bluuebunny/crossref_metadata_2025 huggingface dataset:
Production Responses for Multi-species Fisheries
Authors: Agnello R. J. , Anderson L. G.
Published: May 2008

Production equations are estimated for five major species of fish harvested in the Northwest Atlantic including Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), flounder (Pleuronectiformes), redfish (Sebastes marinus), and herring (Clupea harengus) using data collected by the International Commission for the Northeast Atlantic Fisheries from 1960 to 1974. A log-linear regression specification is used in which the relationship between catch of a vessel and several factors including days fished and vessel characteristics is estimated simultaneously. Vessel characteristics are represented as (0, 1) categorical variables, and include a variable indicating the target species designated by the caption. Various settings for the target species variables allow the estimated equation to represent either a by-catch or target catch equation. The production parameters estimated by the regressions are used to analyze the effects of current quotas set by the New England Fisheries Management Council. For some fleets we find a likelihood of idle capacity given the current quotas.Key words: fisheries economics, multi-species harvesting, Northwest Atlantic fisheries
Twilight Activities and Temporal Structure in a Freshwater Fish Community
Authors: Helfman Gene S.
Published: May 2008

Underwater observations of temperate lake fishes suggest that their twilight activities are basically similar to those described by other researchers for coral reef fishes. At dusk, diurnally active lake fishes progressively increased swimming, ceased feeding, disbanded groups, slowed swimming, and finally stopped. At dawn, this sequence was reversed, although at lower light levels than corresponding dusk behaviors. Aggressive, cleaning, and comfort behavior increased at dusk, and fishes changed from group to individual behaviors. By day, nocturnally active fishes rested singly or in aggregations. Predators were apparently more active during twilight. Older individuals of several species were active later in the evening or were increasingly nocturnal in their activities. Characteristic diel and twilight patterns broke down during the breeding season. Temperate lake species differed from coral reef fishes in that they were less attracted to physical structure at night, twilight migrations were less common, and no apparent "interim period" occurred between cessation of activity by diurnal fishes and initiation of activity by nocturnal ones. In general, twilight changeover in the temperate system was more variable and prolonged. These differences may be due to lake fishes having evolved under variable conditions of community diversity, water clarity, predator abundance, and twilight length. Such factors are more constant or predictable in coral reef communities, where twilight activity patterns appear more precise.Key words: changeover, diel, lake, latitude, light, New York, ontogeny, predation, temperate/tropic comparison
The Structure of Crustacean Zooplankton Communities in Glaciated Eastern North America
Authors: Roff J. C. , Sprules W. G. , Carter J. C. H. , Dadswell M. J.
Published: May 2008

The zooplankton community structure of 696 lakes in Pleistocene glaciated eastern North America indicated to us that glacial influence was the primary determinant of community structure. Using this criterion we successfully discriminated 82% of the lakes between glacial lakes, to which Diaptomus sicilis, Limnocalanus macrurus, Mysis relicta, and Senecella calanoides were restricted, and nonglacial lakes, to which Cyclops scutifer, Eubosmina longispina, Daphnia pulex, D. catawba, and other species were characteristic. A third large group of common species was distributed throughout the study area with no particular relation to glacial lake influence. No clear patterns in community structure with respect to size of zooplankters were discerned. Although some species distributions or abundances were consistent with the well-known predatory and competitive interactions among zooplankters typical of small lakes and ponds, for example, the negative correlation between the predatory Mysis relicta and Eubosmina longispina, most were not. We suggest that this arose partly because the study area is large and heterogeneous and partly because the biological interactions observed in small lakes and ponds may be less intense in the more physically complex environment of large lakes.Key words: zooplankton, community structure, glacial opportunists, multivariate analysis, zoogeography, size-efficiency hypothesis
Larval and Juvenile Stages of the Isopod Holophryxus alaskensis (Epicarida, Dajidae) Parasitic on Decapods
Authors: Coyle Kenneth O. , Mueller George J.
Published: May 2008

Complete descriptions of the epicarid, microniscid, cryptoniscid, and juvenile stages of Holophryxus alaskensis are given. The epicarid differs from other epicarids by its chelate pereopods. The intermediate host is Euchaeta elongate (Copepoda). The cryptoniscid stage differs from others of the Dajidae in lacking a buccal sucker and posterior projection on article 1 of antenna 1. The cryptoniscid attaches to the body wall beneath the carapace of Pasiphaea pacifica (Decapoda), where it metamorphoses to the juvenile stage before migrating to the dorsal side of the carapace.Key words: Isopoda, Epicarida, Dajidae, cryptoniscid, epicarid, microniscid, parasite, Decapoda
Biological and Hydrographical Evidence for Pacific Equatorial Water on the Continental Shelf North of Vancouver Island, British Columbia
Authors: Gardner Grant A.
Published: May 2008

