectors also confirmed the presence of postmetamorphic stages in the water column. Most drifting juveniles ranged from about 300 μm shell length to 800 μm (some up to 1–2 mm). Although settlement by postmetamorphic stages occurred during various periods, they drifted and settled on collectors in much higher numbers during periods of strong wave action generated during storms. Colonization of natural and man-made substrates by postmetamorphic stages may be significant in exposed or turbulent areas and may impact on population dynamics. Whether postmetamorphic drifting is adaptive and which mechanisms are involved are unknown.

ISSN:0706-652X    

DOI:10.1139/f93-001

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Fouling by the recently established zebra mussel (Dreissena polymorpha) causes differential effects among bivalve communities. In 3-mo experiments and surveys conducted in western Lake Erie during 1990, two native bivalves,Lampsilis radiataandAmblema plicata, showed consistent differences in mortality and biochemical indices of fitness in response to fouling byD.polymorpha.Lampsilis radiatawas very sensitive to fouling, experiencing high mortality and reduced fitness in experiments and natural populations. In field experiments, femaleL.radiatasuffered higher mortality and lower fitness than males.Amblema plicatawas less sensitive to fouling; fitness was reduced in experimentally fouledA.plicata, but mortality and fitness in natural populations were not affected byD.polymorpha. Six species of native bivalves showed marked differences in mortality rates at three sites surveyed in western Lake Erie. Mortality was higher in the subfamilies Anodontinae and Lampsilinae (includingL.radiata) than in Ambleminae (includingA.plicata) at all three sites, suggesting that differences in life history strategy and shell morphology among subfamilies may be responsible for differential responses to fouling. These data suggest that fouling byD.polymorphawill result in profound changes in native bivalve community structure.

ISSN:0706-652X    

DOI:10.1139/f93-002

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Reproductive biology of the tropical sepioid cephalopodIdiosepius pygmaeuswas investigated in wild specimens and in individuals maintained in aquaria through the adult life span. This species produced multiple egg batches over 80% of the observable adult weight range, indicating a coordination of reproductive and somatic growth. Reproductive output was consistent within, but variable between, individuals. Oocyte synthesis and maturation occur continuously after sexual maturation has been reached. Senescence and death are not related to an exhaustion of reproductive potential. On average, captive femaleI.pygmaeuswith access to unlimited food produced 640 eggs in 11 batches over 18 d. When reproductive output was expressed as a ratio of dry female body weight, on average, specimens had incorporated five times their body weight into eggs and egg coatings. Under food stress, captive specimens laid fewer eggs but maintained egg size and periodicity of egg laying. Food stress had no effect on either laying duration or weight at death. This study provides further evidence that terminal spawning modes are not ubiquitous amongst cephalopods.

ISSN:0706-652X    

DOI:10.1139/f93-003

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

In 7-m3outdoor tanks filled with lake water, the presence/absence of omnivorous young-of-the-yearMicropterus salmoides, zooplanktivorousMenidia beryllina, and herbivorous larvalHyla chrysoceliswas experimentally manipulated. A cross-classified design was used to assess the interactive effects of these vertebrate consumers on the experimental food webs. Large zooplankters and large, actively swimming macroinvertebrates (Ceriodaphnia,Simocephalus, Corixidae, Notonectidae, and Dytiscidae) were particularly susceptible to depletion by both fish species.Micropterustanks contained greater numbers ofKeratella quadrataand Hebridae but fewer benthic cyclopoid copepods.Menidiatanks contained moreSynedraand algal filaments.Hylaexerted only minor direct effects on the tank communities. When both fish species were in the same tank, both had elevated mortality.Micropterus, in tanks withMenidiaandHyla, were larger and in better condition than in tanks withoutHyla. The primary effects of the experimental manipulations on food web components were two- and three-way interactions in which the effect of a given treatment was dependent on the presence of another treatment. Results suggest that the addition or removal of consumers may not cause linear, additive changes in food webs.

ISSN:0706-652X    

DOI:10.1139/f93-004

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Morphological characteristics of the first larval stage of the American lobster (Homarus americanus) enabled the separation of the Maritime population with stepwise discriminant function analysis into three groups: the southern Gulf of St. Lawrence and its outflow around Cape Breton Island, the Atlantic inshore region of Nova Scotia, and the offshore banks bordering the Gulf of Maine. Once the effect of environmental temperature on larval size was removed, the differences between Georges and Browns banks and the Atlantic inshore disappeared. The remaining differences, chiefly in the dimensions of the second and fifth abdominal segments and the rostrum, between larvae from the Cape Breton sites and elsewhere may be due to other environmental factors or partial genetic isolation. Conservation and management practices over the past century have increased gene flow between regions, and most of this appears to be from the release of Gulf of St. Lawrence lobsters in the Gulf of Maine. A reassessment of previous studies on adult morphology, benthic movements, larval dispersal, enzyme electrophoresis, and commercial landing patterns supports the separation of the Gulf of St. Lawrence stock from the rest of the Canadian Maritimes.