Data from two cruises in April and November 1977 indicate the presence of Pacific equatorial water on the continental shelf north of Vancouver Island. Water with the general temperature/salinity characteristics of the California Undercurrent was found on the shelf at both times. Equatorial water formed ~30% of this deep-water mass, with Pacific subarctic water making up the remainder. Evidence for the presence of equatorial water was supported by the occurrence in the study area of six normally subtropical zooplankton species: Mesocalanus tenuicornis, Lophothrix frontalis, Candacia bipinnata, Lucicutia flavicornis, Heterostylites longicornis, and Pleuromamma xiphias. An increase in the proportion of equatorial water on the shelf, and a concomitant extension of the limits of distribution of oceanic zooplankters in the study area, both infer an intrustion of deep water onto the shelf during the period between the two cruises. This intrusion is probably a regular event with important ramifications for the zooplankton and fish communities of the area.Key words: continental shelf, British Columbia, hydrography, California Undercurrent, zooplankton
Environmental Regulation of Growth Rate, Efficiency, and Swimming Performance in Larval Capelin (Mallotus villosus), and its Application to the Match/Mismatch Hypothesis
Authors: Frank Kenneth T. , Leggett William C.
Published: May 2008

We examined the influence of in situ environmental conditions on the growth rate, growth efficiency, and swimming ability of larval capelin (Mallotus villosus). Larval growth rate and efficiency prior to first feeding were strongly influenced by temperatures in the beach-rearing environment prior to dispersal. The interacting effects of water temperature and hours of sunlight (solar heating) on this intertidal habitat were the major regulators of growth (R2 ≥ 0.96). A model based on these parameters accurately predicted growth rates of larvae in the gravel sampled in two previous years. Larval condition at the time of dispersal into the pelagic environment was a negative function of the length of time spent in the beach gravel and of temperature conditions during that period. Swimming performance at dispersal was directly related to larval condition. Our data indicate that environmental conditions during the early (preexogenous feeding) period can influence growth efficiency, size attained at first feeding and the prey capture ability of larvae independent of the yolk reserves available at hatching, and the quantity and quality of the food available at the obligatory onset of exogenous feeding.Key words: capelin, Mallotus villosus; growth rate, growth efficiency, swimming performance, larvae, intertidal zone, temperature
A Quantitative Study of Economically Important Parasites of Walleye Pollock (Theragra chalcogramma) from British Columbian Waters and Effects of Postmortem Handling on Their Abundance in the Musculature
Authors: Arthur J. R. , Margolis L. , Whitaker D. J. , McDonald T. E.
Published: May 2008

The identity of parasites infecting the musculature and body cavity (including external surfaces of viscera) of walleye pollock (Theragra chalcogramma) collected from two British Columbian localities, their distribution within the host's musculature, and the influence of host sex, length, and method of postmortem handling on parasite prevalence and abundance were determined. Three parasite species were found only in the musculature (Pleistophora sp., pseudophyllidean plerocercoids, and Phocanema decipiens (Krabbe, 1878) larva), two species only in the body cavity (Contracaecum-type larva and Hysterothylacium aduncum (Rudolphi, 1802) larva), and two species in both sites (Anisakis simplex (Rudolphi, 1809) larva and Nybelinia surmenicola Okada in Dollfus, 1929 plerocercoid). In the musculature most A. simplex and N. surmenicola infected the region surrounding the body cavity, with A. simplex being distributed more anteriorly, while most pseudophyllidean plerocercoids occurred in the caudal region. No preferred site of infection was observed for P. decipiens larvae. No statistically significant differences in infection with any of these helminths occurred between right and left body musculature. For pollock of similar lengths, males were more heavily infected than females with larvae of A. simplex and plerocercoids of N. surmenicola. Three species (A. simplex, N. surmenicola, and Pleistophora sp.) occurred with greater prevalence or abundance in larger fish. Storage of eviscerated and round pollock from the Strait of Georgia on ice at 3 °C for periods of up to 7 d did not result in any significant change in the prevalence of infection or abundance of parasites in the musculature. The abundance of these parasites in pollock from Queen Charlotte Sound, northern British Columbia, appears similar to that previously reported for some other areas of the North Pacific Ocean (although not as high as the most heavily infected stocks of the northwest Pacific) while their abundance in fish from the Strait of Georgia, southern British Columbia, appears to be the lowest for any pollock stock examined.Key words: walleye pollock, Theragra chalcogramma; economically important parasites, Pleistophora sp., pseudophyllidean plerocercoids, Nybelinia surmenicola plerocercoid, Phocanema decipiens larva, Contracaecum-type larva, Hysterothylacium aduncum larva, Anisakis simplex larva, British Columbia
An Allometric Model for Pesticide Bioaccumulation
Authors: Griesbach Sara , Peters Robert Henry , Youakim Sami
Published: May 2008

A combination of the frequency distribution of body sizes and appropriate allometric relationships may permit a more operational approach to pesticide bioaccumulation than the more traditional trophic level concept. To demonstrate this potential, we describe patterns of bioaccumulation as functions of time and body size in a computer ecosystem in which no differences in trophic level exist. The qualitative similarity between these patterns and those reported in the literature from laboratory and field experiments suggests that empirical relations describing contaminant fluxes as functions of body weight could form a powerful base for the prediction of contaminant body burden in natural systems. We believe this approach could prove useful for any persistent contaminant with high biological affinity.Key words: modeling, bioaccumulation, ecological magnification, allometry, body size
Zooplankton and Micronekton Abundance in Acoustic Scattering Layers on the Nova Scotian Slope
Authors: Sameoto D. D.
Published: May 2008

Zooplankton and micronekton sampling with a multiple net sampler, the BIONESS, in conjunction with a 120-kHz sounder showed significantly higher numbers of animals on the shelf water side of the shelf–slope water front than in the slope water on the Nova Scotian slope. The dominant copepod in the shelf water was Calanus finmarchicus and in the slope water it was Pleuromamma borealis. The dominant forms of micronekton were the myctophid Benthosema glaciale and the euphausiid Thysanoessa longicaudata. Calanus finmarchicus preferred a temperature of about 6 °C, B. glaciale a temperature < 12 °C. The intense acoustic scattering in the shelf water was probably due to the myctophids and euphausiids. The acoustic scattering disappeared once the warmer slope water was entered. The biomass and numbers of each species of zooplankton and micronekton∙m−2 are given for the shelf and slope water masses, for May 1977 and April 1979; these values are also given for the shelf water in June 1978. Estimates were made of the daily consumption of zooplankton by the euphausiids and myctophids in the two water masses, and it was found that both groups of animals were major consumers of the zooplankton during the spring period. There was no evidence for a food chain dominated by tunicates, chaetognaths, or gelatinous carnivores.Key words: zooplankton, micronekton, copepod, euphausiid, myctophid, acoustic scattering layer, shelf, slope
The Deep Chlorophyll Maximum: Comparing Vertical Profiles of Chlorophyll a
Authors: Cullen John J.
Published: May 2008

The relationship between chlorophyll a and phytoplankton biomass (organic carbon content) is highly variable as is the yield of in vivo fluorescence per unit chlorophyll. Thus, vertical profiles of chlorophyll or in vivo fluorescence must be interpreted with caution if their ecological significance is to be established. Although the variability of carbon-to-chlorophyll ratios and fluorescence yield is large, much of it can be anticipated, corrected for, and usefully interpreted. Vertical profiles from different regions of the sea are presented; each has a deep chlorophyll maximum, but the probable mechanisms of their formation and maintenance differ widely. Most vertical distributions of chlorophyll can be explained by the interaction between hydrography and growth, behavior, or physiological adaptation of phytoplankton with no special consideration of grazing by herbivores, even though vertical distributions of epizooplankton are not uniform. The interaction between vertical profiles of zooplankton and chlorophyll will be better understood when the relationships between chlorophyll and phytoplankton biomass in those profiles is determined.Key words: chlorophyll a, fluorescence, phytoplankton, vertical structure
Trophic Structure, Reproductive Success, and Growth Rate of Fishes in a Natural and Modified Headwater Stream
Authors: Schlosser Isaac J.
Published: May 2008

The impact of removing riparian vegetation, channel straightening, and fluctuations in flow regime on trophic structure, reproductive success, and growth rate of fishes was assessed in a natural (Jordan Creek (JC)) and modified (Big Ditch (BD)) headwater stream in east-central Illinois. Shallow habitats and organic substrates increased more in BD than JC during low flow periods in summer. Insect densities in JC were highest in late spring, declining to low levels by late summer. Insect densities in BD were high throughout summer. Fish in JC were predominantly benthic insectivores and insectivore–piscivores; trophic structure, age structure, and biomass were stable between years and seasons; recruits made up a small and stable portion of community biomass and were primarily insectivore–piscivores and generalized insectivores; younger age-classes were in shallow riffle habitats. Adult fish and recruits in BD were predominantly generalized insectivores, omnivores, and herbivore–detritivores; the last two were primarily mid-river species (Carpoides cyprinus and Dorosoma cepedianum). Considerable seasonal and annual variation in trophic structure, total biomass, and age structure occurred in BD associated with annual fluctuations in flow regime, abundance of organic substrates, and reproductive success of mid-river species. Younger age-classes had higher summer growth rates in BD than JC. The temporally variable physical environment and unstable autotrophic energy base created in modified headwater streams are probably major factors responsible for recent shifts in large river fish communities in the midwestern United States from insectivore and insectivore–piscivore species to omnivores and herbivore–detritivores.Key words: community organization, fishes, Illinois, stream continuum, stream alteration, trophic ecology, warmwater stream
The Impact of Copepod Grazing on the Phytoplankton of Georges Bank and the New York Bight
Authors: Dagg Michael J. , Turner Jefferson T.
Published: May 2008

The grazing rate of the copepod community was calculated at 10-km intervals on transects of the continental shelf south of Long Island, New York, and across Georges Bank during April, July, and October 1978. During the spring when Calanus and Pseudocalanus dominated, grazing tended to be greatest on the outer shelf and slope regions, and community ingestion rates never exceeded primary production rates; much of the spring bloom was not grazed. During the fall when Centropages and Oithona dominated, grazing was greatest in the shallower regions, and community ingestion rates were often equivalent to or slightly greater than primary production rates. About 50% of the annual primary production was grazed by the copepod community in both regions.Key words: community grazing, Georges Bank, New York Bight, phytoplankton
Macroinvertebrate Subsampling: A Simplified Apparatus and Approach
Authors: Wrona F. J. , Culp Joseph M. , Davies Ronald W.
Published: May 2008