ISSN:0706-652X    

DOI:10.1139/f93-005

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A simple model of the size-dependent change in biomass of a cohort of fish larvae based on empirically derived relationships for growth and mortality is presented. Model predictions are compared with data for seven species of larval fish sampled on the Grand Banks of Newfoundland in 1980–81 to determine (1) whether the slope of the size-dependent larval biomass curve is significantly different from the general empirical model, and (2) whether the slope and intercept of the biomass curve are reflective of relative year-class strength and stock abundance, respectively. The slope of the size-dependent larval biomass curve is not significantly different from that predicted by the model in six of seven cases. The slope of the larval biomass curve is not significantly correlated with standardized year-class strength. The height of the curve (i.e. intercept) is only weakly associated with adult stock biomass. I conclude from this set of observations that estimates of larval fish vital rates may not be measured with sufficient accuracy to permit detection of a significant association between deviations from the general empirical model and the factors that may influence survivorship during the larval phase in a comparison across species.

ISSN:0706-652X    

DOI:10.1139/f93-006

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The delaved-type hypersensitivity (DTH) reaction (an in vivo manifestation of cell-mediated immunity) was studied in rainbow trout (Oncorhynchus mykiss) exposed to sealwormPseudoterranova decipiensinfections. Test fish immunized with sealworm extract and live intact worms, were compared with control fish which received either phosphate-buffered saline (negative control) or nonhomologous cestode or nematode antigens (positive control). Test fish immunized with sealworm extract produced a typical DTH reaction to live sealworm, challenge. The DTH reaction was similar to that in mammals and showed lymphoid and mononuclear cell infiltration. The electron microscopical studies revealed the presence of activated macrophages and plasma cells in the reaction zone. The specific response, following immunization with homologous antigens, supports the existence of T-cell function with anamnesis in rainbow trout exposed to sealworm antigens. However, when the test fish were immunized with live sealworms and later challenged with live sealworms, the secondary response was poor and showed no difference from controls and naive fish.

ISSN:0706-652X    

DOI:10.1139/f93-007

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Aggregations of prey fish, golden shiner (Notemigonus crysoleucas), were examined during 7 yr of predator manipulations in two lakes to determine whether they responded to changes in predation pressure and varied with time-of-day, age, and habitat. Regression analysis was used to examine aggregation in 12 replicate prey densities from two time periods, two ages, two habitats, three sample series, and seven predator densities. Aggregation was assessed as the variance of mean densities for each treatment combination. Multiple regression and ANCOVA analyses indicated that (1) golden shiner aggregated more during day than night, (2) their aggregation was positively related to predator density, (3) young shiner aggregated more than older ones at low predator densities, and (4) aggregation in older shiner was more responsive to increased predator densities than aggregation in younger shiner. These results provide empirical evidence that golden shiner aggregation patterns respond to predation pressure and the response varies with time and age. These results also suggest that variance in net catches can provide an index of fish aggregation and that aggregation observed at the population level is not solely dependent on species and density, but is a behavioural response mediated by several factors including predators.

ISSN:0706-652X    

DOI:10.1139/f93-008

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Biomass accumulation and changes in body energy and nutrient (carbon, nitrogen, and phosphorus) composition were evaluated relative to the migration pattern of gulf menhaden (Brevoortia patronus) to determine if biotic transport by fish is an important source of energy and nutrients to coastal marine ecosystems. Gulf menhaden transported significant quantities of energy, C, N, and P from a Louisiana estuary to the nearshore Gulf of Mexico. Transport was always out of the estuary to the marine system, although the magnitude depended on the balance between growth and mortality rates and abundance of fish. Average export per year was 38 g biomass, 930 kJ, 22.5 g C, 3.1 g N, and 0.9 g P∙m−2out of estuaries. This is roughly 5–10% of the total primary production of these estuarine areas. N and P export by fish is of the same magnitude as passive waterborne export; however it is higher quality. This indicates that fish migration can play an important role in exporting the productivity of estuaries to coastal marine ecosystem

ISSN:0706-652X    

DOI:10.1139/f93-009

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Mitochondrial DNA(mtDNA)was analysed to determine the genetic relatedness of striped bass (Morone saxatilis) populations in tributaries to the Gulf of St. Lawrence and the Bay of Funday. Mitochondrial DNA genotype frequencies were compared with those of striped bass from the Shubenacadie River (Bay of Fundy) and the Miramichi and Tabusintac rivers (Gulf of St. Lawrence). These mtDNA genotype frequencies were compared with those of striped bass representative of the Atlantic coastal migratory stock originating in the Hudson River and Chesapeake Bay. Differences in the frequencies of mtDNA length variants permitted discrimination of the Shubenacadie River from the Miramichi River and Tabusintac River populations and all three Canadian populations from the U S. spawned costal migratory stock. No difference in the frequency of mtDNA length variants was observed between Tabusintac River and Miramichi River striped bass. Heteroplasmy for mtDNA length variants was observed in 35% of Gulf of St. Lawrence fish, the highest frequency observed in any striped bass population. These results highlight the genetic heterogeneity of these Canadian striped bass populations and their distinctiveness from U S. stocks. Future efforts to restore these depleted Canadian striped bass populations should consider the impact of stock transfer on endemic striped bass gene pools.

ISSN:0706-652X    

DOI:10.1139/f93-010

出版商:NRC Research Press    

年代:1993

数据来源: NRC