A simple, inexpensive, volumetric, subsampling apparatus for processing macroinvertebrate samples is described. Random mixing of the macroinvertebrates was consistently achieved with the subsampler when applied to either lotic or lentic samples. Protocols for the use of the subsampler are forwarded for the situations when either reliable population density estimates or only general trends in community composition and abundance are required.Key words: subsampling, macroinvertebrates
Hypolimnetic Aeration of A Naturally Eutrophic Lake: Physical and Chemical Effects
Authors: Ashley Kenneth Ian
Published: May 2008

To examine the effect of hypolimnetic aeration on key components (circulation, decomposition, major nutrients, major ions, and pH interactions) of a lake ecosystem, I used a small naturally eutrophic lake. I divided the lake in half with a plastic curtain, and installed and operated a hypolimnetic aerator in the experimental half for a year. Hypolimnetic aeration had no effect on thermal stratification during the ice-free season but circulated the entire experimental half under ice cover. Aeration increased hypolimnetic turbidity via reduced detrital sedimentation but did not affect epilimnetic transparency. Hypolimnetic oxygen concentrations were increased as was oxygen consumption as both sediment and water column oxidation of organic material was enhanced. Hypolimnetic ammonia concentrations were reduced and sufficient oxygen was added for nitrification to occur. Internal phosphorous loading and hypolimnetic orthophosphate concentrations were reduced but aerobic P regeneration increased. Aeration vented accumulated CO2 from the hypolimnion and decreased its calcium, magnesium, bicarbonate, and orthophosphate content via calcium carbonate phosphate coprecipitation. Management applications of hypolimnetic aeration include reduction of internal nutrient loading for eutrophication control, improvement of water quality for domestic use, and prevention of fish winterkill.
Estimation of von Bertalanffy Growth Curve Parameters Using both Length Increment and Age–Length Data
Authors: Kirkwood G. P.
Published: May 2008

Many fish species cannot be aged directly over their full range of lengths. Therefore, to estimate a growth curve, one often uses length increment data from a mark–recapture experiment, supplemented by whatever age–length data are available. I describe a new method for maximum likelihood estimation of the three von Bertalanffy growth curve parameters, using the length increment and age–length data jointly. Also, I describe a likelihood ratio test for determining whether the same growth curve fits both data sets adequately. The von Bertalanffy growth curve can be taken as a predictive regression with either length or age as the dependent variable. Here, age is taken as the dependent variable, as would be appropriate for estimation of age from length, but only minor modifications are necessary for the more common alternative predictive regression of length on age. As an illustration, the techniques are applied to data for southern bluefin tuna, Thunnus maccoyii.
Iron in Eutrophic Clear Lake, California: Its Importance for Algal Nitrogen Fixation and Growth
Authors: Wurtsbaugh Wayne A. , Horne A. J.
Published: May 2008

Clear Lake, California, is warm, shallow, polymictic, and eutrophic. During 1975, levels of dissolved (< 0.45 μm) iron in all three basins of Clear Lake were always low (15–30 μg∙L−1) and decreased to 2 μg∙L−1 during the major bloom of Aphanizomenon flos-aquae. Nitrogen fixation (acetylene reduction) rates of the blue-green algal populations were stimulated as much as 500% above control levels by iron additions in laboratory and in situ large-volume bioassays. Carbon fixation rates and chlorophyll a levels were also significantly stimulated by iron additions, but usually less rapidly and to a lesser extent than N2 fixation. Additions of nitrate stimulated carbon fixation and chlorophyll production but inhibited increases in nitrogen fixation. Phosphate additions either had no effect or produced a mixture of stimulation or depression of all three variables. The bioassays indicate that the growth of blue-green algae and other algae in Clear Lake is usually directly limited by combined nitrogen and occasionally by iron or phosphorus. Low iron levels aggravate the effects of low nitrogen by limiting nitrogen fixation, thus reducing blue-green algal growth.
Survival Value of An Opportunistic Life-stage Transition in Capelin (Mallotus villosus)
Authors: Frank Kenneth T. , Leggett William C.
Published: May 2008

We examined the biological basis of the synchrony between the onset of a pelagic existence in beach-spawned capelin (Mallotus villosus) larvae and the unpredictable occurrence of favorable predator–prey conditions caused by onshore winds. Larvae isolated from the in situ beach sediments, but subject to those changes in water mass characteristics as might remain when such water is introduced into an experimental constant-level tank, emerged in synchrony with larvae in situ. This supports the hypothesis that the larval response to wind-induced water-mass exchange is an active one; it represents an adaptation maximizing feeding success and minimizing mortality due to predation. This "opportunistic" life-stage transition has direct parallels in seed dormancy and diapause in insects.
Age at Sexual Maturity in Icelandic Stocks of Atlantic Salmon (Salmo salar)
Authors: Scarnecchia Dennis L.
Published: May 2008

For Icelandic stocks of Atlantic salmon (Salmo salar) in 77 rivers, the combination of June ocean temperature, length of river ascended by the salmon, discharge of the river in July–September, and latitude explained much of the variation in percentages of grilse — 72% for females and 62% for males. For both sexes, percentage of grilse was directly related to ocean temperature but inversely related to length of river, discharge of river, and latitude. For stocks in 23 Southwest Coast rivers, length of river explained 72% of the variation in percentage of females that were grilse. Females in stocks south of the thermal gradients separating Atlantic from Arctic or Polar water tended to return as grilse; females north of the gradients tended to return after more than one winter at sea. The decline in percentages of grilse clockwise from southwestern to northeastern rivers corresponded closely with the decline in June ocean temperatures between these areas. I hypothesize that the salmon stocks have adapted their age at sexual maturity to the length and discharge of the rivers, natural mortality rates during their second year at sea, and average expected ocean temperatures, reflecting conditions for growth and survival, that the smolts encounter. Age at maturity appears not to be a direct causal response to any of these physical factors, and appears best understood only with reference to the entire life history pattern of each stock.
Sources of Organic Matter for Reservoir Fish Production: A Trophic-Dynamics Analysis
Authors: Adams S. M. , Kimmel B. L. , Ploskey G. R.
Published: May 2008

A trophic-dynamics approach was used to examine the relationships of phytoplankton production, other autochthonous primary producers, and allochthonous organic matter to the organic carbon supply necessary to support the fish community production in 17 southeastern and midwestern U.S. reservoirs. Fish community carbon requirements were estimated using average efficiencies of 10 and 15% per trophic transfer to bracket the range of efficiencies that probably occur in reservoir food webs. At 10% efficiency, most of the reservoir food webs considered appeared to be supplemented significantly by allochthonous organic matter. At 15% efficiency, phytoplankton production accounted for the organic carbon required for fish production in 10 of the 17 reservoirs. In this case, supplementary organic carbon sources were invoked to meet fish production requirements in the remaining seven reservoirs. Our results suggest that, depending on the actual food web efficiencies, autochthonous primary production can often account for the organic carbon supply required for reservoir fish production and that the importance of allochthonous organic matter to reservoir biological productivity may have been previously overemphasized. Although both the morphoedaphic index (MEI) and phytoplankton productivity were strongly correlated with reservoir fish production, a simple relationship does not appear to exist between the MEI and phytoplankton productivity, probably because of the complex aggregate nature of the MEI descriptor.
Distinguishing Beaked Redfishes (Deepwater Redfish, Sebastes mentella and Labrador Redfish, S. fasciatus) by Discriminant Analysis (with Covariance) and Multivariate Analysis of Covariance
Authors: Misra R. K. , Ni I-H.
Published: May 2008

Analysis of morphometric data for differentiating fish species and stocks has frequently been unsatisfactory as a result of sampling bias associated with the varying size of specimens and the large overlapping of characters. These difficulties may be overcome by using a discriminant function with covariance and multivariate analysis of covariance. In a classification study of beaked redfishes, in which the specimens of Labrador redfish (Sebastes fasciatus) are relatively smaller than those of deepwater redfish (S. mentella), a single character would not separate species, but a compound criterion (discriminant function) of several characters separated the species effectively. A discriminant function with covariance separated species/populations remarkably well and better than one without covariance. Seven morphometric characters were identified as pertinent discriminators between S. fasciatus and S. mentella. As much as 89% of the total variation in the sample was accounted for by the discriminant function and only 8 out of 198 individuals (4%) were in the zone of uncertainty. It is explained why using a large number of characters in discriminant analysis may not be appropriate for samples of limited sizes. Also, expressing morphometric measurements as ratios, proportions, or percentages of body length may not be an appropriate way of reducing variation owing to size differences.
Mortality Due to Infectious Hematopoietic Necrosis of Sockeye Salmon (Oncorhynchus nerka) Fry in Streamside Egg Incubation Boxes
Authors: Mulcahy Dan , Pascho Ron , Jenes C. K.
Published: May 2008

Infectious hematopoietic necrosis virus caused mortality of sockeye salmon (Oncorhynchus nerka) in streamside egg incubation boxes. Virus was not detectable in eggs or alevins; its first isolation coincided with the appearance of dead fish in a trap on the outflow from the box. Mortality due to the virus did not occur in every egg box studied. However, when fry from the boxes were held in the laboratory, epizootics began as much as 3 wk later, with total mortality exceeding 90%. More than 96% of the dead fry had titers exceeding 105 plaque-forming units per gram. The peak incidence of virus in fry migrating in the river coincided with the arrival of hatchery-produced fry, although some fry believed to have been produced by natural spawning were also infected.
Influences of Upwelling, Ocean Temperature, and Smolt Abundance on Marine Survival of Coho Salmon (Oncorhynchus kisutch) in the Oregon Production Area
Authors: Nickelson Thomas E.
Published: May 2008

The relationships between the marine survival of hatchery and wild coho salmon (Oncorhynchus kisutch) in the Oregon Production Area and ocean upwelling, ocean temperature, and smolt abundance were investigated. Hatchery coho appear to be more sensitive than wild coho to changes in upwelling-related factors although this difference may be due to errors in the estimates of wild smolts and adults that were used in the analysis. Two levels of upwelling (strong and weak), which are associated with a twofold difference in survival of hatchery coho smolts, were identified. Significant relationships were identified between survival of hatchery smolts and survival of wild smolts that migrated in strong upwelling years and sea-surface temperature during that year. Similar relationships were not as apparent for smolts migrating in weak upwelling years as they were for smolts migrating in strong upwelling years. Each major component of coho production (wild, public hatchery, and private hatchery), when treated separately, as well as public and private hatchery coho combined, exhibited linear smolt-to-adult relationships. Only hatchery plus wild coho that migrated in weak upwelling years and hatchery plus wild coho in all years combined exhibited nonlinear smolt-to-adult relationships. I concluded that these nonlinear relationships were caused by a shift in the stock composition of the Oregon Production Area coho population from predominantly high-survival, wild fish when smolt numbers were low to predominantly low-survival, hatchery fish when smolt numbers were high.
Background Levels of Petroleum Residues in the Waters and Surficial Bottom Sediments of the Labrador Shelf and Hudson Strait/Foxe Basin Regions
Authors: Levy E. M.
Published: May 2008

Background levels of petroleum residues in the form of particles floating on the sea and as substances extracted from the surface microlayer, the water column, and the surficial bottom sediments of the Hudson Strait/Foxe Basin and the Labrador shelf regions were measured during 1982 and 1983. No evidence of floating particulate oil was found in either region. Background levels of extractable petroleum residues in the surface microlayer were highly dependent on ambient sea conditions and ranged from 4.1 μg/L at the entrance to Hudson Strait to 28.3 μg/L on the southern Labrador shelf in 1982, and from 4.5 to 20.9 μg/L on the Labrador shelf in 1983 with the general background level at 8.13 μg/L. The background level in the water column in the Hudson Bay/Hudson Strait region was 0.46 μg/L in 1982 whereas that on the Labrador shelf was 0.42 μg/L during 1982 and 0.57 μg/L in 1983 (overall level of 0.51 μg/L). Concentration levels in the surficial bottom sediments depended primarily on the nature of the sediments and ranged from 1.9 μg/g at the eastern end of Hudson Strait to 52.5 μg/g on the continental slope east of Nain Bank with a general background level of 2.04 μg/g. These background levels are similar to those of other areas of the continental shelf off the east coast of Canada and are, presently, well below those known to have adverse biological consequences.
Distribution and Association of Larval Crabs (Decapoda: Brachyura) on the Scotian Shelf
Authors: Roff J. C. , Fanning L. P. , Stasko A. B.
Published: May 2008

Thirty-five taxa of neustonic larval Brachyura were distinguished and identified to stage of development in 3055 samples from the Scotian Shelf taken from north of Cape Breton to Georges Bank. A maximum of 17 species of larvae was taken in a single tow, with a norm of about 4 per tow. The most abundant species, collected in all stages of development, were the indigenous Chionoecetes opilio, Hyas araneus and Hyas coarctatus, Cancer borealis and Cancer irroratus, and Carcinus maenas. Biomass was dominated by the Hyas and Cancer species. Distributions of the three Majidae species indicated that larvae drift southwest along the shelf, and that they are indigenously derived. Twenty-six expatriate species occurred as megalopas only, predominantly offshore. Reciprocal averaging and factor analysis showed that there was considerable separation of the indigenous and expatriate larval species, but did not reveal strong relationships to environmental variables or ecological gradients. Recurrent group analysis indicated that community structure was weak and variable, but confirmed the virtual separation into indigenous and expatriate associations. An examination of co-occurrences of indigenous and expatriate species by stage of development showed strong patterns. We suggest that concurrent analysis of larval lobster and larval crab distribution patterns on the Scotian Shelf could indicate recruitment origin of lobsters (Homarus americanus).
Significance of Cannibalism in Larval Walleye (Stizostedion vitreum)
Authors: Loadman N. L. , Moodie G. E. E. , Mathias J. A.
Published: May 2008

Cannibalism by larval walleye (Stizostedion vitreum) was studied to determine the ecological consequences and implications of cohort cannibalism in intensive culture systems and in natural communities. Two categories of cannibalistic behavior were observed. Trunk attacks were the most frequent (92%), and nearly always (98%) resulted in the escape of the victim; however, victims suffered a 19% mortality rate within 24 h of the attack. Tail attacks were less frequent but almost always resulted in ingestion of the victim. Tail attacks had a mean duration of 3.5 h and were more easily observed than trunk attacks (mean duration = 20 s). Under conditions of unlimited food, cannibalism could not be shown to confer an advantage in either growth or survival upon cannibals. The rate of cannibalism increased as food density decreased, but depended on the availability of light. Trunk attacks among larval walleye may be a higher source of mortality than the more commonly observed tail attack behavior.
Fidelity of American Shad, Alosa sapidissima (Gupeidae), to its River of Previous Spawning
Authors: Melvin Gary D. , Dadswell Michael J. , Martin James D.
Published: May 2008

Of 5074 adult American shad, Alosa spidissima, tagged in the Annapolis River, Nova Scotia, during the 1981 and 1982 spawning runs, 292 (5.8%) were recaptured, 180 in the river during the same year, 56 in the river in subsequent years, 53 at distant marine sites, and 1 in another Nova Scotia river. Recovery from 6124 adult shad tagged in a marine environment (Cumberland Basin, Bay of Fundy) was similar (395 recaptures, 6.5%) but distribution was markedly different. Thirty-five were taken in the Basin during the same year, but only 7 in subsequent years. Conversely, 139 were recaptured at distant marine sites, and 214 in rivers from the St. Lawrence River, Quebec, to the St. John's River, Florida. Assuming equal probabilities for recapture within this species' geographical range, Annapolis River freshwater recaptures were specific for the Annapolis River but Cumberland freshwater recaptures were nonspecific. Except for two returns, possible strays, fidelity to the Annapolis was 97%.
Zooplankton Community and Species Responses to a Natural Turbidity Gradient in Lake Temiskaming, Ontario–Quebec
Authors: Zettler Erik R. , Carter John C. H.
Published: May 2008

Lake Temiskaming, a long, narrow lake between Ontario and Quebec, contains a permanent turbidity gradient, although seasonal turbidity values continually change throughout. Polar ordination indicated that the crustacean plankton community structure was closely related to the first (turbidity) axis. Mean body size was also positively related to turbidity, suggesting that reduced transparency in turbid waters might protect large zooplankters from visually seeking fish predators. Mysis relicta and Leptodora kindtii, the two largest species, were most abundant at the lake's turbid (northern) end with declining numbers toward the clear (southern) end. Many smaller copepods and cladocerans showed reduced numbers at the northern stations during the turbidity maximum in early June, possibly because of impaired feeding ability, after which they progressively increased through the season relative to numbers in the south. Daphnia galeata mendotae failed to show this seasonal increase at the turbid end, possibly because of selective cropping by Mysis and Leptodora. Many species displayed somewhat higher midday vertical distributions in turbid than in clear waters.
Parr–Smolt Transformation in Female and Sexually Mature Male Anadromous and Nonanadromous Atlantic Salmon,Salmo salar
Authors: Birt Tim P. , Green John M.
Published: May 2008

The parr–smolt transformation was compared in cultured Newfoundland male and female anadromous and nonanadromous Atlantic salmon, Salmo salar. Seasonal patterns of decreasing total lipid content and condition factor accompanied by increasing moisture content, silvering, and branchial Na+-K+ATPase activity indicate that smoltification occurred only in immature anadromous females. Previously mature anadromous males did not smoitify. In general, smoltification did not occur in nonanadromous salmon. Chloride cell length did not increase in any group with smoltification. The lack of smoltification in previously mature male parr of anadromous stock is consistent with reports of small numbers of male salmon in smolt runs in many Newfoundland rivers.
Effects of pH Changes on Zinc Uptake by Chlamydomonas variabilis Grown in Batch Culture
Authors: Harrison Gail I. , Campbell Peter G. C. , Tessier André
Published: May 2008

The effects of changes in H+ activity on the adsorption and intracellular accumulation of Zn by Chlamydomonas variabilis Dangeard have been studied over the pH range 7–5. Other experimental variables included the dissolved free Zn concentration, [Zn2+]b, the antecedent growth conditions (pH of the growth medium = 7, 6, or 5), and the physiological state of the harvested cells. After short-term incubations with 65Zn, algal cells were collected and the concentrations of EDTA-extractable Zn ([Zn]a ~ surface-bound Zn) and nonextractable Zn ([Zn]c ~ transported Zn) were determined. Values for [Zn]a and the flux (F) of Zn across the cell membrane decreased with increasing culture age, but cells harvested at comparable growth stages behaved similarly in the subsequent short-term incubations with Zn, irrespective of their original growth pH. In the incubation solutions, however, pH changes did affect both [Zn]a and F. At constant [Zn2+]b, a decrease in pH from 7 to 5 led to lower values of [Zn]a (~70%), suggesting either a pH-induced change in algal surface potential or a competition between H+ and Zn2+ for specific binding sites at the cell surface; a concomitant decrease in Zn flux (50–65%) was noted. The decrease in pH from 7 to 5 also had the effect of minimizing the dependence of Zn flux on the Zn2+ concentration. Two Zn transport mechanisms may coexist in C. variabilis cells, one involving a diffusion pathway sensitive to pH changes in the range 7–5 and the other a high-affinity porter system operative at both pH 7 and pH 5. These results suggest that the net effect of lake acidification may well be a decrease in the overall bioavailability of Zn to algae.
Relationship between Chrysophyte Assemblages and Environmental Variables in Seventy-Two Sudbury Lakes as Examined by Canonical Correspondence Analysis (CCA)
Authors: Dixit Sushil S. , Dixit Aruna S. , Smol John P.
Published: May 2008

Relationship between surface sediment chrysophyte scales and limnological variables in 72 Sudbury lakes was examined using canonical correspondence analysis (CCA). CCA is a recently developed multivariate direct gradient analysis that has many advantages over indirect gradient analyses. Lakewater pH was identified as the most important variable influencing the distribution of scaled chrysophytes in Sudbury lakes. Almost all common chrysophyte taxa can be assigned a pH indicator value. In addition to pH, many chrysophyte taxa are sensitive to metal concentrations. A calibration model was developed to predict chrysophyte inferred pH using CCA. The model proved to be far superior to traditionally used models derived from multiple regression of pH indicator chyrsophyte assemblages. Applicability of the predictive pH equation was examined by reconstructing the recent pH history of Lohi Lake. The study provides compelling evidence that canonical correspondence analysis offers great promise in surface sediment calibration and pH reconstruction studies.
Habitat Utilization by Juvenile Pacific Salmon (Onchorynchus) in the Glacial Taku River, Southeast Alaska
Authors: Murphy Michael L. , Heifetz Jonathan , Thedinga John F. , Johnson Scott W. , Koski K V.
Published: May 2008

Habitat utilization was determined in summer 1986 by sampling 54 sites of nine habitat types: main channels, backwaters, braids, channel edges, and sloughs in the river; and beaver ponds, terrace tributaries, tributary mouths, and upland sloughs on the valley floor. Physical characteristics were measured at all sites, and all habitats except main channels (current too swift for rearing salmon) were seined to determine fish density. Sockeye (Oncorhynchus nerka) averaged 23 fish/100 m2, nearly twice the density of coho (O. kisutch) and four times that of chinook (O. tshawytscha), 14 and 6 fish/100 m2, respectively. Sockeye were age 0, 27–84 mm fork length (FL), and most abundant in upland sloughs, beaver ponds, and tributary mouths. Coho were ages 0 and 1, 33–132 mm FL, and most abundant in beaver ponds and upland sloughs. Chinook were age 0, 40–93 mm FL, and more abundant than the other species in habitats with faster currents (1–20 cm/s), particularly channel edges. Each species was absent from about one-quarter of the seining sites of each habitat type. Thus, the lower Taku River provides important summer habitat for juvenile salmon, but many suitable areas were unoccupied, possibly because of their distance from spawning areas and poor access for colonizing fish.
Accumulation of Essential and Nonessential Metals by Chironomid Larvae in Relation to Physical and Chemical Properties of the Elements
Authors: Krantzberg G.
Published: May 2008

Molar concentration factors for nine metals, calculated as quotients of concentrations in chironomids divided by concentrations in sediment, were systematically related to fundamental atomic properties using multiple regressions and canonical analyses. Ionization and oxidation potentials, as well as the ionization potential differential and atomic radius, were useful predictors of metal concentration factors. Their relative importance varied with lake pH. Concentration factors were higher for the essential elements Zn, Ca, and Cu than for Ni and the nonessential elements Pb, Cd, and Al. The low concentration factors for Mn and Fe were driven by high sediment concentrations and the tendency for these elements to form insoluble hydroxides.
Breeding ecology of the gadwall at Waterhen Marsh, Saskatchewan
Authors: Hines James E. , Mitchell George J.
Published: May 2008

The nesting and brood ecology of the gadwall (Anas strepera) was studied at Waterhen Marsh, Saskatchewan, during 1972 and 1973. Prior to nesting, breeding pairs dispersed over the marsh in relation to the interspersion of open water and cover but later aggregated their nests in the safest insular habitats. The peak of nest initiation was late May and early June, while the peak of hatching occurred in early to mid-July. Early clutches (N = 295), initiated before June 20, averaged 10.37 ± 0.08 (± SE) eggs and late clutches (N = 27) averaged 8.00 ± 0.19 eggs. Nest densities and nesting success varied greatly between upland, ditchbank, and island habitats. Much of the variation in nesting success was caused by differences in the rate of mammalian predation between areas. Nest failure was attributed to desertion (9%), avian predators (9%), mammalian predators (4%), and unidentified predators (3%). An average of 9.97 ± 0.17 ducklings hatched from 260 successful clutches, but mean brood size decreased by 45% to 5.44 ± 0.50 (N = 9) by the time of flight. The overall productivity of Waterhen Marsh gadwalls was very high. Gadwalls breed later than do other ducks and thus gain several possible benefits including avoidance of competition and higher nesting success.
Variation in richness, evenness, and diversity in diving and dabbling duck guilds in prairie pothole habitats
Authors: Nudds Thomas D.
Published: May 2008

E. J. Tramer (1969. Ecology, 50: 927–929) proposed that the "regulation" of community diversity by changes in richness or evenness are alternatives found in predictable, nonrigorous environments with "equilibrium" communities and unpredictable, rigorous environments with "opportunistic" communities, respectively. Twenty-six years of diving and dabbling duck census data from relatively benign aspen parkland habitats, and 9 years of the same data from more rigorous mixed prairie habitats, showed little agreement with the hypothesis. Over time, only mixed prairie dabbling ducks showed changes in diversity in agreement with the hypothesis; i.e., diversity changed owing to changes in evenness in the more rigorous environment. Within guilds, changes in diversity over space were all related to changes in evenness, but only dabbling ducks had higher evenness in the less rigorous environment; the reverse was true for diving ducks. Thus, studies that use Tramer's hypothesis as a basis for distinguishing between the mechanisms responsible for community diversity in benign and rigorous environments (i.e., competition versus variation in resource abundance and diversity, respectively) are of limited value.
Epidermal cell proliferation in the bottlenose dolphin (Tursiops truncatus)
Authors: Brown W. R. , Geraci J. R. , Hicks B. D. , Aubin D. J. St. , Schroeder J. P.
Published: May 2008

Epidermal cell proliferation in four bottlenose dolphins, Tursiops truncatus, was studied using radioactively labelled thymidine. The epidermal proliferation index (PI) of 7.4 ± 0.6% is 1.3 to 1.9 times higher than that reported for terrestrial mammals. The size of the proliferative pool, a function of the ratio of basal to surface area of the epidermis, was found to be 13.1:1. These two factors combine to give a large proliferative capacity, which contributes to the unusual thickness of the epidermis of Tursiops.